Rapid and convenient detection of Coliforms and E. coli in water samples, especially
in drinking water, by chromogenic and fluorogenic substrates is gaining more and
more acceptance worldwide. For the detection of E. coli, the fluorogenic substrate
MUG is included in various widely used, ready-to-use culture media such as
ReadyCult®, Colilert®, and others. MUG is cleaved by Y-glucuronidase which is
present in 98% of all E. coli strains. However, there is a significant gap in the
detection of the variety of E. coli. Exactly E. coli O157:H7, the most dangerous
serotype, which can lead in very low numbers to serious infections in humans, cannot
be detected in water samples by this method. This serotype typically does not
produce Y-glucuronidase and this in turn results in a lack of fluorescence
development in the enriched culture broth. In order to fill this gap, the application of
the simple biochemical indole test and subsequently of Singlepath® E. coli O157, a
newly developed lateral flow test with improved specificity, was tested with spiked
water samples after enrichment with ReadyCult® for 18-24 h. Tap water samples
were spiked at various levels (2-120 CFU/100 ml) with 43 different bacteria belonging
to various E. coli and non-E. coli isolates. After culturing, color and fluorescence
development was visually analyzed. As expected, all 10 E. coli O157:H7 tested led to
color development indicating their belonging to the Coliforms, but were fluorescence
negative, indicating that they do not represent E. coli. However, all of them gave
positive results with the indole test applied indicating their belonging to E. coli. The
direct application of a small volume (150 ul; without boiling) of the culture to the
Singlepath® E. coli O157 specifically detected all samples in which E. coli O157 were
spiked. Only these E. coli O157 strains led to a clear positive result mostly within 5
min. In summary, the presence of highly pathogenic E. coli O157:H7 in water
samples after enrichment in ready-to-use culture media can be easily detected by
using an inexpensive indole test. If positive, Singlepath® E. coli O157 can then be
applied directly without further preparation of the sample.
Includes table.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 230 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 5 |
| Published : | 11/02/2003 |
