1995 Volume 48 Issue 9 Pages 1027-1033
When Enterobacter cloacae, Citrobacter freundii, and Proteus vulgaris were treated with piperacillin (PIPC) in combination with tazobactam (TAZ), the in vitro frequency of emergence of resistant strains (β-lactamase producing mutants) was lower than with PIPC or ceftazidime (CAZ) treated bacteria. In a mouse intraperitoneal infection model caused by E. cloacae, β-lactamase derepressed mutants were detected following therapy with PIPC or CAZ, although no derepressed mutants were detected after treatment with PIPC in combination with TAZ. This suppression of the selection of derepressed mutants, which produce large amounts of β-lactamases, by the combination of TAZ and PIPC suggests that the combination delays the increase of resistant mutants compared with PIPC alone.