Japanese Journal of Infectious Diseases
Online ISSN : 1884-2836
Print ISSN : 1344-6304
ISSN-L : 1344-6304
Original Article
Molecular Characterization of Carbapenemase-Nonproducing Clinical Isolates of Escherichia coli (from a Thai University Hospital) with Reduced Carbapenem Susceptibility
Sawitree NuramrumAroonwadee ChanawongKamonwan LunhaAroonlug LulitanondArunnee SangkaChotechana WilailuckanaSunpetch AngkititrakulNicha CharoensriLumyai WonglakornPrajuab ChaimaneePloenchan Chetchotisakd
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2017 Volume 70 Issue 6 Pages 628-634


Twelve nonreplicate carbapenemase-negative ertapenem (ETP)-nonsusceptible (CNENS) Escherichia coli isolates obtained at a Thai university hospital between 2010 and 2014 were characterized and compared with 2 carbapenemase-producing E. coli isolates from the same hospital. Eight unique pulsed-field gel electrophoresis patterns were obtained. All the isolates produced CTX-M-15 β-lactamase and 2 either coexpressed CMY-2 cephalosporinase or showed increased efflux pump activity. Amino acid sequence analysis revealed that an OmpF defect (in 7 isolates) due to mutations generating truncated proteins or an IS1 insertion was more prevalent than a defect in OmpC was (no truncated proteins detected). Seven out of 10 isolates possessing OmpC variants with any OmpF defect were weakly ETP-resistant (minimum inhibitory concentrations [MICs] of 1–4 μg/mL) and imipenem (IPM)- and meropenem (MEM)-susceptible (MICs 0.125–0.5 μg/mL). Two isolates with ompC PCR-negative results and an OmpF defect showed higher carbapenem MICs (8–32, 1–8, and 1–4 μg/mL for ETP, IPM, and MEM, respectively) with the highest MICs associated with the additional efflux pump activity. Both carbapenemase producers possessing CTX-M-15 and a porin background identical to that in the CNENS isolates showed ETP, IPM, and MEM MICs of 128–256, 8, and 2–32 μg/mL, respectively. These findings suggest that a porin defect combined with CTX-M-15 production is the major mechanism of low carbapenem susceptibility among our CNENS isolates, which have potential to become strongly carbapenem-resistant because of additional carbapenemase or efflux pump activities.

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