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Molecular Characterization of Carbapenemase-Nonproducing Clinical Isolates of Escherichia coli (from a Thai University Hospital) with Reduced Carbapenem Susceptibility.

Molecular Characterization of Carbapenemase-Nonproducing Clinical Isolates of Escherichia coli (from a Thai University Hospital) with Reduced Carbapenem Susceptibility.
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Nuramrum S, Chanawong A, Lunha K, Lulitanond A, Sangka A, Wilailuckana C, Angkititrakul S, Charoensri N, Wonglakorn L, Chaimanee P, Chetchotisakd P,


Nuramrum S, Chanawong A, Lunha K, Lulitanond A, Sangka A, Wilailuckana C, Angkititrakul S, Charoensri N, Wonglakorn L, Chaimanee P, Chetchotisakd P, (click to view)

Nuramrum S, Chanawong A, Lunha K, Lulitanond A, Sangka A, Wilailuckana C, Angkititrakul S, Charoensri N, Wonglakorn L, Chaimanee P, Chetchotisakd P,

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Japanese journal of infectious diseases 2017 09 1170(6) 628-634 doi 10.7883/yoken.JJID.2017.156
Abstract

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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