Emm type distribution and antibiotic susceptibility of non-invasive group a beta-hemolytic streptococci in Perth, Western Australia

Abstract

Aims To characterise the emm type distribution and antibiotic susceptibility of non-invasive group A streptococci (GAS) in Perth, Western Australia. Methods We collected consecutive, non-invasive GAS isolates received during a 3 month period in 2008. Isolates were categorised as sampled from either skin (impetigo, cellulitis), throat (pharyngitis) or genital (perianal cellulitis, vaginal discharge, perinatal screening) areas. Antibiotic susceptibility to penicillin, erythromycin, clindamycin and tetracycline was determined by disc diffusion and/or Etest methods. Emm typing was performed by sequencing of the N-terminal hypervariable region of the emm gene. Pulse field gel electrophoresis (PFGE) was performed on selected isolates. Results A total of 186 isolates were obtained from patients with a mean age of 24 (range 0.3–78). Most (138;74%) resided in suburbs within the Perth metropolitan area. The isolates were obtained from the skin (58%), throat (29%) and genital (13%) areas. Forty-five different emm types were represented. A significant difference existed between the proportion of genital isolates compared to skin isolates that were emm 4 (28% vs 9%, p = 0.019). All isolates were susceptible to penicillin (mean minimum inhibitory concentration 0.012, range 0.004–0.023). Rates of erythromycin, clindamycin and tetracycline non-susceptibility were 2%, 2% and 14%, respectively. There were significant differences between the proportion of emm 4 versus non-emm 4 isolates (0% vs 17%, p = 0.017) and emm 87 versus non-emm 87 isolates (69% vs 11%) that were tetracycline non-susceptible. PFGE demonstrated this to due to a dominant clone within these emm types. Conclusions A wide diversity of emm types cause non-invasive GAS disease in Western Australia, yet they remain uniform in their susceptibility to penicillin. Resistance to second line therapeutic antibiotics is rare. Ongoing surveillance will be necessary to monitor changes in antibiotic susceptibility, assist in vaccine design and monitor the potential impact of such vaccines on emm type distribution.