Antimicrobial resistance in group B streptococcus: the Australian experience

Area of Science:

• Microbiology
• Infectious Diseases
• Obstetrics & Gynecology

Background:

• Group B Streptococcus (GBS) chemoprophylaxis during labor reduces vertical transmission and associated maternal/neonatal morbidity.
• Penicillin is the recommended intrapartum prophylaxis in Australia, with erythromycin or clindamycin for beta-lactam allergic patients.
• Emerging global resistance to erythromycin and clindamycin necessitates local evidence for Australian clinical guidelines.

Purpose of the Study:

• To assess macrolide and lincosamide resistance rates in Australian group B Streptococcus (GBS) isolates.
• To provide an evidence base for updating local clinical guidelines on GBS chemoprophylaxis.
• To determine the suitability of current antibiotic recommendations for GBS carriers.

Main Methods:

• Standardized susceptibility testing of 1160 invasive and 896 colonizing GBS isolates from 16 Australian laboratories.
• Retrospective (1982-2001) and prospective (2002-2006) collection of invasive isolates; prospective collection of colonizing isolates (2005-2006).
• Genotyping of isolates with phenotypic macrolide or lincosamide resistance.

Main Results:

• No GBS isolates exhibited reduced susceptibility to penicillin or vancomycin.
• Phenotypic erythromycin resistance was observed in 6.4% of invasive isolates; 4.2% were clindamycin resistant.
• Macrolide resistance rates showed no statistically significant change between 1982-2001 and 2002-2006.

Conclusions:

• Penicillin remains an appropriate first-line antibiotic for intrapartum GBS chemoprophylaxis in Australia.
• Erythromycin and clindamycin resistance in GBS is currently low in the Australian population.
• Macrolide sensitivity testing is recommended for beta-lactam allergic patients to ensure effective GBS chemoprophylaxis.