ACTIVITY OF 21 ANTIMICROBIAL AGENTS INCLUDING L-OFLOXACIN AGAINST QUINOLONE-SENSITIVE AND QUINOLONE-RESISTANT, AND METHICILLIN-SENSITIVE AND METHICILLIN-RESISTANT STAPHYLOCOCCUS-AUREUS

There is a need to identify alternative agents to vancomycin for the treatment of infections with methicillin-resistant Staphylococcus aureus (MRSA). One candidate is the l isomer of ofloxacin (DR-3355). We tested 520 frozen MRSA isolates, 248 fresh MRSA isolates, and 375 fresh methicillin-susceptible S. aureus (MSSA) isolates from Minnesota, and 600 clinical isolates of S. aureus (150 MRSA and 450 MSSA) from Illinois. Over 90% of the MRSA strains were resistant to 32 mu g/ml of oxacillin. Of the 520 frozen MRSA, 24% were susceptible to less than or equal to 2 mu g/ml ofloxacin, and an additional 74% were susceptible to ofloxacin between 8 and 16 mu g/ml. More than 98% of all strains were susceptible to less than or equal to 16 mu g/ml ofloxacin or l-ofloxacin. All the quinolones had a bimodal distribution of in vitro activity, but for only ofloxacin and l-ofloxacin was activity confined to a very narrow range.