Antibiotic susceptibility profile of group B streptococcus (Streptococcus agalactiae) at the Maternity Hospital, Kuwait

Abstract

Objectives: This study was designed to determine the antibiotic susceptibility profile of clinical isolates of group B streptococcus(GBS, Streptococcus agalactiae) and to use the information for formulating appropriate intrapartum antibiotic policy for GBS carriage in pregnancy.

Materials and methods: A total of 1,166 clinical isolates (single isolates) of GBS obtained from vaginal/rectal samples of pregnant mothers seen at the Maternity Hospital, Kuwait were studied over a period of 43 months between May 1998 and December 2001. The isolates were identified by standard methods and their susceptibility to penicillin, ampicillin, cephalothin, clindamycin and erythromycin was determined by disk diffusion technique, minimal inhibitory concentration (MIC) using the Vitek automated sensitivity card system and E-test methods.

Results: All the GBS isolates were fully susceptible to penicillin, ampicillin and cephalothin. Only 0.7 and 1.7% were resistant to erythromycin and clindamycin, respectively. Disk diffusion results interpreted by the standard interpretative criteria recommended by the National Committee on Clinical Laboratory Standards correlated well with Vitek results as well as the E-test for penicillin. The MIC of penicillin against all isolates ranged between 0.016 and 0.064 microg/ml. For the 6 months of 1998 and throughout 1999, the percentages of isolates susceptible at MICs of 0.016, 0.023, 0.032, 0.047 and 0.064 microg/ml were 6.5, 9.9, 31, 38.8 and 12%, respectively. The trend was similar in the subsequent years except that the percentage of isolates susceptible at MIC of 0.064 microg/ml increased to 26.6% in 2000, but went down to 4.4% in 2001.

Conclusion: The trend in susceptibility of GBS to a variety of often used antibiotics for therapy and prophylaxis remained unchanged over nearly a 4-year period. The apparent increase in the number of isolates susceptible at higher MIC values of penicillin (0.047 and 0.064 microg/ml) in 2000 appears to be a bleb that cannot be explained by any event in the hospital for that year. Our data, based on susceptibility profiles, supports the use of penicillin or ampicillin for intrapartum chemoprophylaxis to prevent early-onset neonatal GBS infections.