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  • Dichloran Rose Bengal Chloramphenicol (DRBC) agar is based on the formulation described by King et al. and is used for the selective isolation and enumeration of yeasts and moulds from food samples. The peptone provides the required carbon, nitrogen and vitamins. Glucose is a fermentable carbohydrate. Potassium di-hydrogen phosphate is a buffering agent and magnesium sulfate is a source of divalent ions and sulfate. In order to curtail the size of the colony diameters of spreading fungi, the antifungal agent dichloran is added to the base and the pH is reduced to 5.6. Rose Bengal suppresses growth of bacteria and restricts the size and height of colonies of more rapidly growing molds. The inclusion of chloramphenicol ensures the suppression of bacteria present in environmental and food samples. Rose Bengal is absorbed by yeast and mold colonies and this further aids in their enumeration. Occasionally reduced recovery of yeasts may be encountered due to the increased activity of Rose Bengal at pH 5.6.
  • Mannitol Salt Agar is selective medium for the isolation of pathogenic staphylococci. The medium conforms to the requirements of the Harmonised USP/EP/JP. Chapman showed that adding a high level of sodium chloride to Phenol Red Mannitol Agar allowed for the recovery of pathogenic staphylococci. Pathogenic staphylococci produced yellow colonies whereas non-pathogenic staphylococci produced small red colonies. Pancreatic digest of casein, peptic digest of animal tissue and beef extract provide the required nitrogen, carbon and vitamins. The high level of sodium chloride inhibits most organisms other than staphylococci. Mannitol is a carbohydrate that is fermented by coagulase positive staphylococci. Phenol red is the pH indicator.