IDEXX have shared exciting results of a recently-published study, undertaken in Germany by the Institut für “Hygiene und Öffentliche Gesundheit am Universitätsklinikum Bonn”.

The ISO 17994 compliant study compared the performance of the IDEXX Pseudalert^® most probable number (MPN) method (Pseudalert/Quanti-Tray^®) with the ISO 16266 membrane filtration culture-based method for the detection and enumeration of Pseudomonas aeruginosa in cooling tower and related water samples.

The study, published in the Journal of Applied Microbiology,* concluded that Pseudalert “represents a significant improvement in the enumeration of Pseudomonas aeruginosa from cooling tower water and related samples,” and that the MPN method offered “a more efficient and sensitive test for enumerating Pseudomonas aeruginosa from cooling tower waters, thus significantly improving management of occupational safety during cleaning and maintenance activities of cooling towers.”

The VDI Cooling Tower Code of Practice 2047-2 (Verein Deutscher Ingenieure, VDI 2015) is the German technical guideline for hygiene in cooling towers and specifies the requirement for routine monitoring of Pseudomonas aeruginosa by cooling tower operators.

In terms of occupational safety, it is necessary to monitor the Pseudomonas aeruginosa contamination in cooling towers and to initiate disinfection procedures above a concentration level of 100 colony forming units (CFU) per 100 ml.

The study also highlighted that Pseudalert is more rapid and has improved performance over the ISO 16266 method. Pseudalert has a greater than 10-fold higher upper quantification limit when using Quanti-Tray/2000 and a shorter incubation time with no requirement for additional time-consuming confirmation steps.

Launched in 2011, the IDEXX Pseudalert test is based on a bacterial enzyme detection technology that signals the presence of Pseudomonas aeruginosa through the hydrolysis of a substrate in the Pseudalert reagent.

Pseudomonas 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 Pseudomonas aeruginosa have an enzyme that metabolises the substrate in the reagent to produce blue fluorescence under ultraviolet light.

The test is simple to use and requires minimal training and equipment to set up and can accurately detect Pseudomonas aeruginosa at low levels, even with high background flora, giving confirmed results within 24 hours.

In September 2018, Pseudalert became accepted as a global ISO standard for the enumeration of Pseudomonas aeruginosa in hospital waters, drinking water and non‑carbonated bottled waters intended for human consumption, groundwater, swimming pool and spa pool waters including those containing high background counts of heterotrophic bacteria. The standard was published as ISO 16266-2:2018, Water Quality—Detection and Enumeration of Pseudomonas aeruginosa–Part 2: Most Probable Number Method.

Pseudalert is also included in several European country-specific standards and is listed as an alternative method to ISO 16266 for drinking and swimming pool water in the Umweltbundesamt (Liste alternativer mikrobiologischer Nachweisverfahren Juni 2015, Anlage 5. Teil I, Buchstabe c, TrinkwV 2001).

With this latest study, the scope of the product has been enlarged to include the enumeration of Pseudomonas aeruginosa, including cooling tower water using the MPN method.

To achieve such performance, a dilution step has been added (the same as for the standard method). Therefore, the detection limit in cooling towers is no longer 1 per 100 mL but 10 per 100 mL, which is perfectly acceptable with respect to the official regulatory threshold value.