E.Coli Chromogenic Medium

E.Coli Chromogenic Medium is used for fast, accurate detection of E. coli in food, water, milk, ice cream and meat culture for 24 hours, the colonies of E. coli are Blue-green, coliforms are colorless, other bacteria are yellow or colorless, gram-positive bacteria are inhibited.

Ingredients(g/L):

*Adjusted and/or supplemented as required to meet performance criteria.

Directions:

Suspend 50.1g of the medium in 1L of distilled water, boil in 1 minute, dispensing into flasks, at 121 ℃ autoclaving for 15 minutes, add 1mL prepared sample into a sterile in 9cm petri dish, transfer 15mL chromogenic medium cooling down to 45-50 ℃, mix, inverted culture at 36 ± 1 ℃ for 18-24h after solidification.

Or when cooling down to 45-50 ℃, pour into a sterile petri dish, after complete solidification, inverted culture at 37 ℃ in incubator for 1-2 hours, add 1mL uniform liquid sample with a suitable concentration, streak onto the medium , culture at 36 ± 1 ℃ for 18-24h.

Procedures:

1. Prepared sample solution according to national standards, SN standard, FDA standards or other methods.

2. Transfer 1mL sample onto chromogenic medium cooling down to 45-50 ℃, mix thoroughly or coating on plate;

3. Culture at 36 ± 1 ℃ for 18-24h, select the plate which have 30 to 200 typical colonies of E. coli, total count of the colonies on the plate, typically E. coli colonies blue-green, others yellow or colorless colonies.

4. For undermined colonies, streak them on nutrient agar plates, culture at 36 ± 1 ℃ for 12-16h, select single colony to do a full set of E. coli biochemical tests.

Quality Control:

1. Appearance:

The dehydrate powder medium is homogeneous, having good flowability, milky white, prepared medium is colorless solid.

2. Microbial sensitivity test:

Incubated at 36 ± 1 ℃ 18-24h:

Methods limitations:

The medium identification of E. coli, may occur false-positive in a few cases, but no false-negative, sometimes it needs to do other complementary tests

Typical features:

E. coli typical colonies are blue-green, coliforms colonies are colorless, other bacteria are colorless or yellow colonies.

Storage:

The prepared plates must be used immediately, avoid direct exposure to light. The powder medium should be placed in a dark, dry place, storage temperature 2-8 ℃, avoid direct exposure to light.

Failure:

Dry powder media which are over the shelf life, caking and color variation cannot be used.

Note:

This medium is only for laboratory use.

Reference:

1. FRAMPTON, E.W., RESTAINO, L. a. BLASZKO, L.: Evaluation of ß-glucuronidase substrate in a 24 hour direct plating method for Escherichia coli.  J. Food Protection, 51; 402-404 (1988).

2. KILIAN, M. a. BüLOW, P.: Rapid diagnosis of Enterobacteriaceae. I. Detection of bacterial glycosidases.  Acta Pathol. Microbiol. Scand. Sect. B 84; 245-251 (1976).