Evaluation of a most probable number method for the enumeration of Legionella pneumophila from potable and related water samples.

This study compared the performance of a novel MPN method (Legiolert/Quanti-Tray) with the ISO 11731-2 membrane filtration method for the enumeration of Legionella pneumophila from 100 ml potable water and related samples. Data from a multi-laboratory study analysed according to ISO 17994 showed that Legiolert™/Quanti-Tray® yielded on average higher counts of L. pneumophila. The Legiolert medium had a high specificity of 96·4%. The new method represents a significant improvement in the enumeration of L. pneumophila from drinking water-related samples. SIGNIFICANCE AND IMPACT OF THE STUDY: Legionella pneumophila is an opportunistic pathogen of major concern. The current large volume quantitative method employs membrane filtration (MF) and selective culture on GVPC agar followed by confirmation of isolates by serology (ISO 11731-2) We present here the results of a multi-laboratory evaluation of a most probable number (MPN) in-situ confirmed method (Legiolert™/Quanti-Tray®). The results indicate that Legiolert/Quanti-Tray yielded on average higher counts of L. pneumophila than ISO 11731-2. This development significantly improves and simplifies the enumeration of L. pneumophila from potable water samples.