15th January 2016 Content supplied by: IDEXX Laboratories Inc
Study Compares IDEXX Pseudalert® MPN vs. Membrane Filtration
Results of a Pan European study*, have been published recently in Current Microbiology, “Evaluation of the Pseudalert®/Quanti-Tray® MPN Test for the Rapid Enumeration of Pseudomonas aeruginosa in Swimming Pool and Spa Pool Waters.” The paper concludes that the IDEXX Pseudalert/Quanti-Tray method, produces confirmed results in a shorter time than the standard reference international and national membrane ﬁltration-based culture methods for P. aeruginosa, which both use Pseudomonas CN agar. The authors concluded that Pseudalert/Quanti-tray was a valid alternative method for recreational water analysis.
The study was conducted on both routinely analysed pool waters and swimming pool waters spiked with reference and environmental strains (obtained from swimming pool or spa pool water samples) of P. aeruginosa. The data were analysed according to the principles outlined in The Microbiology of Drinking Water—Part 3 (MoDW Part 3)  for the preliminary analysis of the data from each participating laboratory, and ISO 17994:2014  to assess the comparability of performance between the Pseudalert/Quanti-Tray method and the reference method.
The report went on to conclude that the Pseudalert/Quanti-Tray method needed less analyst labour time per sample, with no need for conﬁrmation testing.
Additionally, results are available within 24 hours compared to a minimum of 48 hours for the ISO 16266 and MoDW Part 8 methods, allowing a more rapid response to the presence of P. aeruginosa in pool and spa waters.
Launched in 2011, the IDEXX Pseudalert test is based on a bacterial enzyme detection technology that signals the presence of P. aeruginosa through the hydrolysis of a substrate in the Pseudalert reagent. P. aeruginosa cells rapidly grow and reproduce using the rich supply of amino acids, vitamins and other nutrients present in the Pseudalert reagent. Actively growing strains of P. aeruginosa have an enzyme that metabolises the substrate in the reagent to produce blue fluorescence under ultraviolet light.
Where quantification of a sample is required, IDEXX has developed a simple device known as a Quanti-Tray, which consists of 51 individually sealable cells. The Quanti-Tray can also be incubated for 24 hours after which the fluorescent cells can be counted and quantified by reference to an MPN table.
Date Published: 15th January 2016
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