Selenite Cystine Broth is used for the selective enrichment of Salmonella spp, and is a modified enriched medium by the addition of the amino acid cystine. This amino acid establishes a redox potential that seems to be very good for the enrichment and recovery of Salmonella and some strains of Shigella, present in limited numbers in feces, diverse foods and other products of sanitary concern. Selenite Cystine Broth is used particularly to limit the loss of sensitivity that affects other enrichment media especially in food products with a high content of organic material, for example, foods containing egg or egg powder. Selenite Cystine Broth is recommended for the detection of Salmonella in the non-acute stages of illness when the organisms occur in low numbers in the feces ,and for epidemiological studies to encourage the detection of low numbers of organisms from asymptomatic or convalescent patients. Selenite Cystine Broth inhibits the early multiplication of bacteria such as Coliforms, but allows the Salmonellae to grow with ease. Peptone mixture is a source of nitrogen, vitamins and amino acids essential for growth. Lactose is the carbohydrate energy source; Sodium selenite inhibits Gram-positive bacteria and most enteric Gram-negative bacteria, except Salmonella. L-Cystine lowers the toxicity of Sodium selenite and adds an additional organic sulphur. If the broth is to be used immediately, sterilization is unnecessary. Broth which has been tubed and steamed may be kept for months under refrigeration. After a long storage period of the dehydrated medium, the colour of the prepared broth might change to reddish/red. The microbiological performance, however, is not affected.
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