UV-light fluorescence as a confirmation method for presumptive Legionella colonies isolated from water samples.

This article evaluates the use of ultraviolet (UV) light fluorescence as a confirmation method for detecting Legionella non-pneumophila colonies in water samples, compared to the standard ISO 11731:2017 reference method involving sub-culturing on buffered charcoal yeast extract (BCYE) agar plates with and without l-cysteine. In a collaborative study involving 10 laboratories, 298 strains (157 Legionella and 141 non-Legionella) were tested, showing 100% agreement between the UV-light method and the reference method for both inclusivity (sensitivity) and exclusivity (specificity). The interlaboratory study further confirmed these findings with full concordance across all participating labs. The study concludes that implementing UV-light confirmation can reduce workload, time-to-result, costs, and waste in Legionella testing workflows, although some Legionella species that do not fluoresce under UV light still require traditional confirmation methods.