Mechanisms of carbapenem resistance among a collection of Enterobacteriaceae clinical isolates in a Texas city

Fourteen Enterobacteriaceae isolates with ertapenem MIC >2 mg/mL were analyzed to identify mechanisms of resistance. All isolates produced extended-spectrum β-lactamase or AmpC β-lactamase with variable, but decreased, expression of outer membrane proteins. One Enterobacter cloacae produced derepressed AmpC β-lactamase, 1 Escherichia coli expressed plasmid-mediated AmpC β-lactamase, and 1 E. cloacae produced a carbapenemase.