Full Description

Rapid and convenient detection of Coliforms and E. coli in water samples, especiallyin drinking water, by chromogenic and fluorogenic substrates is gaining more andmore acceptance worldwide. For the detection of E. coli, the fluorogenic substrateMUG is included in various widely used, ready-to-use culture media such asReadyCult, Colilert, and others. MUG is cleaved by Y-glucuronidase which ispresent in 98% of all E. coli strains. However, there is a significant gap in thedetection of the variety of E. coli. Exactly E. coli O157:H7, the most dangerousserotype, which can lead in very low numbers to serious infections in humans, cannotbe detected in water samples by this method. This serotype typically does notproduce Y-glucuronidase and this in turn results in a lack of fluorescencedevelopment in the enriched culture broth. In order to fill this gap, the application ofthe simple biochemical indole test and subsequently of Singlepath E. coli O157, anewly developed lateral flow test with improved specificity, was tested with spikedwater samples after enrichment with ReadyCult for 18-24 h. Tap water sampleswere spiked at various levels (2-120 CFU/100 ml) with 43 different bacteria belongingto various E. coli and non-E. coli isolates. After culturing, color and fluorescencedevelopment was visually analyzed. As expected, all 10 E. coli O157:H7 tested led tocolor development indicating their belonging to the Coliforms, but were fluorescencenegative, indicating that they do not represent E. coli. However, all of them gavepositive results with the indole test applied indicating their belonging to E. coli. Thedirect application of a small volume (150 ul; without boiling) of the culture to theSinglepath E. coli O157 specifically detected all samples in which E. coli O157 werespiked. Only these E. coli O157 strains led to a clear positive result mostly within 5min. In summary, the presence of highly pathogenic E. coli O157:H7 in watersamples after enrichment in ready-to-use culture media can be easily detected byusing an inexpensive indole test. If positive, Singlepath E. coli O157 can then beapplied directly without further preparation of the sample. Includes table.

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Edition: Vol. - No. Published: 11/02/2003 Number of Pages: 5File Size: 1 file , 230 KB