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B8-OP: MICROBIOLOGICAL INHIBITORY METHODS IN ANTIBIOTIC RESIDUE DETECTION

J. Petrović, D. Milanov, D. Stojanović

Scientific Veterinary Institute Novi Sad, Rumenacki put 20, 21000 Novi Sad

Antibiotics are essential for the control of infectious diseases in food producing animals. Therefore, antibiotics are the most frequent veterinary drug residues that may be detected in milk, meat and eggs. Although the adherence of withdrawal time is emphasised, antimicrobial drug residues ocasionally ocur in food. It may be explained by various reasons e.g. failure to observe withdrawal time, overdose or drug misuse. Safe food is free of residues, it means that the level of residues in tissue is lower than MRL (maximum residue limit) according to the national and international regulations.

Systematic control of antibiotic residues includes the analysis and selection of large number of samples, and requires a wide range of screening methods. Screening tests must satisfy the following requirements: they must detect antibiotics of interest such as ß-lactams in dairy products industry, detection limits must comply with the requirements (MRLs), they must be easy to perform and cost effective, test results are to be obtained rapidly, and the tests must be standardized (low variability within and between batches/laboratories).Various screening tests have been developed to detect antibiotic residues at tolerance levels in milk and meat. Microbiological inhibitory methods are widely used as a standard for screening purposes. The most commonly used are Four- plate test for detection of residues in meat and kidneys and Delvo SP test for detection of residues in milk but there are many others. The test principle is the following: growth inhibition of test microorganisme (Bacillus subtilis, Kocuria rhizophila, Micrococcus luteus, E. coli) in agar medium in the presence of antibiotic residue. Test microorganisme acomposition of agar medium, pH vary in different tests but basic principle is the same [1, 2]. The two key features of a screening test for residues are sensitivity and rapidity. The LOD (limit of detection) of a microbiological test depends on the innate sensitivity of the test bacterium, pH and thickness of growth medium [3]. The sensitivity of microbiological inhibitori methods is best towards beta-lactam antibiotics but it is also very good towards sulphonamide, amynoglicoside, teteracycline, quinolone antibiotics. Sensitivity to chloramphenicole is insufficient and much above MRL (zero tolerance for this antimicrobial). One of the limitations of inhibitory methods is that the results are usually obtained only after few hours of incubation. Due to the test principle, i.e. measurement of the inhibition of multiplication (agar diffusion tests) and/or metabolism of the test microorganism (Delvo SP), the microbial inhibitory methods cannot serve as rapid test when results are required within a few minutes [3].

The occurrence of residues of antibiotics is significant problem in food industry. The screening methods for detection of antimicrobials shall ensure the technological and toxicological safety of food. The microbiological inhibitor tests are and will continue to be in future the dominating tests for antibiotic screening in milk, meat and eggs [4, 5].

References

1. J. Petrović, M. Baltić, S. Stefanović, D. Milanov, Acta Veterinaria, 2009, 56, 547-555.
2. J. Petrović, M. Baltić, V. Ćupić, S. Stefanović, D. Stojanović, 2006, 56, 497-506.
3. J. Petrović, V. Katić, Food Analitycal Methods 2008, 1, 119-125.
4. R. Kljajić, B. Vidić, J. Petrović, Savremena poljoprivreda, 2006, 55, 104-111.
5. Ј.Petrović, H. Karabasil, M. Dimitrijević, М. Kapetanov, Živinarstvo, 2007, 8/9, 86-90.