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Journal of Clinical Microbiology, September 2003, p. 4184-4187, Vol. 41, No. 9
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.9.4184-4187.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Recent Emergence of an Epidemic Clindamycin-Resistant Clone of Clostridium difficile among Polish Patients with C. difficile-Associated Diarrhea
Hanna Pituch,1* Alex van Belkum,2 Nicole van den Braak,2 Piotr Obuch-Woszczatynski,1 Henri Verbrugh,2 Felicja Meisel-Miko
ajczyk,1 and Miros
aw
uczak1
Department of Medical Microbiology, Centre of Biostructure Research, The Medical University of Warsaw, Warsaw, Poland,1
Erasmus University Medical Centre Rotterdam (EMCR), Department of Medical Microbiology & Infectious Diseases, 3015 GD Rotterdam, The Netherlands2
Received 17 March 2003/
Returned for modification 2 June 2003/
Accepted 27 June 2003

ABSTRACT
Analysis of both the antibiotic resistance and the virulence
characteristics of anaerobic human microbial pathogens is important
in order to improve our understanding of a number of clinically
significant infectious diseases, including
Clostridium difficile-associated
diarrhea (CDAD). We determined the presence of the clindamycin
resistance-associated gene
ermB and the ribotype of 33
C. difficile strains isolated from Polish patients suffering from CDAD. While
all strains produced cytotoxin B (TcdB), enterotoxin A (TcdA)
was produced by a subset of 15 strains only. The results showed
that a single
ermB-positive, TcdA
-B
+ C. difficile strain with
ribotype A has disseminated widely in the two Warsaw hospitals
under investigation. Although different strains with the same
phenotype were detected, the genotype A strain appeared to be
the only one with a clear epidemic character. Apparently, enhanced
local spread of CDAD-causing
C. difficile may be restricted
to a limited number of bacterial genotypes only.

INTRODUCTION
Clostridium difficile is a gram-positive, spore-forming anaerobic
pathogen capable of causing nosocomial
C. difficile-associated
diarrhea (CDAD) (
8). The severity of the infection ranges from
the usually self-limiting CDAD to life-threatening pseudomembranous
colitis (
4). The pathogenicity of this bacterial species is
primarily determined by the production of two major toxins,
enterotoxin A (TcdA) and cytotoxin B (TcdB). The 308-kDa TcdA
protein induces fluid secretion, mucosal edema, and massive
inflammation, including neutrophil infiltration (
18,
24). The
270-kDa TcdB protein induces profound morphological changes
in cultured cells (
23). Recently, TcdA-negative, TcdB-positive
(TcdA
-B
+) strains, which produce TcdB only, have been recognized
as a cause of CDAD in different countries (
1,
2,
11,
16,
17,
22). The TcdB produced by some well-characterized TcdA
-B
+ C. difficile strains demonstrated an unusually strong cytopathic
effect (CPE), the same as the effect caused by the cytotoxin
produced by
Clostridium sordellii (
7). Hospital-wide use of
clindamycin was identified as an important risk factor for the
development of CDAD (
5,
10). Resistance against clindamycin
is ignited by a special group of the transferable
erm genes
encoding methylases that specifically modify the bacterial ribosome
(
20,
26,
27).
Molecular systems for defining the genotypic characteristics of C. difficile have been developed and validated over the past 10 years. A PCR ribotyping procedure based on polymorphism in the 16S-23S intergenic spacer region is one of the best current methods for epidemiologic typing of C. difficile (25). A recent report from The Netherlands identified a nosocomial outbreak due to a genetically distinct clindamycin-resistant TcdA-B+ C. difficile strain in a university hospital (16). Recently, we reported on the existence of TcdA-B+ C. difficile strains in Polish patients with CDAD (22). The aim of the present study was to determine the distribution of the ermB gene and differentiating ribotypes among CDAD-associated C. difficile strains recently isolated (1999 to 2001) from Polish patients.

MATERIALS AND METHODS
Culture and identification of C. difficile.
C. difficile was identified as described previously (
22). Fecal
samples were inoculated onto Columbia agar containing 100 mg
of cycloserine/liter, 8 mg of cefoxitine/liter, and 2 mg of
amphotericin B/liter (CCCA medium, bioMerieux, Marcy-l'Étoile,
France). Medium was prereduced by 24-h incubation in an anaerobic
atmosphere. During cultivation, plates were incubated anaerobically
in a glove box (Forma Scientific) at 37°C for 4 days. Isolates
were identified as
C. difficile by their characteristic colony
morphology, specific horse odor, green-yellow fluorescence under
UV light, Gram staining, and biochemical tests (API-20 A, bioMerieux).
Bacterial strains.
We investigated all (n = 33) strains of C. difficile isolated from CDAD patients hospitalized in two different institutions between 1999 and 2001. Patients suffering from CDAD were those individuals who produced more than three liquid stools within 48 h, had an antibiotic therapy in their recent medical history, and had a hospitalization period of more than 5 days. Stool cultures should be negative for Salmonella spp., Shigella spp., pathogenic Escherichia coli, rotaviruses, and intestinal parasites, including Giardia. Twenty-four strains were isolated from adults hospitalized in transplantology (n = 7), general surgery (n = 3), internal medicine (n = 7), and orthopedics wards (n = 7). Nine strains were isolated from children hospitalized in the hematology unit of a separate pediatric hospital. For comparative reasons, we included eight ermB-positive TcdA-B+ C. difficile strains. These strains were also isolated from Polish patients and have been described before (22). A small reference set consisted of a single toxigenic strain (VPI 10463) and a nontoxigenic isolate (NIH BRIGGS 8050) which were included as control strains in the cytotoxin assays and TcdA- and TcdB-specific PCR tests. One additional TcdA-B+ strain (GAI 95601) was used as internal control for detection of repeating sequences in the TcdA gene. One ermB-positive strain (number 630) was included in all of the ermB PCR tests.
DNA isolation.
Prior to DNA isolation, the strains were grown in liquid brain heart infusion medium for 96 h. Cells present in 1 ml of the medium were sedimented by centrifugation and incubated in 200 µl of Tris-EDTA-glucose buffer including 100 µg of lysozyme per ml (Sigma, Roosendaal, The Netherlands). After 1 hour at 37°C, 400 µl of lysis buffer prepared according to the methods of Boom et al. (3) was added. DNA was affinity captured to Celite and purified by several washing steps. DNA was ultimately eluted by incubation in 100 µl of T10E at 56°C. The DNA solution was ready to use for PCR and, when needed, could be stored for more than one-half year at -20°C without apparent loss in quality.
Toxigenicity.
TcdA and TcdB were detected from a single colony that was recultured anaerobically in brain heart infusion medium for 96 h. Supernatants were collected by centrifugation (3,000 x g for 15 min). TcdA was determined by means of the C. difficile toxin A test (Oxoid, Basingstoke, United Kingdom). Briefly, 125 µl of supernatant was put onto the sample window of the test unit. After 30 min, a blue line in the results window indicated a positive result. When this test was negative and corroborated by a negative toxin A PCR (see below), the strain was considered toxin A negative. For detection of either or both of the toxins, the TechLab C. difficile TOX A/B test (TechLab, Inc., Blacksburg, Va.) was employed. One drop of conjugate per microwell was added, followed by 2 drops of culture supernatant. Microwells were incubated at 37°C for 50 min and washed five times. One drop of tetramethylbenzidine substrate was added, followed by 1 drop of hydrogen peroxide in citric acid buffer. After a 10-min incubation at room temperature, reactions were interpreted by visual reading of yellow staining. In vitro, TcdB activity measurements were performed on McCoy cells cultured as described previously (19). Supernatant fluids were collected as described above, and tenfold serial dilutions of culture filtrate were added in duplicate to McCoy cells and incubated for 24 h at 37°C in a 5% CO2 atmosphere. CPE was observed by inverse microscopy. When this CPE could be neutralized by polyclonal goat antiserum against the toxin B, the test was considered positive. Albumin was used as a negative control antigen. For detection of the nonrepeating regions in the TcdA and TcdB genes, PCR was performed with the YT28-YT29 and YT17-YT18 primer pairs, respectively (9, 15). PCR involved 35 cycles of 45 s at 94°C, 30 s at 55°C, and 45 s at 70°C. PCR-mediated amplification aiming at the repeats in the toxin A gene was performed as described previously with primer set NK9-NKV011 (12).
PCR ribotyping.
PCR-mediated ribotyping employed the consensus primers SP1 and SP2 (5'-TTG TAC ACA CAC CGC CCG TCA-3' and 5'-GGT ACC TTA GAT GTT TCA GTT C-3' [see reference 14]). Fifty nanograms of DNA was added to a PCR mixture (100 µl) containing 10 mM Tris-HCl (pH 9.0), 50 mM KCl, 2.5 mM MgCl2, 0.01% gelatin (wt/vol), 0.1% Triton X-100 (vol/vol), 0.2 mM concentrations of the four deoxyribonucleotide triphosphates, 1.2 U of TaqDNA polymerase (Sphaero Q, Leiden, The Netherlands), and 50 pmol of each primer. Amplification was performed in a Biomed model 60 cycler (Biomed, Theres, Germany) with predenaturation at 94°C for 120 s followed by 40 cycles of 60 s at 94°C, 60 s at 55°C, and 60 s at 74°C. Amplicons were analyzed by electrophoresis on a 1% agarose gel for 3 h at 100 V. PCR ribotypes were defined on the basis of single band position differences in the fingerprints. Validation of this guideline has been the subject of previous investigations and consensus has been obtained (14, 25).
Determination of antibiotic susceptibility and ermB PCR.
The antibiotic susceptibility of all strains was investigated by using E-tests (AB-BIOdisc, Solna, Sweden) with clindamycin and erythromycin according to the instructions of the manufacturer. A bacterial suspension with a density of 1 McFarland was streaked to confluence on the surface of brucella agar plates. Plastic strips with antibiotic were applied, and the plates were incubated anaerobically at 37°C for 48 h. The MIC was measured at the intercept of the inhibition ellipses, and high-level resistance was defined when the value was higher than 256. PCR for detection of the ermB gene was performed with primers 2980 and 2981 (10). The cycling condition applied during PCR included 30 cycles of 60 s at 95°C, 120 s at 55°C, and 180 s at 72°C.

RESULTS
Among 33 strains of
C. difficile isolated in the period from
1999 to 2001 from patients with CDAD, 15 strains were TcdA
+B
+ as demonstrated by the
C. difficile toxin A test and TcdB-dependent
cytotoxicity testing on McCoy cells. The remaining 18 strains
were TcdA
-B
+, and a CPE was observed after cell line challenge.
TcdA could not be detected by the commercial toxin A test even
when supernatants from 96-h cultures were used. The toxin A/B
tests gave positive results for all 33 strains due to the ubiquitous
presence of the TcdB gene. Note that the historic control strains
(1995 to 1998) are not included in any of the calculations presented
in this section. The strains are listed in Table
1, which also
summarizes all of the test results obtained for these strains.
PCR amplification with YT28-YT29 and YT17-YT18 generated products
of 630 and 399 bp for the TcdA and TcdB genes, respectively,
for all strains. For the 18 TcdA
-B
+ strains, PCR with the NK9-NKV01
primer set generated a 700-bp product similar to that obtained
for the Japanese GAI 95601 strain. Of 24
C. difficile strains
isolated from adults with CDAD, 12 belonged to the TcdA
-B
+ group.
We isolated these strains from stool samples from six orthopedic
patients, three transplant patients, and three patients nursed
in the internal medicine unit. Among nine strains isolated from
children with CDAD hospitalized in the hematology department
(aged 4 to 15 years), three strains belonged to the TcdA
+B
+ group and six strains belonged to the TcdA
-B
+ cluster. Interestingly,
the 18 TcdA
-B
+ strains were not derived from patients who were
clustered in time or space during their hospitalizations (data
not shown). Consequently, we can conclude that we are not witnessing
a local outbreak but rather persistent and multi-institutional
dissemination of a clonal lineage of
C. difficile.
PCR ribotyping identified 12 different ribotypes among the 33 strains (Fig. 1). Eighteen strains belonged to the prevalent ribotype A, three strains belonged to ribotype B, two strains belonged to ribotype D, and two strains belonged to ribotype E. Eight other ribotypes were identified for as many strains. Among the isolates belonging to the TcdA-B+ group, seventeen strains belonged to ribotype A and one strain to ribotype E. Within the group of C. difficile TcdA+B+ strains, we observed more differentiation: 12 different ribotypes were identified. Interestingly, both ribotype A and E were detected in strains with different toxigenicity patterns. Among the 33 strains of C. difficile, 24 (73%) demonstrated high-level resistance to clindamycin and erythromycin. The resistant group included different ribotypes: 17 strains belonged to ribotype A, 2 strains belonged to ribotype B, and 1 strain belonged to each of ribotypes D, G, E, H, and I. All strains which showed high-level resistance to clindamycin possessed the ermB gene, as detected by PCR. All experimental data are summarized in Table 1.

DISCUSSION
We routinely check the susceptibility of
C. difficile to clindamycin
and erythromycin, and we observed an increase in the number
of strains showing elevated levels of resistance. We present
here the results of a detailed investigation into a number of
consecutive isolates from patients hospitalized in four units
of a large university hospital and a separate hematology unit
in an independent pediatric hospital. Among these strains, we
frequently found high-level resistance against clindamycin and
erythromycin associated with
ermB gene presence in both TcdA
+B
+ and TcdA
-B
+ strains. Seventeen out of the TcdA
-B
+ strains from
symptomatic patients represented the same ribotype. This is
in agreement with previous data from our laboratory where we
demonstrated the epidemic spread of TcdA
-B
+ strains isolated
from patients hospitalized in two different institutions and
at different points in time (
22). All TcdA
-B
+ strains possessed
the
ermB gene and were highly resistant to clindamycin and erythromycin.
Interestingly, among the Polish TcdA
-B
+ strains isolated from
stool samples of CDAD patients, ribotype A seems to predominate.
The prevalence of the multiresistant strains was less than 50%
percent before 1999, but it expanded significantly during recent
years. The fact that there was no obvious overlap in hospitalization
periods for most of the patients included suggests that persistence
rather than short-term, focused outbreaks of infection was ongoing.
This feature was particularly clear for the clindamycin-resistant
strain.
Kato et al. investigated isolates of C. difficile from patients with CDAD from three hospitals by three typing methods, including PCR ribotyping. These authors described an epidemic TcdA+B+ strain which was not resistant to clindamycin (13). Similarly, an epidemic ermB-positive C. difficile strain of an unknown toxin status was identified in Sweden (21). Kuijper et al. observed an association between clindamycin resistance and epidemicity of a TcdA-B+ C. difficile strain involved in CDAD (16). This epidemic strain belonged to serogroup F. However, as described by Delmee and Avesani (6), serogroup F strains are usually susceptible to clindamycin and erythromycin. All Polish TcdA-B+ strains, described before (22) and here, possess the ermB gene and share high-level resistance to clindamycin and erythromycin. It is surprising to see that the same ribotype (A or E) is encountered among both the TcdA+B+ and TcdA-B+ C. difficile strains. We suggest that TcdA-B+ C. difficile strains which harbor the ermB gene are significantly associated with CDAD among both adults and children. Whereas the epidemic capacity of some of these strains might be enlarged simultaneously, we propose that determination of macrolide-lincosamide-streptogramin B resistance in TcdA-B+ C. difficile strains is a possible predictor of enhanced CDAD potential.

FOOTNOTES
* Corresponding author. Mailing address: Department of Medical Microbiology, Centre of Biostructure Research, The Medical University of Warsaw, 5 Chalubinski Street, 02-004 Warsaw, Poland. Phone and fax: (48-22) 628-27-39. E-mail:
hanna.pituch{at}ib.amwaw.edu.pl.


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Journal of Clinical Microbiology, September 2003, p. 4184-4187, Vol. 41, No. 9
0095-1137/03/$08.00+0 DOI: 10.1128/JCM.41.9.4184-4187.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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