The in vitro activities of two new antimicrobial agents, apalcillin and cefpiramide (SM-1652), were evaluated against 324 strains of anaerobic bacteria. Apalcillin (a penicillin derivative) and cefpiramide (a semisynthetic cephalosporin) were compared with piperacillin, moxalactam, and cefoxitin. Organisms studied included the Bacteroides fragilis group, other Bacteroides species, fusobacteria, clostridia, nonsporeforming gram-positive rods, and anaerobic cocci. Piperacillin was found to be the most active overall, inhibiting 96% of the strains tested at its achievable level in serum (128 p.g/ml). Apalcillin was comparable in activity to piperacillin, inhibiting 93% of anaerobes tested at this concentration. The other antibiotics inhibited ca. 80% of the strains at 32 pLg/ml. In terms of activities against particular species, apalcillin was active against 75% of B. fragilis group strains and 97 to 100%o of all other anaerobes. Cefpiramide inhibited 37% of B. fragilis group strains at 32 Lg/ml and 68% at 64 pg/ml (a level that may be achievable with this drug). Cefpiramide inhibited 92% of all other anaerobes at 32 ,ug/ml and 95% at 64 ,g/ml. The clostridia other than Clostridium perfringens were the most resistant (84% inhibited at 32 ,ug/ml and 95% inhibited at 64 ,ug/ml).Many new beta-lactam antibiotics have been introduced in the last several years, many of which have limited activity against anaerobic bacteria (2, 3, 10, 13). Apalcillin is a naphthyridine derivative of ampicillin which has been reported to have levels of activity comparable to those of other broad-spectrum penicillin derivatives (e.g., azlocillin, mezlocillin, and piperacillin) against a wide range of organisms and particularly good activity against Pseudomonas aeruginosa (12). Cefpiramide (SM-1652) is a semisynthetic cephalosporin whose structure, antibacterial activity, and stability to P-lactamases have been described previously (4). Cefpiramide has been reported to have excellent activity against P. aeruginosa (4, 7, 9). The purpose of this study was to investigate the activities of these two new antimicrobial agents against a wide range of anaerobic bacteria, with particular attention to the Bacteroides fragilis group, which exhibits resistance to many of the newly developed antimicrobial agents. (Table 2). Apalcillin was moderately active against some of the B. fragilis group (MIC50 = 32 ,ug/ml), but 12 of the 37 strains of B. fragilis were resistant even at 256 ,ug/ml. Thus, 25% (18 of 74) of B. fragilis group strains were resistant to the highest concentration of antibiotic tested. Others (12) have also reported similar results. Other Bacteroides species were more susceptible to apalcillin; only 2 of 75 strains were resistant at 256 ,ugIml. B. oralis, B. bivius, B. capillosus, and B. melaninogenicus subsp. melaninogenicus were more resistant than the other non-B. fragilis group Bacteroides strains tested. All of the other anaerobes tested were susceptible to apalcillin at a concentration of 64 pug/ml or less. MATERIALS AND METHODSCe...

The in vitro activity of cefbuperazone was compared with that of cefoxitin, moxalactam, and piperacillin against 305 strains of anaerobic bacteria. Piperacillin was the most active overall, inhibiting 97% of all anaerobes tested at 128 ,ug/ml. Cefbuperazone had poor activity against the Bacteroides fragilis group and Clostridium difficile (43 and 0% susceptible, respectively) but good activity (90.5%) against all other anaerobic bacterial species tested.The ever increasing introduction of 1-lactam antibiotics into the antimicrobial market, along with expanded awareness of the importance of anaerobic bacteria in infectious diseases, has underlined the need for information on the efficacy of these agents against anaerobic bacteria (1). It is important to note that methodological differences between laboratories may affect the results; thus, it is difficult to draw conclusions from a number of studies unless the same techniques are used throughout.In this report, the activity against anaerobic bacteria of cefbuperazone, a new semisynthetic parenterally administered cephamycin antibiotic, was compared with that of cefoxitin, moxalactam, and piperacillin, drugs commonly used in anaerobic infections.All bacteria were randomly selected recent clinical isolates from the Veterans Administration Wadsworth Medical Center, Los Angeles. Bacteria were identified by using established procedures (2,3). MICs were determined by an agar dilution technique described previously (3) and 69% of all strains tested, respectively. These results for cefoxitin and moxalactam are in excellent agreement with other recent studies from our laboratory (4). Cefbuperazone had particularly poor activity against the B. fragilis group overall (43% susceptible) and Clostridium difficile (0% susceptible) but relatively good activity (90.5% susceptible) against all other species tested. Moxalactam and cefoxitin also displayed relatively poor activity (64 and 77% susceptible, respectively) against the B. fragilis group overall, although activity against the species B. fragilis itself was excellent (see below). Moxalactam and cefoxitin were inactive against C. difficile as noted in previous reports from our laboratory; moxalactam inhibited 83% and cefoxitin inhibited 90% of all other strains tested (excluding C. difficile).Piperacillin was the only antimicrobial agent tested that was active against C. difficile and was the most active agent against other Clostridium species. Gram-positive, nonsporeforming rods were very susceptible to both piperacillin (100%o) and cefoxitin (97%) and less so to both cefbuperazone and moxalactam (81%