Antibiotic Residues In Food Research Articles

Antibiotic residues in food and their significance

(2000). Antibiotic residues in food and their significance. Food Biotechnology: Vol. 14, No. 3, pp. 147-171.

Variability Encountered in Model Systems Designed to Test Antimicrobial Effects on the Intestinal Microflora

One function of the microbial ecosystem formed by the bacterial flora of the gastrointestinal tract is to create a barrier to colonization by ingested bacteria, including opportunistic pathogens. There are no validated tests that predict the amount of antibiotic residue in food that can be ingested by humans without causing an effect on this barrier. Semi-continuous cultures (S-CC) of fecal bacteria are frequently used as models of the colon flora, since bacteria in these cultures form relatively stable microbial ecosystems. These models may provide a basis for developing a test system to determine no effect concentrations of antibiotic residues, and thereby derive (for drug registration purposes) a human acceptable daily intake of antibiotic residues in foods from treated animals. Clindamycin is one of many antibiotics that can disrupt the colonization barrier of the colonic microflora in vivo in humans. This may be evidenced clinically as pseudomembranous colitis, if toxigenic Clostridium difficile are present and proliferate in the intestinal tract. Therefore, we tested clindamycin as a reference compound and used proliferation of Clostridium difficile as a functional indicator of disruption of the otherwise stable populations of human fecal bacteria in an S-CC test system. The objective of the studies was to examine test conditions and responses that could be used in an S-CC in vitro test to detect colonization barrier disruption in this model of the human gut flora. The hypothesis was that a clindamycin dose response would be detectable by monitoring the C. difficile concentration within the S-CCs.

Detection of antimicrobial substances in individual cow and quarter milk samples using Delvotest microbial inhibitor tests.

The use of antibiotic therapy to treat and prevent udder infections of cows during the dry period is a key component of mastitis control in many countries. At the same time, the general public is becoming increasingly aware of potential hazards from antibiotic residues in foods. Consequently, Delvotest Cow Test (Royal Gist-brocades NV, Delft, The Netherlands), an on-farm version of Delvotest P, a microbial inhibitor test for antimicrobials, is being increasingly used by farmers to assess that milk from individual cows is fit for consignment to the bulk tank. Occasional reports of unexplained positive test results have led to suggestions of possible false-positive reactions in milk from individual cows. To investigate the potential causes of such positive test results, three separate investigations were undertaken. In a field survey of unexplained positive reports from farmers, 14 milk samples from six farms that tested positive were all found to contain antibiotic residues. In more formal investigations of individual quarter milk samples from an experimental herd, none of 134 milk samples from midlactation cows yielded positive reactions; for cows that had just calved, 16 of 144 milk samples were positive, and, of those, 13 had somatic cell counts > 4,000,000/ml. Natural inhibitors were responsible for 1 positive reaction, 8 positive reactions were related to incomplete milking, and 7 samples contained beta-lactam antibiotics. Positive reactions caused by antibiotic persisted in individual quarter samples for up to 7 d postcalving compared with 4 d for milk samples from the whole udder. Delvotest was sensitive to cephalonium, the active ingredient of Cepravin Dry Cow (Mallinckrodt Veterinary Ltd., Uxbridge, United Kingdom), which is the market-leading product in the United Kingdom. Test results yielded a partial purple color reaction in the presence of 8 micrograms/kg of cephalonium and a completely purple reaction at 16 micrograms/kg. These results confirm the validity of Delvotest when used to examine composite milk samples from individual cows supplying the United Kingdom dairy industry and suggest that, with proper attention to milk withdrawal periods and complete milking, there is no obvious risk of antibiotic contamination of milk.

Heat Stability of 24 Antibiotics in Food Extracts

For estimation of antibiotic residues in food, heat treatments of extract solutions spiked with antibiotics were performed under 4 conditions: heated in boiling water, heated in an autoclave (121°C, 15min), heated in an autoclave under an acid (pH 2) condition, heated in an autoclave under an alkaline (pH 12.5) condition.Heat stabilities of 24 antibiotics were evaluated as the ratio of the reduction of inhibition zone diameter in the paper disk method after/before heat treatments. Each antibiotic exhibited a characteristic heat stability pattern. Therefore, heat treatments of food extract solutions containing unknown antibiotics are a useful approach for estimation of antibiotic residues.