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Journal of Clinical Microbiology, August 2004, p. 3844-3846, Vol. 42, No. 8
0095-1137/04/$08.00+0 DOI: 10.1128/JCM.42.8.3844-3846.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Clonal Spread of emm Type 28 Isolates of Streptococcus pyogenes That Are Multiresistant to Antibiotics
Liliana Mihaila-Amrouche, Anne Bouvet, and Julien Loubinoux*
Centre National de Référence des Streptocoques, Service de Microbiologie, Hôtel Dieu, Assistance Publique-Hôpitaux de Paris, Université Paris V, 75181 Paris Cedex 04, France
Received 6 January 2004/
Returned for modification 17 February 2004/
Accepted 27 April 2004

ABSTRACT
Fifty-three pharyngitis-related and invasive isolates of
Streptococcus pyogenes that are resistant to bacitracin were collected. They
were also resistant to streptomycin, kanamycin, macrolides,
lincosamides, and streptogramin B. These multiresistant isolates
were of
emm type 28 and clonally related as shown by pulsed-field
gel electrophoresis.

TEXT
Streptococcus pyogenes (Lancefield group A beta-hemolytic streptococcus)
is responsible for suppurative local infections such as pharyngitis
and severe invasive infections, such as necrotizing fasciitis
and streptococcal toxic shock syndrome (
7). The M protein is
a major virulence factor, and a limited number of
emm types,
mainly 1, 3, 4, 6, 12, and 28, have been associated with invasive
isolates of
S. pyogenes (
8,
13,
20). Besides
emm typing, pulsed-field
gel electrophoresis (PFGE) is also currently used for clonality
studies (
1,
21). Erythromycin or clindamycin are recommended
as an alternative treatment of streptococcal pharyngitis in
case of allergy to beta-lactams (
3). Moreover, clindamycin is
used in combination with penicillin for treatment of necrotizing
fasciitis or streptococcal toxic shock syndrome (
17). However,
resistance of
S. pyogenes to macrolides and lincosamides has
been reported (
2,
9,
10,
15). Susceptibility to bacitracin has
been used as a preliminary laboratory test for the differentiation
of
S. pyogenes from other beta-hemolytic streptococci. Strains
of
S. pyogenes resistant to bacitracin are uncommon but, since
2000, we collected 53 strains of
S. pyogenes resistant to bacitracin.
(A preliminary report of this work was presented at the 13th European Congress of Clinical Microbiology and Infectious Diseases, Glasgow, United Kingdom, 10 to 13 May 2003.)
Thirty bacitracin-resistant isolates of S. pyogenes out of 247 were obtained from November 2000 to May 2001 during a prospective survey of pharyngitis in Bourgogne, France. They were compared to 23 bacitracin-resistant invasive strains of S. pyogenes isolated in different regions of France from 2001 to 2003. Invasive strains were responsible for puerperal sepsis (n = 7), necrotizing fasciitis (n = 7), peritonitis of genital origin (n = 4), bacteremia (n = 3), endocarditis (n = 1), or meningitis (n = 1). Strains were identified as S. pyogenes by morphology, beta-hemolysis, absence of catalase, presence of pyrrolidonyl arylamidase, and presence of group A antigen. Biotype was determined by the presence of beta-glucuronidase and results of carbohydrate fermentation when tested on the strip Rapid ID32 STREP (bioMérieux, Marcy l'Etoile, France) as reported previously (4). Serotype T was determined by slide agglutination with type-specific antisera (Institute of Sera and Vaccines, Prague, Czech Republic). Antimicrobial susceptibility was studied by the disk diffusion method on Mueller-Hinton agar with 5% sheep blood according to the guidelines of the Antibiogram Committee of the French Society for Microbiology (http://www.sfm.asso.fr) (12). Eleven antimicrobial agents were tested: penicillin G, amoxicillin, vancomycin, teicoplanin, rifampin, tetracycline, streptomycin, kanamycin, gentamicin, erythromycin, and clindamycin. High-level resistance to aminoglycosides was tested with disks containing 500 µg of streptomycin, 1 mg of kanamycin, or 500 µg of gentamicin. Resistance to bacitracin was determined by an absence of inhibition of growth around the disk of bacitracin (0.02 IU). Disks were from Bio-Rad, Marnes-la-Coquette, France. Erythromycin-resistant isolates were further studied by the determination of MICs (erythromycin, azithromycin, josamycin, and clindamycin) using the agar dilution method (12) and by the triple-disk test (erythromycin, clindamycin, and josamycin) as previously described (9). Macrolide resistance genes [erm(B), erm(A), and mef(A)] were identified by PCR in all isolates resistant to erythromycin according to previously described procedures (16, 18). Clonality of isolates was studied by emm typing and PFGE. emm types were determined by sequencing the variable 5' end of the emm gene after amplification by PCR according to the Centers for Disease Control and Prevention recommen-dations (http://www.cdc.gov/ncidod/biotech/strep/doc.htm).PFGE was performed with a CHEF-DR III apparatus (Bio-Rad). Chromosomal DNA was digested with SmaI by a method described elsewhere (1). PFGE patterns were compared according to the criteria of Tenover et al. (19). Isolates were considered to be clonally related if they showed differences of three or fewer bands between strains. They were considered to be possibly clonally related if they showed differences of four to six bands between strains.
The 53 pharyngitis-related and invasive isolates of S. pyogenes resistant to bacitracin were of biotype 1 (4), serotype T28, and emm type 28. They were susceptible to penicillin G, amoxicillin, vancomycin, teicoplanin, rifampin, and tetracycline. They showed a low level of resistance to gentamicin and a high level of resistance to streptomycin and kanamycin. They were also resistant to erythromycin and clindamycin. MIC results were as follows: erythromycin, >64 µg/ml; azithromycin, >64 µg/ml; josamycin, >64 µg/ml; clindamycin, >32 µg/ml. The triple-disk test showed that all isolates were constitutively resistant to macrolides, lincosamides, and streptogramin B (cMLS phenotype). This resistance was due to the presence of the gene erm(B). PFGE showed that 51 multiresistant emm28 pharyngitis-related and invasive isolates were clonally related and two invasive isolates were possibly clonally related to the former isolates (Fig. 1).
Susceptibility to bacitracin has been used as a preliminary
test for the differentiation of
S. pyogenes from other beta-hemolytic
streptococci. Because this test lacks specificity, most laboratories
currently use the presence of pyrrolidonyl arylamidase as a
better test to identify
S. pyogenes. Our results confirm the
importance of using an alternative to bacitracin susceptibility
testing. The emergence of strains of
S. pyogenes resistant to
macrolides has been observed, but they have not been multiresistant
to antibiotics (
2,
9,
10,
15). In this study, 53 pharyngitis-related
and invasive isolates of
S. pyogenes resistant to bacitracin
were shown to also be resistant to streptomycin, kanamycin,
macrolides, lincosamides, and streptogramin B. The constitutive
resistance to macrolides was due to the presence of the gene
erm(B). All these multiresistant isolates were of
emm type 28
and clonally related as shown by PFGE. The high prevalence of
12% (30 of 247 isolates) of this multiresistant clone among
pharyngitis isolates contrasts with the rare cases of bacitracin-resistant
isolates reported previously (
11,
14,
21). The results reported
previously and those described in this study suggest a clonal
relationship between all the bacitracin-resistant isolates.
The multiresistant clone of
S. pyogenes of
emm type 28 was not
only responsible for pharyngitis but also for invasive infections.
emm type 28 is frequently associated with invasive infections
and has even been reported as the second-most-common invasive
type (
13). Moreover,
emm type 28 is predominant in invasive
postpartum
S. pyogenes infections, which may be due to tropism
for vaginal tissue (
5,
6). Our results also demonstrate that
PFGE is a valuable epidemiological marker for differentiation
of epidemiologically related
emm28 S. pyogenes isolates. PFGE
was performed on all
emm28 S. pyogenes strains isolated during
the prospective survey of pharyngitis. Twenty-one bacitracin-susceptible
isolates were compared to the 30 bacitracin-resistant clonal
isolates. The 21 bacitracin-susceptible isolates were susceptible
to all antibiotics tested, including erythromycin and clindamycin.
They had heterogeneous PFGE patterns, distinct from those of
the bacitracin-resistant clone, and were thus not clonally related
(data not shown). The emergence of this multiresistant
S. pyogenes clone may be of importance in clinical practice as macrolides
or clindamycin may be used for treatment of
S. pyogenes infections.

ACKNOWLEDGMENTS
We are particularly grateful to H. Portier (Université
de Dijon, France) who conducted the survey. We are indebted
to all participants in the prospective survey of pharyngitis
in Bourgogne, France, and to the microbiologists who sent the
invasive strains. We thank also Gislène Collobert for
excellent technical assistance.

FOOTNOTES
* Corresponding author. Mailing address: Centre National de Référence des Streptocoques, Service de Microbiologie, Hôtel Dieu, 1 place du Parvis Notre-Dame, 75181 Paris Cedex 04, France. Phone: (33) 1 42 34 82 73. Fax: (33) 1 42 34 87 19. E-mail:
julien.loubinoux{at}htd.ap-hop-paris.fr.


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Journal of Clinical Microbiology, August 2004, p. 3844-3846, Vol. 42, No. 8
0095-1137/04/$08.00+0 DOI: 10.1128/JCM.42.8.3844-3846.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
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