Antimicrobial resistance among invasive Streptococcus pyogenes isolates in Portugal

Abstract number: O481

Friaes A., Ramirez M., Melo-Cristino J.

Objectives: Although S. pyogenes is universally susceptible to penicillin, in the treatment of complicated Group A Streptococci (GAS) infections such as necrotizing fasciitis or STSS, the association of penicillin with clindamycin has been advocated. Resistance to the latter has been described in GAS, associated with resistance to macrolides. The aim of this work was to evaluate the resistance of GAS invasive isolates to several antimicrobial agents and to further characterize the macrolide resistance isolates.

Methods: A total of 306 invasive GAS isolates recovered in Portugal during 2000–2008 were tested for susceptibility to penicillin, vancomycin, erythromycin, tetracycline, levofloxacin, chloramphenicol, clindamycin, quinupristin-dalfopristin, and linezolid by disk diffusion. Intermediate susceptibilities were confirmed by MIC determination using E-test strips. Resistance genotypes were determined by PCR.

Results: All the 306 GAS isolates were susceptible to penicillin, vancomycin, chloramphenicol, quinupristin-dalfopristin, and linezolid, and only two (0.7%) presented reduced susceptibility to levofloxacin (MIC = 3 and 4 ug/ml). A total of 32 isolates (10.5%) were resistant to erythromycin. Of these, 20 were also constitutively resistant to clindamycin (cMLSB phenotype, 62.5%), whereas 12 presented the M phenotype (37.5%). The cMLSB phenotype was associated with the presence of the erm(B) gene, whereas the M phenotype was associated with mef(A). Non-susceptibility to tetracycline was found in 42 isolates (13.7%), of which 8 also expressed the cMLSB phenotype and 1 the M phenotype.

Conclusion: Erythromycin resistance among invasive GAS isolates in Portugal did not vary significantly during 2000–2008, contrarily to what has been reported for isolates causing pharyngitis, whose macrolide resistance decreased from 1999 to 2006. The macrolide resistance observed in this study for invasive GAS isolates (10.5%) is in line with reports from other countries, as well as with the overall rate reported for pharyngitis isolates in Portugal during 2004–2006 (13.2%).

Session Details

Date: 10/04/2010
Time: 00:00-00:00
Session name: Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases
Location: Vienna, Austria, 10 - 13 April 2010
Presentation type:
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