Antibacterial activity of a new 1-oxa cephalosporin compared with that of other beta-lactam compounds.

The in vitro activity of (6R,7R)-7-{[carboxy(4-hydroxyphenyl)acetyl]amino}-7-methoxy-3-[[(1-methyl -1H-tetrazol-5-yl)thio]methyl]-8-oxo-5-oxa-1-azabicyclo-[4.2.0]oct-2-ene -2-carboxylic acid was tested against isolates of gram-positive and negative bacteria and compared with those of cephalothin, cefuroxime, cefamandole, cefoxitin, cefotaxime, and carbenicillin. The compound was less active than the other compounds when tested against Staphylococcus aureus and Staphylococcus epidermidis. It had equal or slightly less activity than did cefotaxime when tested against members of the Enterobacteriaceae, but was 8- to 32-fold more active than the other cephalosporins against the Enterobacteriaceae, inhibiting most isolates at concentrations less than 0.5 mug/ml. The compound was twofold more active than cefotaxime and cefoxitin against Bacteroides, and it was twofold more active than cefotaxime and fourfold more active than carbenicillin against Pseudomonas aeruginosa. In vitro activity did not correlate with either the presence or type of beta-lactamase in either Enterobacteriaceae or Pseudomonas. The compound showed minimal synergy when combined with aminoglycosides or carbenicillin.