Can multidrug-resistant organisms become resistant to ultraviolet (UV) light following serial exposures? Characterization of post-UV genomic changes using whole-genome sequencing.

ABSTRACT

OBJECTIVES: No-touch disinfection systems like xenon- or mercury-based ultraviolet (UV) are now commonly being used for hospital room disinfection. However, serial exposure to UV light can potentially lead to the development of bacterial resistance. We sought to determine whether UV resistance develops due to serial exposure to UV light using 3 epidemiologically important multidrug-resistant microbial strains. METHODS: Methicillin-resistant Staphylococcus aureus (MRSA), carbapenemase-producing Klebsiella pneumoniae (KPC) and metallo-ß-lactamase-producing Klebsiella pneumoniae (MBL) were serially exposed to 25 growth-irradiation cycles of UV produced by a xenon-based UV (Xe-UV) lamp for 5 minutes or a mercury-based UV (Hg-UV) lamp for 10 minutes. After each UV exposure cycle, the surviving colony-forming units (CFUs) were measured and compared with the initial inoculum of each cycle for each strain, respectively. RESULTS: In each cycle, ˜1-10 million of MRSA, KPC, and MBL were used to test the effect of UV irradiation. Postexposure colony counts remained low (3-100 colonies) throughout the 25 serial exposures to both xenon- and mercury-based UV. The log-kill rate after each exposure showed no changes following UV disinfection by Xe-UV. The MRSA log-kill rate increased after repeated exposure to Hg-UV unlike KPC and MBL K. pneumoniae, which did not change. Whole-genome sequencing (WGS) analyses performed on these 3 strains demonstrated no significant genetic changes after multiple UV irradiation cycles. CONCLUSIONS: Exposure of multidrug-resistant bacteria to UV produced from 2 different UV sources did not engender UV resistance after 25 serial exposures, as demonstrated by WGS analysis; thus, UV disinfection is unlikely to generate UV-resistant hospital flora.