Antibiotic resistance patterns of group B streptococci in late third-trimester rectovaginal cultures

OBJECTIVE: Our purpose was to determine the antibiotic sensitivity patterns of rectovaginal group B streptococcal isolates obtained from a heterogeneous obstetric population in the late third trimester. STUDY DESIGN: We performed a prospective observational study of rectovaginal group B streptococcal isolates obtained in the late third trimester during routine screening over a 12-month period. All cultures were prepared in a selective broth medium for 18 to 24 hours before plating onto sheep blood agar. Susceptibility testing of all isolates was performed for ampicillin, cefazolin, clindamycin, erythromycin, penicillin G, and vancomycin with the E-test method. RESULTS: A total of 2111 consecutive rectovaginal cultures were performed in which group B streptococci were isolated from 574 (27.2%) different patients. The "antibiogram" of the susceptible percentage is as follows: vancomycin, 100%; ampicillin, 98.2%; penicillin G, 98.2%; cefazolin, 98.1%; clindamycin, 92%; erythromycin, 81%. Ten isolates (1.8%) demonstrated intermediate susceptibility to both ampicillin and penicillin G. CONCLUSION: Routine susceptibility testing of group B streptoccal isolates collected during pregnancy should be considered because of the emergence of antibiotic resistance among group B streptococcal strains.