EC BROTH

 

A liquid medium used for the detection of faecal coliform organisms in waters and foodstuff.

 

Code: CB1/3252

 

Typical formula g/l

 

Tryptone	20.0
Lactose	5.0
Dipotassium phosphate	4.0
Monopotassium phosphate	1.5
Sodium chloride	5.0
Bile salts No. 3	1.5

  

 

Final pH 6.9 +/- 0.2

 

Directions

Suspend 37g in 1000ml of cold distilled water, heat to dissolve, distribute into fermentation tubes and sterilise at 121^_°C for 15 minutes. Inoculate not more than 1ml of sample in 10ml of medium, or use multiple strength medium.

 

Description

EC Broth is prepared according to the formulation proposed by Haj­na and Perry and reported by APHA, ICMSF and ISO 7251. EC Broth is lactose buffered broth, with bile salts to obtain the inhibition of Gram-positive cocci and spo­re-forming organisms, which are often responsible for false positi­ve results in Lactose Broth or Lauryl Sulphate Broth. The me­dium is recommended by APHA for the detection of faecal coliform organisms in waters and foodstuff, together with Faecal Coliform Broth, which can be mainly ap­plied to treated waters and sea water and by ISO 7251, for the enumeration of E.coli with MPN technique.

 

In use technique

ISO method for E.coli: Prepare the test sample and the decimal dilution in accordance with the specific Laboratory method using Maximum Recovery Diluent or another suitable diluent.

Take three tubes of double-strength Lauryl Peptone Broth and three tubes of single-strength Lauryl Peptone Broth and by means of a sterile pipette transfer to each tube 10ml or 1ml respectively of the test sample, if liquid or 10ml or 1ml of the initial suspension in the case of other products. Repeat the inoculation of the single strength and the double strength liquid medium for each of the further decimal dilutions, using a fresh pipette for each dilution.

Incubate the tubes at 35- 37°C for 24 +/- 2 hours. From each of the incubated tubes showing gas production inoculate with a loop a tube of EC Broth and incubate at 45°C for 24 +/- 2 hours. From each of the EC Broth tubes showing gas production inoculate with a loop a tube of Peptone-Tryptone Water and incubate at 45°C for 48 hours. Carry on the indole test by adding 0.5 ml of Kovacs’ Reagent Express the results as the Most Probable Number of E.coli on the ba­sis of gas production in the EC Broth and the positive result to indole test, in Peptone Water. APHA method for faecal coliforms: Transfer by means of 3mm loop, from all the tubes of Lauryl Peptone Broth showing gas formation within 24 hours and from all the tubes showing growth within 48 hours, to EC Broth tubes. Within 30 minutes from the inoculum, place the tubes in a water-bath and incubate at 44^°C for 24 hours.

Consider the tubes showing gas production as positive. Calculate the density of the faecal coliform organisms by using MPN tables.

 

User quality assurance  (44°C - 24 h)  

 

Productivity control

E.coli  ATCC 25922: growth, gas production

 

Selectivity control

P.aeruginosa ATCC 27853: inhibited

 

Storage

Dehydrated medium: 15-30°C

User prepared tubes: 1 month at 2-8°C

 

References  

APHA (1985) Standard Methods for the Examination of Water and Wastewater, 16th Ed., pp. 878-882.

APHA (1985) Compendium of Methods for the Microbiological Examination of Foods, 2nd Ed.

ISO 7251 Microbiology - General Guidance for enumeration of presumptive E. coli - Most Probable Number Technique. 2nd Ed. 1993 - 12 - 15

Perry and Hajna (1943) Am. J. Pub. Hlth., 33, 550.