We investigated ertapenem-susceptible and -resistant extended-spectrum beta-lactamase-producing Enterobacter cloacae isolates obtained from the same patient. Gene transcription of OmpD and OmpF was diminished in the ertapenem-resistant isolate. An efflux pump inhibitor decreased the MICs of ertapenem in the resistant strain, suggesting a potential role of efflux pumps in ertapenem resistance.
