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

A clinical isolate of Escherichia coli susceptible to cefotaxime and c eftazidime from a polytraumatic pediatric patient, transferred a serie s of determinants of resistance to antibiotics, including cephalotin-c efazolin, to a recipient strain of E. coli K-12. When cephalotin-resis tant 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 w ere able to transfer this resistance, associated with resistance to ce phalotin cefazolin, to the K-12 recipient. Mutations to ceftazidime re sistance could be obtained by a similar procedure from cephalotin cefo taxime-resistant transconjugants of the first cycle of transfers. It i s concluded that transferable resistance to cefotaxime, and probably a lso to ceftazidime, could originate by selection of spontaneous mutant s of cephalotin-resistant E. coli, transferring this resistance.