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

• Published in: Japanese Journal of Infectious Diseases Vol. 70; no. 6; pp. 628 - 634
• Main Authors: Nuramrum, Sawitree, Chanawong, Aroonwadee, Lunha, Kamonwan, Lulitanond, Aroonlug, Sangka, Arunnee, Wilailuckana, Chotechana, Angkititrakul, Sunpetch, Charoensri, Nicha, Wonglakorn, Lumyai, Chaimanee, Prajuab, Chetchotisakd, Ploenchan
• Format: Journal Article
• Language: English
• Published: Japan National Institute of Infectious Diseases, Japanese Journal of Infectious Diseases Editorial Committee 2017; Japan Science and Technology Agency
• Subjects: Amino Acid Sequence; Anti-Bacterial Agents - pharmacology; Bacteria; Bacterial Proteins - biosynthesis; Bacterial Proteins - chemistry; Bacterial Proteins - genetics; beta-Lactamases - biosynthesis; beta-Lactamases - chemistry; beta-Lactamases - genetics; carbapenem resistance; Carbapenemase; Cephalosporinase; Clinical isolates; Cluster Analysis; Cross Infection; Defects; E coli; Efflux; efflux pump; Ertapenem; ESBL; Escherichia coli; Escherichia coli - classification; Escherichia coli - drug effects; Escherichia coli - genetics; Escherichia coli - isolation & purification; Escherichia coli Infections - epidemiology; Escherichia coli Infections - microbiology; Gel electrophoresis; Hospitals, University; Humans; Imipenem; Meropenem; Microbial Sensitivity Tests; Molecular Typing; Mutation; OmpC; OmpF; Porins - genetics; Proteins; Pulsed-field gel electrophoresis; Thailand - epidemiology; ESBL; efflux pump; OmpF; OmpC; carbapenem resistance
• ISSN: 1344-6304; 1884-2836
• DOI: 10.7883/yoken.JJID.2017.156

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.