The polymerase chain reaction (PCR) is effective at detecting bacterial DNA in samples, but it is unable to differentiate viable bacteria from inactivated cells or free DNA fragments. New PCR-based analytical strategies have been developed to address this limitation. Molecular viability testing (MVT) correlates bacterial viability with the ability to rapidly synthesize species-specific ribosomal RNA precursor (pre-rRNA) in response to brief nutritional stimulation. Previous studies demonstrated that MVT can assess bacterial inactivation by chlorine, serum, and low-temperature pasteurization. Here, we demonstrate that MVT can detect inactivation of Escherichia coli, Aeromonas hydrophila, and Enterococcus faecalis cells by ultraviolet (UV) irradiation. Some UV-inactivated E. coli cells transiently retained the ability to synthesize pre-rRNA post-irradiation (generating false-positive MVT results), but this activity ceased within one hour following UV exposure. Viable but transiently undetectable (by culture) E. coli cells were consistently detected by MVT. An alternative viability testing method, viability PCR (vPCR), correlates viability with cell envelope integrity. This method did not distinguish viable from UV-inactivated bacteria under some conditions, indicating that the inactivated cells retained intact cell envelopes. MVT holds promise as a means to rapidly assess microbial inactivation by UV treatment.
IMPORTANCE Ultraviolet (UV) irradiation is increasingly used to disinfect water, food, and other materials for human use. Confirming the effectiveness of UV disinfection remains a challenging task. In particular, microbiological methods that rely on rapid detection of microbial DNA can yield misleading results. This is due to the detection of “remnant” DNA associated with dead microbial cells. This report describes a novel method that rapidly distinguishes living from dead microbial cells after UV disinfection.
REFERENCE:
Kris M. Weigel, et al.
Molecular Viability Testing of UV-Inactivated Bacteria. Appl Environ Microbiol. 2017 May 15; 83(10): e00331-17. Prepublished online 2017 Mar 10. Published online 2017 May 1. doi: 10.1128/AEM.00331-17. PMCID: PMC5411506
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