Susceptibility in vitro of gram-positive aerobe and anaerobe bacteria to ofloxacin.

Ofloxacin is a new fluoroquinolone derivative active against Gram-positive and Gram-negative bacteria including obligate anaerobes. In this study the in vitro activity of ofloxacin was evaluated against 325 Gram-positive organisms freshly isolated from clinical specimens, in comparison with that of ampicillin, erythromycin, clindamycin and ceftazidime. Susceptibility tests indicated that the MIC90 was 2 mg/l (range 0.25-2) against both methicillin-susceptible (MS) and methicillin-resistant (MR) Staphylococcus aureus. A value of 2 mg/l (range 0.5-4) was also found for all other staphylococci. The MIC of ofloxacin was 8 mg/l for 90% of Streptococcus faecalis (range 1-16), Str. faecium (range 2-8) and members of JK group (range 0.5-16). Propionibacterium acnes strains were all inhibited by 2 mg/l and 90% of Clostridia spp. (range 2-16) by 8 mg/l. Ofloxacin activity compared favourably with that of ampicillin, erythromycin, clindamycin and ceftazidime determined on the same isolates. MBC and time-kill studies indicated that this compound is rapidly bactericidal against enterococci. The great intrinsic activity against MS and MR staphylococci, refractory enterococci and JK bacteria may make ofloxacin a useful adjunct to the therapeutic arsenal.