Antibiotics antimicrobial residues

In order to eliminate the potential hazard from the effect of antimicrobial residues on human intestinal microflora, regulatory agencies have determined a maximum safe concentration of 1 ppm in a total diet of 1.5 kg as the level of total antimicrobial residues in food that would produce no effects on the intestinal microflora. All studies on antibiotics performed to date support 1 ppm as being below the effect level for humans (58). 

There has been considerable debate over the role of antimicrobial residues as factors contributing to the relatively high levels of resistance found in human enteric bacterial populations. Whether the relatively high levels of antimicrobial resistance found among enteric bacterial populations arise from medical use, from selection due to exposure to antimicrobial residues, from colonization by antibiotic-resistant organisms related to food production, or from transient colonization of antibiotic-resistant species and transfer of resistance to indigenous populations is undefined (59-62). 

Three decades ago, a survey of animals slaughtered in four US states indicated that 27% of the swine sampled were treated with antimicrobial drugs before slaughter. Some 10% of those cases resulted from lack of adherence to withdrawal periods or from exceeding the levels cleared for feeding of the antimicrobial substances. Among beef cattle, a total of 9% were found positive to antimicrobials with 2% attributed to penicillin residues. In veal calves, 17% contained antibiotic residues with 7% ascribed to penicillin. Twenty-one percent of the market lambs contained antimicrobial residues, 4% with penicillin residues. Chickens exhibited a 26% contamination by antimicrobials, 6% containing penicillin residues (1). 

A wide variety of commercial LFIA kits for the detection of antibiotic residues is available and the most well-characterised of these are summarized in Table 5.4, including the rapid one-step assay (ROSA) range from Charm Sciences Inc., and the Tetrasensor, Twinsensor, Trisensor, and Sulfasensor from Unisensor SA and the Betastar from Neogen Corporation. Other LFIA assays have been reported in the scientific literature for the detection of antimicrobial residues, including a lateral-flow device for nicarbazin detection in animal feedstuffs. However, at present these are not commercially available. These LFIA tests incorporate either a receptor protein or an antibody as the specific capture molecule and operate in the competitive assay format (most applicable for small-molecule detection). The sample preparation protocols are based on either direct analysis of the liquid sample (e.g., milk) or a simple extraction step for solid or complex matrices using buffer(s) supplied in the test kit. In general, the time required to perform these tests is less than 30 min with only basic laboratory equipment, if any, required. 

Pikkemaat MG, Oostra-van Dijk S, Schouten J, Rapahini M, van Egmond HJ, A new microbial screening method for the detection of antimicrobial residues in slaughter animals The Nouws antibiotic test (NAT-screening), Food Control 2007 19 781-789. 

I am in full agreement with Halpern s conclusion that the preservation of the effectiveness of antibiotics is essential to protect the health of animals and humans and that insufficient evidence currently exists to support prohibitions on the use of antibiotics in food animals. The advantages provided to both human and animal populations from continued use of antibiotics in food animals outweigh the minimal risk to humans currently documented. I similarly believe that there is a lack of documented evidence that antimicrobial residues significantly contribute to adverse human health outcomes. 

Antimicrobial residues can cause serious illness, and therefore present a hazard to public health. Drug allergies are mediated by a number of different immunological mechanisms, including type 1 immediate immune response mediated through Immunoglobulin E (IgE). Symptoms include anaphylaxis, skin-rashes, urticaria and angioedema (FAO/OIEAVHO, 2006). The antibiotics used in aquaculture, either for prophylactic or therapeutic purposes, often accumulate in the tissue of aquatic animals. 

The data from the 2000 FSIS/USDA monitoring program (Table 12.4) present very similar results to those found in the 1998 data (USDA, 2000). For the sake of simplicity, the data presented show the violations and the upper 95% confidence limits. These data confirm the consistently low incidence of antibiotic and sulfonamide residues in animals grown for food. Even in the worst-case situation, the upper range of the violative incidence remains relatively low, usually less than 2%. There are some hot spots, namely in veal calves, hogs, and horses. Horses appear to be a special case because these animals are rarely used for food in the U.S. It may be that horses are treated with antibiotics or antimicrobials to ensure the animals or carcasses are in the best shape for marketing. 

Notes STOP = swab test on premises, measures antibiotic residues in the kidney FAST = fast antimicrobial screen test, measures antibiotic and sulfonamide residue in kidney and liver SOS = sulfa-on-site, measures for sulfonamide residues. 

The data in Table 12.5 are the result of a pooling of results from a number of different products that were spot-checked for a number of different residues (drugs, antibiotics, sulfonamides, pesticides, antimicrobials). As can be seen from these limited data, the number of samples is quite small in total but can be reflective of the residue status of various products. Overall, the data indicate a very low incidence of both antibiotic and sulfonamide residues in the imported products. 

No milk can be considered hormone free as natural hormones are always present. The question that has been under heated debate since approximately 1995 is whether the bovine somatotropin hormone (BST) injected into cows to increase milk production results in harmful levels of hormone in milk. The use of BST, which is based upon an economic return rather than any health benefit to the animal, raises two important questions what are the health risks to the human consumer, primarily children and what are the effects on the animals It is fairly well accepted that the use of BST increases the incidence of mastitis and therefore the potential for increased residues of antibiotic and antimicrobials in milk. Because of this Canada, Australia, Japan, the U.K., and other European Union countries decided that the health impact on animals was unacceptable and that BST was not to be used in their jurisdictions. Their decisions were not based upon any human health concerns, but strictly on concerns for animal health. 

FSIS has developed a series of overnight, inexpensive, easy to perform swab bioassay tests for screening tissues, body fluids, or feed extracts for antibiotic residues. The swab tests are used on the farm, in the slaughter plant, or in the laboratory for their designated purpose. Swab test results indicate whether antimicrobial activity is present in the sample at or above allowable levels or absent. Further testing with more sophisticated tests is required to identify and quantify the antibiotics producing the antimicrobial activity. These are usually done in a laboratory as required. 

FSIS laboratories also use chemical techniques and instrumentation to identify select antibiotic residues. The tetracyclines of interest are identified by thin layer chromatography. Sulfonamides are detected and quantified by fluorescence thin lay chromatography and confirmed by gas chromatography/mass spectrometry. Amoxicillin and gentamycin are identified and/or quantified by high pressure liquid chromatography. Similar techniques are used to identify ionophores and other antimicrobials of interest. 

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