EC Broth

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EC Medium  (Escherichia coli Medium)

Description:

EC Medium (Escherichia coli Medium) is a selective enrichment broth designed for the isolation of coliforms, including E. coli, from
water and food samples. It is the recommended medium of the American Public Health Association (APHA) and the AOAC.
EC Medium is made selective for coliforms by the inclusion of Bile Salts No.3 in the dehydrated medium. The selective nature of this
medium ensures that the growth of non-coliform bacteria is minimised. The medium is buffered by the addition of potassium phosphates
and osmotically balanced by sodium chloride. The medium is used at 37°C for coliform organisms and 45.5°C is recommended for the
isolation E. coli.

Formula g/litre
Tryptone 20.0
Lactose 5.0
K2HPO4 4.0
KH2PO4 1.5
Sodium chloride 5.0
Bile Salts No. 3 1.5

Method for reconstitution
Weigh 37.0 grams of powder and disperse in 1 litre of deionised water. Allow the mixture to soak for 10 minutes, swirl to mix. Dispense
into tubes of appropriate volume and, where applicable, add Durham tubes. Sterilise by autoclaving at 121°C for 15 minutes.

Appearance: Clear straw broth.

pH: 6.9 ± 0.2

Minimum Q.C. organisms:
Escherichia coli NCIMB 50034
Enterococcus faecalis NCIMB 50030 (inhibition)
Bacillus subtilis NCIMB 13061 (inhibition)

Storage of Prepared Medium: Capped containers – up to 3 months at 15-20°C in the dark.

Inoculation: Coliforms: Follow the methods and procedures as stated in Standard Methods for the Examination of Water and Wastewater
and Compendium of Methods for the Microbiological Examination of Foods.
Incubation: 45.5°C for 18-24 hours aerobically for E. coli and 37°C for 18-24 hours, aerobically for coliforms.

Interpretation: Turbidity of broth and gas collection in the Durham tube indicates the presumptive growth of organisms from the
coliaerogenes group. All broths should be sub-cultured onto selective media whether turbid or not.

References
American Public health Association, (1980). Standards Methods for the Examination of Water and Wastewater, 15th Edition, American
Public Health Association, Inc., Washington, D.C.
American Public health Association, (1976). Compendium of Methods for the Microbiological Examination of Foods, American Public
Health Association, Inc., Washington, D.C.
Association of Official Analytical chemists. (1995). Bacteriological analytical manual, 8th ed. AOAC International, Gaithersburg, MD.
Perry and Hajna, (1943). American Journal of Public Health, 33:550.
Perry and Hajna, (1944). American Journal of Public Health, 34:735.