IDEXX have announced the publication of a peer reviewed study ¹, “Evaluation of a most probable number method for the enumeration of Legionella pneumophila from potable and related water samples,” by leading water microbiology consultant, David Sartory, in the April 2017 issue of Letters in Applied Microbiology. The paper concludes that the IDEXX Legiolert™/Quanti-Tray® test is superior to the standard method for quantifying L. pneumophila, the primary cause of Legionnaires’ disease.

The study compared the performance of the IDEXX Legiolert/Quanti-Tray most probable number (MPN) method, with the ISO 11731-2 membrane filtration method for the enumeration of L. pneumophila from 100 ml potable water and related samples. Data from a multi-laboratory study analysed according to ISO 17994² showed that Legiolert/Quanti-Tray yielded on average higher counts of L. pneumophila. The report also quantified the Legiolert medium as having a high specificity of 96·4%, and concluded that the new method represented a significant improvement in the enumeration of L. pneumophila from drinking water-related samples.

“This study clearly demonstrates that Legiolert is an effective test which gives confirmed, quantified results for L. pneumophila quickly, enabling users to identify where there may be a risk of Legionnaires’ disease to vulnerable populations,” commented Andrew Headland, Senior Business Manager, for IDEXX EMEA. “The test is much simpler than current traditional methods, and removes the need for laborious colony counting or confirmation steps, giving a fast, accurate and efficient alternative to the more time-consuming membrane filtration methods.”

Launched in 2016 in the United States, the IDEXX Legiolert test is based on a bacterial enzyme detection technology that signals the presence of L. pneumophila through utilisation of a substrate present in the Legiolert reagent. L. pneumophila cells grow rapidly and reproduce using the rich supply of amino acids, vitamins and other nutrients present in the Legiolert reagent. Actively growing strains of L. pneumophila use the added substrate to produce a brown colour indicator. Legiolert detects L. pneumophila at 1 organism in a 100 ml sample within 7 days.

References:

1. “Evaluation of a most probable number method for the enumeration of Legionella pneumophila from potable and related water samples” D.P. Sartory, K. Spies, B. Lange, S. Schneider, B. Langer onlinelibrary.wiley.com/doi/10.1111/lam.12719/full

2. ISO 17994:2014 specifies an evaluation procedure for comparing two methods with established performance characteristics according to ISO/TR 13843 and intended for the quantification of the same target group or species of microorganisms.