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This study assessed the performance of a new most probable number test (Pseudalert/Quanti-Tray) for the enumeration of Pseudomonas aeruginosa from swimming pool and spa pool waters by comparing it to the international and national membrane filtration-based culture methods for P. aeruginosa: ISO 16266:2006 and UK The Microbiology of Drinking Water-Part 8 (MoDW Part 8) which both use Pseudomonas CN agar. The comparison was based on the calculation of mean relative differences between the two methods conducted according to ISO 17994:2014. Using both routine pool water samples (149 from 8 laboratories) and artificially contaminated samples (309 from 7 laboratories), paired counts from each sample and enumeration method were analysed. For routine samples, there were insufficient data for a conclusive assessment, but the data do indicate at least equivalent performance of Pseudalert/Quanti-Tray to the reference methods. For the artificially contaminated samples, the data also did not result in a statistically conclusive assessment but did indicate potentially better performance of Pseudalert/Quanti-Tray. Combining the data from the routine samples and artificially contaminated samples resulted in an ISO 17994 outcome that the two methods were not statistically significantly different. Thus, the Pseudalert/Quanti-Tray method is an acceptable alternative to ISO 16266 and MoDW Part 8. The Pseudalert/Quanti-Tray method has the advantage in that it does not require confirmation testing, and of providing confirmed counts within 24-28 h incubation compared to 40-48 h or longer for the ISO 16266 and MoDW Part 8 methods.

In this study, the performance of a new most probable number (MPN) test (Pseudalert(®)/Quanti-Tray(®)) for the enumeration of Pseudomonas aeruginosa from hospital waters was compared with both international and national membrane filtration-based culture methods for P. aeruginosa: ISO 16266:2006 and UK The Microbiology of Drinking Water - Part 8 (MoDW Part 8), which both use Pseudomonas CN agar. The comparison based on the calculation of mean relative differences between the two methods was conducted according to ISO 17994:2014. Using both routine hospital water samples (80 from six laboratories) and artificially contaminated samples (192 from five laboratories), paired counts from each sample and the enumeration method were analysed. For routine samples, there were insufficient data for a conclusive assessment, but the data do indicate at least equivalent performance of Pseudalert(®)/Quanti-Tray(®). For the artificially contaminated samples, the data revealed higher counts of P. aeruginosa being recorded by Pseudalert(®)/Quanti-Tray(®). The Pseudalert(®)/Quanti-Tray(®) method does not require confirmation testing for atypical strains of P. aeruginosa, saving up to 6 days of additional analysis, and has the added advantage of providing confirmed counts within 24-28 hours incubation compared to 40-48 hours or longer for the ISO 16266 and MoDW Part 8 methods.

This study compared the Quanti-Disc most probable number (MPN) test for heterotrophic bacteria from drinking water with the widely used yeast extract agar (YEA) pour plate method. The Quanti-Disc test module contains 50 reaction wells in which a medium has been pre-deposited. The medium contains a suite of three fluorogenic enzyme substrates selected for the detection of enzymes expressed widely by heterotrophic bacteria. The MPN of heterotrophic bacteria is calculated from the number of fluorescing reaction wells after incubation of a sample. Quanti-Disc and the YEA pour plate method were compared according to guidance on comparing methods given in United Kingdom national guidance and ISO 17994:2004. The two methods were also challenged with reference strains and isolates of heterotrophic bacteria from drinking water. This indicated that heterotrophic bacteria commonly encountered in drinking water are detected by both the YEA pour plate method and Quanti-Disc. Analysis of data from split water samples (723 for 37 degrees C tests and 872 for 22 degrees C tests) from nine geographically diverse laboratories in England and Wales demonstrated that the Quanti-Disc method is equivalent to the YEA pour plate method for the analysis of heterotrophic bacteria from drinking and similar waters at 37 degrees C, and superior to YEA for the analysis at 22 degrees C. The Quanti-Disc method is a simple and efficient alternative method for the enumeration of heterotrophic bacteria from drinking water.

The count of general or heterotrophic bacterial populations in treated drinking water in the UK has been undertaken since the 1880s. Counts of heterotrophic bacteria at 22 and 37 degrees C are used widely as part of an overall assessment of treated drinking water quality. There were no legislated standards for water quality in the UK until adoption of the first EU Directive in 1989. The UK has, however, never stipulated numerical standards or guidelines for heterotrophic bacteria, although their enumeration has long been part of the assessment of 'wholesome' water, on which advice regarding microbiological quality was given in a series of documents known as 'Report 71'. The current regulations stipulate only that there should be 'no abnormal change' in numbers normally associated with a given supply. This paper reviews the historical context regarding the enumeration, and interpretation of results, of heterotrophic bacteria from treated drinking water, and information regarding current practices by UK water suppliers. The appropriateness of using heterotrophic bacteria counts as an operational tool or as a health parameter is briefly discussed in the light of the UK experience., (Copyright 2003 Elsevier B.V.)