title: Susceptibility of 539 gram-positive and gram-negative anaerobes to new agents, including RP59500, biapenem, trospectomycin and piperacillin/tazobactam.
abstract: Susceptibilities of 539 Gram-positive and Gram-negative anaerobes were tested by agar dilution against 15 new and existing antimicrobial agents. Organisms included 218 Bacteroides fragilis group strains, 15 non-fragilis group Bacteroides, 130 Porphyromonas/Prevotella, 49 fusobacteria, 50 peptostreptococci, 53 clostridia and 24 Gram-positive non-sporeforming bacilli. Of 412 Gram-negative bacilli, 89% were beta-lactamase-positive, while only two of the Gram-positive strains (both clostridia) produced this enzyme. Using established and preliminary breakpoints, all strains were susceptible to biapenem and imipenem (MIC90s 1 mg/L) and chloramphenicol (MIC90 8 mg/L). Only one of all the strains tested (a Cl. innocuum) was resistant (MIC > 4 mg/L) to RP59500; the latter had MIC90 2 mg/L, while 98% of strains were susceptible to trospectomycin (MIC90 16 mg/L). Ninety-nine per cent of strains were susceptible to piperacillin/tazobactam (MIC90 8 mg/L) compared to 86% to piperacillin (MIC90 > 64 mg/L). Corresponding data for ticarcillin/clavulanate versus ticarcillin were 97% susceptible (MIC90 8 mg/L) compared to 83% (MIC90 > 64 mg/L). Enhancement of the beta-lactam by the inhibitors was only seen in beta-lactamase-producing strains. Amoxycillin and cefoperazone were less often active (36% susceptible, MIC90 > 256 mg/L and 66% susceptible, MIC90 64 mg/L, respectively). Cefoxitin had greater activity than cefotetan (90% susceptible, MIC90 32 mg/L, compared to 72% susceptible, MIC90 > 64 mg/L). Metronidazole was active against 94% of strains (MIC90 4 mg/L). All metronidazole-resistant strains were Gram-positive (75% of non-sporeforming bacilli, 9% of clostridia and 6% of peptostreptococci). Ninety per cent of strains were susceptible to clindamycin (MIC90 4 mg/L).
authors.affiliation: Department of Pathology (Clinical Microbiology), Hershey Medical Center, Hershey, PA 17033.
authors.forename: P C
authors.initials: PC
authors.lastname: Appelbaum
authors.forename: S K
authors.initials: SK
authors.lastname: Spangler
authors.forename: M R
authors.initials: MR
authors.lastname: Jacobs
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001421:Bacteria, Anaerobic / Q000187:drug effects*; D004338:Drug Combinations; D004359:Drug Therapy, Combination / Q000494:pharmacology*; D006089:Gram-Negative Anaerobic Bacteria / Q000187:drug effects*; D006094:Gram-Positive Bacteria / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D010397:Penicillanic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D010878:Piperacillin / Q000494:pharmacology*; D000198:Spectinomycin / Q000031:analogs & derivatives* / Q000494:pharmacology; D000078142:Tazobactam; D013845:Thienamycins / Q000494:pharmacology*; D014769:Virginiamycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D004338:Drug Combinations; D013845:Thienamycins; D014769:Virginiamycin; C062940:quinupristin-dalfopristin; C043267:trospectomycin; D010397:Penicillanic Acid; D000198:Spectinomycin; D000078142:Tazobactam; D010878:Piperacillin; C065257:biapenem