Novel mutations in a patient isolate of Streptococcus agalactiae with reduced penicillin susceptibility emerging after long-term oral suppressive therapy.

Penicillin nonsusceptibility has been demonstrated in group B streptococci (GBS), but there is limited information regarding mechanisms of resistance. We report a case of GBS with reduced susceptibility to penicillin emerging after long-term suppressive oral penicillin therapy for a prosthetic joint infection. Molecular characterization of the isolate before and after long-term penicillin therapy revealed 5 mutations in the ligand-binding regions of PBP1a, -2a, and -2x not previously reported in GBS.