Antimicrobial Susceptibility Studies
Macrolide resistance in Streptococcus pyogenes: prevalence, resistance determinants, and emm types,☆☆

https://doi.org/10.1016/j.diagmicrobio.2009.03.004Get rights and content

Abstract

To investigate the antimicrobial resistance trends and the distribution of emm types of group A streptococci (GAS), we examined 1160 clinical isolates of GAS collected between 2003 and 2006. Susceptibilities to commonly used antimicrobial agents were determined by Etest, and macrolide resistance genes were detected by polymerase chain reaction (PCR). GAS isolates were typed by polymerase chain reaction PCR and sequencing of emm gene. The rates of resistance to erythromycin (ERY), clindamycin, azithromycin, tetracycline, and chloramphenicol were 14.9%, 1.4%, 14.9%, 18.9%, 0.6%, respectively. None of the isolates exhibited resistance to penicillin, ceftriaxone, linezolid, moxifloxacin, rifampicin, or vancomycin.

Macrolide resistance increased from 12.1% in 2003 to 18.8% in 2006 (P = 0.02). Of 173 ERY-resistant GAS isolates, 93 (53.7%) harbored the mefA gene, 70 (40.4%) the ermA, and 10 (5.8%) the ermB. Eighty percent of the observed emm types are covered by the proposed 26-valent GAS vaccine. Among 173 ERY-resistant isolates, the predominant emm types were 12 (19.5%), 77 (17.9%), and 4 (16.8%), and among 770 ERY-susceptible isolates, the predominant types were 1 (18.8%), 12 (17.5%), 28 (13.8%). The observed antimicrobial resistance trends and the distribution of specific emm types have implications in guiding empiric therapy and in developing vaccine strategies to prevent GAS infections.

Introduction

The group A streptococcus (GAS) or Streptococcus pyogenes is among the most common human pathogens responsible for a wide spectrum of human diseases, ranging from trivial to lethal. Although penicillin is the drug of choice for the treatment of S. pyogenes infections, macrolides are used for patients who are allergic to β-lactams. The emergence of macrolide resistance in GAS is an increasing problem worldwide.

Two main mechanisms are accounted for macrolide resistance in GAS: i) an active drug efflux system via a transmembrane pump encoded by mefA gene (Sutcliffe et al., 1996) and ii) target modification due to ribosomal methylation, encoded by ermB or ermA gene. Isolates harboring the mefA gene confer resistance to 14- and 15-membered ring macrolides only, and not to 16-membered ring macrolide, lincosamide, and streptogramin B (phenotype M) (Bemer-Melchior et al., 2000). GAS isolates carrying the ermB gene, express an rRNA erm methylase that alters a site in 23S rRNA, common to the binding of macrolides, lincosamides, and streptogramin B antibiotics, leading to resistance to all these compounds (constitutive MLSB phenotype [cMLSB]). Strains with the ermA gene have an “inducible” MLSB phenotype (iMLSB) that requires exposure to a macrolide inducer before clindamycin (CLI) resistance becomes evident (Giovanetti et al., 2002). Other mechanisms of GAS macrolide resistance strains have been described because of mutations of L4, L22 ribosomal protein, and 23S rRNA (Jalava et al., 2004, Malbruny et al., 2002).

GAS M-protein plays an important role in the pathogenesis of streptococcal disease. A GAS typing system based on sequencing of the N-terminal hypervariable region of the M-protein (emm) gene has been used for identification of different emm types. With this methodology, more than 150 types have been recognized worldwide, and specific emm types have been associated with particular clinical syndromes (Bisno et al., 2003, Cohen-Poradosu and Kasper, 2007).

Limited data have been published regarding the phenotypic and genotypic characterization of macrolide-resistant GAS isolates as well as the emm-type distribution in Athens metropolitan area (Grivea et al., 2006, Zachariadou et al., 2003). The aims of the present study were 1) to investigate the antimicrobial resistance patterns and especially the macrolide resistance prevalence among GAS strains isolated in our geographic region, 2) to identify the responsible mechanisms for macrolide resistance, and 3) to determine the emm-type distribution among the macrolide-resistant and macrolide-susceptible isolates.

Section snippets

Bacterial isolates

The study was conducted at Aghia Sophia Children's Hospital, Athens, Greece, a tertiary care medical center, serving approximately 40% of children residing in the Athens metropolitan area. All consecutive isolates recovered in Infectious Diseases Research Laboratory from patients with GAS infections between January 2003 and December 2006 were included in the study. The identification of the isolates was confirmed by colony morphology, typical β-hemolysis on 5% sheep blood agar (Becton

Results

A total of 1160 S. pyogenes isolates were collected; 1121 from throat, 19 from blood, 11 from ear fluids, and 9 from other sources. Patient ages varied from 1 month to 12 years.

Discussion

The present study investigated the prevalence of macrolide resistance among GAS isolates recovered from children living in the Athens metropolitan area during a 4-year period. A significant increase of macrolide resistance was observed from 12.1% in 2003 to 18.8% in 2006. Previous reports from Greece have also shown an increase in macrolide resistance from 6.5% during the period 1993 to 1995 to 38% for the period 1998 to 2000 and 24% during the period 1999 to 2002, although these studies were

Acknowledgments

The authors thank Fotini Haidopoulou for expert technical assistance.

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    Financial support. This study was co-funded by the European Social Fund & National Resource - EPEAEK II – PYTHAGORAS».

    ☆☆

    Preliminary results from this study were presented at the 12th International Congress of Infectious Diseases, Lisbon, Portugal, June 15–18, 2006, Abstract P30031, and the 18th European Congress of Clinical Microbiology and Infectious Diseases, Barcelona, Spain, April 19–22, 2008, Abstract P1207.

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