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. 2021 Jun;72(6):750-756.
doi: 10.1111/lam.13469. Epub 2021 Mar 15.

Cross-reactivity of the IDEXX Legiolert method with other Gram-negative bacteria and waterborne pathogens leads to false-positive assay results

M Hirsh  1 , J L Baron  1 , S Mietzner  1 , J D Rihs  1 , J E Stout  1   2
Affiliations

Cross-reactivity of the IDEXX Legiolert method with other Gram-negative bacteria and waterborne pathogens leads to false-positive assay results

M Hirsh et al. Lett Appl Microbiol. 2021 Jun.

Abstract

Legionella species are the causative agent of Legionnaires' disease, a potentially fatal bacterial pneumonia. New regulations and standards have prioritized the development of water safety plans to minimize the growth and spread of Legionella species in buildings. To determine the presence and type of Legionella in a water system, microbiological culturing is the gold standard method. However, recently new methodologies have been developed that claim to be sensitive and specific for Legionella at the genus or L. pneumophila at the species level. Published and anecdotal reports suggest that one of these newer culture-based, enzyme-substrate methods, the IDEXX Legiolert test, may exhibit false positivity with other microbes common to water sources. We experimentally evaluated the IDEXX Legiolert method using these other waterborne bacteria including Elizabethkingia meningoseptica, Pseudomonas aeruginosa, Proteus mirabilis and Serratia marcescens at real-world environmental concentrations. We saw false-positive results for the Legiolert test with several of these organisms, at sample concentrations as low as 60 CFU per ml. False-positive Legionella results can trigger costly remediation and water-use restrictions, that may be implemented while waiting for additional, confirmatory microbiological testing that could, in this case, yield no L. pneumophila.

Keywords: Legionella pneumophila; IDEXX; Legiolert; cross-reaction; false positivity; waterborne pathogens.

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References

    1. Anon (2016) Part 4- protection against Legionella. In VOLUME A (Title 10) ed. New York Codes, R., and Regulations: New York State.
    1. ASHRAE (2018) ANSI/ASHRAE Standard 188-2018. Legionellosis: Risk Management for Building Water Systems. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers.
    1. Barrette, I. (2019) Comparison of Legiolert and a conventional culture method for detection of Legionella pneumophila from cooling towers in Quebec. J AOAC Int 102, 1235-1240.
    1. Bharucha, T., Sharma, D., Sharma, H., Kandil, H. and Collier, S. (2017) Ochromobactrum intermedium: an emerging opportunistic pathogen-case of recurrent bacteraemia associated with infective endocarditis in a haemodialysis patient. New Microbes New Infect 15, 14-15.
    1. Budnick, G.E., Howard, R.T. and Mayo, D.R. (1996) Evaluation of Enterolert for enumeration of enterococci in recreational waters. Appl Environ Microbiol 62, 3881-3884.

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