SOYBEAN CASEIN DIGEST MEDIUM BASE W/O POLYMYXIN

Bacillus cereus is a large, 1 ? 3-4 ?m, Gram-positive, rod-shaped, endospore forming, and facultative aerobic bacterium. They are mesophilic and can grow in a wide range of environments and are commonly found in nature, vegetables and in several processed foods. Under favorable circumstances the microorganism grows to sufficient numbers and cause gastrointestinal illness. Outbreaks of food borne illness have been associated with boiled and cooked rice, cooked meat and vegetables. The infection mediates diarrhoeal illness that is attributed by a heat and acid labile enterotoxin. Soyabean Casein Digest Medium Base with polymyxin B is recommended for the selective isolation and MPN method of Bacillus cereus in accordance with FDA BAM, 1998. B. cereus in general is resistant to polymyxin B and the addition of it into the medium helps in the selective isolation of the organism. Without supplement, SCDM is a highly nutritious medium used for cultivation of a wide variety of organisms. FDA BAM suggests two methods to check the presence of B. cereus that are Serial dilution method and MPN Method. According to the serial dilution protocol, appropriate dilutions of the suspected samples are made in Butterfield?s Phosphate Buffered Dilution Water and spread plate was done with 0.1 ml of respective dilutions in MYP Agar Base. According to the MPN method, 1 ml each of 10-1, 10-2 and 10-3 are inoculated into Soyabean Casein Digest Medium Base with polymyxin incubate for 48 ? 2 h at 30 ? 2?C. Observation of turbid growth after the incubation time is indicative of the presence of B. cereus. Positive cultures are further inoculated into MYP Agar Base and incubated 18-24 h at 30?C. B. cereus appears as pink coloured colonies surrounded by a precipitate zone of lecithinase activity. Biochemical tests are performed to confirm the species.

for selective isolation and MPN method of B.cereus in accordance with FDA BAM