Several new
beta-lactam antimicrobial agents have been introduced in the last few years. In this investigation, the in vitro activities of several recently introduced
cephalosporins (
cefoperazone,
cefotaxime,
ceftazidime, and
ceftizoxime),
moxalactam, and N-formimidoyl
thienamycin were compared with those of
cefoxitin,
clindamycin, and
metronidazole against 203 strains of anaerobic bacteria. At achievable serum levels, all of the
antimicrobial agents were active against essentially 100% of the strains of anaerobic gram-positive cocci, Clostridium perfringens, Leptotrichia buccalis, and species of Selenomonas, Veillonella, and Eubacterium.
Clindamycin,
metronidazole, and N-formimidoyl
thienamycin were the most active agents against the Bacteroides fragilis group, inhibiting all strains at concentrations which can be achieved in serum. Of the remaining agents tested against the B. fragilis group,
cefoxitin (which required 64 mug/ml to inhibit 90% of the strains) was the most active, followed by
cefoperazone (128 mug/ml),
cefotaxime (128 mug/ml),
moxalactam (128 mug/ml),
ceftizoxime (256 mug/ml), and
ceftazidime (>256 mug/ml). Important differences in
cephalosporin susceptibility among species of the B. fragilis group were observed.
Metronidazole and N-formimidoyl
thienamycin were the most active drugs against species of clostridia other than C. perfringens; the other
antibiotics displayed poor activity, although this is partly due to inclusion of a relatively large number of strains of Clostridium difficile which were very resistant to several of the
cephalosporins. Only
metronidazole was active against all species of Fusobacterium.
Clindamycin and N-formimidoyl
thienamycin displayed excellent activity against gram-positive, non-spore-forming bacilli, requiring </=8 mug/ml to inhibit 100% of the strains.
Ceftazidime,
cefoperazone, and
moxalactam were bactericidal for 25 strains of B. fragilis at concentrations equal or close to those required for inhibition. On the basis of its activity in vitro, N-formimidoyl
thienamycin appears to be the most promising of the new
beta-lactam antibiotics for the treatment of
infections involving anaerobic bacteria.