Yeast Glucose Beef Agar (Revised as Yeast Glucose HM Peptone B Agar)

Principle And Interpretation

The Lactic Acid Bacteria (LAB) comprise a clad of gram positve low-GC, acid tolerant, non-sporulating, non-respiring rod or cocci that are associated by their common metabolic and physiological characteristics. These bacteria produce lactic acid as the major metabolic endproduct of carbohydrate fermentation. The industrial importance of the LAB is evidenced by their generally regarded safe (GRAS) status, due to their ubiquitous appearance in food and their contribution to the healthy microflora of human mucosal surfaces. The genera that comprise the LAB are at its core Lactobacillus, Leuconostoc, Pediococcus, Lactococcus, and Streptococcus as well as the more peripheral Aerococcus, Teragenococcus, Vagococcus, and Weisella (1, 2).

Lactococci (formerly Lancefield group N streptococci) are used extensively as starter innocula in dairy fermentations, with humans estimated to consume 10¹⁸ lactococci annually. Partly due to their industrial relevance, both Lactococcus lactis subspecies (lactis and cremoris) are widely used as generic LAB models for research. Yeast Glucose Beef Agar is used for the cultivation of lactic Streptococci (3).

Dextrose provides an energy source for the growth of microorganisms. Yeast extract, peptic digest of animal tissue and beef extract provide the necessary growth factors and nutrients. Sodium chloride helps to maintain osmotic balance of the cells.