A 210-min solid phase cytometry test for the enumeration of Escherichia coli in drinking water.
A 210-min-test for the enumeration of Escherichia coli in drinking water is described, based on solid phase cytometry (SPC) and a two-step enzymatic procedure for fluorescence labelling of single cells and small microcolonies. The test involves membrane filtration through a 25-mm black polyester filter, induction of beta-glucuronidase in the retained target cells, fluorescence labelling with fluorescein-di-beta-Dglucuronide as an enzyme substrate and laser scanning of the membrane filter. Scan results can be confirmed on-line by epifluorescence microscopy. Application to 149 naturally contaminated and uncontaminated well, tap, out-of-pump centre (distribution), surface and sewage-spiked water samples indicated > or =90% agreement and equivalence with plate count methods, including Chromocult Coliform agar and m FC agar. In 5.4% of all samples examined, SPC detected between 1 and 11 E. coli per 100 ml, while the two plate methods yielded negative results. Cases of a negative SPC result but a positive E. coli count on both reference media were not observed. This test would primarily be useful for 'emergency' monitoring of drinking water when rapid results are crucial.
Van Poucke
S O
SO
University of Ghent, Laboratory for Pharmaceutical Microbiology, Belgium.
Nelis
H J
HJ
D015169:Colony Count, Microbial / Q000379:methods*; D004926:Escherichia coli / Q000302:isolation & purification*; D005374:Filtration; D005470:Fluorometry; D005618:Fresh Water / Q000382:microbiology; D005966:Glucuronidase / Q000032:analysis; D012680:Sensitivity and Specificity; D012722:Sewage / Q000382:microbiology; D014871:Water Microbiology; D001616:beta-Galactosidase / Q000032:analysis
D012722:Sewage; D001616:beta-Galactosidase; D005966:Glucuronidase