Mutation in Serratia marcescens AmpC beta-lactamase producing high-level resistance to ceftazidime and cefpirome.

ABSTRACT: Starting from a clinical isolate of Serratia marcescens that produced a chromosomally encoded AmpC beta-lactamase inducibly, we isolated by stepwise selection two laboratory mutants that showed high levels of resistance to some cephalosporins. The 98R mutant apparently overproduced the unaltered beta-lactamase constitutively, but the 520R mutant produced an altered enzyme, also constitutively. Ceftazidime and cefpirome MICs for the 520R mutant were much higher (512 and 64 microg/ml, respectively) than those for the 98R mutant (16 and 16 microg/ml, respectively). Yet the MICs of cephaloridine and piperacillin for the 520R mutant were four- to eightfold lower than those for the 98R mutant. Cloning and sequencing of the ampC alleles showed that in the 520R mutant enzyme, the Thr64 residue, ab

SUBMITTER: Raimondi A 

PROVIDER: S-EPMC90650 | biostudies-literature | 2001 Aug

REPOSITORIES: biostudies-literature