Ampicillin susceptibilities of vaginal and placental isolates of group B Streptococcus and Escherichia coli obtained between 1992 and 1994

Vaginal group B streptococcus (GBS) and Escherichia coli isolates were tested for their susceptibilities to ampicillin, All 414 GBS isolates tested were susceptible to ampicillin; the MIC at which 90% of the isolates were inhibited (MIC90) was 0.125 mu g/ml, and the range was 0.06 to 0.25 mu g/ml. The MIG(50) for the 342 E. coli isolates tested was 4.0 mu g/ml, and 27% were resistant to ampicillin.