Would removing bile salts andlor crystal violet from MacConkey agar alter the me

Question

Would removing bile salts andlor crystal violet from MacConkey agar alter the medinem's sensitivity or specificity? Explain your answer. (See pages 8 and 9, "A Word About Experimental Design," for assistance with these terms.) 8 Suppose a mistake is made in preparing a batch of 6.9-7.3. Would that affect the medim's sensitivity or specificity? Explain your answer. (See pages 8 and 9, "A Word About Experimental Design," for assistance with these terms.) MacConkey agar and the starting pH is 7.6 instead of 9 Compare the recipes of nutrient agar and MacConkey agar.If an organism can grow on both medis, on which would you expect it to grow better? Explain your answer

Explanation / Answer

Peptic digest of animal tissue, Sodium chloride, Beef extract, Yeast extract, Agar,Final pH ( at 25°C) 7.4±0.2

MacConkey agar is used for the isolation of gram-negative enteric bacteria and the differentiation of lactose fermenting from lactose non-fermenting gram-negative bacteria. Pancreatic digest of gelatin and peptones (meat and casein) provide the essential nutrients, vitamins and nitrogenous factors required for growth of microorganisms. Lactose monohydrate is the fermentable source of carbohydrate. The selective action of this medium is attributed to crystal violet and bile salts,which are inhibitory to most species of gram-positive bacteria. Sodium chloride maintains the osmotic balance in the medium. Neutral red is a pH indicator that turns red at a pH below 6.8 and is colorless at any pH greater than 6.8. Agar is the solidifying agent.

Since the nutrient agar is a basic media, wide microorganisms will grow better on this media. Nutrient Agar is ideal for the purpose where a more prolonged survival of cultures at ambient temperature is often required without risk of overgrowth that can occur with more nutritious substrate.

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