Figure 5.

Intracellular group B streptococci (GBS) are protected from antibiotics. Bone marrow–derived macrophages (BMDMs) containing intracellular acaspular GBS (ΔcpsE, ΔcovRΔcpsE) were exposed to increasing concentrations of ampicillin (A) or clindamycin (B) for 2 hours. The infected BMDMs were lysed to determine the bactericidal effects of antibiotics on intracellular GBS (n = 2). As controls, extracellular GBS (GBS in RPMI medium) were also exposed to increasing concentrations of these antibiotics and colony-forming units (CFU) were enumerated after 2 hours. Linear regression was used to evaluate the relationship between antibiotic concentration and bacterial CFU (colored line represents regression and dashed lines represent 95% confidence intervals). The F-test for each regression comparing antibiotic concentration and bacterial CFU was significant (P < .05) for extracellular bacteria (EC) and nonsignificant (P > .05) for intracellular bacteria (IC).