Characterization of NDM-5 Carbapenemase-Encoding Gene (bla_NDM-5) – Positive Multidrug Resistant Commensal Escherichia coli from Diarrheal Patients

Purpose: The multidrug resistance Enterobacteriaceae cause many serious infections resulting in prolonged hospitalization, increased treatment charges and mortality rate. In this study, we characterized bla_NDM-5-positive multidrug resistance commensal Escherichia coli (CE) isolated from diarrheal patients in Kolkata, India. Methods: Three CE strains were isolated from diarrheal stools, which were negative for different pathogroups of diarrheagenic E. coli (DEC). The presence of carbapenemases encoding genes and other antimicrobial resistance genes (ARGs) was detected using PCR. The genetic arrangement adjoining bla_NDM-5 was investigated by plasmid genome sequencing. The genetic relatedness of the strains was determined by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) methods. Results: In addition to colistin, the bla_NDM-5-positive CE strains showed resistance to most of the antibiotics. Higher MICs were detected for ciprofloxacin (>32 mg/L) and imipenem (8 mg/L). Molecular typing revealed that three CE strains belonged to two different STs (ST 101 and ST 648) but they were 95% similar in the PFGE analysis. Screening for ARGs revealed that CE strains harbored Int-1, bla_TEM, bla_CTX-M3, bla_OXA-1, bla_OXA-7, bla_OXA-9, tetA, strA, aadA1, aadB, sul2, floR, mph(A), and aac(6´)-Ib-cr. In conjugation experiment, transfer frequencies ranged from 2.5×10⁻³ to 8.4x10⁻⁵. The bla_NDM-5 gene was located on a 94-kb pNDM-TC-CE-89 type plasmid, which is highly similar to the IncFII plasmid harboring an IS26-IS30-bla_NDM-5-ble_MBL-trpF-dsbd-IS91-dhps structure. Conclusion: To the best of our knowledge, this is the first report on carbapenem resistance involving the bla_NDM-5 gene in CE from diarrheal patients. The circulation of bla_NDM-5 gene in CE is worrisome, since it has the potential to transfer bla_NDM-5 gene to other enteric pathogens.