Optochin disc is placed on inoculated lawn blood agar where it can then

Optochin disc is placed on inoculated lawn blood agar

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Optochin disc is placed on inoculated (lawn) blood agar where it can then diffuses into the media Inhibition of growth will result in a clearing around the disc Used to differentiate Streptococcus pneumoniae from other α- hemolytic Streptococcus spp. Antibiotics-Furazolidone Susceptibility Antibiotic which interferes with bacterial cell division by cross-linking to DNA No longer used in clinical settings, unless as a last resort, but useful in differentiating between Staphylococcus (S) and Micrococcus (R) Test is done with a disc as with Optochin and Bacitracin Urease Production Enzyme which breaks down urea Source of nitrogen for amino acid and nucleotide production Detoxification of waste products Assay performed on a slant of agar containing high concentration of urea and pH indicator methyl red Ammonia (high pH) causes media to change color from yellow to pink Applies more to catalase positive Gram + rods Helps differentiate among Corynebacterium spp.
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Nitrate Reduction and Denitrification Some bacteria use nitrates (in place of oxygen) during anaerobic respiration Nitrate is reduced to nitrite – some reduce further to ammonia, N 2 O , or nitrogen (denitrification) Enzyme is nitrate reductase: Assay detects the reduction of nitrate to nitrite Nitrate broth media contains a small amount of agar, nutrients and KNO 3 Agar in media favors anaerobic growth Solution A – sulfanilic acid Solution B – α-naphthylamine Nitrous acid formed when nitrite is present and reacts with the reagents to form a red compound No color does not necessarily mean negative result! Could have been reduced to molecular nitrogen Adding zinc is a definitive negative – zinc reduces nitrate to nitrite Voges-Proskauer Test Fermentation of glucose and pyruvate by some bacteria   The assay tests for the intermediate acetoin, since the product, 2,3-butanediol is not very reactive α-naphthol catalyzes the conversion of acetoin to diacetyl only in the presence of potassium hydroxide Methyl Red Test Sometimes glucose is fermented using the mixed acid fermentation pathway producing very strong acids
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