‘ Colilert-18 is much more selective , so counting up wells on a tray is simpler , and it has less ambiguity .’
assures that all is well but E . coli was indeed present and gets out into the water distribution system , the costs of remediation will be significant , especially if a boil notice is issued . When E . coli or coliforms are detected , the decision to take corrective action can be taken promptly and with confidence . Following the corrective action , any re-tests can also be read at 18 hours , enabling the operations team to know the effectiveness of their remedial actions quickly .
Bullock also chooses to use Colilert-18 on all raw water samples , whether from rivers or reservoirs , because he believes the consistency this gives is important . But it ’ s also much more accurate and easy to use . ‘ Raw water contains a lot of background flora that will also be growing ,’ he says . ‘ Colilert-18 is much more selective , so counting up wells on a tray is simpler , and it has less ambiguity .’ The test ’ s Quanti- Tray ® displays wells with a yellow coloration for coliforms and also fluorescence under UV light if E . coli is present .
Furthermore , he uses the technique on sludge cake , where it is important to show a sufficient reduction on E . coli from raw sewage before it is released , as it is used as a fertiliser and could enter the food chain . Again , Colilert-18 is able to eliminate the background flora , and just focus in on E . coli . The confidence that there will be an accurate result which is simple to interpret is particularly important here .
The batches of Colilert-18 have a 15 month shelf-life , in contrast to agar plates with a two-week shelflife . Bullock chooses to buy two batches a year . As well as ensuring supply chain security , this enables him to make a QC chart for that test that will be good for the whole six months . ‘ I know that any out-ofspec test results are highly unlikely to have been caused by the test media , as it has a robust history of good performance ’ he says . ‘ With other media , the short shelflife adds variability to a method ’ s performance , and there is not that long-term assurance .’
Another advantage is that IDEXX takes full ownership of the entire test process , unlike other test suppliers . ‘ If any element of the methodology falters , whether it ’ s the equipment or we get an abnormal result we can ’ t explain , they will always help , whether it turns out to be their problem or not ,’ Bullock says . ‘ They take accountability and support us because they understand our value as a customer .’