Prevalence and antibiotic resistance of bacteria in two ethnic milk based products

Abstract

Prevalence of food borne pathogens in milk products, khoya (a common ingredient in many
traditional Indian sweets made by slowly evaporating milk under heat) and burfi (khoya cooked with
sugar until it solidifies) and their sensitivity against different antibiotics was evaluated. Coliform
indicated the lowest count (7.5x103 CFU/g) and the highest (5.3x106 CFU/g) in burfi whereas 6.5x103
and 5.2x106 CFU/g in khoya for 28 selected samples. Presence of Staphylococcus aureus, Escherichia
coli and Klebsiella spp., was also confirmed in a large number in khoya and burfi samples. S. aureus
represented the major part of bacterial flora in burfi and khoya. Enterobacter spp., and E. coli spp.,
constituted ~ 1.2%, in both burfi and khoya. The unidentified microflora comprised 12.56% and
8.41% in burfi and khoya, respectively. E. coli and Enterobacter spp., isolated from both khoya and
burfi showed more susceptibility to Septran and Amikin. Ampiclox and Tetracycline exhibited higher
degree of sensitivity against these isolates. However, Klebsiella spp., Enterobacter spp., and E. coli
were found to be resistant to Urixin. Locally prepared milk products might be a potential source of
bacterial contamination which poses a significant clinical threat to consumers through excessive use of various antibiotics against these micro-organisms.

Full text

Pak. J. Bot., 41(2): 935-943, 2009.
PREVALENCE AND ANTIBIOTIC RESISTANCE OF BACTERIA
IN TWO ETHNIC MILK BASED PRODUCTS
KALSOOM FARZANA1, SAEED AKHTAR2* AND F. JABEEN 3
1Department of Pharmacy, Bahauddin Zakariya University, Multan, Pakistan
2University College of Agriculture, Bahauddin Zakariya University, Multan, Pakistan
3Quality Control Manager, Jeans Pharmaceuticals, Lahore, Pakistan.
Abstract
Prevalence of food borne pathogens in milk products, khoya (a common ingredient in many
traditional Indian sweets made by slowly evaporating milk under heat) and burfi (khoya cooked with
sugar until it solidifies) and their sensitivity against different antibiotics was evaluated. Coliform
indicated the lowest count (7.5x103 CFU/g) and the highest (5.3x106 CFU/g) in burfi whereas 6.5x103
and 5.2x106 CFU/g in khoya for 28 selected samples. Presence of Staphylococcus aureus, Escherichia
coli and Klebsiella spp., was also confirmed in a large number in khoya and burfi samples. S. aureus
represented the major part of bacterial flora in burfi and khoya. Enterobacter spp., and E. coli spp.,
constituted ~ 1.2%, in both burfi and khoya. The unidentified microflora comprised 12.56% and
8.41% in burfi and khoya, respectively. E. coli and Enterobacter spp., isolated from both khoya and
burfi showed more susceptibility to Septran and Amikin. Ampiclox and Tetracycline exhibited higher
degree of sensitivity against these isolates. However, Klebsiella spp., Enterobacter spp., and E. coli
were found to be resistant to Urixin. Locally prepared milk products might be a potential source of
bacterial contamination which poses a significant clinical threat to consumers through excessive use of
various antibiotics against these micro-organisms.
Introduction
The origin of contamination by pathogenic bacteria varies with the type of product
and the mode of production and processing. Contamination of milk and dairy products by
pathogenic micro-organisms can be of endogenous origin, following excretion from the
udder of an infected animal and /or exogenous origin, through direct contact with infected
herds or through the environment (e.g., water, personnel). Treatment and processing of
milk can inhibit or encourage the multiplication of micro-organisms (Brisabois et al.,
1997). Food borne pathogens can survive and thrive in post-pasteurization processing
environments, thus leading to recontamination of dairy products. These pathways pose a
risk to the consumers from direct exposure to food borne pathogens present in
unpasteurized dairy products as well as dairy products that become re-contaminated after
pasteurization (Oliver et al., 2005).
Staphylococcus aureus by far is the most frequent pathogen associated with
outbreaks (85.5% of the outbreaks), followed by Salmonella (10.1%) (De Buyser et al.,
2001). Cooked food products and raw milk were most commonly contaminated with food
borne pathogens and many of them were resistant to different antibiotics. Milk products
are often contaminated with enterotoxigenic strains of S. aureus (Chao et al., 2007). It is
currently not possible to effectively and consistently exclude such multiantibiotic-
resistant strains from the human food chain, which means that they continue to pose a
significant clinical threat to consumers and concomitant economic threats to the food
production and processing industry (Walsh et al., 2005).
*Corresponding author E-mail: saeedbzu@yahoo.com

KALSOOM FARZANA ET AL.,
936
Presence of enterotoxigenic and antimicrobial resistant strains of S. aureus have
become remarkably widespread in foods. This requires a better control of food
contamination sources and distribution of antimicrobial-resistance organisms (Normanno
et al., 2007).
Around 100 to 130 patients suffering from food poisoning and gastroenteritis were
daily admitted to emergency wards of all major hospitals in Pakistan in 2007. A large
number of children were also hospitalized for eating unhygienic food (Ali, 2007).
Contamination of dairy foods with virulent pathogens render them to be a source of
public health hazard. The possible contamination sources are either mastitis dairy cow or
the milk itself (Carter, 1995). Growing concerns over food safety among the consumers
call for the manufacturing and processing of foods under extremely hygienic conditions
to avoid possible health challenges. Food safety conditions in Pakistan are not
encouraging and milk products, specifically prepared by local manufactures, being
unpasteurized, either exposed or improperly packed, are highly contaminated. The
objective of the present study was to evaluate the level of prevalence of micoflora viz., S.
aureus, Enterobacter spp., E. coli and Klebsiella spp., in frequently consumed dairy
products and to asses their sensitivity against the most commonly used antibiotics.
Materials and Methods
Collection of samples: Thirty samples of burfi and khoya were collected in sterilized
glass bottles from retail shops and were brought to the laboratory under low temperature
for microbiological assay. The inocula were prepared by homogenizing 10 g of cooled
and well-mixed samples in 100 ml chilled sterile normal saline solution containing 0.1
percent peptone.
Control strains: E. coli (ATCC 25922) and S. aureus (ATCC 25923) were used as
control strains in this study.
Aerobic colony count (ACC): ACC was carried out by pour plate technique as reported
previously (Case & Johnson, 1984). The homogenates were serially diluted in sterilized
water, pour-plated in a thin layer of Nutrient Agar (Difco, BD Diagnostic Systems,
Sparks, MD, USA) and were incubated at 37oC for 24 h to determine CFU/g. The
experiment was repeated twice and reported data represent mean values (CFU/g) of these
measurements.
Coliform count: Klebsiella spp., E. coli and Enterobacter spp., were enumerated in their
selective media as coliform count. Coliform count was conducted by MPN technique,
tubes containing gas in the inverted durham tubes were considered positive for the
coliforms. To measure number of coliforms present in the milk products (khoya and
burfi), dilution was read from MPN table and results were computed by multiplying this
number with the dilution factor (Cappuccino and Sherman, 1992).
Fecal coliform count: Fecal coliforms were obtained by MPN technique. 0.5 ml of
coliform culture present in the tubes was incubated into 10 ml brilliant green bile broth
tubes. The broth tubes were incubated at 44.5oC for 48 hours and the results were
recorded from MPN-table. Presences of fecal coliforms were confirmed by streaking

ANTIBIOTIC RESISTANCE OF BACTERIA ETHNIC MILK BASED PRODUCTS 937
from positive brilliant green broth culture on eosin methylene blue agar (EMB) plates.
Bacterial colonies developed were considered as fecal coliforms and were counted.
Identification, morphological and biochemical characterization of bacterial strains:
The colonies isolated after purification were initially Gram stained and the isolates were
biochemically characterized and identified up to species level by applying Baird parker
agar, Manitol salt agar, Dnase test, Coagulase test, Oxidase catalase, Indole, methyl red,
Voges-proskauer, simmons citrate, EMB as reported previously (Davidson & Henson,
1995; Holt, 1993; Pelczar et al., 1999)
Antibiotic sensitivity profile
Disc Diffusion Susceptibility Test: Burfi and khoya isolates; Enterobacter spp., E. coli
and Klebsiella spp. were assessed for their sensitivity against different antibiotics viz.,
Urixin, Chloramphenicol, Ampicillin, Ampiclox, Nitrofurantoin, Tetracycline, Amikin,
Amoxil, Augumentin and Septran as reported previously (Bauer et al., 1966).
The Disc Diffusion Susceptibility Test was used for each Gram-negative rod on
Mueller-Hinton agar (CM337-OXOID) as growth medium. Medium was prepared
according to manufacturer’s instructions and sterilized by autoclaving at 121°C for 15
min. These plates were stored at 2-8°C in sealed plastic bags for use within two weeks
(Bauer et al., 1966). Tryptone soya broth (TSB) (CM129-OXOID) was dispensed in
screw-capped test tubes and sterilized by autoclaving at 121°C for 15 min., for inoculum
preparation. The test tubes were cooled and kept in an incubator for 24 h at 35°C to
confirm sterility. Each isolated clinical strain was inoculated in the sterilized test tubes
containing the medium and placed in an incubator overnight at 35°C. The presence of
turbidity in broth cultures was adjusted according to 0.5 McFarland standard to obtain
standardized suspension by adding sterile saline against a white background according to
the methods outlined by National Committee for Clinical Laboratory Standards, NCCLS
(Anon., 1993). Inoculum was spread evenly over the entire surface of the Mueller-Hinton
agar plates by swabbing back and forth across the agar in three directions to give a
uniform inoculum. Then the discs of given potency were applied on the inoculated plates
with the help of forceps and incubated at 35ºC for 18 h in an inverted position. The
results were recorded as zone of inhibition from the standard table.
Results and Discussion
The frequency distribution of burfi and khoya samples in relation to various
microbial counts is given in Tables 1 and 2 respectively. The ACC, coliforms, fecal
coliforms and S. aureus count examined by Standard Plate Count (SPC), indicated an
excessive contamination in both types of dairy products. Khoya in general revealed more
bacterial contamination as compared to burfi samples. The ACC was found to rang from
106 to 1011 CFU/g for both khoya and burfi and the highest number of samples i.e., 10 of
28, manifested a bacterial count of 107-108 CFU /g. Coliforms were found almost at the
similar extent ranging from 103 to 107 CFU/g for both khoya and burfi samples however,
a little variability in the number of samples of khoya and burfi, exhibiting extent of
coliforms and fecal coliforms was observed (Tables 1 and 2).

KALSOOM FARZANA ET AL.,
938
Table 1. Microbiological profile (CFU/g) of milk products (khoya).
Bacterial range (CFU/g)
Test No. of
samples 103-104 104-105 105-106 106-107 107-108 108-109 109-1010 1010-1011
ACCa 28 - - - 4 10 6 7 1
MPN-Cb 26 4 8 9 5 - - - -
MPN-FCc 26 4 8 9 5 - - - -
S. aureus 24 - - 12 8 4 - - -
ACCa = Aerobic colony count, Cb = Coliform, FCc = Fecal Coliform.
The values are the mean of two experiments
Table 2. Microbiological profile (CFU/g) of milk products (burfi).
Bacterial range (CFU/g)
Test No. of
samples 103-104 104-105 105-106 106-107 107-108 108-109 109-1010 1010-1011
ACCa 28 - - - 5 10 5 7 1
MPN-Cb 26 3 8 10 5 - - - -
MPN-FCc 26 3 8 10 5 - - - -
S. aureus 24 - - 10 8 6 - - -
ACCa = Aerobic colony count, Cb = Coliform, FCc = Fecal Coliform.
The values are the mean of two experiments
S. aureus count in both khoya and burfi were found to be 105 to 108 CFU/g (Table 1
and 2) with 50% (12 of 24) samples of khoya indicating 105-106 CFU/g as compared to
42% (10 of 24) samples of burfi samples representing the similar extent of bacterial
growth. With a little variability, level of contamination detected in both khoya and burfi
for this pathogenic microorganism revealed a consistent and identical pattern (Tables 1
and 2). Microbiological assay of khoya and burfi clearly manifested a higher count of
ACC (3 to 4 logs) as compared to other bacterial isolates i.e., coliforms and S. aureus
(Tables 3 and 4). The degree of prevalence of the micro flora in these dairy products was
found to be above acceptable limits and coliforms were found in 93% of the total samples
examined. The highest CFU/g were 5.3x106, 5.2x106 and the lowest were 7.5x103 and
6.5x103 in 86 % of the total samples tested for coliform and fecal coliform for burfi and
khoya respectively (Tables 3 and 4). The average coliform load determined was 4.15x104,
3.51x105 in burfi and khoya, respectively (Tables 3 and 4).
Microbiological analysis of khoya and burfi samples revealed that S. aureus was the
major part of bacterial flora in burfi (30.5%) and khoya (33.56%) (Fig. 1). The level of
contamination with coliforms was found to be 28.49% and 30.95% in burfi and khoya
respectively. The overall coliforms were 16.16% and 16.54%; and for Enterobacter spp.,
E. coli and, Klebsiella spp., the level of contamination with Klebsiella spp., was the
highest i.e., ~ 11.17% and 7.6% in burfi and khoya samples respectively (Fig. 1).
Prevalence of Enterobacter spp., and E. coli did not exceed 1.2%, in both burfi and
khoya. The results of the present study clearly indicated that S. aureus, coliforms and
fecal coliforms were the major contaminants of milk products (burfi and khoya).
This study also pointed out major count of coliforms (Enterobacter spp., Klebsiella
spp., E. coli), fecal coliforms and S. aureus. Coliforms contamination was shown to be
relatively less in both types of tested products as compared to fecal coliforms,
Staphylococcal contamination was normally attributed to food handlers, since
nasopharyngeal cavity of human beings is the reservoir of microflora from which these
bacteria get localized on the skin, especially on hands (Kaplan 2005; Masud et al., 1988;
Patel, 1985; Stone et al., 2001).

ANTIBIOTIC RESISTANCE OF BACTERIA ETHNIC MILK BASED PRODUCTS 939
Table 3. Maximum, minimum and average values of various bacterial count (burfi ) (CFU/g).
Nature of test Samples
(No.) Max Min Avg
ACCa 28 2.0 x1 011 1.5 x 106 8.50 x 108
MPN-Cb 26 5.3 x 106 7.5 x 103 4.15 x 104
MPN-FCC 26 5.3 x 106 7.5 x 103 4.15 x 104
S. aureus 24 7.0 x 107 2.2 x 104 1.45 x 105
ACCa = Aerobic colony count, Cb = Coliform, FCc = Fecal Coliform.
The values are the mean of two experiments
Table 4. Maximum, minimum and average values of various bacterial count (khoya) (CFU/g).
Nature of test Samples
(No.) Max Min Avg
ACCa 28 2.5x1011 1.6x106 9.25x108
MPN-Cb 26 5.2x106 6.5x103 3.51x105
MPN-FCC 26 5.2x106 6.5x103 3.51x105
S. aureus 24 7.2x107 2.4x104 1.56x105
ACCa = Aerobic colony count, Cb = Coliform, FCc = Fecal Coliform.
The values are the mean of two experiments
Fig. 1. Prevalence of bacteria in locally prepared dairy products Khoya (White bars) and Burfi
(Black bars). Bacterial isolates Staphylococcus aureus (S.a), coliforms (Co), Enterobacters (En),
Escherichia coli (E.c) and unidentified flora were determined as described in Materials and
Methods, Data points shown are the mean of at least two repetitions, Bars represent ± SD.
The higher Staphylococcal count, as 1.7 x 106 for khoya and 1.9 x 103 for burfi was
observed and the comparable range was present in milk products 105 to 108. (Gordon &
Gibbon, 1999). Our study demonstrated 30.5% and 33.18% S. aureus in khoya and burfi
and for Enterobacter spp. isolates, 56.92% and 55.8% were present in burfi and khoya,
respectively.
Dust and skin of human beings were also known to contaminate food items with
pathogens like S. aureus and Klebsiella spp., Manufacturers contaminate khoya and burfi
during the process of sugar mixing and cutting of sweets into small pieces (Hobb's &
Gilbert, 1978). S. aureus isolated from the milk products produce enterotoxins strains.
Coliforms and fecal coliforms may enter the food through contamination with dust either
directly or indirectly through utensils and equipments used in preparation of these milk

KALSOOM FARZANA ET AL.,
940
products. The food handlers and dust, constitute the major sources of microbial
contamination of sweets. The food handlers also significantly contribute in contamination
of khoya than in burfi (Masud et al., 1988). However, the presence of S. aureus and
Klebsiella spp., will render these products unfit for human consumption, since sufficient
number of these organisms will cause infection and intoxication. Multiplication and
production of S. aureus would however, depend upon environmental factor like time,
temperature, relative humidity and duration of storage and food factors, potential water
activity (aw), moisture contents, nutrients present, additives used and associated
microflora like S. aureus and coliforms and fecal coliforms (Garg & Mandokhot, 1984).
According to United States Environmental Protection Agency, (Anon., 2003), the
presence of E. coli in the intestine and feces of warm-blooded animals is an indicator of
fecal pollution. The grazing of cattle and land application of animal wastes may lead to the
occurrence of enteric pathogens near the surface and ground waters. This potential
contamination due to animal husbandry operations can be a serious threat to public health.
The present work reports high count of S. aureus in all samples of khoya and burf
and that can be due to careless handling at various stages of processing. The presence of
coliforms and fecal coliforms like Enterobacter spp., Klebsiella spp., and E. coli shows
the unhygienic nature of these sweets prepared from milk (Hobb's & Gilbert, 1978).
Antibiotic sensitivity of gram-negative bacteria: Antibiotics resistance pattern of E.
coli, Enterobacter spp., and Klebsiella spp., isolated from burfi and khoya samples has
been shown in Figs. 2 and 3. E. coli isolated from burfi and khoya exhibited 100%
resistance against Urixin, Chloramphenicol and Ampicillin. The level of resistance of E.
coli against Ampiclox, Nitrofurantoin and Tetracycline declined almost with the same
magnitude in both types of dairy products. The susceptibility of E. coli isolated from
burfi and khoya when tested against Amikin, Amoxil, Septran and Augmentin was 100%
(Figs. 2 and 3). Enterobacter spp., isolated from khoya demonstrated a greater degree of
resistance against different antibiotics, particulary Ampicillin and Nitrofurantoin as
compared to Enterobacter spp., isolated from burfi (Figs. 2 and 3). However, Amikin,
Septran and Augmentin were still found to be as effective against Enterobacter spp., as
E. coli from both burfi and khoya samples. One noticeable exception was observed with
Amoxil, manifesting the similar efficacy i.e., ~ 29% resistance of Enterobacter spp., from
both type of dairy products (Figs. 2 and 3).
Urixin, Chloramphenicol, Ampicillin, Ampiclox and Nitrofurantoin, remained
ineffective against Klebsiella spp. In khoya and burfi isolates showing a greater
variability (100, 64, 61, 36 and 39% resistance level of Klebsiella spp., respectively) in
their effectiveness. Amikin and Amoxil demonstrated a simlar extent of susceptibility
i.e., 14% resistance against burfi isolates while khoya isolates of Klebsiella spp.,
manifested relatively higher resistance (25 and 29% respectively) for these antibiotics.
Similarly, Klebsiella spp., only showed some low resistance against Septran, among all
the tested antibiotics (4%). Tetracycline and Augumentin indicated 100% efficacy against
all burfi and khoya isolates examined in this study (Figs. 2 and 3). The activity of
Septran, Tetracycline and Augmentin remained at the maximum for Klebsiella spp.,
Enterobacter spp., and E. coli isolates and the maximum resistance was observed towards
Urixin against the Klebsiella spp., Enterobacter spp., and E. coli isolates of khoya and
burfi (Figs. 2 and 3).

ANTIBIOTIC RESISTANCE OF BACTERIA ETHNIC MILK BASED PRODUCTS 941
Fig. 2. Resistance of Gram- negative bacteria (%) against different antibiotics. Isolates from burfi
were tested against Urixin (white bars), Chloramphenicol (grey bars), Ampicillin (black bars),
Ampiclox (vertical lines), Nitrofurantoin (horizontal lines), Tetracycline (downward diagonal),
Amikin (dotted lines), Amoxil (upward diagonal). Augumentin and Septran indicated 0 %
resistance in all isolates and do not appear in the figure.
Fig. 3. Resistance of Gram- negative bacteria (%) against different antibiotics. Isolates from khoya
were tested against Urixin (white bars), Chloramphenicol (grey bars), Ampicillin (black bars),
Ampiclox (vertical lines), Nitrofurantoin (horizontal lines), Tetracycline (downward diagonal),
Septran (large confetti) Amikin (dotted lines), Amoxil (upward diagonal). Augumentin indicated
0% resistance in all isolates and does not appear in the figure.
Dupont et al., (1978) confirmed the efficacy pattern of these antibiotics against
Enterobacter spp., E. coli and Klebsiella spp. The researchers investigated different
antibiotics for their resistances and found Amikin to be active against Enterobacter spp.,
E. coli and Klebsiella spp., which is consistent with the present results.

KALSOOM FARZANA ET AL.,
942
In the present study, E. coli was quite resistant to Ampiclox, but Klebsiella spp., and
Enterobacter spp., were sensitive to Ampiclox. Blumberg & Strominger, 1974
investigated the mechanism of antibiotics efficacy substantiating Ampiclox to be
effective against Enterobacter spp., E. coli and Klebsiella spp., by inhibiting the
synthesis of cell wall mucopeptide. The resistance of this antibiotic against Gram-
negative bacteria was caused by mutation of acquisition of R-plasmids (Chamberlain,
1976). It was further demonstrated that Amoxil's was highly effective against
Enterobacter spp., E. coli and Klebsiella spp. (Stone et al., 2001). Changes in micro-
organisms lead to the constant evolution of new pathogens, development of antibiotic
resistance and changes in virulence of known pathogens. In many countries, as people
increasingly consume food prepared outside the home, growing numbers are potentially
exposed to the risks of poor hygiene in commercial food service settings (Anon., 2007).
Current evidence exists to suggest that not only are such antibiotic resistant strains more
difficult to control in terms of human infection, they may also be more resistant to heat
processes (Davidson & Henson, 1995). In our study, Enterobacter spp., and Klebsiella
spp., were sensitive but resistance was also reported, when isolated from burfi and khoya.
Roupas & Pitton (1974) studied the resistant strains of Enterobacter spp., E. coli and
Klebsiella spp., by forming β-lactamase production. Chamberlain, (1976) suggested that
this resistance might be due to the induction, mutation or by acquisition of R-plasmids.
It was noticed that E. coli and Klebsiella spp., were resistant to Chloramphenicol but
Enterobacter spp., was less resistant to this antibiotic. Moreover, ribosome located
bacterial resistance to Chloramphenicol is uncommon and resistance of Gram-negative
bacteria is usually acquired by means of R-plasmids (Chamberlain, 1976). In our study,
E. coli, Enterobacter spp., and Klebsiella spp. were found to be resistant to Urixin either
isolated from burfi or khoya samples.
The current results indicated that locally prepared milk products might be a potential
hazardous sources of pathogenic S. aureus, Klebsiella spp., E. coli and Enterobacter spp.,
Strict control measures must be applied to minimize and eliminate the contamination
possibilities through milk and its products leading to minimized use of various antibiotics
which are excessively used and becoming ineffective against such bacterial strains.
References
Ali, M. 2007. Food Poisoning cases on the rise. Daily Times, August 11, 2007, Pakistan.
Anonymous. 1993. Methods for determining bactericidal activity of antimicrobial agents. National
Committee for Clinical Laboratory Standards, Tentative guidelines. Villanova, PA.
Anonymous. 2003. Concentrated animal feeding operations. Federal Register, 68: 71-76.
Anonymous. 2007. Foodborne Disease Outbreaks. Guidelines for Investigation and Control,
Geneva, Switzerland.
Bauer, A.W., W.M.M. Kirby, J.C. Sherris and M. Turk. 1966. Antibiotic susceptibility testing by a
standardized single disc method. American Journal of Clinical Pathology, 45:493-496.
Blumberg, P.M. and J.L. Strominger. 1974. Interaction of penicillin with the bacterial cell: penicillin-
binding proteins and penicillin-sensitive enzymes. Bacteriology Reviews, 38: 291-335.
Brisabois, A., V. Lafarge, A. Brouillaud, M.L. de Buyser, C. Collette, B. Garin-Bastuji and M.F.
Thorel. 1997. Pathogenic organisms in milk and milk products: the situation in France and in
Europe. Reviews Science. & Technology, 16: 452-71.
Cappuccino, G.J. and N. Sherman. 1992. Microbiology, A Laboratory Manual. The
Benjamin/Cummings Publishing Company, Inc., Redwood City, CA.
Carter, G.R. 1995. Veterinary Microbiology. Academic Press, Philadelphia.

ANTIBIOTIC RESISTANCE OF BACTERIA ETHNIC MILK BASED PRODUCTS 943
Case, C.L. and T.R. Johnson. 1984. Laboratory experiments in microbiology. The Benjamin/
Cummings Publishing Company, Inc. CA.
Chamberlain, R.E. 1976. Chemotherapeutic properties of prominent nitrofurans. Journal of
Antimicrobial. Chemotherapy, 2: 325-36.
Chao, G., X. Zhou, X. Jiao, X. Qian and L. Xu. 2007. Prevalence and antimicrobial resistance of
foodborne pathogens isolated from food products in China. Foodborne Pathogens and
Disease, 4: 277-84.
Davidson, P.M. and T.M. Henson. 1995. Comparison of D55C - values of antibiotic resistant and
antibiotic sensitive strains of Salmonella. Journal of Food Protection, 58: 40.
De Buyser, M.L., B. Dufour, M. Maire and V. Lafarge. 2001. Implication of milk and milk
products in food-borne diseases in France and in different industrialized countries.
International Journal of Food Microbiology, 67: 1-17.
Dupont, H.L., H. West, D.G. Evans, J. Olarte and D.J. Evans, Jr. 1978. Antimicrobial susceptibility
of enterotoxigenic Escherichia coli. Journal of Antimicrobial Chemotherapy, 4: 100-2.
Garg, S.R. and V.U. Mandokhot. 1984. Studies on microbial and chemical profile of some Indian
sweet meats and their significance. Indian Journal of Dairy Science, 37: 326-333.
Gordon, D.M. and F.F. Gibbon. 1999. The distribution of enteric bacteria from Australian
mammals: host and geographical effects. Microbiology, 145: 2663-71.
Hobb's, B.C. and R.J. Gilbert. 1978.Food Poisoning and Food Hygiene. Edward Arnold.
Holt, J.G. 1993. Bergey’s Manual of Determinative Bacteriology. Williams and Wilkins, Baltimore MD.
Kaplan, S.L. 2005. Implications of methicillin-resistant Staphylococcus aureus as a community-acquired
pathogen in pediatric patients. Infectious. Disease. Clinics of North America, 19: 747-57.
Masud, T., A. Bari and A.A. Shah. 1988. Screening of milk and milk products for staphylococcal counts
with special reference to public health. Journal of Pakistan. Medical Association, 38: 286-8.
Normanno, G., G. La Salandra, A. Dambrosio, N.C. Quaglia, M. Corrente, A. Parisi, G. Santagada,
A. Firinu, E. Crisetti and G.V. Celano. 2007. Occurrence, characterization and antimicrobial
resistance of enterotoxigenic Staphylococcus aureus isolated from meat and dairy products.
International Journal of Food Microbiology, 115: 290-6.
Oliver, S.P., B.M. Jayarao and R.A. Almeida. 2005. Foodborne pathogens in milk and the dairy
farm environment: food safety and public health implications. Foodborne Pathogens and
disease, 2: 115-29.
Patel, G.S. 1985. Bacteriological quality of pedha and burfi with special reference to certain
bacteria of public health significance. Journal of Food Science & Technology, 22: 133-136.
Pelczar, M.J., E.C.S. Chan and N.R. Krieg. 1999. Host-Parasite Interaction; Nonspecific Host
Resistance, In: Microbiology concepts and applications. McGraw-Hill., Inc. New York.
Roupas, A. and J.S. Pitton. 1974. R factor-mediated and chromosomal resistance to ampicillin in
Escherichia coli. Antimicrobial Agents and Chemotherapy, 5: 186-91.
Stone, S.P., L. Teare and B.D. Cookson. 2001. The evidence for hand-hygiene. Lancet, 357: 479-480.
Walsh, C., G. Duffy, J.J. Sheridan, S. Fanning, I.S. Blair and D.A. Mcdowell. 2005. Thermal
resistance of antibiotic-resistant and antibiotic-sensitive Salmonella spp., on chicken meat.
Journal of Food Safety, 25: 288-302.
(Received for publication 3 September 2008)