Abstract:
BACKGROUND. Streptococcus agalactiae or group B streptococcus (GBS) is a significant cause of neonatal sepsis. Intrapartum antibiotic
prophylaxis is recommended for pregnant women identified to be rectovaginally colonised between 34 and 37 weeks’ gestational age to
decrease the risk of invasive disease in their newborns. An effective multivalent GBS vaccine may prevent a broader scope of GBS-associated
diseases, such as GBS early-onset disease, GBS late-onset disease, spontaneous abortion, stillbirth and maternal bacteraemia. Serotype
distribution of GBS isolates is essential to determine the efficacy of such a vaccine.
OBJECTIVES. To investigate serotype distribution and antimicrobial susceptibility patterns of GBS isolates cultured from rectovaginal
specimens during pregnancy.
METHODS. Sixty-nine archived maternal colonising isolates were tested against penicillin, erythromycin, clindamycin, vancomycin and
levofloxacin. Minimum inhibitory concentration testing was performed using the ETEST method. Serotyping was performed by the latex
agglutination method.
RESULTS. The most common serotypes detected were Ia (54%), III (20%), V (16%), II (6%), IV (2%) and Ib (1%). All isolates were fully
susceptible to penicillin, vancomycin and levofloxacin. Eight (11%) and 50 (56%) isolates showed intermediate resistance to erythromycin
and clindamycin, respectively, and 1 isolate was resistant to erythromycin. The macrolide-lincosamide-streptogramin B (MLSB) phenomenon
was noted in 3 (4%) of the isolates.
CONCLUSIONS. GBS-colonising isolates remain susceptible to penicillin, which remains the drug of choice for intrapartum antibiotic
prophylaxis and treatment of invasive disease in newborns. Macrolides should only be used if clinically indicated due to the high prevalence
of intermediate resistance. A pentavalent GBS vaccine currently in phase I trials should provide coverage for 97% of the isolates identified
in this study.
