Salmonella species cause many types of infections, from mild self-limiting gastroenteritis to life threatening typhoid fever. The most common form of Salmonella disease is self-limiting gastroenteritis with fever lasting less than 2 days and diarrhoea lasting less than 7 days (9).
Brilliant Green Agar Base, Modified, as a primary plating medium for isolation of Salmonella species was first described by Kristensen et. al. (1) and further modified by Kauffmann (2). Brilliant Green Agar is also recommended by APHA (3,4) FDA (5) and described in EP, BP and IP (6,7,8).
This medium contains brilliant green, which inhibits growth of majority of Gram-negative and Gram-positive bacteria. Salmonella Typhi, Shigella species Escherichia coli, Pseudomonas species, Staphylococcus aureus are mostly inhibited. Clinical specimens can be directly plated on this medium. However, being highly selective, it is recommended that this medium should be used along with a less inhibitory medium to increase the chances of recovery. Often cultures enriched in Selenite or Tetrathionate Broth is plated on Brilliant Green Agar along with Bismuth Sulphite Agar, SS Agar, MacConkey Agar.
The medium contains proteose peptone and yeast extract as sources of carbon, nitrogen, vitamins, amino acids and essential nutrients. The two sugars namely lactose and sucrose serve as energy sources. Fermentation of lactose and/or sucrose in the medium results in the formation of acidic pH which is detected by phenol red indicator. Sodium chloride maintains the osmotic equilibrium. Brilliant green helps to inhibit the contaminating microflora. The medium can further supplemented with sulphacetamide (1g/l) and sodium mandelate (0.25g/l) to inhibit contaminating microorganisms when the sample is suspected to contain large number of competing organisms along with Salmonella species (10).
Non-lactose fermenting bacteria develop white to pinkish red colonies within 18 - 24 hours of incubation. Salmonella Typhi and Shigella species may not grow on this medium. Moreover Proteus, Pseudomonas and Citrobacter species may mimic enteric pathogens by producing small red colonies.
Storage and Shelf-life:
Store below 30°C in tightly closed container and the prepared medium between 2 - 8°C.Use before expiry date on the label.
References:
1. Kristensen M., Lester V, and Jurgens A., 1925, Brit.J.Exp.Pathol.,6:291.
2. Kauffman F., 1935, Seit F. Hyg. 177:26.
3. Downes F. P. and Ito K. (Ed), 2001, Compendium of Methods for Microbiological Examination of Foods, 4th Ed. APHA, Washington D.C.
4. Standard Methods for the Microbiological Examination of Dairy Products, 1995, 19th Ed, APHA, Washington, D.C.
5. Bacteriological Analytical Manual, 5th Ed, 1978, AOAC, Washington D.C.
6. The European Pharmacopoeia, 2008, Council or Europe, Strasbourg.
7. The British Pharmacopoeia, 2007 vol. II, London.
8. Indian Pharmacopoeia, 2007, Ministry of Health and Family Welfare, Govt., of India.