A bridging study for oxytetracycline in the edible fillet of rainbow trout: analysis by a liquid chromatographic method and the official microbial inhibition assay.

Oxytetracycline (OTC) is a drug approved by the U.S. Food and Drug Administration (FDA) to control certain diseases in salmonids and catfish. OTC is also a likely control agent for diseases of other fish species and for other diseases of salmonids and catfish not currently on the label. One requirement for FDA to extend and expand the approval of this antibacterial agent to other fish species is residue depletion studies. The current regulatory method for OTC in fish tissue, based on microbial inhibition, lacks sensitivity and specificity. To conduct residue depletion studies for OTC in fish with a liquid chromatographic method, a bridging study was required to determine its relationship with the official microbial inhibition assay. Triplicate samples of rainbow trout fillet tissue fortified with OTC at 0.3, 0.6, 1.2, 2.4, 4.8, and 9.6 ppm and fillet tissue with incurred OTC at approximately 0.75, 1.5, and 3.75 ppm were analyzed by high-performance liquid chromatography (HPLC) and the microbial inhibition assay. The results indicated that the 2 methods are essentially identical in the tested range, with mean coefficients of variation of 1.05% for the HPLC method and 3.94% for the microbial inhibition assay.

Quantitation of penicillin G in medicated premix feeds by micellar electrokinetic capillary chromatography.

A micellar electrokinetic capillary chromatographic (MECC) method for quantitation of penicillin G in medicated premix feeds was compared with the AOAC microbiological cylinder plate method. Feed was extracted according to the AOAC method, enabling comparison of both methods with the same extract. The MECC method detected penicillin G within 20 min, using a 150 mM sodium dodecyl sulfate (SDS)-20 mM sodium borate run buffer and a UV photodiode array detector at 210 nm. Recoveries from 5 replicates of medicated feed containing 117 g penicillin G/kg and then spiked to give a concentration of 176 g/kg were 98.4-108%, with a relative standard deviation (RSD) of 3.76% for the MECC method, and 102-104% with RSD of 1.06% for the AOAC microbiological cylinder plate method. Using a 5-point calibration curve, the MECC method detected and quantitated penicillin G in medicated premix feeds within 3 h, versus 24 h for the AOAC microbiological cylinder plate method.

Agarose gel electrophoretic detection of six beta-lactam antibiotic residues in milk.

An electrophoretic method coupled with bioautography was developed for detection and identification of penicillin G, ampicillin, amoxicillin, cloxacillin, cephapirin, and ceftiofur residues in milk. The method uses a 2% agarose gel for electrophoresis, an overlay of PM indicator agar seeded with Bacillus stearothermophilus var. calidolactis, and incubation at 55 degrees C for 16-18 h. The new method separated and detected residues in milk at the levels of concern for the Food and Drug Administration (FDA) for penicillin G (5 ppb), cephapirin (20 ppb), and ceftiofur (50 ppb). The method also detected ampicillin, amoxicillin, and cloxacillin at 20, 30, and 30 ppb, respectively, but these levels are above those of concern for FDA (10 ppb).