Lactobacillus Bulgaricus Agar Base

Principle And Interpretation

Lactobacillus bulgaricus (Lactobacillus delbrueckii subsp. bulgaricus) is one of several bacteria used for the production of Kisselo mlyako (Bulgarian) - "Sour milk" yoghurt (yogurt). The bacterium was first identified in 1905 by the Bulgarian doctor Stamen Grigorov. It is named after Bulgaria, the country where it was first used (it thrives freely on the Balkan Peninsula). The bacterium feeds on milk and produces lactic acid which also helps to preserve the milk. Lactobacillus Bulgaricus Agar was originally formulated by Kulp and White (1) for the recovery of Lactobacilli. Further modification is recommended by APHA (2) for isolation and identification of L. bulgaricus from foods. Streptococcus thermophilus and L. bulgaricus are the essential microbial species and are active in symbiotic relationship in yoghurt. Because of the emphasis on maintaining a balance between cocci and rods, techniques are needed to determine the relative proportions of S. thermophilus and L. bulgaricus when grown together in milk cultures.

Tryptone, yeast extract and HM peptone B in the medium provide nitrogenous compounds, minerals, vitamins and trace ingredients. Polysorbate 80 supplies fatty acids required for the metabolism of Lactobacilli. Dextrose is the fermentable carbohydrate. Tomato juice along with acetate maintains the low pH of the medium and thus inhibits microorganisms other than Lactobacilli. Acetate also restricts the swarming of L. bulgaricus and along with dipotassium phosphate forms the buffering system.