Acetic, succinic, lactic, and formic acids – also very stable end productsMethyl red is a pH indicator which detects only very strong acids (pH 4.4 and below)MR/VP TestBoth the Voges Proskaeur and Methyl Red tests are conducted using MR/VP broth, which containglucose.Fermentation is detected with various reagentsVP - α-naphthol and 40% KOH – pink/rose color indicates the presence of acetoinMR – methyl red pH indicator – is normally red and will lose color in pH higher than 4.4 – positive will remain red; strong acids present
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Bile EsculinUsed to differentiate gamma-hemolytic Streptococcusfrom Enterococcus. Bile salts are the selective ingredient, while esculin is the differential ingredientEnterococcus(Group D streptococci) hydrolyze esculinBreakdown products react with ferric citrate in the medium to produce insoluble iron saltsAs a result, the media changes color to black.Carbohydrate Fermentation(a.k.a. Acid & Gas Production)Different m/o utilize carbohydrates differentlyDepends on enzymes availableSome use respiration (aerobic or anaerobic)Some use fermentationCarbohydrate Fermentation metabolic process in which organic molecules (carbs) act as e-donors and one or more of its organic products act as the final e-acceptor = ENERGYDifferent fermentation pathways are named for their end productsGas is sometimes given off (usually CO2)Carbohydrate FermentationThe test2 tubes (phenol red broth)Specific carb (glucose, mannitol)pH indicator phenol redpH < 6.8 = yellow = acid production =fermentationpH > 7.4 = pinkPeptone (growth enhancer containing a.a.)Durham tube Bubble = GasNo Bubble = No GasMeasures ability of bacteria to ferment a specificcarbohydrate and produce gas Yellow = + fermentationBubble = + gas productionLack of fermentation does NOT indicate absence ofgrowthSome m/o use other nutrients (peptides) as energysourcespeptides a.a. keto – a.a. ammonia alkaline pHAlkaline pH = pink
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