Microbiological safety in water and food industries is paramount, particularly in detecting coliform bacteria and Escherichia coli. EC Broth, a selective liquid medium, is extensively used for this purpose. This article elucidates the properties, preparation, application, and importance of EC Broth in accordance with ISO 7251 standards.
EC Broth is a selective liquid medium for detecting and enumerating coliform bacteria and E. coli in water, wastewater, food, and other sanitary materials. It conforms to ISO 7251 standards. The medium comprises enzymatic digest of casein, lactose, bile salts, dipotassium phosphate, monopotassium phosphate, and sodium chloride, with a final pH of 6.9 ± 0.2 at 25°C. The medium’s formula is specifically designed to promote growth of coliforms while inhibiting Gram-positive bacteria, particularly enterococci, thereby ensuring accurate and reliable microbiological testing. It is available in both dehydrated form and prepared tubes for versatile laboratory applications.
Composition and Principle
The composition of EC Broth includes 20.0 g/l enzymatic digest of casein, 5.0 g/l lactose, 1.5 g/l bile salts, 4.0 g/l dipotassium phosphate, 1.5 g/l monopotassium phosphate, and 5.0 g/l sodium chloride. The enzymatic digest of casein provides essential nutrients, while lactose acts as the fermentable carbohydrate. Bile salts selectively inhibit Gram-positive bacteria, and phosphates serve as buffering agents, maintaining the medium’s pH. Sodium chloride ensures osmotic balance.
Preparation and Sterilization
Preparation involves suspending 37.0 g of the dehydrated medium in 1 liter of distilled or deionized water, boiling until dissolved, and distributing into 10 ml tubes with Durham tubes for gas collection. The medium is sterilized in an autoclave at 121°C for 15 minutes.
Testing Procedure and Interpretation
For detecting E. coli, ISO 7251 recommends initial inoculation of the sample into Lauryl Sulfate Tryptose Broth, followed by incubation and examination for turbidity and gas production. Positive tubes are then subcultured in EC Broth and incubated at 44°C. Gas production in EC Broth is considered a preliminary positive result for coliforms or E. coli, requiring confirmation with further biochemical tests.
Storage and Shelf Life
EC Broth powder should be stored at 10-30°C in a dry environment, with a shelf life of 4 years. Prepared tubes are stored at 10-25°C away from light, with a shelf life of 2 years.
Quality control involves inoculating tubes with specific microbial strains like E. coli and Enterococcus faecalis to ensure the medium’s productivity and selectivity. Good growth of E. coli and inhibited growth of Enterococcus faecalis validate the medium’s performance.
EC Broth is a crucial medium for the detection and enumeration of coliform bacteria and E. coli in various samples. Its selective formulation, adherence to ISO standards, and ease of use make it an indispensable tool in microbiological laboratories, contributing significantly to the safety and quality control in the water and food industries.