SUSCEPTIBILITIES OF 428 GRAM-POSITIVE AND GRAM-NEGATIVE ANAEROBIC-BACTERIA TO BAY Y3118 COMPARED WITH THEIR SUSCEPTIBILITIES TO CIPROFLOXACIN, CLINDAMYCIN, METRONIDAZOLE, PIPERACILLIN, PIPERACILLIN-TAZOBACTAM, AND CEFOXITIN

The susceptibilities of 428 gram-negative and gram-positive anaerobes (including selected cefoxitin-resistant strains) to Bay y3118 (a new fluoroquinolone), ciprofloxacin, clindamycin, metronidazole, cefoxitin, piperacillin, and piperacillin-tazobactam were tested. Organisms comprised 115 Bacteroides fragilis group, 116 non-B. fragilis Bacteroides, Prevotella, and Porphyromonas spp., 40 fusobacteria, 58 peptostreptococci, 48 gram-positive non-spore-forming rods, and 51 clostridia. Beta-Lactamase production was demonstrated in 87% of the gram-negative rods but in none of the gram-positive organisms. Overall, Bay y3118 was the most active agent, with all organisms inhibited at an MIC of less-than-or-equal-to 2.0 mug/ml (MICs for 50% [MIC50] and 90% [MIC90] of strains tested, 0.125 and 0.5 mug/ml, respectively). By contrast, ciprofloxacin was much less active, with only 42% of strains susceptible at a breakpoint of 2.0 mug/ml (MIC50, 4.0 mug/ml; MIC90, 16.0 mug/ml). Metronidazole was active against all gram-negative rods, but 7% of peptostreptococci, 83% of gram-positive non-spore-forming rods, and 4% of non-Clostridium perfringens, non-Clostridium difficile clostridia were resistant to this agent (MICs, >16.0 mug/ml). Clindamycin was active against 94% of Bacteroides, Prevotella, and Porphyromonas spp., 91% of peptostreptococci, and 100% of gram-positive non-spore-forming rods, but was active against only 70% of fusobacteria and 53% of clostridia. Cefoxitin was active against greater-than-or-equal-to 90% of all groups except the B. fragilis group and non-Propionibacterium acnes gram-positive non-spore-forming rods (both 85%) and C. difficile (20%). Significant enhancement of piperacillin by tazobactam was seen in all beta-lactamase-positive strains (99% susceptible; MIC90, 8.0 mug/ml), and all beta-lactamase-negative strains were susceptible to piperacillin (MIC90, 8.0 mug/ml). Clinical studies are required to delineate the role of Bay y3118 in the treatment of anaerobic infections.