Coliforms Chromogenic Agar Plates

Coliforms Chromogenic Agar Plates are suitable for the detection and enumeration of total coliform and E. coli in water samples by the membrane-filtration technique.

Coliforms Chromogenic Agar Plates are ready-to-use plates to detect and enumerate total coliform and E. coli in water samples. The combined action of peptone, pyruvate, and sorbitol allows rapid colony growth in this phosphate-buffered medium, which also permits simple recovery of sublethal thermally injured coliforms. Sodium chloride provides the correct osmotic environment necessary for growth. The selectivity is attained partially by the Tergitol^™ 7, which inhibits the growth of Gram-positive and some Gram-negative bacteria without affecting the coliform bacteria. The culture medium is formulated without antibiotics for water samples with low bacterial background flora. The colonial differentiation is due to the chromogenic mixture, composed of two enzyme substrates: 6-chloro-3-indoxyl-ß-D-galacto-pyranoside (Salmon-GAL) and 5-bromo-4-chloro-3-indoxyl-ß-D-glucuronide (X-Glucuronide). ß-D-galactosidase in coliforms cleaves the first substrate, giving a salmon-red color to the coliform colonies. The ß-D-glucuronidase enzyme, characteristic of E. coli, cleaves the second chromogenic substrate, giving blue color to their colonies.E. coli has two enzymes that cleave both chromogenic substances giving dark blue to violet colonies. Total coliforms are the sum of E. coli colonies and the salmon-red colonies. The IPTG enhances the metabolism of chromogens. Other Gram-negative bacteria produce colorless colonies. However, some Gram-negative bacteria possessing glucuronidase activity (not galactosidase) produce light blue to turquoise colonies.E. coli colonies are confirmed by including a small amount of tryptophane in the medium and coating the blue-violet colonies with a drop of Kovacs Reagent. The color change of the reagent to cherry-red in a few seconds confirms the production of indole and thereby, the presence of E. coli. When the Chromogenic Agar for Coliform is used with the membrane filter method, the color and growth of the colonies can be modified by the characteristics of the membrane filter. It is advisable to perform validation of the membrane filter type used.

1 box containing: 6 plastic bags with 5 plates of 55 mm/bag

If the membrane filtration method is used, it must be considered that the nature and characteristics of the filter membrane used also influences the size and color of the colonies grown on this culture medium.

TERGITOL is a trademark of The Dow Chemical Company ("Dow") or an affiliated company of Dow