WL Differential Medium is used for isolating bacteria encountered in brewing and industrial fermentation processes. Summary and Explanation
WL (Wallerstein Laboratory) nutrient media were developed by Green and Gray1,2 in their study of various fermentation processes. An exhaustive study examining the methods of fermentation control procedures in worts, beers, liquid yeasts and similar fermentation products led to the development of these media. At a pH of 5.5, counts of viable bakers’ yeast may be made on the WL Nutrient Medium. By adjusting the pH to 6.5, the medium is suitable for obtaining counts of bakers’ and distiller’s yeast. The medium can support the growth of bacteria, but unless the number of yeast cells is small the bacteria may not be detected. Due to this limitation, Green and Gray developed WL Differential Medium that inhibits the growth of yeasts without inhibiting the growth of bacteria present in beers. The WL Differential agar plate is incubated anaerobically for growth of lactic acid bacteria and Pediococcus. Principles of the Procedure
Yeast extract is a source of trace elements, vitamins and amino acids. Peptone provides nitrogen, amino acids and carbon. Dextrose is the source of carbohydrate. Monopotassium phosphate buffers the media. Potassium chloride, calcium chloride and ferric chloride are essential ions and help to maintain osmotic balance. Magnesium sulfate and manganese sulfate are sources of divalent cations. Bromcresol green is a pH indicator. Agar is the solidifying agent in WL Nutrient Medium and WL Differential Medium. Cycloheximide inhibits yeasts and molds in WL Differential Medium. User Quality Control
Difco™ WL Nutrient Medium or WL Differential Medium
Dehydrated Appearance: Light beige with a greenish tint, freeflowing, homogeneous. Solution: 8.0% solution, soluble in purified water upon boiling. Solution is blue to greenish blue, very slightly...