High prevalence of carbapenem-resistant Enterobacter cloacae complex in a tertiary hospital over a decade

The aim of this study was to explore the mechanisms and molecular epidemiology of carbapenem resistance in the carbapenem-resistant Enterobacter cloacae complex (CRECC) over a decade in a tertiary hospital in Zhejiang, China. From January 2011 to December 2021, we collected a total of 931 Enterobacter cloacae complex (ECC) isolates from a tertiary hospital in Zhejiang, China. Antimicrobial susceptibility tests were performed. Whole-genome sequencing was used to analyze the molecular characteristics of the CRECC isolates. For carbapenem-resistant strains, efflux inhibitor assay and quantitative real-time PCR (qRT-PCR) were performed to evaluate the function of efflux pumps. A total of 82 CRECC isolates were detected, and the rate of resistance for carbapenems was 8.8%, increasing from 5.5% in 2011 to 18.3% in 2019, with an overall increasing trend, with Enterobacter hormaechei subsp. hoffmannii being the predominant species. Among the CRECC, 24 (24/931) isolates were found to produce carbapenemases, including NDM-1, NDM-5, IMP-4, and KPC-2. Among all carbapenemases, NDM-1 was the most prevalent, accounting for 62.5% (15/24) of carbapenemases, followed by NDM-5 (5/24). Genes encoding extended-spectrum beta-lactamases (47/82) and AmpC (76/82) were also identified, with bla _SHV-12 and bla _ACT being the predominant ones, respectively. Multilocus sequence typing revealed 28 different sequence types, among which ST78 was the predominant, followed by ST93 and ST177. IncFIB was the most common type of plasmid replicon. Efflux inhibitor assay and qRT-PCR indicated that the overexpression of efflux pumps was involved in carbapenem resistance mechanisms. Additionally, disrupted outer membrane proteins also contribute to carbapenem resistance. The detection rate of CRECC was rising in the tertiary hospital. Bla _NDM-1 and bla _NDM-5 were the main carbapenem resistance genes. Our study revealed the presence of carbapenem-resistant ECC strains, emphasizing the need for effective infection prevention approaches to reduce the prevalence of CRECC.

The emergence and spread of the carbapenem-resistant Enterobacter cloacae complex (CRECC) have become a significant public health problem. CRECC strains frequently harbor multiple drug resistance genes and can be epidemic within healthcare facilities. The study explored the characteristics and prevalence of CRECC strains in the same hospital over a decade, which provides a theoretical basis for epidemiologic surveillance and clinical treatment.