Agar Test pH 8,0 for Inhibition Test in combination with Agar test pH 7,2 and 6,0 is used for the detection of antimicrobial inhibitors in meat and organ samples. Antimicrobial inhibitors contained in the samples diffuse into the nutrient media and cause growth-free inhibition zones to develop on the otherwise thickly covered plates. Repeated tests with pH 6,0, pH 8,0 and pH 7,2 are necessary, as penicillin and streptomycin are optimally active at pH 6,0 and 8,0 respectively and the activity optimum of sulfonamide is found at pH 7.2. Addition of trimethoprim to Test Agar pH 7,2 considerably increases the sensitivity of the test system to sulfonamides. Complete inhibition of growth with a zone of inhibition of at least 2 mm is considered as a positive result. An inhibitory zone of 1-2 mm must be regarded as questionable. This only applies if the controls, prepared at the same time show inhibition zones measuring about 6 mm.
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