Practical disk diffusion test for detecting group B streptococcus with reduced penicillin susceptibility.

Although group B streptococcus (GBS) has been considered to be uniformly susceptible to beta-lactams, the presence of GBS with reduced penicillin susceptibility (PRGBS) was recently confirmed genetically. We developed a feasible and reliable method for screening PRGBS in clinical microbiology laboratories using a combination of ceftibuten, oxacillin, and ceftizoxime disks.