Surveillance and Genomic Characterization of Colistin-Resistant Gram-Negative Bacteria in Drains of Hospital High-Risk Units.

Abstract

Objectives: The healthcare water environment, including sinks and drainage systems, can be a long-term reservoir of nosocomial pathogens. In this study, we aimed to investigate the presence of colistin-resistant Gram-negative (ColR-GN) bacteria in humid compartments of high-risk hospital units at the University Medical Center Groningen (UMCG).

Methods: Environmental sampling was conducted in sinks and showers drains of high-risk hospital units. Colistin minimum inhibitory concentrations (MIC) were determined using broth microdilution (BMD). Whole-genome sequencing was performed to investigate the presence of mobile colistin resistance (mcr) genes, chromosomal point mutations and gene alterations linked to colistin resistance.

Results: ColR-GN bacteria were detected in all investigated units, with Enterobacter spp. being the most abundant genus. Twelve isolates exhibited colistin resistance (MIC >2 mg/L), including Enterobacter cloacae complex (n=11) and Klebsiella pneumoniae (n=1). Chromosomal mutations in genes involved in lipopolysaccharide structure modifications, were the main mechanisms contributing to colistin resistance in Enterobacter spp. and Klebsiella spp. (91.6%, 11/12). Additionally, two Enterobacter kobei isolates harbored mobile colistin resistance genes, mcr-4.3 and mcr-9.1.

Conclusions: The presence and persistence of ColR-GN bacterial clones in the sink and shower drains of high-risk hospital units highlights the importance of monitoring such environment for antibiotic resistant bacteria to identify reservoirs and prevent their further spread.