Cefaclor: in vitro spectrum of activity and beta-lactamase stability.

The in vitro activity of cefaclor against 556 clinical isolates of gram-positive and gram-negative bacteria was compared with that of other cephalosporins. Cefaclor had activity similar to that of cephalexin against gram-positive bacteria. It showed greater activity against Haemophilus strains than did cephalexin and inhibited beta-lactamase-producing Haemophilus isolates. Cefaclor was more active than cephalexin or cephalothin against Escherichia coli, Salmonella, and Shigella isolates but did not act against Serratia, Acinetobacter, indole-positive Proteus, or Bacteroides isolates. Cefaclor was resistant to type III (TEM) beta-lactamases but was destroyed by type I beta-lactamases and, to a lesser degree, by type IV and type V beta-lactamases.