Actinomyces species: A Danish Survey on Human Infections and Microbiological Characteristics.
ABSTRACT This study compared phenotypic and genotypic identification of Actinomyces strains, tested susceptibility to antibiotics and evaluated their clinical importance. Thirty-four Actinomyces strains were examined; sixteen type strains, and 18 clinical strains from different hospitals in Denmark from the period 2003-2005. Partial 16S rDNA sequencing using a stretch of 526 bases was used for genotypic identification. Susceptibility testing was done by E-test. The antibiotics examined were: benzylpenicillin, piperacillin with tazobactam, ceftriaxone, meropenem, erythromycin, clindamycin, linezolid, moxifloxacin, tetracycline and tigecycline. Clinical parameters were obtained by reviewing patient records. There was poor agreement between the phenotypic and genotypic identification. Phenotypic tests were helpful in identifying strains closely related by DNA sequences. The strains were sensitive to the examined antibiotics except for moxifloxacin to which most strains were resistant, and a few strains were resistant to meropenem and tetracycline. The clinical strains were from many different types of infections and locations. None of the patients was described as having typical actinomycetic lesions, and an apparently good outcome was obtained with different treatment regimens.
- SourceAvailable from: sciencedirect.com[Show abstract] [Hide abstract]
ABSTRACT: Bacteremia due to Actinomyces neuii has been reported in the literature 14 times. A. neuii is an endogenous organism that has been cultured in clinical specimens of the genitourinary tract; we are reporting a unique case of Actinomyces neuii postoperative testicular abscess with bacteremia which was successfully treated with surgery and a short course of parenteral antimicrobials.IDCases. 01/2014;
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ABSTRACT: We describe the first case of bacteremia due to Actinomyces urogenitalis. Bacteremia was secondary to a tubo-ovarian abscess following transvaginal oocyte retrieval. Identification was established by MALDI-TOF MS and confirmed by 16S rRNA gene sequencing. A. urogenitalis should be considered as a potential causative agent of infection after gynecological procedures.Journal of clinical microbiology 09/2013; · 4.16 Impact Factor
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ABSTRACT: There have been few studies of pulmonary actinomycosis, which is an uncommon anaerobic infection. Consequently, the optimal therapeutic regimen, appropriate duration of treatment, long-term prognosis, and factors predicting prognosis are not well established. We retrospectively reviewed the medical records of histopathologically confirmed cases of pulmonary actinomycosis seen between November 2003 and December 2012. The study included 68 patients with a mean age of 58.4 +/- 11.6 years. Of the 68, initial surgery was performed in 15 patients (22.1%), while the remaining 53 (77.9%) received antibiotic therapy initially. In the initial antibiotic group, 45/53 (84.9%) were cured without relapse (median antibiotic duration 5.3 months). 5/53 (9.4%) patients were refractory medically (median antibiotic duration 9.7 months), and 3/53 (5.7%) experienced a recurrence (median time to relapse 35.3 months). In the initial surgery group, 14/15 (93.3%) were cured and treatment failure occurred in one (6.7%). In the multivariate analysis, the absence of an antibiotic response at 1 month was the only independent factor associated with a poor treatment outcome, with an adjusted odds ratio of 49.2 (95% CI, 3.34-724.30). There was no significant difference in treatment outcome based on the size of the parenchymal lesion, comorbidities, whether intravenous antibiotics were used, antibiotic therapy duration, or whether the initial treatment was surgical. Antibiotic treatment with or without surgery was effective for treatment of pulmonary actinomycosis. Nevertheless, treatment failure or recurrence occurred in a considerable proportion of patients, especially those resistant to the initial antibiotic treatment.BMC Infectious Diseases 01/2014; 14(1):10. · 3.03 Impact Factor
The Open Microbiology Journal, 2009, 3, 113-120 113
1874-2858/09 2009 Bentham Open
Actinomyces species: A Danish Survey on Human Infections and
J.M. Hansen1,2,*, H. Fjeldsøe-Nielsen1,3, S. Sulim1,4, M. Kemp1 and J.J. Christensen1
1Department of Bacteriology, Mycology and Parasitology, Statens Serum Institute, Copenhagen, Departments of
Clinical Microbiology at 2Hvidovre Hospital, Hvidovre, 3Naestved Hospital, Naestved and 4Viborg Hospital, Viborg,
Abstract: This study compared phenotypic and genotypic identification of Actinomyces strains, tested susceptibility to
antibiotics and evaluated their clinical importance. Thirty-four Actinomyces strains were examined; sixteen type strains,
and 18 clinical strains from different hospitals in Denmark from the period 2003-2005. Partial 16S rDNA sequencing
using a stretch of 526 bases was used for genotypic identification. Susceptibility testing was done by E-test. The antibiotics
examined were: benzylpenicillin, piperacillin with tazobactam, ceftriaxone, meropenem, erythromycin, clindamycin, line-
zolid, moxifloxacin, tetracycline and tigecycline. Clinical parameters were obtained by reviewing patient records. There
was poor agreement between the phenotypic and genotypic identification. Phenotypic tests were helpful in identifying
strains closely related by DNA sequences. The strains were sensitive to the examined antibiotics except for moxifloxacin
to which most strains were resistant, and a few strains were resistant to meropenem and tetracycline. The clinical
strains were from many different types of infections and locations. None of the patients was described as having typical
actinomycetic lesions, and an apparently good outcome was obtained with different treatment regimens.
Keywords: Actinomyces species, Bacterial identification, phenotypic characterization, partial 16S rDNA sequencing.
group of anaerobic and facultative anaerobic, asporogenous,
Gram-positive, non-acid-fast, rod-shaped organisms ,
many of which occur as inhabitants of mucosal surfaces,
particularly the oral cavity, of humans and animals. Actino-
myces species can cause actinomycosis, a chronic granulo-
matous lesion, forming suppurative abscesses and draining
sinuses. Localization is most often cervicofacial (60%),
thoracic (15%) or abdominal (20%) . Both laboratory
identification and clinical diagnosis is often troublesome.
Coryneform bacteria are difficult to classify at the species or
even at the genus level  and poses major problems for
clinical microbiology laboratories in terms of labour, time,
and cost, when conventional methods are used. Panels of
phenotypic characteristics useful in identifying species have
been described by Funke et al.  and Sarkonen et al. .
An increased recognition of the importance of coryne-
form bacteria as opportunistic human pathogens within the
last decade , has occurred in a period where new diagnos-
tic tools for identification of bacteria progressively have
been introduced. These techniques, especially sequencing of
genes coding for rRNA have revolutionized the insight into
phylogeny and taxonomy of bacteria.
The genus Actinomyces consists of a heterogeneous
of Actinomyces species from humans, 18 recent Danish
We therefore found it relevant to characterize 34 strains
*Address correspondence to this author at the Department of Clinical
Microbiology, Hvidovre Hospital, Kettegaard Allé 30, 2650 Hvidovre,
Denmark; E-mail: email@example.com
clinical strains and 16 type strains of different species, using
a recent phenotypical identification scheme, and compare
the results to genotypic identification using partial 16S
rDNA sequencing. In addition, susceptibility to antibiotics
was determined and data on clinical manifestations of the
respective patients was obtained.
MATERIALS AND METHODS
strains, received from CCUG (Culture Collection, University
of Göteborg, Göteborg, Sweden), were included: A.
europaeus CCUG 32789AT, A. funkei CCUG 42773T, A.
georgiae CCUG 32935T, A. gerencseriae CCUG 32936T, A.
graevenitzii CCUG 27294T, A. israelii CCUG 18307T, A.
meyeri CCUG 21024T, A. naeslundii CCUG 18310T, A. neuii
subsp. neuii CCUG 32252T, A. neuii subsp. anitratus CCUG
32253T, A. odontolyticus CCUG 20536T, A. radicidentis
CCUG 36733T, A. radingae CCUG 32394T, A. turicensis
CCUG 34269T, A. urogenitalis CCUG 38702T, A. viscosus
CCUG 14476T. Eighteen strains were clinical strains submit-
ted from Danish Departments of Clinical Microbiology
to the National Reference Laboratory for identification
of bacteria, at Statens Serum Institut (SSI), in the period
February 2003 - March 2005. All strains were kept as frozen
(- 80 °C) stocks.
We examined 34 Actinomyces strains. Sixteen type
(SSI Diagnostica, Hillerød, Denmark), and the agar plates
The strains were subcultured on 10 % horse blood agar
114 The Open Microbiology Journal, 2009, Volume 3 Hansen et al.
were incubated for five days at 35 °C in ambient air, a CO2-
enriched (5 %) and an anaerobic atmosphere, respectively.
Colonial morphology and microscopic appearance in Gram-
stained preparations were noted. CAMP reaction was
examined on CAMP agar (SSI Diagnostica) with a beta-
hemolysin-producing strain of Staphylococcus aureus.
CAMP-plates were incubated at 35 °C in a CO2-enriched (5
%) and an anaerobic atmosphere, respectively, and were read
after 24-h and 48-h incubation. Testing for nitrate reduction
was performed using a nitrate broth culture (semi-solid agar)
incubated at 35 °C in an anaerobic atmosphere for a
minimum of five days, prior to addition of sulfanilic acid,
Cleves acid, and if necessary zinc powder [5, 6]. Rosco
diagnostic tablets (Rosco A/S, Taastrup, Denmark) were
used for testing hydrolysis of urea and esculin, production of
?-fucosidase, ?-glucosidase, ?-N-acetylglucosaminidase
(?-NAG) and ?-galactosidase (ONPG), and acid production
from L-arabinose, following the instructions of the manufac-
turer. A. israelii and A. gerencseriae were differentiated
from each other by the presence of ?-mannosidase and
arginine dihydrolase (ADH). Acid production from L-
arabinose, maltose, mannitol, raffinose, rhamnose, sucrose,
xylose and trehalose was tested in tubes with extract-
bouillon and the carbohydrate (SSI Diagnostica) , incu-
bated at 35 °C in an anaerobic atmosphere for a minimum of
five days. Horse citrate plasma was added to promote
growth. All tests, except testing for the presence of ?-
mannosidase, were performed by more than one method, as
the strains were also tested with the API? strips, Rapid ID
32 A and API 20 A? (bioMérieux? as, Marcy l’Etoile,
France) following the instructions of the manufacturer.
Rapid ID 32 A tested: ability to reduce nitrate, the presence
of urease, ?-fucosidase, ?-glucosidase, ?-NAG, ONPG and
ADH, and acid production from raffinose. API 20 A?
tested: presence of urease, hydrolysis of esculin, acid
production from arabinose, maltose, mannitol, raffinose,
rhamnose, sucrose, xylose and trehalose. Catalase was
detected with 10 % H2O2 in a well in the API 20 A? strip
with a positive reaction.
Ribosomal DNA Sequencing
heating isolated bacteria at 95°C for 5 min. PCR amplifica-
tion of part of the 16S rRNA gene was performed using
the primers BSF-8 and BSR-534 as previously described .
DNA sequences were aligned and edited at http://bioinfo.
genotoul.fr/multalin/multalin.html resulting in comparable
sequences ranging from 324 to 351 basepairs. Furthermore,
all edited sequences were compared to deposited sequences
in the Bio Informatic Bacteria Identification database.
Sequences obtained for clinical strains were compared to
original CCUG sequences of collection strains. Results were
illustrated in a phylogentic tree using CLC workbench 4.5
For molecular biological study DNA was released by
(AB Biodisk, Solna, Sweden) for the following antibiotics:
benzylpenicillin, piperacillin with tazobactam, ceftriaxone,
meropenem, erythromycin, clindamycin, linezolid, moxi-
floxacin, tetracycline, and tigecycline. All tests were per-
The MICs of all the strains were determined using E-test
formed on anaerobic plates (SSI Diagnostica). Plates were
inoculated with the bacterial isolates in API suspension
medium (demineralised water) (bioMérieux? as, Marcy
l’Etoile, France) with a turbidity equivalent of McFarland
standard 4,0  and incubated anaerobically at 35 ºC for 48-
72 hours. Results were read according to the manufacturer’s
guidelines. Quality controls were performed using Bacteroi-
des fragilis (ATCC 25285). MIC measurements (at least
triplicate) for the control strain were as follows: Penicillin:
> 32 μg/ml, piperacillin/tazobactam: 0.25-0.5 μg/ml, cef-
triaxone: 32 μg/ml, meropenem: 0.064 μg/ml, erythromycin:
1.5 μg/ml, clindamycin: 0.75-2.0 μg/ml, linezolid: 1.5 μg/ml.
antibiotic treatment was recorded from patient files.
Information on predisposing factors, actual diagnosis and
stained preparations and with growth on agar. Micro-
scopically many strains were without visible branching,
many were small rods with an appearance similar to the
coryneforms, other were coccoid or long and curved rods.
On agar most strains were grey or white, colony-sizes ranged
from pinpoint to three mm in diameter, and some had ?-
haemolysis. Colonies could be rough or smooth, elevated or
flat, and some adhered to agar. The incubation atmosphere
influenced appearance and growth; some strains did not
grow in ambient air.
The appearance of the strains varied both in the Gram-
Actinomyces strains following the recommendations of
Sarkonen et al. . All type strains were correctly identified.
We used the same type strains as Sarkonen et al. except for
the type strain of A. israelii. The clinical strains were
grouped from the phenotypic identification; one strain could
not be designated to a species by the performed phenotypic
Table 1 shows results of phenotypic identification of
differed when tested with different methods. This was for
example seen when testing nitrate reduction, esculin
hydrolysis and acid production from carbohydrates.
Results of individual biochemical reactions sometimes
strains best taxon match had scores from 642 to 672 bits and
differences to next best taxon matches between 22 and 260
bits. Some species were more closely related than others;
A. meyerii and A. odontolyticus were most closely related,
followed by A. viscosus and A. naeslundii. A. radingae was
least connected to the other species. For 18 clinical strains
scores of 480 to 670 bits were found with differences to next
best taxon matches between 2 and 245 bits.
All type strains were correctly identified. For the 16 type
species on phenotypic characteristics, wherefore 17 clinical
strains could be compared (Fig. 1).
One of the clinical strains could not be allocated to a
Actinomyces species: A Danish Survey The Open Microbiology Journal, 2009, Volume 3 115
Table 1. Results from Phenotypic Identification of Strains of Actinomycesa
Hydrolysis of: Production of: Fermentation of:
Urea Esculin ? ?-Fuco-
CCUG 32789 AT
? + +
? v v v
? + + +
? v + + + +
CCUG 32936T, 1
? v, ?
?, + +
?, v + v, +
? + + +
? + + +
CCUG 18307T, 2
? +, v
? + v + v + v, ? + + +
A. meyeri CCUG
? + + v
A. neuii subsp.
CCUG 32252T, 2
? + +, v +
? + + v
? + + +, v
A. neuii subsp.
? + + +
? + + +
CCUG 20536T, 2
?, v +, v +
? v +, v + +
? + v
? + + +
CCUG 32394T, 2
? v, + + + v, ? + +, v + v +, v
? + +, v +, v
CCUG 34269T, 5
? +, v +
?, v v, +
? + +
? + + + v +
? + + + + +
CCUG 14476T, 3
?, v +
?, v v
? + v +
? + +
a ?, negative result; +, positive result; v, variable reaction (by different methods or among strains). Results for type strains are given first if different from the results obtained on
116 The Open Microbiology Journal, 2009, Volume 3 Hansen et al.
Fig. (1). Phylogenetic tree illustrating the relationship between the 16 type strains and the 18 clinical strains. Six clinical strains did not reach
concordance between genotypic / phenotypic* identification (five with different species names and one with no species identification). The
remaining 12 strains were allocated to the same species when comparing the two methods of identification.
agreement at the species level. Two additional strains
showed concordance as BLAST examinations could not
separate (bits score difference < 30) between A. viscosus and
A. naeslundii; the latter was proposed from phenotypic char-
acterization (and second BLAST choice) and the former
from first BLAST choice. Thus, for 12 of 17 strains results
from phenotypic and molecular examinations were in agree-
ment. BLAST examinations for all strains seemed very con-
vincing when taking all parameters into consideration (Fig.
1). Thus, for five of 17 clinical strains identifications by
genotypic/phenotypic methods were in disagreement as indi-
cated in Fig. (1) with an *. One isolate could not be desig-
nated to a species based on phenotypic characterization,
which by genotypic identification belonged to the species A.
meyerii. The isolates with disagreeing identifications were
(genotypic/phenotypic identification): 1) A. odontolyticus/A.
radingae (n=1), 2) A. radingae/A. gerencseriae (n=1), 3) A.
gerencseriae/A. israelii (n=1), 4) A. israelii/A. viscosus and
5) A. meyerii/A. turicensis.
Ten of the 17 clinical strains showed methodological
strains were sensitive to benzylpenicillin, piperacillin/
The MICs for the 34 strains are shown in Table 2. All
tazobactam, ceftriaxone, meropenem, erythromycin, clin-
damycin, linezolid, tetracycline and tigecycline, except for
meropenem and tetracycline where one strain for each anti-
biotic had MIC values above the upper limits for sensitivity.
Notably for moxifloxacin, 21 strains had MIC`s above the
upper limit for being sensitive though most strains (n=16)
were close to the breaking point. We experienced difficulties
reading zone diameters due to hazy zone edges, which
explains why it was not possible to define an MIC value for
1-5 strains for each antibiotic.
patients from whom Actinomyces species were isolated. The
patients have been divided into groups based on species
designations from the genotypic identification. The clinical
strains were chosen at random during the period February
2003 - March 2005. The median age was 54 years, 10 were
men and 8 women.
Table 3 shows clinical and microbiological data on the 18
blood (4), intraabdominal abscesses (3), periodontal infec-
tions (2), and one strain each from pus from bladder,
empyema of the pleural space, spinal fluid and a swab from
The strains were from soft tissue infections (5 strains),
Actinomyces species: A Danish Survey The Open Microbiology Journal, 2009, Volume 3 117
antibiotic treatment and, respectively, 5 and 4 patients
received either antibiotic treatment or surgical intervention.
When antibiotics were given, the drug(s) and duration
varied, but always included ?-lactam antibiotics. The follow-
ing ?-lactam antibiotics were used: penicillin, ampicillin,
dicloxacillin, mecillinam, cefuroxime, ceftriaxone and
meropenem. In some cases ciprofloxacin, gentamicin and
metronidazole were added. The patient with keratitis was
treated with topical agents containing chloramphenicol,
tetracycline, polymyxin and gentamicin. All patients recov-
ered, except one who died from other causes. Two patients
had sequelae; one each with neurologic sequelae following
meningitis and reduced vision following keratitis.
Nine patients received both surgical intervention and
Funke et al. used 15 phenotypic characteristics to differenti-
ate the species from other human-derived, aerobically grow-
ing Actinomyces and Arcanobacterium species. In the
scheme by Sarkonen et al.  using 18 characteristics, which
also is used in this study, the same characteristics were used
except that pyrazinamidase production and acid production
from glucose plus glycogen was not tested for. However,
additionally the scheme by Sarkonen et al.  takes into
consideration pigmentation, production of ?-fucosidase and
acid production from arabinose, raffinose, rhamnose and
trehalose. The number of Actinomyces species has increased
since these schemes were made. Often new species have
been created from subgroups of existing species, complicat-
ing the destinction between species based on phenotypic
characteristics as inclusion of new tests have been needed
for differentiation between species . The fact that the
When describing the species A. europaeus in 1997 ,
same reaction done with different methods, as also seen in
this study, may result in diverse results complicates pheno-
typic identification even more. Recently, former genospecies
1 and 2 of A. naeslundii have been validly published as
A. oris sp. nov. and A. johnsonii sp. nov.; these new species
cannot be readily differentiated using conventional pheno-
typic testing . All these developments stresses the need
for applicating molecular methods for identification of
microscope. It may be the typical Gram-positive branching
bacilli, which often present with a beaded appearance,
but not seldom more coccoid or variable forms occurs. Like-
wise, the typical molar tooth appearance of A. israelii may
be absent. The appearance may be similar to common
relatively avirulent pathogens, which often may be present
together with Actinomyces species. It is therefore likely
that Actinomyces sometimes is overlooked in samples.
Misidentifications or non-identifications are presumed to
occur in the routine microbiology laboratory. 16S rRNA
gene sequence analysis has shown to be a powerful test
in confirming or identifying suspected or non-identified
Actinomyces species has a varied appearance in the
in scores between best and next best taxon matches. When
examining phylogenetic trees based on a comparison of
approximately 1,320 nucleotides, A. meyerii and A. odon-
tolyticus, and A. viscosus and A. naeslundii, are closely
related explaining the low bits-differences . Results of
phenotypic reaction may be helpful in species identification
in such cases. All in all, 16S rDNA sequencing of a 526 base-
pair stretch gave a good separation into proposed species.
Three of the examined strains had very low differences
Table 2. Minimal Inhibitory Concentrations of 10 Antimicrobial Agents Against Actinomyces species. (n=34), Including Type
Strains of 16 Different Species
0.004 0.008 0.016 0.032 0.064 0.125 0.25 0.5 1 2 8 16 32
Benzylpenicillin# 2* 1 1 9 6 6 4 5 0,004-0,5
Piperacillin/tazobactam# 1 1 2 2 7 7 4 7 3
Ceftriaxone 1 1 2 6 8 5 6 4
Meropenem 5 5 4 8 5 2 1 4
Erythromycin# 21 8 1 4
Clindamycin# 4 13 3 5 4 1 1 3
Linezolid 2 9 18 1 4
Moxifloxacin 1 3 8 10 6 4 1 1
Tetracycline# 1 11 11 5 1 1 4
Tigecycline 1 10 12 8 3
1)* Number of strains with adequate growth for reading MIC
2)** Number of strains with undefined MIC due to poor growth.
3) Grey shadings mark the upper limit for sensitivity according to international guidelines. Values above indicates resistance. (Pharmacological breakpoints 2007 from SRGA are
used for antibiotics marked#. Pk/pd breakpoints from EUCAST are used for the other antibiotics).
118 The Open Microbiology Journal, 2009, Volume 3 Hansen et al.
Table 3. Clinical and Microbiological Data on 18 Patients from whom Actinomyces species were Isolated
Species/ no. of
Isolated from Underlying Illness Major Clinical
Coisolates Treatment Outcome
A. odontolyticus/ 1 56 F blood cirrhosis
-a antibiotics (m, mt)
death from other
A. turicensis/ 4 24 F pus (nates) -a
soft tissue abscess
- surgery recovery
56 M tissue (necrotic)
fasciitis of face and
H. parainfluenzae, NHS,
CNS, Prevotella spp.
surgery, 17 and
later 15 days of
antibiotics (p/cu + mt, d)
63 F pus (bladder) chronic dialysis cystitis
B. fragilis, CNS
rinsing of the bladder,
25 days of antibiotics
(d, ci + mt)
46 F pus (rectum) - rectum abscess -
drainage, 6 weeks of
antibiotics (p, g, mt,
followed by p alone)
A. neuii/ 2 91 M blood
9 days of antibiotics
67 M blood
perirenal abscess CNS, coryneforms
drainage, min. 37 days
(a, followed by p + ci)
A. meyeri/ 4 34 M pus (cheek)
soft tissue abscess
*does not show for
33 M root of a tooth -
dental treatment and
36 M pus (pleura)
microscopy also showed
Gram-pos. cocci in chains
2-3 weeks of antibiotics
*does not show for
66 M pus (abdomen)
long episode of
drainage (twice) recovery
38 M spinal fluid alcoholism meningitis -
antibiotics (initially high
doses of p, a, ct)
A. israelii/ 2
35 F pus (abdomen) -
surgery, 4 days of
antibiotics (cu, mt)
A. radingae/ 2 52 M pus (scrotum) -
soft tissue abscess
cocci and Gram-neg. rods
surgery, a prior to
74 F pus (back) -
soft tissue abscess
on the back
- surgery recovery
A. viscosus/ 1 87 F blood COLD, Mb. cordis source unknown -
9 days of antibiotics
(cu, p, mc)
A. naeslundii/ 1 52 F swab (cornea)
injury of the cornea
Lactobacillus sp. found
in other samples
topical antibiotics reduced vision
A. gerencseriae/ 1 66 M swab (oral cavity) -
surgery, 4 weeks of
F, female, M, male, a-, none, *, assumed recovery
H., Hæmophilus, B., Bacteroides, NHS, non-hemolytic streptococci, CNS, coagulase-negative staphylococci, pos., positive, neg., negative
a, ampicillin/amoxicillin, ci, ciprofloxacin, ct, ceftriaxone, cu, cefuroxime, d, dicloxacillin, g, gentamicin, m, meropenem, mc, mecillinam, mt, metronidazole, p, penicillin.
Actinomyces species: A Danish Survey
Sequence analysis is especially useful when a rapid identifi-
cation is desired due to for example clinical circumstances.
Thus, molecular bacterial identification is a powerful tool
for national reference laboratories enhancing both the speed
and validity of performed examinations. Using BLAST
examinations may also be helpful in giving up to date
The Open Microbiology Journal, 2009, Volume 3 119
species is quite predictable . Strains are generally sensi-
tive to ?-lactams. However, some may exhibit higher MIC
values as also shown by McNeil and Schaal. The medium we
used for susceptibility testing contains L-cystein, which
reduces the activity of ?-lactam antibiotics ; therefore,
underestimated susceptibility for these antimicrobial agents
can be expected. Erythromycin was the most active antimi-
crobial agent in vitro, followed by tigecycline. Clindamycin,
linezolid and tetracycline also showed good in-vitro activity
with MICs within the therapeutic range for all strains, except
one strain, that was resistant to tetracycline. It is important
knowing that fluorquinolones generally have poor activity
against Actinomyces species . In agreement with this
moxifloxacin for most strains in this study had MIC values
above the upper limit for sensitivity. Susceptibility testing
of Actinomyces species can be problematic; therefore, it
would be relevant to elaborate standard guidelines for
susceptibility testing procedure and to determine species-
In vitro antimicrobial susceptibility of Actinomyces
number of clinical Actinomyces species were examined. Sev-
enty-three strains were identified by genotypic identification.
A. turicensis was the most frequently isolated species. With
genotypic identification the most frequently identified
species in our study were A. turicensis and A. meyeri. The
normal niche of A. turicensis has been assessed  to be
gastrointestinal, genital or skin in that area. Some strains
were also isolated from abscesses of the face, neck, breast,
chest and back. Our findings are in accordance with this, see
Table 3. The normal niche of A. meyeri, A. israelii and A.
odontolyticus was assessed to be oropharynx, and this is in
accordance with three of our A. meyeri strains being from
abscess of cheek, root of tooth and empyema of pleural
space, respectively. Finally, A. radingae was associated with
chronic soft tissue abscesses of the breast, chest and back,
and the normal niche was assessed to be skin of the upper
body. One of our two strains was from an abscess on the
In the article by Clarridge III and Zhang  a large
needing surgery and a long course of antibiotics [13, 14].
Typical actinomycetic lesions contain between 1 and 10 bac-
terial species in addition to the pathogenic Actinomycetes
. We do not have information of typical actinomycotic
lesions in our patients. Several of the patients did not receive
antibiotics at all or only short courses of treatment with
recovery. These cases were especially soft tissue infections,
but also abscesses in the abdomen and positive blood
cultures. Thus, it is important to be aware of that many infec-
tions involving Actinomyces species may not present as typi-
cal actinomycetic lesions. The great recovery rate may be
Actinomyces is often difficult to diagnose and eradicate,
associated to the wide range of antibiotic sensitivity (except
quinolones) among Actinomyces species and that infections
may have a milder/different course than the classic severe
A. israelii infections and therefore not necessitating the
very long periods of high doses of forenstance penicillin as
phenotypic and genotypic identification of Actinomyces
species. Phenotypic tests were helpful in identifying strains
closely related by DNA sequences. The examined Actinomy-
ces strains were in-vitro sensitive to many antibiotics includ-
ing ß-lactams, but not quinolones, and two strains were resis-
tant to meropenem and tetracycline, respectively. Standard
guidelines for susceptibility testing of Actinomyces are
lacking. With a varied appearance, both microscopically
and on agar, often looking like common relatively avirulent
bacteria, Actinomyces may easily be overlooked in samples.
Actinomyces can be present in infections without typical
actinomycetic lesions, and some of these infections probably
do not need the same aggressive and long treatment as
In conclusion, we find poor agreement between the
Denmark and the Hospital Departments where patients were
admitted for their contributions and help in connection with
this project. Many thanks to Annemarie Hesselbjerg, Sandra
Isling and Rimtas Dargis for excellent technical support.
We thank the Departments of Clinical Microbiology in
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Received: June 17, 2009
Revised: June 24, 2009 Accepted: June 26, 2009
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