Colilert-18/Quanti-Tray detects E. coli and total coliforms in water within 18 hours.
It was launched in 1996 for the drinking water market in Europe and the firm said it has become the largest selling water microbiology test for E. coli and coliforms worldwide and is relied upon by water utility companies to deliver clean water to consumers.
Increasing industry awareness
"Given the increasing number of reports of foodborne outbreaks of infectious disease, the industry has become more aware of the need for testing for indicators of contamination,” said Andrew Headland, senior business manager, EMEA, IDEXX Water.
“There is particular concern over the levels of faecal indicator bacteria in wash water used for processing of leafy greens and other vegetables," he told FoodQualityNews.
“The sector currently uses membrane filtration procedures for the examination of 100 ml samples which is a more laborious procedure that generally requires confirmation of colonies leading to slower detection times.
“Smaller samples of water can be analysed using other systems but the sensitivity of such system is around two orders of magnitude lower.”
Headland said tests for E. coli as an indicator of faecal contamination are a daily occurrence within the food processing industry but Colilert-18 does not reveal the serotype of E. coli.
“The absence of E. coli is a good indication that pathogens transmitted by the faecal-oral route are unlikely to be present. For example, E. coli would typically outnumber Salmonella bacteria by a ratio of greater than 100:1," he said.
“There are no reliable tests for the presence of viable E. coli in water (other than Colilert-18) that can be completed in 18 hours. Some tests claim to have an 18 hour completion time but they require confirmation or have been shown to be deficient in terms of sensitivity at 18 hours.”
How the test works
The product consists of a reagent powder, which is added to a 100ml water sample and incubated for 18 hours in the case of presence/absence determination. The base technology is Defined Substrate Technology (DST).
The medium contains substrates for the two enzymes β-D-galactosidase (for total coliforms) and β-D-glucuronidase (for E. coli).
These components constitute the primary carbon and energy sources “forcing” bacteria to use the substrates releasing coloured or fluorescent by-products into the surrounding medium.
Presence of E. coli and total coliforms is determined following incubation, with coliforms indicated by the sample turning yellow and fluorescence indicating presence of E. coli.
Where quantification of a sample is required, IDEXX has Quanti-Tray, which consists of 51 individually sealable cells.
The Quanti-Tray can also be incubated for 18 hours after which the fluorescent cells can be counted and quantified.
The test was specified as a reference method, under EN ISO 9308-2, in the European Drinking Water Directive 2015/1787. It became the ISO 9308-2 standard for detection of E. coli and total coliforms in water in 2012 and later as EN ISO 9308-2 in 2014 following validation.