In vitro susceptibility of cephalothin-resistant Enterobacteriaceae to cefoxitin and BL-S786

The in vitro antibacterial activity of two agents relatively resistant to beta-lactamases, BL-S786 and cefoxitin, was tested against 123 recent different clinical isolates of cephalothin-resistant Enterobacteriaceae. BL-S786 showed considerable activity against Escherichia coli and lesser activity against Klebsiella pneumoniae with, respectively, 68% and 41% inhibited at 32 microng/ml. Cefoxitin showed more activity in vitro against E. coli, K. pneumoniae, Serratia marcescens and Providencia stuartii. Cefoxitin appears to be a more promising agent for treating infections caused by cephalothin-resistant Enterobacteriaceae.