OXOID BISMUTH SULPHITE AGAR (MOD. WILSON & BLAIR) 500 GR - CM0201B

Description
Bismuth Sulphite Agar is a modification of the original Wilson and Blair1 selective medium for the isolation and preliminary identification of Salmonella typhi and other salmonellae from pathological material, sewage, water supplies, food and other products suspected of containing these pathogens. In this medium freshly precipitated bismuth sulphite acts together with brilliant green as a selective agent by suppressing the growth of coliforms, whilst permitting the growth of salmonellae. Sulphur compounds provide a substrate for hydrogen sulphide production, whilst the metallic salts in the medium stain the colony and surrounding medium black or brown in the presence of hydrogen sulphide.
Atypical colonies may appear if the medium is heavily inoculated with organic matter. Such a situation may be prevented by suspending the sample in sterile saline and using the supernatant for inoculation.
The freshly prepared medium has a strong inhibitory action2 and is suitable for heavily contaminated samples. Storing the poured plates at 4°C for 3 days causes the medium to change colour to green, making it less selective with small numbers of salmonellae being recovered3. However, for Salmonella typhi recovery the latter technique is not recommended 4.
Where the number of salmonellae is expected to be small, enrichment methods may be employed. The use of this medium is advocated by several authorities5,6,7.