The composition of medium is as per British Pharmacopoeia and is cited as Agar medium L (1). Brilliant Green, Phenol Red, Lactose Monohydrate, Sucrose Agar is used as a primary plating medium for isolation of Salmonella species was first described by Kristensen et al as medium for differentiation of paratyphoid B from other Gram negative enteric bacteria (2). It was further modified by Kauffmann for isolation of Salmonella from stool samples (3). Brilliant green agar is also recommended by APHA (4,5) FDA (6). This medium is employed in testing clinical specimens. Heavy inocula and heavily contaminated samples can be analyzed due to the outstanding selectivity of this medium. Brilliant Green Agar is used in themicrobial limits test and with novobiocin for testing food samples.
Peptones (meat and casein) and yeast extract supplies essential amino acids and long chains of peptides for enhanced growth. Sodium chloride maintains the osmotic equilibrium. Lactose monohydrate and sucrose are the fermentable carbohydrate sources. Phenol red serves as an acid base indicator giving yellow colour to lactose and or sucrose fermenting bacteria. This medium also contains brilliant green, which inhibits growth of majority of Gram-negative and Gram-positive bacteria. Salmonella Typhi, Shigella species, Escherichia coli, Proteus species, Pseudomonas species, and 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 are plated on Brilliant Green Agar along with Bismuth Sulphite Agar, SS Agar, MacConkey Agar. Nonlactose 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 a tightly closed container and the prepared medium between 2 - 8°C Use before expiry date on the label.
References:
1. British Pharmacopoeia, 2009, The Stationery office British Pharmacopoeia.
2.Kristensen M., Lester V, and Jurgens A., 1925, Brit.J.Exp.Pathol.,6:291.
3. Kauffman F., 1935, Seit F. Hyg. 177:26.
4. Downes F P and Ito K(Eds.), 2001, Compendium of Methods For The Microbiological Examination of Foods, 4th ed., APHA, Washington, D.C.
5. Wehr H M and Frank J H., 2004, Standard Methods for the Examination of Dairy Products, 17th ed., APHA Inc., Washington, D.C.
6. FDA Bacteriological Analytical Manual, 2005, 18th ed., AOAC, Washington, DC.