Performance of Legiolert Test vs. ISO 11731 to Confirm Legionella pneumophila Contamination in Potable Water Samples

Abstract

Detection and enumeration of <i>Legionella</i> in water samples is of great importance for risk assessment analysis. The plate culture method is the gold standard, but has received several well-known criticisms, which have induced researchers to develop alternative methods. The purpose of this study was to compare <i>Legionella</i> counts obtained by the analysis of potable water samples through the plate culture method and through the IDEXX liquid culture Legiolert method. <i>Legionella</i> plate culture, according to ISO 11731:1998, was performed using 1 L of water. Legiolert was performed using both the 10 mL and 100 mL Legiolert protocols. Overall, 123 potable water samples were analyzed. Thirty-seven (30%) of them, positive for <i>L. pneumophila</i>, serogroups 1 or 2-14 by plate culture, were used for comparison with the Legiolert results. The Legiolert 10 mL test detected 34 positive samples (27.6%) and the Legiolert 100 mL test detected 37 positive samples, 27.6% and 30% respectively, out of the total samples analyzed. No significant difference was found between either the Legiolert 10 mL and Legiolert 100 mL vs. the plate culture (<i>p</i> = 0.9 and <i>p</i> = 0.3, respectively) or between the Legiolert 10 mL and Legiolert 100 mL tests (<i>p</i> = 0.83). This study confirms the reliability of the IDEXX Legiolert test for <i>Legionella pneumophila</i> detection and enumeration, as already shown in similar studies. Like the plate culture method, the Legiolert assay is also suitable for obtaining isolates for typing purposes, relevant for epidemiological investigations.