Technical Information

Product Overview

Colitag™ is a selective and differential medium for the determination of the presence or absence of total coliforms and E. coli in drinking water. It is a one-step, ready to use medium, to be combined with a water sample. This product is designed to test water samples for total coliform and/or E. coli bacteria within a 16 to 48 hour window and does not require further confirmation or verification steps. Colitag™ detects 1 colony-forming unit (CFU) of E. coli and other total coliform bacteria in 100mL of water.

The Colitag™ method is based on the detection of two enzymes, ß-glucuronidase and ß-galactosidase, which are characteristic of E. coli and the coliform groups, respectively. Colitag™ detects total coliforms using the chromogenic substrate ortho-nitrophenyl-ß-D-galactopyranoside (ONPG). Upon hydrolysis by ß-galactosidase, ONPG produces a distinct yellow color, confirming the presence of coliforms in the sample.

For detection of E. coli, Colitag™ utilizes the fluorogenic enzyme substrate 4-methylumbelliferyl-ß-D-glucuronide (MUG). Upon hydrolysis by ß-glucuronidase, MUG releases 4methylumbelliferone. This reaction by-product fluoresces when exposed to UV light. The ß-glucuronidase enzyme is specific to E. coli and observation of fluorescence differentiates this organism from other members of the coliform group.

Method Summary:

For sample reading between 16 to 22 hours:

1. Aseptically add the Colitag™ to a 100-mL test water sample in a sterile vessel.
2. Secure vessel top and agitate to begin dissolution.
3. If sample is not already at 33-38°C, then place vessel in a 44.5°C water bath for 7 to 10 minutes.
4. Incubate sample at 35 °C ± 0.5 °C for the remainder of the desired incubation time, 16 to 22 hours.
5. Read results according to the sample interpretation method listed below.

For sample reading between 22 to 48 hours:

1. Aseptically add the Colitag™ to a 100-mL test water sample in a sterile vessel.
2. Secure vessel top and agitate to begin dissolution.
3. Incubate the sample at 35 °C ± 0.5 °C for 22 to 48 hours.
4. Read results according to the sample interpretation method listed below.

Sample Interpretation:

1. Visually check each sample against the Colitag™ Comparator (P/A).

a. If sample color is yellow, and of equal or greater color than the yellow Colitag™ Comparator (P/A), then the sample is positive for coliform bacteria.

b. If no yellow coloring is observed in the sample, then the sample should be recorded as negative for coliform bacteria.

2. Examine the solution for fluorescence using a long wavelength (365 nm) UV lamp

a. If bright blue fluorescence is observed, E. coli bacteria are present.

b. If no fluorescence is observed, the sample should be recorded as negative for E. coli.