Background: This study aimed to clarify the microbiological characteristics of carbapenem-resistant Escherichia coli (CRECO) due to New Delhi metallo-β-lactamase (NDM)-producing from recurrent urinary tract infection (RUTI) patients.
Methods: CRECO isolates were isolated from the urine of RUTI patients, identified with VITEK 2 compact system, and confirmed by MALDI-TOF MS. Antimicrobial susceptibility testing (AST) was performed with VITEK 2 compact system and Kirby-Bauer (K-B) method. Disk diffusion was used for extended spectrum beta-lactamase (ESBL) test. Phenotypic assays, including modified Hodge test (MHT), EDTA-modified carbapenem inactivation method (eCIM), and modified carbapenem inactivation method (mCIM), were performed to screen the carba-penemase. The antibiotic resistance genes were detected by polymerase chain reaction (PCR). Multilocus sequence typing (MLST) was performed for molecular typing of the strains.
Results: Among 63 CRECO strains, 22 (34.9%) strains were NDM-positive, in which NDM-5 accounted for 68.2% (15/22), NDM-1 accounted for 22.7% (5/22), and NDM-3 accounted for 9.1% (2/22). Among the 22 strains, 20 (90.9%) strains were co-carrying ESBLs genes, 12 (54.6%) strains were co-carrying blaCTX and blaTEM, 8 (36.4%) strains were co-carrying blaCTX or blaTEM, and 5 strains were co-carrying AmpC genes. BlaCMY-6 and blaCMY-156 ac-counted for 9.1% (2/22) and blaCMY-42 and blaDHA-1 accounted for 4.5% (1/22). Ten (45.5%) strains were co-carrying quinolone resistance genes. Three (13.6%) strains were co-carrying colistin resistance genes mcr-1. Six (27.3%) strains showed OmpF-expressed loss. Fourteen strains were positive and 8 strains were negative in the MHT, but mCIM and eCIM were both positive; the results of double-disc synergy method for detection of ESBLs were all negative in NDM-positive CRECO strains. The NDM-producing CRECO strains showed high-resistant rate to most antibiotics.
Conclusions: The antibiotic resistance mechanisms of NDM-positive CRECO are the coexistence of multiple resistance genes and/or the loss of or lesser expression of OMP. The emergence of mcr-1 gene in CRECO should be paid more attention by clinicians and microbiologists. Further surveillance should be strengthened to study the microbiological characteristics in order to control infection caused by NDM-positive CRECO better.