I ?Differential medium - give definition and explain how it works by using specific medium as an example (what components do what)
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Step 1: A differential medium is a type of growth medium that is used to differentiate between different types of bacteria. Show more…
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Explain the purpose of using differential media in microbiology.
Adi S.
Introduction: Selective and differential media are used frequently in Microbiology Pathology Labs to identify a known group of bacteria from a complex mix of other bacteria. The medium is designed to select against as many of the background organisms as possible by using a medium in which they will not grow but the organisms under investigation can grow hence the ‐Selective‐ part of the name. Any assayable characteristic that can be used to differentiate a specific group of interest from the selected group of organisms can be incorporated into the medium to distinguish that group. The aim of this Lab is to understand use of selective/differential media and the interpretation of their results. Mannitol salt agar Contains: 7.5% NaCl included with the sugar mannitol, a source of protein, pH indicator (phenol red) Selection: The high salt concentration selects against salt intolerant organisms and for halophiles (salt tolerant organisms). Describe your results Eosin methylene agar Contains: EMB contains: peptone, lactose, dipotassium phosphate, eosin Y (dye), methylene blue (dye). Selection: Eosin and methylene blue together inhibit the growth of gram positive bacteria and encourage the growth of gram negative bacteria including coliforms Differentiation: Lactose is a fermentable carbohydrate that differentiates between organisms that ferment lactose (e.g., E. coli) and those that do not. In our plate Escherichia coli went through fermentation because it produced a metallic green sheen. The other samples produced pink colonies, which means they were slow or weak fermenters MacConkey agar: Contains: Protein source, lactose, bile salts, and the dyes crystal violet and neutral red. Selection: Bile salts and crystal violet make the medium selective by inhibiting the growth of gram-positive bacteria but allowing many gram negatives (including coliforms) to grow. Differentiation: Lactose is a fermentable carbohydrate that differentiates between organisms that ferment lactose (e.g., E. coli) and those like Pseudomonas and Klebsiellosis that do not. In our plates we did not yield any results because the plates were covered with a thin layer of MacConkey agar. Describe your results Triple sugar iron agar Contains: Carbon sources Three sugars, glucose (0.1%), sucrose (1%), and lactose (1%) and peptone as a source of protein.
Josee P.
Clinical samples are routinely inoculated onto differential and selective media. Determine whether the media listed below are selective or differential: a. Nutrient agar that contains vancomycin is selective or differential for ______________. b. EMB agar that contains sorbitol is used to select or differentiate E. coli O157. Explain:______________ c. Nutrient agar with tellurite is selective/differential for ______________.
Sri K.
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