Mueller Kauffman Tetrathionate Novobiocin HiCynth™ Broth Base

Principle And Interpretation

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 sub cultured 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 (10).

Mueller (8) recommended Tetrathionate Broth as a selective medium for the isolation of Salmonella. Kauffman (6) 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 (7). It is also a recommended selective broth for isolating Salmonella from animal faeces and sewage-polluted water (9). 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 (2). Mueller Kauffman Tetrathionate Novobiocin HiCynth™ Broth Base is prepared by replacing animal and vegetable peptones with chemically defined peptones to avoid BSE/TSE risks associated with animal peptones. HiCynth™ Peptone No.1 serves as sources of carbon, nitrogen, vitamins and minerals. Synthetic detergent No. I and brilliant green are selective agents, which inhibit gram-positive and other gram-negative organisms. Calcium carbonate is the buffer.

Sodium chloride maintains osmotic equilibrium. Sodium thiosulphate is a source of sulfur. The tetrathionate (S406) anions constitute the principle selective agent in these enrichment media.

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.