In vitro evaluation of contemporary beta-lactam drugs tested against viridans group and beta-haemolytic streptococci.

Streptococci continue to be prevalent causes of mild as well as of serious, life-threatening infections. Furthermore, some species harbor antimicrobial resistances (pneumococcus, viridans gr. streptococci) that compromise effective chemotherapy with beta-lactam drugs or other antimicrobial classes. In this study, the potency and spectrum of 12 beta-lactams was assessed versus 274 contemporary isolates of viridans group and beta-haemolytic streptococci using reference methods. Cefotaxime and ceftriaxone (MIC90s, 0.015 to 2 micrograms/ml, 84 to 100% susceptible) were consistently most potent among the agents tested. Ceftazidime (MIC90s, 0.25 to 8 micrograms/ml) and ticarcillin (MIC90s, 0.5 to > 32 micrograms/ml) were least active among the cephalosporins and penicillins, respectively. When 25% pooled serum was added to the reference test medium, ceftriaxone activity decreased fourfold, and cefotaxime remained highly active. As penicillin/beta-lactam-resistant streptococci with altered penicillin-binding protein target sites become more prevalent, only a few "third-generation" cephems seem to have sustained activity when used alone or possibly with a carefully selected co-drug. Routine testing of these species against beta-lactams and alternative drugs should be encouraged to detect emerging resistance patterns.