6-Lactam antibiotic detection methods

Table II. Chromatographic Methods for Detection of B-lactam Antibiotic Residues in Foods...

Penicillins form several major metabolites which are excreted in the urine (83,84). These metabolites are usually inactive microbio-logically and they would not be detected by the usual microbiological tests. There are no analytical methods for these metabolites in tissues and, therefore, little is known as to their occurrence and persistence in tissues. There are no methods available for identifying residues of some commonly used B-lactam antibiotics including carbenicillin and ticarcillin. For cephapirin and ampicillin, except for one HPLC method for ampicillin in milk (79) only TLC procedures (72-74,76) with detection by bioautography are reported. 

Following their extraction and cleanup, residues of -lactam antibiotics in sample extracts can be detected by either direct nonchromatographic methods, or thin-layer, gas, or liquid chromatographic methods (Table 29.3). 

Confirmation of the identity of the -lactam residues detected by liquid chromatography has been attempted through use of photodiode array detectors (73, 75,11-19. This procedure is relatively simple, but does not offer the specificity and the sensitivity required to determine or identify trace levels of residual -lactam antibiotics in edible animal products. Better residue confirmation can be more readily attained by treatment of the suspected samples with -lactamase or penicillinase and their reanalysis (71, 80, 86-89, 105, 106-111). In this instance, absence of a chromatographic peak with the proper retention time provides unequivocal evidence that a given residue is not present above the detection limit of the method. Thus, use of -lactamase provides a simple, inexpensive and... 

Another source of concern in food safety control is the increasing amounts of residues of veterinary drugs that can be found in foods. These drugs are mostly antibiotics of different structures, such as tetracyclines, macrolides, quinolones, sulphona-mides, and 6-lactams. The preferred analytical technique for antibiotic residue determination is HPLC, and specific methods for each family of antibiotics can be fovmd in the scientific literature. Most of the published methods use RP columns with gradient elution. Every available detection method can be used, depending on the application, though MS is a powerful technique for the identification and confirmation of veterinary drug residues in food samples, and at the moment, LC-MS is the method of reference. 

Lactam antibiotic drugs,amino acids, and biogenic amine as a PTC derivative, BTC amino acids,thiouracils, pyrimidines, and pyridines were separated in HPTLC and detected with the suggested method. 

The technique of carbon-13 labelling in the study of antibiotic biosynthesis utilising NMR detection methods has been reviewed with specific reference to the -lactam antibiotics [204). The biosynthesis of penicillins and cephalosporins has recently been reviewed and stable isotopes have played a significant role in these studies [208]. 

Antisera to cloxacillin/oxacillin/dicloxacillin and cefuroxime were also produced by similar procedures and successfully utilized in methods for the detection of these antibiotics in milk (34). Unfortunately, a number of other -lactams including aminopenicillins and some cephalosporins were not amenable to this mixed anhydride procedure. Thus, a carrier protein derivatization procedure was used to allow cross-linking of cephalosporins, such as cephataxime that has an acetoxy side chain, to ovalbumin. Because acetoxy groups react readily with the heterocyclic nitrogen atoms, the latter were introduced into ovalbumin through the carbodiimide-mediated derivatization of protein carboxyl groups with amino-methylpyridine (34). 

In summary, rapid tests, either immunoassay or enzymatic formats, are the methods of choice when qualitative or semi-quantitative results are required within a short timescale, specifically, around 30 min for targeted residue screening. In general, these assay formats are portable (suitable for in situ testing) and simple to both operate and interpret. A wide variety of test formats are commercially available, many of which are applicable for the detection of classes of antibiotics, such as P-lactams and tetracyclines with detection capabilities at or below the appropriate RLs. As with other test kits, it is important to determine the applicability of the assay for the specific matrix type prior to use as certain matrices are known to contain interference that causes elevated false non-compliant/compliant rates. 

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