A COMPARISON BETWEEN CHROMOGENIC SUBSTRATE TECHNOLOGY - QUANTITRAY? - AND THE MEMBRANE FILTRATION METHOD

摘要

Advances in chromogenic substrate testing leading to the Quanti-Tray? (QT) application (Environetics, IDEXX Laboratories Inc., Westbrook, ME) have made QT technology a possible alternative to other standard methods used to enumerate coliforms from water sources. The requirement for quantitative data (currently met using the membrane filtration (MF) method and m-Endo agar LES) is met by QT, and was investigated as an alternative to MF.rnThe feasibility of using QT as an alternative to MF was analyzed in light of the different criteria each method is based upon for the recovery of coliform organisms. When using the MF method, the coliform group is defined as being comprised of facultative anaerobic, gram-negative, non-spore forming, rod-shaped bacteria which develop red colonies with a golden metallic sheen on an Endo type medium containing lactose. Verification of the coliform organisms includes transferring the colonies to lauryl tryptose broth (LTB) with incubation at 35 + 0.5 °C for 48 hours. Gas formed in LTB and confirmed in brilliant green lactose broth within 48 hours verifies the colony as a coliform (1). These organisms are primarily from the Escherichia, Klebsiella, Enterobacter and Citrobacter genera. They are common constituents of the human intestine and frequent causes of disease.rnColiforms, as determined by chromogenic substrate methods, are oxidase negative bacteria, possessing the enzyme (3-D galactosidase, capable of cleaving ortho-nitrophenyl-|3-D-galactopyranoside to produce a yellow color, and include the four genera listed above, as well as other genera in the family Enterobacteriaciae.rn582 water samples from varied sources (see Table I) were analyzed by both QT and MF, and isolates from the positive samples were identified by MicroScan (Baxter Diagnostics Inc., West Sacramento, CA). The isolates were comprised mainly of Escherichia, Klebsiella, Enterobacter, Citrobacter, and Serratia species. The total number of coliform positive samples identified by either method was 65, of which QT identified 100% and MF identified 48%. Twenty-six different species were isolated from samples, of which QT reported 22 and MF reported 14. Total coliforms (reported on positive samples per 100 ml), were broken down into five range levels of contamination. In each of these ranges