The Efficiency of Br-Test and Intest in Determination of Chemotherapeutic Residues in Raw and Preserved Milk

Veterinarni Medicina 38, 1993, 215-222

Negative detection of residues of inhibitory substances has become one of the standard quality traits of raw milk also in the Czech Republic. Hence a requirement appeared in 1991 to evaluate the usability of two commercially produced microtitration tests for this purpose. The tests of BR-TEST (Enterotox) and INTEST (Mlekarensky prumysl) were performed in weekly intervals for the time longer by a week than is the declared expiration, that means seven replications in BR-TEST and five replications in INTEST. Compact and stripped microplates (STRIPS) designated BR-TEST ''AS'', BR-TEST 12x8 ''AS'' and INTEST C-96 type and INTEST 0-96/6x16 were used for the tests. The principle of inhibition demonstration in the concentration series of selected drugs was applied. The drugs were chosen with respect to the frequency of their use for clinical treatments in the CR. Tab. II shows the used drugs and concentration series. The following parameters were tested: detection limits, reproducibility, effect of milk preservation, and the declared expiration. Tab. III shows detection limits. It is apparent the BR-TEST detection responses to streptomycin and chloramphenicol were lower in BR-TEST than in INTEST in our experiments. The responses to penicillin, oxacillin and oxytetracycline were lower in some cases, and equal in other ones. On the other hand, the INTEST detection response to sulfadimidin was markedly lower in comparison with BR-TEST. Tab. IV summarizes the range of detection limits in milk with Heeschen's reagent. In our experiments the detection response of BR-TEST to the tested chemotherapeutics was lower in some cases, in other cases it was the same as in INTEST. Similarly like in unpreserved milk, the detection response to sulfadimidin was markedly higher in INTEST if compared with BR-TEST. Tabs. III and IV show the reproducibilities. It is apparent that INTEST is superior in this respect. Tabs. III and IV show the effects of milk preservation. The preservation does not influence detection responses. But it is necessary to prolong the incubation time by about one hour. Tabs. III and IV also show the check of the expiration time. Both tests were operative during their declared expiration. On the basis of the above-mentioned results, INTEST can be recommended for systematic global screening of residues of inhibitory substances belonging to antibiotics. But none of the tests was sensitive enough to detect admissible residue concentrations

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