The Contribution of Chemistry to the Detection and Enumeration of Legionella pneumophila in Environmental Water Samples: Experience With the MICA Method

Legionella is widespread in natural aquatic habitats and can contaminate man-made water systems. Due to public-health risks, measuring microbial load in water samples is essential. This study compared a new lipopolysaccharide bioprobe method (Microcolony Counter Analysis-MICA), which detects and counts Legionella pneumophila in 2 days, with the standard culture method (ISO 11731:2017), which may take up to 10 days. Our results on 108 water samples showed 82.4% agreement. Fifteen were ISO+/MICA- and four ISO-/MICA+; MICA sensitivity was 67.4%. Analysis of culture-media factors (Legionella inhibition by contaminating flora; culture on Glycine Vancomycin Polymyxin Cycloheximide agar (GVPC) and MICA factors (possible killing/growth inhibition due to acid treatment) showed that (a) ISO counts tended to be higher than MICA, with little difference whether GVPC results or the maximum yield between Buffered Charcoal Yeast Extract agar (BCYE) and GVPC were used. (b) Acid-treated MICA samples tended to yield higher counts than untreated ones, especially at high MICA counts. Considering what has been disclosed, a short 48-h incubation may reduce MICA recovery for some wild L. pneumophila strains, affecting click-based detection. With refinement, MICA could be a practical, user-friendly diagnostic tool, simpler sample prep, no large-volume filtration, no colony isolation or extra confirmation and provides confirmed results in 2 days versus >= 10 days for ISO culture.