Antimicrobial residues

Diaz-Cruz MS, Barcelo D (2006) Determination of antimicrobial residues and metabolites in the aquatic environment by liquid chromatography tandem mass spectrometry. Anal Bioanal Chem 386(4) 973-985... 

Nowadays HPLC is widely used for analytical determination of a large number of food contaminants. A number of recent works well review HPLC determination of major food contaminants such as mycotoxins [640-643], antimicrobial residues [644-646], residues of growth promoters [647], pesticide residues [648-651], and nitrosamines [652-654]. 

Campagnolo E.R., K.R. Johnson, A. Karpati, C.S. Rubin, D.W. Kolpin, M.T. Meyer, J.E. Esteban, R.W. Currier, K. Smith, K.M. Thug, and M. McGeehin (2002). Antimicrobial residues in animal waste and water resources proximal to large-scale swine and poultry feeding operations. Science of the Total Environment 299 89-95. 

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). 

By now, it has not been made possible to determine the levels of antimicrobials that can cause an increase of primarily resistant Enterobacteriaceae in the gut of the consumer. As a result, measuring the microbial significance of antimicrobial residues continues to be the subject of considerable discussion. Much of the discussion involves the development of model systems that will reflect the effects of residue levels of antimicrobials on human intestinal microbial populations. The consensus of opinion at a recent symposium is that no such single system is available (64). The human intestine is a very complex microbial ecosystem, about which little is known of the effects of antimicrobial residues on the population dynamics and biochenoical responses (65). 

The question is not whether there may be in vitro evidence but whether residue levels, singly or in combination, can select for resistant populations in vivo experiments. Under in vivo conditions, an antimicrobial residue that is stable to cooking processes would have to move through the stomach and the intestine, would then be metabolized during the passage or would be absorbed and excreted. A portion of it will not occur in the colon, the site of this specific action. Only a small portion of the ingested dose will reach the colon and remain there for a certain time, since many conditions have an influence upon the final concentration at the site of action in the colon. 

Among the antimicrobial residues giving rise to such technological problems in the manufacture of dairy products, residues of penicillin G in particular have been determined as most important. This is the reason why measures to reduce the presence of penicillin G residues in milk were originally taken to prevent economic loss and not due to public health concerns. 

The use of drugs in food-producing animals inevitably results in the appearance of drug-related residues in milk, meat, and eggs. Antimicrobial residues occur more frequently than desired violative residues occur much less frequently, but in definitely significant numbers. 

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). 

Under the pressure of an increasing number of drugs with fixed tolerance or maximum residue limits (MRLs), demands on methods to detect antimicrobial residues in edible animal products have changed markedly during recent decades (1). To satisfy these demands and prevent contaminated products from entering the food chain, many microbiological tests with sufficient detection sensitivity of as many analytes as possible in animal tissues, milk, eggs, honey, and fish have been developed or modified. 

Assays for detection of antimicrobial residues in foods are based on the microbial growth inhibition, microbial receptor, and enzymatic colorimetric formats. 

The ATP test is a bioluminescence procedure based on the reaction between adenosine-5-triphosphate (ATP) and a luciferin-luciferase enzymatic system (42, 43). The principle of the test relies on the fact that after a certain incubation period the intracellular ATP level, which gives a reliable indication of the state of development of a suitable bacterial culture (44), will remain low relative to a control, when antimicrobial residues are present. In its first version the ATP test employed Bacillus subtilis ATCC 6633 as the test organism, but a current version is based on the use of Streptococcus thermophilus T.J. culture. 

Common immunochemical assay formats to select from include the 96-well microtiter plates, dipsticks, coated test tubes, and membrane-based flow through devices. If the end-user is a trained technician working in a well-equipped laboratory and needs to detect and tentatively identify, for example, antimicrobial residues in hundreds of meat samples per day, a multiwell or other high-through-put format should be chosen. If, on the other hand, the end user is a quality control inspector at a milk factory who has limited time to find out whether the penicillin residues in the milk waiting to be unloaded exceed a certain level, the same reagents used in the first instance may require a more user-friendly format such as dipstick or membrane-based flow through device. 

HPLC Determination of Antimicrobial Residues in Edible Animal Products... 

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