Abstract
In vitro selection of mutants with decreased susceptibility to ertapenem was performed using Escherichia coli and Klebsiella pneumoniae clinical strains producing either the bla(CTX-M-2), bla(CTX-M-3), bla(CTX-M-9), or bla(CTX-M-15) gene. Frequencies of mutants with decreased susceptibilities to ertapenem were similar for all beta-lactamases expressed.