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Inhibitors prevent the growth of micro-organisms or destroy them, and are present in veterinary products and other products. Their use is subject to statutory regulation. Milk and dairy products therefore have to be tested for the presence of inhibitors.
Methods of detection
The method specified under the German Lebensmittel- und futtermittelgesetz (LfGB) [food and feedstuff Act] involves a test system with the test organism Bacillus stearo-thermophilus and agar medium. This micro-organism is particularly sensitive to penicillin. Assay discs of filter paper are immersed in the sample under test and then laid on the agar. If the sample contains an inhibitor then a clear, transparent ring will form around the disc because of the inhibition of growth.
Importance of the inhibitor test
Bulk milk must be tested every two weeks under § 2 of the Milchgüte-Verordnung [Milk Quality Regulations] for the presence of inhibitors. one aim is to protect con-sumers, who may be allergic to certain antibiotics. furthermore, the excessive use of antibiotics may lead to an increased resistance to their action. A further impor-tant reason for testing is that the presence of inhibitors can adversely affect the production of fermented dairy products. fermentation may be stopped and complete failure of the production process may result.
Incubation conditions according to the analytical method given in § 64 LFGB *
*Amtliche Sammlung von Untersuchungsverfahren nach § 64 LfGB (vormals § 35 LMBG), Band I (L), L 01.00-6: nachweis von hemmstoffen in Milch; Agar-diffusions-Verfahren (Blättchentest).1997[official collection of test methods in accordance with § 64 of the LfGB (previously § 35 of the LMBG), Vol. I (L) L 01.00-6: demonstration of inhibitors in milk; the agar diffusion test (assay disc test). 1997]