Chromogenic medium for detection and enumeration of Escherichia coli and coliform bacteria in food and water

DESCRIPTION
ChromaticTM Coli Coliform is a chromogenic selective medium used for the detection and enumeration of
β-glucuronidase-positive E. coli and coliform bacteria in food and water samples.

METHOD PRINCIPLE
Peptone provides amino acids, nitrogen, carbon, vitamins and minerals for organisms growth. Yeast extract is a source of vitamins, particularly of B-group. Sodium chloride maintains the osmotic balance of the medium. Chromogenic and selective mix allows to identify microorganisms on the basis of the color and morphology of the colonies while inhibiting most of Gram-positive organisms. Agar is the solidifying agent.

TYPICAL FORMULA (g/l)

PREPARATION

Dehydrated medium

Suspend 39.7 g of the powder in 1 liter of distilled or deionized water. Mix well. Heat to boil shaking frequently until completely dissolved. DO NOT AUTOCLAVE.

Medium in bottles

Melt the content of the bottle in a water bath at 100°C (loosing the cap partially removed) until completely dissolved. Then screw the cap and check the homogeneity of the dissolved medium, if it is the case turning the bottle upside down. Cool at 45-50°C, mix well avoiding foam formation and aseptically distribute into Petri dishes.

TEST PROCEDURE
Inoculate solid samples by direct streaking on the medium surface. Liquid samples can be inoculated by spread plating, pour plating or membrane filtration method.
Use RODAC plates for surface sampling by firmly pressing the agar medium against the test area.
Incubate aerobically at 35 ± 2°C for 18-24 hours.Incubation conditions may vary depending on the target of the analysis:
• 44 ± 1°C for 24 ± 2 hours if research is focused on fecal coliform bacteria;
• 30 ± 1°C for 24-48 hours to maximize total coliform detection.

INTERPRETING RESULTS
After incubation observe the color and the morphology of the colonies and interpret the results as indicated in
the ID table.

*β-glucuronidase-negative E. coli strains, such as E. coli O157, are colorless on this medium.

APPEARANCE
Dehydrated medium: free-flowing, homogeneous, light-beige.
Prepared medium: slightly opalescent, light amber.

STORAGE
The powder is very hygroscopic, store the powder at 10-30°C, in a dry environment, in its original container tightly closed. Store bottles and prepared plates at 2-8°C away from light. Do not use the product beyond its expiry date on the label or if product shows any evidence of contamination or any sign of deterioration.

SHELF LIFE
Dehydrated medium: 2 years.
Medium in bottles: 1 year.
Ready-to-use plates: 4 months.

QUALITY CONTROL
Plates are inoculated with the microbial strains indicated in the QC table.
Inoculum for productivity: 50-100 CFU.
Inoculum for selectivity: 10⁴-10⁶ CFU.
Incubation conditions: aerobically at 35 ± 2°C for 18-24 hours.

QC Table.

WARNING AND PRECAUTIONS
The product does not contain hazardous substances in concentrations exceeding the limits set by current legislation and therefore is not classified as dangerous. It is nevertheless recommended to consult the safety data sheet for its correct use. The product is intended for professional use only and must be used by properly trained operators.

DISPOSAL OF WASTE
Disposal of waste must be carried out according to national and local regulations in force.

PRESENTATION

BIBLIOGRAPHY

1. Comparison of enumeration of E. coli on CHROMagar E. coli and MPN methods. Study by S. Weissman, Israel, July 1994.
2. Quantitative determination of Escherichia coli in water using CHROMagar E.coli. Jose L.Alonso et al. Journal of Microbiological Methods, 25, 1996, p.309-315.

For inquiry please kindly email to : lisa@prolabios.com