![]() 1N HCl is bactericidal for Staphylococci.Serratia and Moraxella species also produce deoxyribonuclease.Some MRSA strains do not give positive DNase test result and some strains of the coagulase-negative staphylococci such as Staphylococcus capitis may give weak reactions.Neisseria gonorrhoeae & Neisseria meningitidis) of human origin. catarrhalis from all other gram-negative diplococci (e.g. The DNase test is particularly useful when plasma is not available to perform a coagulase test or when the results of a coagulase test are difficult to interpret. It is used to differentiate S.aureus (DNase +ve) from other Staphylococci that do not produce such enzyme.Neisseria gonorrhoeae Uses of DNase Test:.Negative: If there is no degradation of DNA, the medium remains green.Positive: When DNA is hydrolyzed, methyl green is released turning the medium colorless around the test organism.When organisms produce DNase, an acidic end product is formed and the pH indicator changes from red (alkaline) to yellow (acid). catarrhalis (+ve) and N.gonorrhoeae (-ve). Decant excess hydrochloric acid and then examine the plate within 5 minutes against a dark background. Leave the plate to stand for a few minutes to allow the reagent to absorb into the plate.Flood the plate with 1N Hydrochloric Acid.When using DNase agar without the indicator,.Use a heavy inoculum and draw a line 3-4 cm long from the rim to the center of the DNase test agar plate.Incubate the plate at 37☌ for 18-24hr.Touch a colony of the organism under test with a loop and inoculate it onto a small area of the DNase test agar plate, in the middle of one of the marked sections to form a thick plaque of growth 5-10 mm in diameter after incubation.Inoculate the test agar medium: There are two types of inoculation that can be done.Each plate may be divided into sections by drawing lines on the bottom of the plate. Dry the surface of agar plates before use.Others: Inoculating loop, Bunsen burner Procedure of DNase (DNA hydrolysis test).Reagent: Hydrochloric acid (1mol/L) only when DNase agar without an indicator is used.Media: DNase Agar or DNase agar with Methyl green indicator.Procedure of DNase (DNA hydrolysis test).
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