Sensitivity of gentamicin-resistant Enterobacteriaceae to cefamandole and cefoxitin.

A collection of gentamicin-resistant Enterobacteriaceae strains was significantly more resistant to cefamandole than a species-matched collection of gentamicin-sensitive organisms. Cefamandole and gentamicin resistance could be simultaneously transferred by conjugation from four different species, Citrobacter freundii, Escherichia coli, Klebsiella pneumoniae and Serratia marcescens, to a recipient E. coli strain. Plasmids specifying linked resistance to cefamandole and gentamicin are thus commonly present in the environment of our medical center despite the fact that cefamandole has never been used here. Gentamicin-resistant organisms were not more resistant to cefoxitin than gentamicin-sensitive isolates. Conjugal transfer of cefoxitin resistance could not be demonstrated. Relative resistance to cefoxitin was nevertheless common among Enterobacter and Serratia isolates.