Effect of antimicrobial therapy for experimental infections due to group B Streptococcus on mortality and clearance of bacteria.

In an effort to develop more effective antimicrobial therapy, we evaluated three alternative regimens currently available to clinicians for their efficacy against experimental bacteremia and meningitis due to group B Streptococcus (GBS) in newborn rats: various doses of penicillin G (100, 200, 400, or 800 mg/kg per day), combined penicillin G-gentamicin vs. penicillin G, and ceftriaxone vs. penicillin G. Higher doses of penicillin G and ceftriaxone exhibited significantly greater bactericidal activity in blood and cerebrospinal fluid (CSF), whereas the bactericidal activity of penicillin G plus gentamicin was not significantly different from that of penicillin G. Clearance of GBS from blood was significantly more rapid in animals receiving ceftriaxone. However, differences in death rates were not apparent with any single regimen. These findings suggest that clearance of GBS from blood and CSF can be improved by more potent antimicrobial agents, but further reduction in the death rate may be difficult to achieve by antimicrobial therapy alone.