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Email: Nagendra.Shah@vu.edu.au
Tel: (+61-3)-9919-8289; Fax: (+61-3)-99198284
International Food Research Journal 18(3): 837-853 (2011)
Ashraf, R. and
*
Shah, N. P.
School of Biomedical and Health Sciences, Faculty of Health, Engineering and
Science, Victoria University, Werribee Campus, P.O. Box 14428, Melbourne,
Victoria 8001, Australia
Review Article
Antibiotic resistance of probiotic organisms and safety
of probiotic dairy products
Abstract: Intrinsic resistances to tetracycline, vancomycin and erythromycin are common in Lactobacillus
species; however, resistance to streptomycin, clindamycin, gentamicin, oxacillin and lincosamide is also reported
in these species. Resistant markers tet(W), tet(M) and erm(B) have been frequently detected in the resistant
strains while van(A), lnu(A) and tet(L) have also been found in some strains of Lactobacillus. Bidobacteria are
commonly resistant to tetracycline, streptomycin, erythromycin, gentamicin and clindamycin. Resistance genes
van(A), tet(L) and tet(M) are often detected in Enterococcus. Reports suggest enterococci to transfer tet(M)
to E. faecalis or Listeria strains and van(A) to commercial strain of Lactobacillus acidophilus. Streptococcus
species are highly resistant to tetracycline, ciprooxacin and aztreonam and tet(M) was detected in strains of
dairy origin. Clinical cases of endocarditis, septicemia, bacteremia and septic arthritis due to the species of
Lactobacillus, Saccharomyces, Leuconostoc, Pediococcus and Bidobacterium have been reported in patients
with some underlying medical conditions.
Keywords: Antibiotic resistance, probiotics, minimum inhibitory concentration
Introduction
The overwhelming use of antibiotics has played
a signicant role in the outspread/emergence of
antibiotic resistance bacteria. Antibiotics added
to animal-feed and given to livestock that are used
as human food contribute to additional resistance.
Reports suggest that commensal bacteria may act
as potential reservoirs for antimicrobial resistance
genes, hence bacteria used as probiotics for humans
or animals should not carry any transferable
antimicrobial resistance genes (von Wright, 2005;
European Food Safety Authority-EFSA, 2008; The
panel on additives and products or substances used
in animal feed-FEEDAP, 2008). According to World
Health Organization (WHO) global strategy for the
containment of antimicrobial resistance (World Health
Organization-WHO, 2001), the rate of emergence of
antimicrobial resistance is expected to be increased
by misuse of antibacterial substances. The resistant
micro-organisms present in food products originating
from animal source may cause infections in humans
that are difcult to treat. A summary of risk factors
for antibiotic resistance particularly relevant to, but
not limited to, developing countries is outlined in
Table 1.
The European Food Safety Authority (2005) has
outlined a scheme based on the qualied presumption
of safety (QPS) that involves the individual
assessment and evaluation of acquired antibiotic
resistance determinants in lactic acid bacteria (LAB).
According to the scheme, the members of the
Lactococcus and Lactobacillus are most commonly
given “generally regarded as safe” (GRAS) status,
whilst members of the genera Streptococcus and
Enterococcus and some other genera of LAB contain
some opportunistic pathogens. Microorganisms
used in animal feed in the European Union (EU) are
mainly strains of Bacillus (B. cereus var. toyoi, B.
licheniformis, B. subtilis), Enterococcus (E. faecium),
Lactobacillus (L. acidophilus, L. casei, L. farciminis,
L. plantarum, L. rhamnosus), Pediococcus (P.
acidilactici), Streptococcus (S. infantarius), and yeast
of Saccharomyces cerevisiae and Kluyveromyces
species (Anadón et al., 2006).
Table 1. Human activities that exacerbate resistance
(adapted from Okeke et al. (2005))
The guidelines updated by the FEEDAP Panel
in 2008 are expected to eliminate the possibility of
microorganisms from food chain to carry transmissible
resistances genes. However, no such guidelines exist
Selective pressure
Appropriate antimicrobial use in chemotherapy•
Use of a narrow repertoire of antimicrobials on most •
patients
Antimicrobial misuse and abuse in human beings•
Agricultural antimicrobial use and misuse•
Use of poor quality antimicrobials•
Dissemination of resistant organisms
Inadequate infection control in health-care institutions•
Shortfalls in hygiene, sanitation, and public health•
Lack of surveillance and consequent late detection•
838
Rabia, A. and Shah, N. P.
International Food Research Journal 18(3): 837-853
concerning yeast resistance to antimycotics. As a
result, the use of antimicrobial growth promoters
such as avoparcin, carbadox and alaquindox has
been banned in the EU since 2006. The emergence
of vancomycin-resistant enterococci in food-animals
is correlated with the use of avoparcin. Avoparcin
is a glycopeptide that is used as a feed additive for
adding the growth of animals that can cause spread
of vancomycin-resistance from animals to humans
(Wegener, 2003). Since the resistance in many cases
is transmissible, non-pathogenic bacteria added into
the food chain could act as a reservoir of resistance
and transfer this trait to pathogens.
Types of antibiotic resistance
There are three types of resistance: natural
(intrinsic or innate), acquired and mutational.
According to FEEDAP (2008), strains carrying the
acquired resistance due to acquisition of exogenous
resistance genes are unacceptable for use as animal
feed additives.
Resistance gene reservoir hypothesis
Colonic bacteria normally residing in colon act
as reservoirs for resistance genes that can be acquired
from ingested bacteria (Figure 1). According to
reservoir hypothesis “commensal bacteria in the
colon including those that could act as opportunistic
pathogens and those that are truly non-pathogenic,
exchange DNA with one another” (Salyers et
al., 2008).The reservoir hypothesis suggests that
antibiotic-resistant bacteria came into existence
because of the selective pressures applied by antibiotic
drugs (Table 1). ‘After antibiotic treatment, there is
a decline in the populations of susceptible bacteria,
naturally resistant bacteria begin to thrive, creating a
reservoir of antibiotic-resistant bacteria’ (Salyers et
al., 2004).
Methods for determining antibiotic resistance
Methods that are routinely used for testing
antibiotic susceptibility of bacteria include Kirby-
Bauer (disc diffusion) method, Stokes method, E-test
(based on antibiotic diffusion), agar and broth dilution
or agar dilution methods for the determination of
minimum inhibitory concentration (MIC). The E-
test (Epsilometer Testprinzip, Ellipse gradient test-
AB Biodisk) is a popular quantitative technique for
determining antimicrobial susceptibility. It is based
on the combined concepts of in vitro dilution and
diffusion tests. In the assay, ‘there is an immediate and
effective release of the antimicrobials in a continuous
exponential gradient when they are applied to an
agar surface’ (Ribeiro et al., 2005). The technique is
accurate and reproducible because of the stability of
the antibiotics (Sader et al., 1994).
These methods have been tested and compared
for different LAB and bidobacteria. MICs can be
determined by agar or broth dilution techniques by
following the reference standards established by
various authorities such as the Clinical and Laboratory
Standards Institute (CLSI, USA), British Society for
Antimicrobial Chemotherapy (BSAC, UK), Agence
Francaise de Securite Sanitaire des Produits de Sante
(AFFSAPS, France), Deutsches Institut für Normung
e.V. (DIN, Germany) & ISC/WHO. FEEDAP has
published guidelines regarding the testing procedures
since 2001. FEEDAP requires the determination of
the MICs of the most relevant antimicrobials for
each bacterial strain that is used as a feed additive
in order to eliminate the possibility of transmissible
resistances.
Mayrhofer et al. (2008) tested 104 strains of L.
acidophilus using broth microdilution, disk diffusion,
and E-test. A good agreement was found between
MICs from the broth microdilution method and the
E- test method. Agar based methods such as E- test
and agar disk diffusion were suggested as valid
methods compared to the broth microdilution method.
Blandino et al. (2008) found MICs as identical to those
obtained with the E-test. Danielsen and Wind (2003)
suggested that MICs can be used as a microbiological
breakpoint when screening Lactobacillus strains
for transferable resistance genes. For antimicrobial
susceptibility testing of bidobacteria, Mättö et al.
(2007) suggested that the E-test on LAB susceptibility
test medium supplemented with cysteine was useful.
The swab and agar overlay gradient diffusion method
was found to be reliable by Charteris et al. (2001) for
antibiotic susceptibility testing of rapidly growing,
facultative anaerobic lactobacilli, using MRS agar as
test medium.
Figure1. The reservoir gene hypothesis. Bacteria residing in human
colon can act as reservoir of resistant genes that can be acquired from
ingested bacteria (adapted from Salyers et al. (2008)
Antibiotic resistance of probiotic organisms and safety of probiotic dairy products
839
International Food Research Journal 18(3): 837-853
Egervärn et al. (2007) found that results obtained
with the E-test or the broth microdilution method for
the assessment of antibiotic susceptibility of L. reuteri
and L. fermentum strains (56 each) corresponded
well with each other. This is supported by the study
of Brown and Brown (1991) that showed a good
correlation between MICs by the agar dilution and
E-test methods. Turnidge and Paterson (2007) found
that the distribution of MICs for wildtype strains of a
single species was log-normal.
Acquisition and spread of resistances
The antibiotic resistance gene can be transferred
by conjugation, transduction or transformation
(Figure 1). At present, reports regarding the spread of
antibiotic resistance among LAB and bidobacteria
suggest that resistant strains from human and animal
colons are rather common, that conrms the transfer
of resistances between commensal organisms in the
complex ecosystem of gastro-intestinal tract (GIT)
(Ammor et al., 2007). There is a general concern that
such microbes may harbor genes that may contribute
to opportunistic infections (Tompkins et al., 2008).
Theoretical risks that have been raised with respect
to the use of probiotics in humans include the
potential for transmigration and colonization and
an adverse immunological effect. There is also a
potential for antibiotic resistance transfer within the
gastrointestinal tract from commensal or probiotic
bacteria to other bacteria or potential pathogen
(Snydman, 2008).
Starter cultures used in food products could
also be a source of spread of antibiotic resistance.
Hence, strains intended for use in feed and food
systems should be systematically monitored for
resistance in order to avoid their inclusion in starters
and probiotic preparations (Ammor et al., 2007).
Two genes namely, transposon-associated tet(M)
gene and plasmid-carried tet(L) gene that mediate
2 different tetracycline resistance mechanisms have
been described in L. sakei Rits 9 strain isolated from
Italian Sola cheese made from raw milk (Ammor et
al., 2008). Tetracycline resistance gene tet(K) in 5
Staphylococcus isolates used as meat starter cultures
were detected by Kastner et al. (2006). In a recent
report where the gene tet(M) of L. plantarum isolated
from pork abattoir was transferred to Lc. lactis BU-2-
60 and to E. faecalis JH2-2 (Toomey et al., 2010).
Antibiotic resistance in LAB, Bidobacterium and
Bacillus spp.
In the EFSA guidelines (The panel on additives
and products or substances used in animal feed-
FEEDAP, 2008), the MICs for relevant antimicrobials
have been set for the following genera (and in some
cases individual species): Lactobacillus, Lactococcus,
Streptococcus thermophilus, Pediococcus,
Leuconostoc, Enterococcus, Propionibacterium,
Bidobacterium and Bacillus. These genera also cover
the recent QPS lists for bacteria, and consequently
the FEEDAP approach can be directly applied.
LAB are intrinsically resistant to many antibiotics.
In many cases, resistance is not always transmissible,
and the species are also sensitive to many clinically
used antibiotics in the case of a LAB-associated
opportunistic infection. Therefore no particular
safety concern is associated with intrinsic type of
resistance. Plasmid-associated antibiotic resistance,
which occasionally occurs, may spread resistance to
other more harmful species and genera.
Using the disc diffusion method, antibiotic
resistance among 187 isolates from 55 European
probiotic products showed that 79% of the isolates
were resistant against kanamycin and 65% of the
isolates were vancomycin resistant. Remaining
resistances were in the order of tetracycline (26%),
penicillin G (23%), erythromycin (16%) and
chloramphenicol (11%). Overall, 68.4% of the
isolates showed resistance against multiple antibiotics
including intrinsic resistance (Temmerman et al.,
2003). In a study by Toomey et al. (2010), intrinsic
streptomycin resistance was observed in lactobacilli,
streptococci, lactococci and Leuconostoc spp.
Several studies have been carried out to test the
antimicrobial susceptibility of different probiotic
and LAB in different food products but only some
of these have demonstrated the genetic basis of these
resistances. Also, the data is available regarding
antimicrobial resistance pattern in food-associated
LAB such as lactobacilli but it is mostly based on
non-standardized methodologies and/or has been
obtained for only a limited number of strains (Huys
et al., 2008). Studies regarding antimicrobial testing
of different LAB, bidobacteria and Bacillus strains
have been summarized in Table 2 and discussed
below.
Lactobacillus
Lactobacilli display a wide range of antibiotic
resistance naturally, but in most cases antibiotic
resistance is not of the transmissible type.
Lactobacillus strains with non-transmissible
antibiotic resistance do not form a safety concern.
In a study by Danielsen and Wind (2003), out of 62
strains tested for antibiotic susceptibility, 6 strains
840
Rabia, A. and Shah, N. P.
International Food Research Journal 18(3): 837-853
Table 2. Antibiotic resistance and safety implication of different LAB, bidobacteria and Bacillus spp.
Probiotic
studied
Antibiotics found to be resistant* Resistance gene
Acquisition or
spread of resistance/
Origin/ source of probiotic
(Country of study conducted)
Method used for
antibiotic resistance
analysis
References Implication (Safety)
L. farciminis
BFE 7438
Cip, Gen, Str - Intrinsic
3 strains were newly developed
and 2 from commercial
probiotic product. (Germany)
E-test, PCR,
Southern
hybridization, lter
mating experiment
Hummel et al.
(2007)
Incidences of erythromycin,
chloramphenicol, tetracycline, or β-lactam
resistance in this study were low (<7%). In
contrast, aminoglycoside (gentamicin and
streptomycin) and ciprooxacin resistances
were higher than 70%, indicating that these
may constitute intrinsic resistance, which
could not be transferred in lter-mating
experiments.
L. salivarius
BFE 7441
Cip, Ery, Gen, Str ermB
Chromosomal
L. rhamnosus
BFE 7442
Cip, Gen, Str - Intrinsic
L. acidophilus
BFE 7444
Cip, Gen, Str -
Intrinsic, inactive
cat genes
L. casei BFE
7445
Cip, Gen, Str - Intrinsic
L. paracasei Gen, Van - Intrinsic (Van)
Probiotic product -dried food
supplements and fermented
functional foods (Italy)
E-test, broth
microdilution test
Blandino et al.
(2008)
The observed resistance in tested strains
seemed to be intrinsic, except for L.
salivarius strain. Vancomycin and
erythromycin resitance was present.
Antibiotic resistance determinants are likely
to be present or can be transferred.
L. plantarum Ery, Gen, Van - Intrinsic (Van)
L. salivarius Ery, Van -
Intrinsic (Van),
Atypical (Ery)
L. acidophilus Gen - Intrinsic
S. thermophilus Cip - Intrinsic
L. rhamnosus
HN001
(DR20
TM
)
Fus, Gen, Kan, Nal, Neo, Pol,
Str, Van
-
Intrinsic (contain
plasmids but
antibiotic resistance
is not linked)
Fonterra Research
Centre Culture Collection (New
Zealand, USA)
Disk diffusion
method
Zhou et al.
(2005)
None of the 4 new probiotic strains
(L. rhamnosus HN001 and HN067, L.
acidophilus HN017 and B. lactis HN019)
tested in this study contained clinically
signicant transmissible antibiotic
resistance genes. While some of the strains
were intrinsically vancomycin resistant,
all strains were sensitive to a number of
clinically effective antibiotics. None of
these new probiotic strains were any more
resistant than the present-day commercial
probiotic strains GG and LA-1.
L. rhamnosus
HN067
Fus, Kan, Nal, Neo, Pol, Van, - Intrinsic
B. lactis
HN019
(DR10
TM
)
Clo, Gen, Kan, Nal, Neo, Pol, Str - Intrinsic
L. acidophilus
HN017
Fus, Kan, Nal, Pol, Str - Intrinsic
L. plantarum
HN045
Clo, Fus, Gen, Kan, Nal, Neo,
Pol, Str, Van,
- Intrinsic
L. rhamnosus
GG
Clo, Fus, Gen, Kan, Nal, Neo,
Pol, Str, Van
- Intrinsic
Commercial strain, Fonterra
Research Centre Culture
Collection (New Zealand,
USA)
L. acidophilus
LA-1
Fus, Gen, Kan, Nal, Neo, Pol, Str - Intrinsic
B. lactis Bb12
Clo, Fus, Gen, Kan, Nal, Neo,
Pol, Str, Van
- Intrinsic
B. lactis HN049 Clo, Gen, Kan, Nal, Neo, Pol, Str - Intrinsic
B. lactis HN098
Clo, Fus, Gen, Kan, Nal, Neo,
Pol, Str
- Intrinsic
B. breve
(Yakult)
Str
rpsL gene
Atypical
Culture Collection Research
Laboratory of Yakult Central
Institute for Microbiological
Research (Tokyo, Japan)
Broth microdilution
method, PCR
and sequencing
experiment
Kiwaki and
Sato (2009)
Chromosomal mutation of the rpsL gene
for ribosomal protein S12 cause resistance
so it is unlikely to be transferred to other
microorganisms.
Antibiotic resistance of probiotic organisms and safety of probiotic dairy products
841
International Food Research Journal 18(3): 837-853
B. lactis DSM
10140
Gen, Kan, Nal, O, Str, Tet, Tob
(conrmed by E-test)
tet(W) Plasmid borne French yogurt (Switzerland)
Disk diffusion,
E-test, microarray
and membrane
hybridization
techniques, PCR,
partial sequencing
methods and lter
mating experiments
Kastner et al.
(2006)
Antibiotic resistance determinants are
likely to be transferred or spread, so these
strains should be tested for the presence of
transferable resistance gene before being
used as probiotics.
L. reuteri SD
2112
(ATCC 55730)
Cli, Ctx, Fus, Kan, Lin, Met, Nal,
Nit, O, Oxa, Pen, Str, Tet, Tob,
Van
tet(W), Inu(A) Plasmid borne
Human origin. One strain
obtained from ATCC and
other from commercial tablet
(Switzerland)
L. rhamnosus
strain GG
(ATCC 53103)
Fus, Kan, Nal, Nit, Tob, Oxa, Str,
Va n
vanE
c
, vatE
c
,
mef
c
(detected
by microchip
hybridization)
Phenotypic Human (Switzerland)
Bacillus subtilis
VKPM B2335
Oxa
n/a n/a
Ukrainian Collection of
Microorganisms (France,
Russia, UK)
Disk diffusion
method, serial
antibiotic dilution
procedure
Sorokulova et
al. (2008)
Both strains did not harbour plasmid.
Certain risks may exist for the B.
licheniformis strain considering antibiotic
resistance, complementary studies
are necessary in order to exclude that
chloramphenicol and clindamycin
resistances are harboured in a transposable
element. B. subtilis strain may be
considered as non-pathogenic and safe for
human consumption
Bacillus
licheniformis
VKPM B2336
Amp, Cet, Cex, Chl, Cli, Ctx, Met,
Oxa,
n/a Intrinsic (Cli)
L. acidophilus
Apr, Cep, Cip, Col, Gen, Kan, Nan,
Neo, Sul, Tri
gyrA (Cip) Intrinsic
Human, adult biopsy, Europe
(Denmark)
Micro-broth and
agar dilution, PCR
and conjugation
experiments
Ouoba et al.
(2008)
Positive amplicons were obtained for
resistance genes encoding aminoglycoside
(aph(3′)-III, aadA, aadE) and tetracycline
(tet(S). Higher prevalence of phenotypic
resistance for aminoglycoside was
found. The reduce susceptibility to the
cephalosporin and cefpodoxime can
be attributed to intrinsic resistance of
the different species since none of these
bacteria were resistant to penicillin (rst
generation β- lactam). These organisms
could act as reservoir of antimicrobial
resistant genes and can transfer the
resistances to other bacteria.
L. rhamnosus
Apr, Cep, Cip, Col, Gen, Kan, Nan,
Neo, Spe, Sul, Tri, Van
- Intrinsic
L. plantarum
Amp, Cip, Col, Ery, Gen, Kan,
Nan, Neo, Spe, Str, Sul, Tet, Tri,
Va n
gyrA (Cip),
aadE (Str)
Intrinsic
L. casei
Amp, Apr, Cep, Cip, Col, Gen,
Kan, Nan, Neo, Sul, Tet, Tri, Van
- Intrinsic
L.
paraplantarum
Amp, Apr, Cip, Nan, Neo, Spe,
Sul, Tet, Tri, Van
gyrA (Cip),
tet(S)
Intrinsic
B. longum
Apr, Cip, Col, Gen, Kan, Nan, Neo
aadE (Str) Intrinsic
B. bidum
Apr, Cip, Col, Gen, Kan, Nan,
Neo, Tri
gyrA (Cip) Intrinsic
L. rhamnosus
Apr, Cep, Cip, Col, Gen, Kan, Nan,
Neo, Spe, Sul, Tri, Van
- Intrinsic
L. rhamnosus
Apr, Cep, Cip, Col, Gen, Kan, Nan,
Neo, Sul, Tri, Van
- Intrinsic
Human, child feces, Europe
(Denmark)
L. paracasei
Amp, Apr, Cep, Cip, Col, Gen,
Kan, Nan, Neo, Str, Sul, Tri, Van
aph(3′)-III
(Kanamycin,
Neo) aadA (Str)
Intrinsic
Human, adult feces, Europe
(Denmark)
L. casei
Amp, Apr, Cep, Cip, Col, Gen,
Kan, Nan, Neo, Spe, Str, Sul, Tri,
Va n
aph(3′)-III
(Kan, Neo)
aadA, aadE
(Str), aadA
(Spe)
Intrinsic
Semi-hard cheese, Europe
(Denmark)
Bidobacterium
sp
Apr, Cip, Col, Gen, Kan, Nan,
Neo, Tri
- Intrinsic
Human, child biopsy, Europe
(Denmark)
842
Rabia, A. and Shah, N. P.
International Food Research Journal 18(3): 837-853
E. faecium Chl, Ery, Gen, Str,
erm(B),
cat(pC194),
cat(piP501),
aad(E), aad(E)-
aph(A)
Phenotypic and
genetic resistances
6 strains from Probiotic
products, 2 strains as probiotics
for human and animal
consumption comes from
fecal ora (Sweden; 1968) and
dairy product, cheese (Italy),
2 strains used commercially
as a probiotic for human
consumption. (Belgium,
Germany)
Broth microdilution,
lter mating
experiments, PCR-
based detection
of resistant genes,
PFGE and (GTG)
5
-
PCR, multiplex PCR
Vankerckhoven
et al. (2008)
Resistant to fusidic acid was demonstrated
in a high percentage (92%) of isolates.
Two probiotic isolates were phenotypically
resistant to erythromycin, one of which
contained an erm(B) gene that was not
transferable to enterococcal recipients.
L. reuteri DSM
20016
Cip, Gen, Oxa, Sul/Tri, Van, n/a
Strain collection of BioGaia
Biologics, Inc., Raleigh, NC,
USA (USA)
Microdilution, PCR
for vanA- and vanB-
genes, Southern
hybridization, probe
and DNA/DNA
hybridization for
the detection of the
van genes, plasmid
analysis
Klein et al.
(2000)
Neither none of the strains possessed
vanA, vanH, vanR, vanS, vanX, vanY,
vanZ or vanB genes nor they hybridized
with vanA, vanB or vanC specic probes.
Plasmids could be found in only two of the
six strains. Six plasmid bands in L. reuteri
SD2112 and 5 bands in L. reuteri 11284
were identied. Safety of these strains
as probiotic with regard to vancomycin
resistance has been reassured.
L. reuteri T-1
(ATCC 55149)
Cip, Gen, Oxa, Sul/ Tri, Van n/a
L. reuteri 1063
(ATCC 53608)
Cip, Gen, Oxa, Sul/Tri, Van n/a
L. reuteri
SD2112
(ATCC55730)
Amp, Cep, Cip, Gen, Oxa, Sul/
Tri, Tet, Van
n/a Plasmid borne
L. reuteri 11284
(ATCC 55148)
Cip, Gen, Oxa, Sul/Tri, Tet, Van n/a Plasmid borne
L. rhamnosus
GG (ATCC
53103)
Cip, Gen, Oxa, Sul/Tri, Van n/a
L. reuteri
ATCC 55730
(SD2112)
Amp, Lin, Tet tet(W), lnu(A)
Plasmid borne and
intrinsic resistances
Biogaia AB, Human milk.
(Sweden)
Broth microdilution,
E-test, draft genome
sequence analysis,
BLAST, PCR based
methods
Rosander et al.
(2008)
No known β-lactam resistance genes were
found. The β-lactam resistance is probably
caused by a number of alterations in the
corresponding genes and can be regarded
as not transferable. It harbor two plasmids
carrying tet(W) and lnu(A) resistance genes
which were cured and daughter strains
retained probiotic properties, conrmed
after series of in vitro properties and human
clinical trials.
Lactobacillus
strain GG
Gen, Mez, Tri/Sul, Str, Van n/a n/a
Adult human feces. Prof.
Range Fondén (Panove Partner
AB, Arla group, Stockholm
Sweden). (Ireland)
Agar overlay disc
diffusion test,
gradient diffusion
test (E-test),
Charteris et al.
(2001)
All strains were resistant to vancomycin but
the nature of resistance was not determined.
The swab and agar overlay gradient diffusion
was proposed to be a reliable method for
antibiotic susceptibility testing.
L. rhamnosus Gen, Mez, Tri/Sul, Str, Van n/a n/a
Dairy product, NCFB(NCIMB
Ltd., Aberdeen, Scotland).
(Ireland)
* Amp, Ampicillin; Apr, Apramycin; Ctx, Cefotaxime; Cex, Cefoxitin; Cep, Cefpodoxime; Cet, Ceftriaxon; Cep, Cephalthoin; Chl, Chloramphenicol; Cip, Ciprooxacin; Cli, Clindamycin; Clo, Cloxacillin; Col, Colistin; Ery, Erythromycin; Fus, Fusidic
acid; Gen, Gentamicin; Kan, Kanamycin; Lin, Lincomycin; Met, Methicillin; Mez, Metronidazole; Nan, Nalidixan; Nal, Nalidixic acid; Neo, Neomycin; Nit, Nitrofurantoin; O, Ooxacin; Oxa, Oxacillin; Pen, Penicillin; Pol, Polymyxin B; Spe,
Spectinomycin; Str, Streptomycin; Sul, Sulphamethoxazole; Tet, Tetracycline; Tob, Tobramycin; Tri, Trimethoprim; Van, Vancomycin
Antibiotic resistance of probiotic organisms and safety of probiotic dairy products
843
International Food Research Journal 18(3): 837-853
of lactobacilli showed transferable resistance genes
on the basis of their resistance to chloramphenicol,
erythromycin/clindamycin, and tetracycline. One
strain of L. rhamnosus exhibited an elevated MIC for
oxacillin. The genetic basis of this kind of resistance
was proposed to be either due to mutations in the
penicillin-binding proteins or due to the presence of
a β-lactamase.
In the study of D’Aimmo et al. (2007), lactobacilli
were found resistant to nalidixic acid, aztreonam,
cycloserin, kanamycin, metronidazole, polymyxin
B, spectinomycin and susceptible to rifampicin,
bacitracin, clindamycin, erythromycin, novobiocin
and penicillin. High resistance to nalidixic acid
was found among all strains of L. acidophilus and
L. casei whereas L. casei also demonstrated high
resistance to aztreonam, cycloserine, polymyxin B
and vancomycin.
MICs of 16 antimicrobials for 473 isolates of LAB
comprising of the genera Lactobacillus, Pediococcus
and Lactococcus were determined by Klare et al.
(2007). The results suggested that majority of LAB
were susceptible to penicillin, ampicillin, ampicillin/
sulbactam, quinupristin/dalfopristin, chloramphenicol
and linezolid. LAB exhibited a broad or partly species-
dependent MIC prole of trimethoprim, trimethoprim/
sulfamthoxazole, vancomycin, teicoplanin and fusidic
acid. Noticeably, 3 probiotic Lactobacillus strains
were highly resistant to streptomycin. Although
erythromycin, clindamycin, and oxytetracycline
possessed high antimicrobial activities, 17
Lactobacillus isolates were resistant to one or more of
these antibiotics. Eight of them, including 6 probiotic
and nutritional cultures possessed erm(B) and/or
tet(W), tet(M) or unidentied members of the tet(M)
group. High resistance against streptomycin has also
been reported in 1 strain of Lactobacillus isolated
from Norwegian dairy product (Katla et al., 2001).
In the study of Huys et al. (2008), genotypically
unique 65 strains of L. paracasei and L. casei
were assayed for antibiotic resistance with broth
microdilution and E-test assays using the LAB
susceptibility test medium. In both methodologies,
strains appeared uniformly susceptible to ampicillin
and clindamycin but exhibited natural resistance to
streptomycin and gentamicin. Three L. paracasei
strains from cheese displayed acquired resistance
to tetracycline (MIC ≥ 32 μg per mL) and/or
erythromycin (MIC >16 μg per mL), which were
linked to the presence of a tet(M) or tet(W) gene and/or
an erm(B) gene, respectively. In the study of Kastner
et al. (2006), L. reuteri SD 2112 has been shown to
harbor tetracycline resistance gene tet(W) (residing
on a plasmid) and the lincosamide resistance gene
lnu(A). Two plasmids carrying tet(W) tetracycline,
and lnu(A) lincosamide resistance genes were also
identied by Rosander et al. (2008) in a commercial
strain of L. reuteri ATCC55730.
Both a transposon-associated tet(M) gene, and
plasmid-carried tet(L) gene presenting 2 different
tetracycline resistance mechanisms have been
characterized in L. sakei Rits 9 strain isolated from
Italian Sola cheese made from raw milk (Ammor et
al., 2008). The 2 resistance determinants conferred
different levels of resistance and their expression is
induced by different tetracycline concentrations.
In a recent double blind clinical study by
Egervärn et al. (2010), the transferability of
tetracycline resistance gene tet(W) from L. reuteri
to human gut ora was investigated particularly to
fecal enterococci, bidobacteria and lactobacilli. L.
reuteri ATCC 55730 harboring a plasmid-encoded
tet(W) gene was consumed by 7 subjects and an
equal number of subjects consumed L. reuteri DSM
17938. No tet(W)-reuteri signal was produced from
any of the DNA samples and thus evidence of gene
transfer to entrococci, bidobacteria and lactobacilli
during intestinal passage of the probiotic strain was
not found under the conditions tested.
In the study of Gfeller et al. (2003), L. fermentum
ROT1 isolated from a raw milk dairy product was found
resistant to novobiocin, tetracycline, erythromycin and
dalfopristin. A chromosomal tetracycline-resistance
determinant tet(M) was identied in the strain and
a 19,398-bp plasmid (pLME300), present in several
erythromycin-resistant strains of L. fermentum, was
isolated and completely sequenced.
Several species of Lactobacillus including L.
rhamnosus and L. casei are intrinsically resistant to
vancomycin. There is an underlying possibility that
vancomycin resistance could be transferred to other
bacteria but there are no such reports to date. However,
the transfer of vancomycin resistance (vanA) from
enterococci to a commercial L. acidophilus strain
was observed in vitro and in vivo in mice (Mater
et al., 2008). In a study by Klein et al. (2000), all
Lactobacillus strains namely 6 L. reuteri strains
(ATCC 55730, ATCC 55149, ATCC 55148, ATCC
53608 and DSM 20016
T
) and 1 L. rhamnosus strain GG
(ATCC 53103) were found resistant to vancomycin
but susceptible to a broad range of antibiotics. Four
of the Lactobacillus strains (including L. rhamnosus
strains) did not harbor any plasmid but 2 of them
showed 5 and 6 plasmid bands, respectively. None
of the strains possessed the vanA, vanB or vanC
gene. The ndings established the safety of the
Lactobacillus strains for use as probiotics concerning
their vancomycin resistance (Klein et al., 2000). Zhou
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International Food Research Journal 18(3): 837-853
et al. (2005) found 3 L. rhamnosus strains (HN001,
HN067 and GG) resistant to vancomycin and of the 4
new probiotic strains namely, L. rhamnosus HN001,
HN067, L. acidophilus HN017 and B. lactis HN019,
only L. rhamnosus HN001 contained plasmids. A
plasmid-free derivative of the strain had the same
antibiotic susceptibility prole as the parent strain.
Charteris et al. (2001) found vancomycin
resistance in all tested strains of Lactobacillus
strain GG and 11 closely related, rapidly growing,
facultatively anaerobic, potentially probiotic L.
rhamnosus strains. Moreover, these strains were
also resistant to co-trimoxazole, metronidazole,
gentamicin, and streptomycin but sensitive to
pencillin G, ampicillin, rifampicin, tetracycline,
chloramphenicol, and erythromycin. Antibiotic
susceptibility pattern of the strains derived from 10
Italian probiotic products was determined by Blandino
et al. (2008). Intrinsic resistance to vancomycin was
conrmed for L. paracasei, L. salivarius and L.
plantarum, and atypical resistance to erythromycin
was detected in 1 strain of L. salivarius according to
FEEDAP and CLSI breakpoints (MIC ≥8 mg per L)
(Blandino et al., 2008).
In the study of Toomey et al. (2010), all strains of
Lactobacillus spp. including L. paracasei, L. reuteri
and L. curvatus, except L. plantarum were resistant
to erythromycin containing erm(B) and msrA/B
genes. Tetracycline resistance was demonstrated by
only L. plantarum determined by tet(M) gene and
Leuconostoc mesenteroides spp. containing tet(S)
gene, respectively. L. plantarum was also intrinsically
resistant to vancomycin, however no vancomycin
gene markers were found in Lactobacillus species.
Intrinsic streptomycin resistance was observed in
lactobacilli besides streptococci, lactococci and
Leuconostoc species. In another report, L. reuteri
12002 of African origin, isolated from pig feces and
used as probiotic intervention studies was found to
harbor the erm(B) gene that could be transferred in
vitro to enterococci. Twelve probiotic isolates of
European origin demonstrated high prevalence of
phenotypic resistance for aminoglycosides (Ouoba et
al., 2008).
In a study by Egervärn et al. (2007), L. reuteri
and L. fermentum (56 strains of each) were assessed
for antibiotic susceptibility using an E-test kit and
a broth microdilution method. L. fermentum has
shown an uniform distribution for tested antibiotics
including ampicillin, tetracycline, erythromycin,
clindamycin, streptomycin, and gentamicin, whereas
L. reuteri strains displayed bimodal distribution
of MICs or above the test range for erythromycin,
clindamycin, kanamycin, vancomycin, tetracycline,
and trimethoprim. L. reuteri strains with high MICs
for both ampicillin, and tetracycline exhibited genetic
relatedness and 6 strains with high MICs for both
erythromycin and clindamycin were also closely
related.
Bidobacterium
In the study of Mättö et al. (2007), human or
probiotic associated Bidobacterium species (203
strains) showed high MIC for tetracycline i.e. ≥16
mg per mL (prevalence of 4-18%) that was attributed
to the presence of tet gene, where tet(W), and tet(O)
were detected. Occasional erythromycin (2%) and/or
clindamycin (5%) resistant strains were found, while
the strains were uniformly susceptible to ampicillin
and vancomycin. MICs of tetracyclines were
determined for 86 human Bidobacterium isolates and
3 environmental strains. The tet(O) gene was absent
in these isolates. tet(W), and tet(M) were found in 26,
and 7%, respectively, of the Bidobacterium isolates,
and one isolate contained both genes. Chromosomal
DNA hybridization showed that there was one
chromosomal copy of tet(W), and/or tet(M) (Aires
et al., 2007). The tetracycline resistance gene tet(W)
in the probiotic culture of B. lactis DSM 10140 was
detected by Kastner et al. (2006).
Kiwaki and Sato (2009) determined the MICs
of 17 antimicrobials for 26 Bidobacterium breve
strains of various origins by broth microdilution. MIC
distributions for 17 antimicrobials were unimodal
except streptomycin and tetracycline, in which it
was bimodal. The probiotic B. breve strain Yakult
showed intrinsic susceptibility to all antimicrobials
except streptomycin to which the strain showed
an atypically higher MIC of >256 μg per mL. The
resistance of B. breve strain Yakult to streptomycin
was caused by a chromosomal mutation of the rps(L)
gene for ribosomal protein S12, and thus unlikely to
be transferred to other microorganisms.
In another study by Blandino et al. (2008), the
strains of Bidobacterium were found susceptible
to ampicillin, cefotaxime and erythromycin. In the
study of Mättö et al. (2007), Bidobacterium strains
displayed generally high MICs for streptomycin and
gentamicin suggesting intrinsic resistance. D’Aimmo
et al. (2007) found that bidobacteria were resistant
to aminoglycosides, cycloserine, nalidixic acid and
strongly resistant to kanamycin, polymixin B, and
aztreonam (MIC90 = 1000 µg per mL).
Enterococcus
Members of Enterococcus contain some
Antibiotic resistance of probiotic organisms and safety of probiotic dairy products
845
International Food Research Journal 18(3): 837-853
opportunistic pathogens, hence, it is debated as to
whether these organisms could be used as probiotics.
Several studies have examined the antibiotic
resistance prole, and evaluated the transferability of
the resistance determinants to other microorganisms.
Rizzotti et al. (2009) studied the diversity and
transferability of tetracycline gene tet(M) of 20
enterococci belonging to species of E. faecalis (12
strains), E. faecium (4), E. durans (2), E. hirae (1),
and E. mundtii (1) originating from swine meat. The
gene tet(L) was observed in the 50% of the strains and
tet(M) was found correlated with a transposon of the
Tn916-1545 family. Moreover 50% of enterococcal
strains showed the ability to transfer tet(M) gene to
E. faecalis or Listeria innocua strains, which afrms
the spread of tetracycline resistance in enterococci
to potentially pathogenic bacteria occurring in food
chain.
Mater et al. (2008) observed the transfer of
vancomycin resistance (vanA) from enterococci to
a commercial strain of L. acidophilus in vitro and
in vivo in mice. The transconjugants were obtained
in high ferquency and were capable of persisting
in the digestive environment of mice. Since the
same transfer is expected to occur in human
digestive tract, it raises a safety concern regarding
the use of probiotics comprising lactobacilli in
either immunocompromised individuals or during
antibiotic therapy. In vancomycin resistant E. faecium
isolates collected from Michigan hospitals, the
location of vanA genes was found on both plasmid
and chromosome that suggests the possibility of
transposon dissemination among these isolates (Thal
et al., 1998).
Regarding the prevalence of antimicrobial
resistance of enterococcal strains in different
environments, the frequency of various antimicrobial
resistances was much lower in food isolates in
comparison to clinical strains (Abriouel et al., 2008).
Similar ndings were reported by Blandino et al.
(2008) where E. faecium derived from probiotic
product from Italy was susceptible to all the tested
antibiotics including vancomycin, ampicillin,
cefaclor, cefotaxime, erythromycin, ciprooxacin and
gentamicin. However, in the Moroccan food isolates
studied by Valenzuela et al. (2008), the frequency of
antimicrobial resistance was remarkably high. The
resistance proles of E. faecalis were different from
those of E. faecium, tetracycline resistance being
typical to the former and erythromycin resistance to
the latter. Similarly, in the study of (Devirgiliis et al.,
2010), high MIC values for tetracycline were found
among 16 strains of E. faecalis isolated from Italian
fermented dairy products. The presence of tet(M)
was demonstrated by the resistant strains that pose
a potential risk of horizontal transfer of the resistant
gene among other food borne commensal bacteria.
E. faecalis strains isolated from Irish pork and
beef abattoirs were susceptible to vancomycin,
however, 4 of 10 strains of E. faecium were resistant
to vancomycin but no corresponding genetic
determinants for this phenotype were detected (Toomey
et al., 2010). E. faecium isolated from an European
probiotic product was found resistant to vancomycin
using disc diffusion method but later it was conrmed
by broth dilution and PCR that the isolates were
vancomycin sensitive (Temmerman et al., 2003).
Susceptibility of 128 isolates of E. faecium used as
probiotic cultures was tested for 16 antimicrobial
agents using broth microdilution. Two isolates were
phenotypically resistant to erythromycin, 1 of which
contained an erm(B) gene that was not transferable to
enterococcal recipients (Vankerckhoven et al., 2008).
In the study of Tompkins et al. (2008), MIC values
for E. faecium R0026 for 17 antimicrobials were
below the break-point values published by EFSA.
The strain used in different commercial probiotic
products was susceptible to gentamicin, streptomycin
and vancomycin.
Use of growth promoters creates a major food
animal reservoir of resistant bacteria, with a potential
for spread to humans through food intake or by contact
with animal (Wegener, 2003). Butaye et al. (2000)
tested 76 E. faecium strains originated from poultry
meat, cheese and raw pork for their susceptibility and
resistance to growth-promoting antibacterials used
in animals and antibiotics used therapeutically in
humans. High-level of streptomycin resistance was
observed in strains of all origins, though infrequently
but the strains isolated from poultry meat showed
more resistances against bacitracin, virginiamycin,
narasin, tylosin (a macrolide antibiotic), ampicillin,
glycopeptides avoparcin and vancomycin.
Enterococcus species can be found in the same
habitat as of the Listeria species. Hence, these can be
important sources of transferring antibiotic resistance
through mobile genetic elements such as transposons
to Listeria. A horizontal spread of resistance to
Listeria spp. could be possible in some steps of the
food production (Rizzotti et al., 2009).
Streptococcus
A strain of S. thermophilus isolated from a
probiotic product available in Italy was found
resistant only to ciprooxacin among the tested
antibiotics (Blandino et al., 2008). D’Aimmo et al.
(2007) reported that S. thermophilus was resistant
846
Rabia, A. and Shah, N. P.
International Food Research Journal 18(3): 837-853
to cycloserine, kanamycin, metronidazole, nalidixic
acid, neomycin, paromomycin, polymyxin B,
spectinomycin, and streptomycin (MIC
90
ranging
from 64 to 500 µg per mL). It was found highly
resistant to aztreonam having a MIC
90
of 1000 µg per
mL.
Antibiotic resistance of 39 srains of S. bovis
representing the microora of a typical Italian dairy
product was found. It displayed high MIC values
for tetracycline and the presence of tet(M) was
detected in these strains. This poses a potential risk
of horizontal transfer of antibiotic-resistance genes
among foodborne commensal bacteria (Devirgiliis et
al., 2010).
Bacillus
Bacillus strains have been increasingly proposed
for prophylactic and therapeutic use against several
gastro-intestinal diseases (Sorokulova et al., 2008).
Reports suggest higher MIC for Bacillus strains.
In the study of Luna et al. (2007), all B. anthracis
isolates (18) were found resistant to trimethoprim/
sulfamethoxazole. Only B. thuringinesis (19) was
resistant to β-lactams, 3 of 42 isolate of B. cereus,
1 of 5 isolates of B. mycoides and all species of
B. pseudomycoides (6 isolates) were resistant
to clindamycin. Of 7 erythromycin resistant/
intermediate B. cereus species, 3 were clindamycin
resistant and 1 was both clarithromycin and
clindamycin resistant. Vancomycin-resistant B. cereus
was isolated from respiratory samples from patients
in a paediatric intensive care unit of a hospital Kalpoe
et al. (2008). B. licheniformis strain was reported to
be resistant to chloramphenicol and clindamycin
(Sorokulova et al., 2008).
Presence of mobile plasmid-encoded tetracycline
resistance in the B. cereus group was mentioned in
the EFSA opinion on QPS (European Food Safety
Authority-EFSA, 2007). B. brevis and B. rmus
intended to be used as biomass for animal feed
were inappropriate for QPS (European Food Safety
Authority-EFSA, 2008).
Lactococcus
Some potential risks are involved regarding the
use of fermented foods that could act as potential
vehicles for the spread of antibiotic resistance to
consumers through the food chain. Tetracycline and
erythromycin-resistance genes were found among
the strains of Lc. lactis, representing the fermenting
microora of typical Italian traditional cheese
Mozzarella di Bufala Campana. High MIC values
for tetracycline were found for 26 strains while 17
strains showed high MIC values for both tetracycline
and erythromycin (Devirgiliis et al., 2010).
Safety of probiotic foods
Lactobacillus, Bidobacterium, Pediococcus,
and Lactococcus have long history of use in food
and extensively been used as probiotics (Shah,
2007). It is estimated that per capita consumption of
fermented milk in Europe is 22 kg; this amounts to
approximately 8.5 billion kg per year, a total of 8.5
x 10
20
LAB (assuming 10
8
cfu per g), and 3400 tones
of LAB cells (assuming each cell weighs 4 x 10
-12
g)
(Shah, 2010). US sales of probiotics were estimated
to be worth $764 million in 2005 and were projected
to be worth $1.1 billion in 2010. Sales of probiotics
used in the manufacture of food supplements were
projected to reach at $291.4 million in 2010, and food
applications are expected to dominate the market,
with sales estimated at $700 million in 2010 which
include yogurts, ker, and cultured drinks as major
categories (Vanderhoof et al., 2008).
The most common microorganisms used in
fermented products belong to the genera Lactococcus,
Leuconostoc, Pediococcus, and Lactobacillus.
Lactobacilli and bidobacteria are important
indigenous microbiotia of man and animals, rarely
being implicated as cause of infection with quite
few exceptions and generally recognized as safe
(GRAS). However B. dentium, a causative agent of
dental caries, was found to be pathogenic. Similarly,
B. animalis naturally colonizes animal habitats, so its
use in humans appears to be inappropriate because the
criteria for a probiotic product consumed by humans
must contain bacteria from human origin (D’Aimmo
et al., 2007).
Based on safety records, microorganisms can
be placed in 3 groups: safe strains (Lactococcus,
Leuconostoc, Pediococcus, Lactobacillus,
Oenococcus, S. thermophilus, Bidobacterium,
Carnobacterium, E. saccharolyticus, and E. faecium),
doubtful strains (Enterococcus, L. rhamnosus, L.
catenaforme, Vagococcus, and B. dentium) and risky
strains (Peptostreptococcus, and Streptococcus)
(Mogensen, 2003). There are 3 theoretical concerns
regarding the safety of probiotic organisms: (1)
the occurrence of disease, such as bacteremia or
endocarditis; (2) toxic or metabolic effects on the
gastrointestinal tract; and (3) the transfer of antibiotic
resistance in the gastrointestinal ora (Snydman,
2008).
According to Food and Agriculture Organisation
(FAO)/WHO guidelines for the evaluation of
Antibiotic resistance of probiotic organisms and safety of probiotic dairy products
847
International Food Research Journal 18(3): 837-853
probiotics in food (2002), it is suggested that probiotic
organisms may theoretically be responsible for side-
effects including systemic infections, deleterious
metabolic activities, excessive immune stimulation in
susceptible individuals and gene transfer. Regarding
the safety assurance of probiotic organisms in
food, FAO/ WHO guidelines (2002) suggest testing
probiotic strains for antibiotic resistance patterns,
certain metabolic (e.g., D-lactate production, bile
salt deconjugation) and hemolytic potential, toxin
production, side-effects, and epidemiological
surveillance of adverse incidents during human
studies and infectivity decit in immunocompromised
animals.
Animal studies
The safety concerning the use of these bacteria has
not been doubted for many years. However, some of
the members of genera Lactobacillus, Leuconostoc,
Pediococcus, Enterococcus, and Bidobacterium
have been frequently reported to be the cause of
various infections in patients with clinical conditions
such as endocarditis and bloodstream infections
(Gasser, 1994). There are many sources of exposure
to these bacteria including probiotic preparations,
fermented food products as well as the host’s own
microora (Borriello et al., 2003). Since these
organisms can adhere to epithelial lining and can
survive gastric conditions, they may pose risks
of translocation. They can translocate from the
gastrointestinal lining to extraintestinal sites. They
can enter regional lymph nodes, spleen, liver, blood
vessels, and other tissues (Shou et al., 1994) causing
systemic infections, bacteremia, septicemia and
multiple organ faliure (Berg, 1992; Liong, 2008).
Indigenous microorganisms are not normally
found in mesenteric lymph nodes, spleen, liver, or
blood of healthy subjects. They are eliminated by the
host’s immune system as they attempt to translocate
across the mucosal epithelium. Thus translocation
of probiotic organism is not detected in most of the
studies, in which probiotic organisms are administered
even at high doses to healthy subjects (Liong, 2008).
Lara-Villoslada et al. (2009) found that the strain
L. fermentum CECT5716 orally administrated to
Balb/c mice was non-pathogenic for mice even in
doses 10,000 times higher (expressed per kg of body
weight) than those normally consumed by humans.
Bacterial translocation does not occur commonly
in healthy specic pathogen-free animals but it
can be found for a long duration in germ-free mice
(Ishibashi et al., 2001). Tanslocation was observed in
sterile born mice; however, lactobacilli did not cause
any harm and the organisms cleared in 2 to 3 weeks
(Mogensen, 2003). L. delbrueckii ssp. bulgaricus, L.
rhamnosus, and B. lactis did not translocate. Lara-
Villoslada et al. (2007) carried out safety assessment
of two probiotic strains including L. coryniformis
CECT5711 and L. gasseri CECT5714 using 20
Balb/c mice which were orally treated with L.
coryniformis CECT5711 or L. gasseri CECT5714 for
30 days and reported no treatment-associated bacterial
translocation as these organisms were not present
in liver or spleen. In another study, L. fermentum
CECT5716, a probiotic strain isolated from human
milk, was orally administered for 28 days to half of 40
Balb/c mice with a dose of 10
10
colony forming units
(cfu) per mouse per day and observed no bacteremia
and no treatment-associated bacterial translocation to
liver or spleen (Lara-Villoslada et al., 2009). Liong
and Shah (2006; 2007) administered L. casei and B.
infantis to 24 rats and no probiotics were detected
in the spleen, liver, and kidney suggesting that the
organisms were not translocated to these organs.
(Tompkins et al., 2008) reported absence of both
strains in the liver, kidneys, spleen or heart after 28-
days repeated high-dose oral treatment of E. faecium
R0026, and Bacillus subtilis R0179 used in Asian
probiotic products, to 30 Sprague-Dawly albino rats.
Intestinal microora of a subject also plays
an important role in the prevention of probiotic
translocation to internal organs. In a recent study by
Gronbach et al. (2010), it was reported that if both
intestinal microbiotia and adaptive immunity are
defective, translocation across the intestinal epithelium
and dissemination of probiotic bacteria such as
E. coli Nissle could occur with potentially severe
adverse effects. Although translocation of probiotic
bacteria to internal organs of immunodecient mice
was observed in the study of Wagner et al. (1997),
there was no evidence of increased inammation
or other pathologic ndings in tissue sections from
mice. Zhou et al. (2000) administered L. acidophilus.
B. lactis, and L. rhamnosus to 78 mice at 3 levels
including 5 ×10
7
, 5 ×10
9
, 5 ×10
10
cfu per day and
found that the organisms were safe, and no adverse
effects were observed.
Animal model could be useful in evaluating the
safety of new probiotics in immunocompromised
hosts (Borriello et al., 2003). In most of experiments
performed in mice, translocation of bacteria is
usually observed in immuno-compromised subjects
only but the response may vary with age of the
animal. Wagner et al. (1997) suggested that the use
of probiotic is likely to be safe for immunocompetent
and immunodecient adults, but they should be tested
for safety in immunodecient neonates.
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International Food Research Journal 18(3): 837-853
In vitro and in vivo assessments of the safety of
two species of Bacillus, including B. subtilis , and B.
indicus as a food probiotic were carried out by Hong
et al. (2008). The Natto strain of B. subtilis invaded
and lysed cells but neither species was able to adhere
signicantly to any cell line. The Natto strain formed
biolms and none of strains produced any of the
known Bacillus enterotoxins. Only B. indicus carried
resistance to clindamycin at higher MIC than EFSA
breakpoints. In vivo assessments of acute and chronic
dosing in guinea pigs and rabbits, no toxicity was
observed in animals under these conditions. The
authors reported that B. indicus and B. subtilis were
safe for oral use but further study is required regarding
the transmissibility of clindamycin resistance of B.
indicus.
The safety assessment of two Bacillus strains
including B. subtilis, and B. licheniformis incorporated
into a popular East European probiotic product was
carried out. Both were non-hemolytic and did not
produce Hbl or Nhe enterotoxins. Similarly, no bceT
and cytK toxin genes were found. Study of acute
toxicity in BALB/c mice demonstrated no treatment-
related deaths. The oral LD
50
for both strains was
more than 2 × 10
11
cfu per g. Chronic toxicity studies
showed no signs of toxicity or histological changes
in either organs or tissues of experimental animals.
B. subtilis strain was sensitive to all antibiotics listed
by the EFSA but B. licheniformis strain was resistant
to chloramphenicol and clindamycin that enclosed
safety risks of using B. licheniformis strain. However,
B. subtilis strain was found to be non-pathogenic
and safe for human consumption (Sorokulova et al.,
2008).
Tompkins et al. (2008) carried out safety
evaluation of 2 probiotic strains namely, E. faecium
R0026 and B. subtilis R0179 used in Asian probiotic
products and found absence of both diarrheal
and emetic toxins in the latter strain. The authors
established, on the basis of the results of this study in
combination with the observations of clinical studies
in both infants and adults, that these microbes were
safe for use as pharmaceutical probiotics and pose
low risk to the consumer.
Some of the studies have proposed benecial
effects of probiotic organisms in translocation and
they have been tested to prevent bacterial translocation
in animal model. The ndings by Zareie et al.
(2006) indicated that probiotic bacteria can prevent
chronic stress induced intestinal abnormalities and,
thereby, exert benecial effects in the intestinal tract.
Bacterial species such as enteric gram-negatives and
gram-positive cocci are more prone to translocation,
whereas lactobacilli appear to have a protective
effect (Jeppsson et al., 2004). Administration of
live lactobacilli including strains of L. reuteri, L.
plantarum and L. fermentum to male Sprague-Dawley
rats reduced the bacterial translocation (Adawi et al.,
1997). This is supported by another study that showed
probiotic supplementation containing B. bidum,
L. acidophilus, and L. bulgaricus (2 x 10
9
cfu per
day) reduced bacterial translocation and decreased
intestinal mucosal atrophy in male Sprague-Dawley
rats with thermal injury (Gun et al., 2005). Moreover,
in a rat model of small bowel syndrome, probiotic
organisms decreased the bacterial translocation
through mechanisms dependant on intestinal mucosal
integrity (Mogilner et al., 2007).
Clinical cases
Docummented correlations between systemic
infections and probiotic consumptions are few and
all occurred in patients with underlying medical
conditions (Food and Agricultural Organization of
the United Nations/ World Health Organization-
FAO/WHO, 2002; Bernardeau et al., 2008). Many
of the probiotic organisms have a safe history in
patients receiving nutritional support, although some
probiotic products have shown to increase the risk of
complications in specic patient groups (Whelan et
al., 2010).
Aguirre and Collins (1993) and Gasser (1994)
have reviewed clinical cases involving LAB and
bidobacteria between 1938 and 1993, and the
results are summarized in Table 3. Analysis of
cases of infections revealed that out of 155 cases
of infections involving LAB or bidobacteria, 95
cases involved Lactobacillus spp., 33 of Leuconostoc
spp., 18 of Pediococcus spp. and 9 cases involved
Bidobacterium spp. (Table 3) (Gasser, 1994).
Endocarditis was the most frequent infection in
which Lactobacillus species have been involved, in
particular strains of species of L. rhamnosus/casei
have been most often isolated.
Only about 180 cases of septicemia in humans
involving LAB have been reported. In only 1 of
Table 3. Clinical cases in which lactic acid bacteria
or bidobacteria have been isolated (Adapted from
Mogensen et al., 2002)
Clinical outcome Endocarditis Bacteremia Other
infection
Total
Lactobacillus
7 8 19 34
L. acidophilus
3 3 2 8
L. casei
12 - - 12
L. plantarum
11 2 1 14
L. rhamnosus
19 5 3 27
Bidobacterium
- 9 - 9
Leuconostoc
2 23 8 33
Pediococcus
- 11 7 18
Total 54 61 40 155
Antibiotic resistance of probiotic organisms and safety of probiotic dairy products
849
International Food Research Journal 18(3): 837-853
these cases, the identied LAB was identical with a
commercially available dairy strain. E. faecium and
E. faecalis are more frequently involved in clinical
infection. In most cases of infection, people were
reported to be infected by their own ora, however, in
a few cases consumption of probiotic organisms was
a potential source. About 30 cases of fungaemia have
been reported in patients treated with Saccharomyces
boulardii (Gasser, 1994), and 2 cases of infection were
with food-borne L. rhamnosus (Mackay et al., 1999).
In another report, 62 patients became colonized with
B. cereus including 2 with non-fatal Bacillus sepsis
and a death due to pneumoniae associated with the
organism (Bryce et al., 1993).
Saxelin et al. (1996) studied the prevalence
of bacteremia caused by Lactobacillus species in
Southern Finland and compared the characteristics
of the blood culture isolates with probiotic dairy
strains. Lactobacillus was identied in eight of
3317 blood culture isolates; however, there was no
isolate from dairy strain. In a 74-year-old woman
with several years history of hypertension and non-
insulin dependant diabetes mellitus, liver abscess was
reported due to L. rhamnosus strain indistinguishable
from L. rhamnosus strain GG (Rautio et al., 1999).
In a study by Kalliomäki et al. (2001), L.
rhamnosus GG was given to 132 women who
were at high risk of their babies developing atopic
dermatitis. There was no report of adverse effects in
mothers indicating that the probiotic organism was
safe. Reports by Salminen et al. (2002) suggest that
L. rhamnosus GG has been used widely in Finland
since late 1980s and despite the long term use of this
probiotic organism, there has been only few cases of
bacteremia (0.05 cases per 100 000 cases).
Whelan and Myers (2010) reviewed of total
of 1966 articles, of which they found 72 to full
the inclusion criteria. There were 20 case reports
of adverse events in 32 patients, all of which were
infections due to L. rhamnosus GG or Saccharomyces
boulardii. The risk factors included central venous
catheters and disorders associated with increased
bacterial translocation. There were 52 articles
reporting 53 trials in which 4131 patients received
probiotic organisms. Most trials showed either no
effect or a positive effect on outcomes related to
safety (e.g., mortality and infections). Only 3 trials
showed increased complications, which were largely
non-infectious in nature and in specic patient groups
(e.g., transplant and pancreatitis).
Cannon et al. (2005) reviewed 241 clinical cases
of Lactobacillus infections and found 129 cases of
bacteremia and 73 cases of endocarditis. L. casei
and L. rhamnosus were most common species and
the overall mortality was reported nearly 30%.
Patients of all ages and both gender were afftected.
The main underlying conditions were recognized
as cancer, diabetes, transplantation particularly
of liver, abscesses, and hypertension. Husni et
al. (1997) reviewed 45 cases of Lactobacillus
infections occuring over 15 years and the organisms
causing infections were characterized. The common
underlying conditions were cancer (40%), recent
surgery (38%), and diabetes mellitus (27%). One in
39 deaths was attributed to Lactobacillus bacteremia.
Cannon et al. (2005) recognized a very small
percentage (1.7%) of cases associated with heavy
dairy consumption, where 3 cases were associated
with endocarditis and 1 with a liver abscess. A case of
aortic valve endocarditis caused by L. casei in a 53-
year-old immunocompetent patient with past history
of rheumatic fever was reported by Zé-Zé et al.
(2004). Noticeably clinical symptoms appeared after
a dental extraction and the patient’s diet included
several tubs of yogurts per day. Presterl et al. (2001)
reported a young man having diet comprising large
quantities of probiotic yogurt developed endocarditis
and septic arthritis caused by L. rhamnosus. However
the contradictory ndings were reported by Wallet
et al. (2002), where a case of endocarditis due to L.
casei subsp. rhamnosus was found in 73-year-old
man without previous history of dental manipulation
or daily yogurt intake. In relation to a consumption
of about 20 million tons of fermented milk annually,
the above numbers are negligible (Mogensen, 2003).
There is no foundation for safety concern in relation
to probiotic dairy products on the market today.
Probiotic organisms are generally considered safe. As
evidenced by epidemiologic studies, bacteremia or
sepsis from lactobacilli is extremely rare. Numerous
probiotic organisms have a long history of safe use
and no health concerns have been observed. A long
history of safe use is still the most credible safety
test.
Conclusions
Selective pressure of using antibiotic in both
human and animal treatment, and dissemination of
antibiotic resistance bacteria has the possibility to
aggravate acquisition and spread of resistant genes.
In this context, probiotic organisms are considered to
pool the resistant genes and transfer these to pathogenic
bacteria. In order to eliminate this possibility, MIC of
the most relevant antimicrobials for each strain used
as a probiotic organism, food or feed additives could
be determined using protocols given by EFSA and
on rm genetic grounds. Several studies regarding
850
Rabia, A. and Shah, N. P.
International Food Research Journal 18(3): 837-853
the antibiotic susceptibilities of LAB, bidobacteria
have been reviewed but only few have determined
the genetic basis of these resistances. Majority of
resistance found in the species of Lactobacillus,
Bidobacterium, Enterococcus, Streptococcus
and Bacillus were of intrinsic type. Resistances to
tetracycline, vancomycin and erythromycin were
frequent in these species and some showed to harbour
genes tet(W), tet(M), van(A) and erm(B) mostly on
chromosome with only few on plasmid or transposon.
Intrinsic resistance, and resistance due to mutation of
chromosomal genes present a low risk of horizontal
dissemination, and such strains should be acceptable
for food consumption. However, acquired resistance
mediated by added genes may present a risk for public
health. Starter culture bacteria in dairy products do not
appear to represent an important source for the spread
of genes encoding resistance to antimicrobial agents.
However antibiotic resistance proles of novel strains
used as starters or probiotics in dairy products must
be checked for fermented dairy products. In case of
Enterococcus strains, resistance genes van(A), tet(L),
and tet(M) were often detected and 2 reports have
found enterococci to transfer tet(M) to E. faecalis or
Listeria strains and van(A) to a commercial strain L.
acidophilus.
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