A photoactivation-free viability PCR reagent for rapid, culture-independent detection of live bacteria

Detection of viable bacteria in complex samples is a long-standing challenge in microbiology and public health. Traditional culture methods are slow and often fail to capture viable but non-culturable cells, while PCR-based methods can overestimate bacterial loads by amplifying DNA from non-viable (dead) cells. To address this challenge, we evaluated a novel, photoactivation-free viability PCR (vPCR) reagent from Promega Corporation that selectively crosslinks DNA from non-viable cells, rendering it unamplifiable by qPCR. This approach enables accurate, culture-independent quantification of viable bacteria. We optimized key parameters in both gram-positive (Listeria) and gram-negative (Pseudomonas and Legionella) bacteria, including reagent concentration, amplicon length, and workflow format to ensure robust viability discrimination. We demonstrate that this method detects reductions in viable Legionella following heat treatment and is compatible with filter-concentrated samples. This is the first description of a chemically defined, non-photoactivated vPCR reagent and its successful application to rapid, accurate detection of viable Legionella, with implications for building water safety and public health surveillance.

Rapid and reliable detection of viable bacteria is essential for protecting public health, monitoring water quality, ensuring food safety, and advancing clinical diagnostics. Conventional culture methods underestimate viable cells and require days to deliver results, while conventional PCR-based tests cannot distinguish viable (live) from non-viable (dead) organisms. Here, we describe a photoactivation-free viability PCR reagent that overcomes these limitations by selectively blocking PCR amplification from non-viable cells. Using Legionella pneumophila, a waterborne pathogen that causes severe pneumonia, we show that this method provides accurate, culture-independent measurements of viable bacteria in water samples within hours. Results align with culture-based methods while avoiding long delays and technical drawbacks of traditional approaches. By simplifying workflows and improving accuracy, this reagent offers a broadly applicable tool for detecting viable microbes, enabling faster interventions and supporting microbial testing across environmental, clinical, and industrial settings.