Product Code TM 1400
The examination of various types of food products for Salmonella requires methods different from those used in clinical laboratories. The need for such method is due to the generally low numbers of Salmonellae in foods and the frequently poor physiological state of these pathogens following exposure to stressful conditions during food processing or storage. Injured Salmonella are resuscitated in non-selective broth medium, which facilitates detection of sublethally injured Salmonella. The ideal pre-enrichment broth should provide for the repair of cell damage, dilute toxic or inhibitory substances and nutritive enough to favour growth of Salmonella. In the analysis of food for Salmonella, pre-enrichment cultures are usually incubated at 35-37?C for 18-24 hours and then a portion is subcultured to one or more selective enrichment broths. Normally 1 ml of pre-enrichment culture is inoculated to 9 ml of selective enrichment broth. Selective enrichment media contains selective ingredients that allow the proliferation of Salmonella and inhibit the growth of competing non-salmonella microorganisms. Lactose Broth is recommended by BAM for pre-enrichment of Salmonella from food. Selective enrichment is done in Tetrathionate Broth and Rappaport Vassiliadis Medium. For the detection of foodborne Salmonella, various modifications of Tetrathionate Broth have generally found wider applications.
Mueller recommended Tetrathionate Broth as a selective medium for the isolation of Salmonella. Kauffman modified the formula to include ox bile and brilliant green as selective agents to suppress bacteria such as Proteus species. The British Standard Specification specifies Brilliant Green Tetrathionate Broth for isolating Salmonella from meat and meat products and from poultry and poultry products. It is also a recommended selective broth for isolating Salmonella from animal feces and sewage-polluted water. Selectivity is conferred by tetrathionate (from the reaction of thiosulphate and iodine). Using more than one selective broth increases the isolation of Salmonella from samples with multiple serotypes. Mueller Kauffman Tetrathionate Broth Base conforms to ISO specifications.
If desired, 4 mg of novobiocin per litre of broth can be added to suppress Proteus species. Add approximately 10 grams of sample to 100 ml of broth. Shake well and place the flask in a 45?C water bath for 15 minutes. Remove the flasks and place in an incubator or water bath at 43?C. Several studies have shown increased recovery of Salmonella following incubation of selective enrichment at 43?C. After an incubation for 18-24 hours and 48 hours, subculture on Brilliant Green Agar, Modified. This medium is not suitable for the growth of Salmonella Typhi, Salmonella Sendai, and Salmonella Pullorum etc. The complete medium is unstable and should be used immediately. It may be stored at 2-8?C in the dark for no more than 7 days. Organisms other than Salmonellae, such as Morganella morganii and some Enterobacteriaceae may grow in the medium. Therefore, confirmatory tests should be carried out on all presumptive Salmonella colonies that are recovered.
for enrichment and isolation of Salmonellae by surpassing Proteus species