Description
The milk secreted in an uninfected cow’s udder is sterile. Contamination of this milk can occur during milking, cooling and storage. Milk is an excellent medium for bacteria, yeast and moulds. Their rapid growth can cause marked deterioration, spoiling the milk for liquid consumption or manufacture into dairy products. Human infection can occur by consumption of such contaminated milk or milk products. Milk Agar is recommended for performing plate count tests on milk, rinse waters and dairy products. It is formulated as per the official medium described by Department of Health Memo. It is also recommended by EUROGLACE (EEC Ice Cream Industries) for the examination of ice cream. For milk, dilutions of 1/10, 1/100 and 1/1000 are prepared with 1/4 strength Ringer solution. 1 ml of each dilution is pipetted aseptically into sterile Petri plates to which 10 ml of sterile and cooled Milk Agar is added and mixed well. Plates should be poured within 15 minutes of dilution preparation. After solidification of medium the plates are allowed to stand for 1 hour before transferring to the incubator. Incubate at 35?C for 2 or 3 days at 30?C. Higher counts may be obtained after an incubation at 22?C and 30?C temperature rather than at 35?C. Count the colonies within 4 hours after the incubation and read it as per ml of sample.
