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

Abstract

Detection and enumeration of Legionella 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 Legionella counts obtained by the analysis of potable water samples through the plate culture method and through the IDEXX liquid culture Legiolert method. Legionella 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 L. pneumophila, 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 (p = 0.9 and p = 0.3, respectively) or between the Legiolert 10 mL and Legiolert 100 mL tests (p = 0.83). This study confirms the reliability of the IDEXX Legiolert test for Legionella pneumophila 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.

Legionella pneumophila recovery using Legiolert and a traditional culture method

“…This study confirms results reported from 10 previous studies using Legiolert, indicating this method works as well or better than BCYE‐based methods for recovery and detection of L. pneumophila in water samples: cooling towers (Barrette, 2019); drinking water in distribution systems (LeChevallier, 2019a, 2019b); public bathing water and hot springs (Inoue et al, 2020), potable and nonpotable (Monteiro et al, 2021; Petrisik & Hall, 2018); nonpotable, cooling towers (Rech et al, 2018); building potable and nonpotable (Sartory et al, 2017); potable water (Scaturro et al, 2020); and building potable and nonpotable (Spies et al, 2018).…”

Assessing the Risk of Legionella Infection through Showering with Untreated Rain Cistern Water in a Tropical Environment

“…Significant progress has been made in recent years on improving the method for culture detection of Legionella in drinking water and the water distribution network [35][36][37]. The Legionella monitoring methods by ISO 11731 and the U.S. CDC also provide a reliable framework for culturing Legionella in drinking water [38,39].…”

“…In drawing comparisons between the Legionella concentrations, it should be noted that qPCR results may overestimate the viable Legionella. Previous studies concluded that qPCR is useful for rapid detection and risk assessment, but often detect higher amounts than by culture methods, especially from water tanks which have been disinfected [34,35]. On the other hand, Hamilton et al, (2017) [33] noted in a study on seasonality and RHRW premise plumbing pathogens that culture-based methods can underestimate concentrations due to the presence of viable but nonculturable (VBNC) cells.…”

Guidance on Developing a Legionella pneumophila Monitoring Program for Utility Distribution Systems

“…The test detects one L. pneumophila in 100 mL, with results ready in 7 days. Extensive studies have found that the Legiolert assay performed better than conventional methods, with a higher specificity for L. pneumophila in both potable and non-potable water [10][11][12][13][14]. The analytical technique for the Legiolert test is similar to the total coliform Colilert test, so the process is familiar to water utility laboratories [5].…”