[Appearance of Escherichia coli strain with high production of cephalosporinase during treatment with an amoxicillin and clavulanic acid combination].

In the course of an Escherichia coli cholecystitis, demonstrated by positive blood cultures, the authors observed a therapeutic failure with amoxicillin/clavulanate, probably related to the isolation in blood cultures, nine days after the beginning of the treatment, of a beta-lactam resistant E. coli strain (MICs of the amoxicillin combined with clavulanate was 64 mg/l and ceftazidim 16 mg/l). The strains which were recovered before and after treatment were shown to have the same biotype and the same electrophoretic profile for bacterial esterases. The second strain exhibited a high level production of the mediated chromosomal cephalosporinase. In the agar diffusion test, this mutant was more easily detected by ceftazidim than by other third generation cephalosporins. In the middle-stay unit where the patient was cured, cephalosporinase high producing mutants of E. coli were recovered in 0.6 p. cent of the strains versus 5, 1 p. cent for strains with cephalosporinase phenotype and 46.6 p. cent for strains with penicillinase phenotype. This report illustrates the importance of associating two synergistic antibiotics to prevent the emergence of beta-lactam resistant mutants in the course of severe E. coli infections.