ORIGIN OF TRANSFERABLE CEFOTAXIME RESISTANCE IN A CLINICAL ISOLATE OF ESCHERICHIA-COLI MUTATION

A clinical isolate of Escherichia coli susceptible to cefotaxime and ceftazidime from a polytraumatic pediatric patient, transferred a series of determinants of resistance to antibiotics, including cephalotin-cefazolin, to a recipient strain of E. coli K-12. When cephalotin-resistant clones of K-12 were tested for their resistance to cefotaxime on solid media with this antibiotic, nine clones could be isolated which were resistant to high concentrations of cefotaxime. All nine clones were able to transfer this resistance, associated with resistance to cephalotin cefazolin, to the K-12 recipient. Mutations to ceftazidime resistance could be obtained by a similar procedure from cephalotin cefotaxime-resistant transconjugants of the first cycle of transfers. It is concluded that transferable resistance to cefotaxime, and probably also to ceftazidime, could originate by selection of spontaneous mutants of cephalotin-resistant E. coli, transferring this resistance.