Is penicillin and/or erythromycin resistance present in clinical isolates of group B streptococcus in our community?

Traditionally group B streptococcus (GBS) has not exhibited resistance to the antibiotics penicillin and erythromycin. Recently there are reports from North America whereby some GBS isolates have exhibited resistance to erythromycin. There have been no studies reported to date to determine whether this resistance trend is also occurring in the Australian population. Over a period of six months from January to June 1999, 250 GBS isolates were collected at the Royal Women's Hospital, Melbourne. Sensitivity to penicillin, erythromycin and vancomycin was determined by disk diffusion. Any isolates that had reduced zones to penicillin, vancomycin or erythromycin had minimum inhibitory concentrations (MIC) determined. No isolates had reduced susceptibility to penicillin or vancomycin. Of the 250 isolates, seven (2.8%, 95% CI = 1.1-5.6%) had resistant MICs to erythromycin of > 1.0 microg/mL. These preliminary data suggest that penicillin therapy is still an effective first-line antibiotic for intrapartum chemoprophylaxis and that erythromycin resistance is low in our population.