MIMG 100L #10 - For Gram and Gram Differentiates between...

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For: Gram + and Gram - Differentiates between bile-esculin+ and bile esculin - Differential Undefined Ingredients: - beef extract, digest of gelatin, esculin, oxgall (bile), and ferric citrate. 1.esculin is a glycoside made of glucose and esculetin. 2. Beef extract and gelatin bring nutrients and energy. 3.Bile is the selective agent which separates the streptococcus bovis group and enterococci from the rest. 4. Ferric citrate is a source of oxidized iron to indicate a + test . Esculin + iron 2+=black/dark brown, GRAM NEGATIVE: MacConkey Agar Selective For: Selects for gram -, against gram +. Bile salts and crystal violet prevent growth of gram + bacteria Differential: used to isolate enterobacteriaceae based on the ability to ferment lactose. Ex: E.coli Ex: salmonella would grow in it too b/c gram -. Keep color of plate b.c non fermenter. Non-Lactose fermenting bacteria such as Salmonella, Proteus species, Yersinia, Pseudomonas (oxidase +) aeruginosa, and Shigella cannot utilize lactose. This causes the to utilize another pathway that forms ammonia, which raises the pH of the agar, and leads to the formation of white/colorless colonies on the petri plate Ex: Staphylococcus wouldn’t grow on it. NOT THE ONE that looks for vigorous fermenters Lactose fermenter : turn pink/ red (lower pH) Lactose non-fermenter : keeps color of the plate Defined Ingredients: lactose, bile salts, neutral red, crystal violet. -neutral red dye means colorless and pH is above 6.8 Red means pH is less than 6.8 ( lactose fermentation produces acid and turns it red) -without crystal violet encourages growth of enterococcus and some staphylococcus ( lactose fermenters and turn pink) Also includes: pancreatic digest of gelatin, pancreatic digest of casein, and pancreatic digest of animal tissue
Eosin Methylene Blue Agar (Levine) EMB ONE FOR AGGRESSIVE LACTOSE FERMENTERS Selective: Selects for Gram-, against Gram+ Eosin Y and methylene blue inhibit G+, and react with vigorous lactose fermenter (indicator) Lactose fermentation produces acids, which lower the pH. This encourages dye absorption by the colonies, which are now colored purple-black. Lactose non-fermenters increase the pH. This ensures that the dye is not absorbed. The colonies will be colorless Exceptions: Enterococcus and Staphylococcus Vigorous fermenter: E.coli Less aggressive lactose fermenters : enterobacter/Klebsiella Lactose nonfermenters : Proteus, Shigella, Salmonella (breaktown animal tissue) → next Differential: Lactose and/or sucrose fermentation Undefined Ingredients: Eosin and Methylene blue Lactose, sucrose (nutritional components/substrates) Ex: poor growth (P)/ no growth (N)-organism inhibited by eosin or MB: gram positive

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