Pet and food animal (hogs, chicken, and fish) feeds were recently found to be contaminated with melamine (MEL). A quantitative and confirmatory method is presented to determine MEL residues in edible tissues from fish fed this contaminant. Edible tissues were extracted with acidic acetonitrile, defatted with dichloromethane, and cleaned up using mixed-mode cation exchange solid-phase extraction cartridges. Extracts were analyzed by liquid chromatography with tandem mass spectrometry with hydrophilic interaction chromatography and electrospray ionization in positive ion mode. Fish and shrimp tissues were fortified with 10-500 microg/kg (ppb) of MEL with an average recovery of 63.8% (21.5% relative standard deviation, n = 121). Incurred fish tissues were generated by feeding fish up to 400 mg/kg of MEL or a combination of MEL and the related triazine cyanuric acid (CYA). MEL and CYA are known to form an insoluble complex in the kidneys, which may lead to renal failure. Fifty-five treated catfish, trout, tilapia, and salmon were analyzed after withdrawal times of 1-14 days. MEL residues were found in edible tissues from all of the fish with concentrations ranging from 0.011 to 210 mg/kg (ppm). Incurred shrimp and a survey of market seafood products were also analyzed as part of this study.

Although melamine and cyanuric acid appeared to have low toxicity when administered separately, they induced extensive renal crystal formation when administered together. The subsequent renal failure may be similar to acute uric acid nephropathy in humans, in which crystal spherulites obstruct renal tubules.

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Two hundred and fifty cases of percutaneous nephrolithotomy (PNL) are described. One hundred and fifty cases were treated in two stages, 100 in a single stage. The one-stage method has been shown to be as safe as the two-stage method but should be reserved for those with experience of the technique and who possess adequate instrumentation. PNL has proved to be a preferable option to open stone surgery and a useful alternative to extracorporeal shock wave lithotripsy (ESWL).

ᰔFlorfenicol (FFC) has recently been approved by the Food and Drug Administration for the treatment of several bacterial diseases of cultured fish species in the United States, including enteric septicemia of catfish (ESC) caused by Edwardsiella ictaluri. The FFC-resistant E. ictaluri strain (M07-1) described herein was isolated from a moribund catfish obtained from the Thad Cochran National Warmwater Aquaculture Research Center (Stoneville, MS) in May of 2007 and was confirmed to be E. ictaluri by 16S rRNA gene sequencing (6). Fish showing signs of ESC were examined for FFC-resistant E. ictaluri because losses due to ESC persisted in this population despite FFC treatment. To characterize the resistance properties of this strain, conjugative transfer experiments were performed as described previously (14) using FFC (30 g/ml) for selection. The antimicrobial susceptibilities of M07-1, the corresponding FFCresistant transconjugant, and the isogenic parent strain (Table 1) were quantified using standard microdilution assays (3, 4, 11), demonstrating that the resistance phenotype observed in strain M07-1 was self-transmissible, conferring resistance to FFC, chloramphenicol, tetracycline, streptomycin, ampicillin, amoxicillin-clavulanic acid, ceftiofur, and cefoxitin, as well as decreased susceptibility to trimethoprim-sulfamethoxazole and ceftriaxone. Resistance transfer correlated to a 150-kb plasmid (referred to hereinafter as pM07-1), suggesting the presence of a multidrug resistance plasmid in this isolate (data not shown). PCR analysis (15) followed by sequencing confirmed that E. ictaluri M07-1 and its multidrugresistant (MDR) transconjugant harbored the floR gene.E. ictaluri plasmid pM07-1 also conferred resistance to ceftiofur and concomitant decreased susceptibility to ceftriaxone, implying the presence of the bla CMY-2 beta-lactamase gene. Recent data indicate a rapid increase in the dissemination of cephalosporin resistance linked to self-transmissible MDR plasmids harboring bla 16). Plasmid-borne bla CMY-2 genes in bacteria isolated from food animals, retail meats, and humans in the United States have been identified previously (1, 2, 5, 8, 16) but have not been detected before in bacteria associated with U.S. aquaculture and were not expected, as there are currently no cephalosporin antimicrobials approved for use in U.S. aquaculture. Therefore, PCR analysis using previously described primers specific to bla CMY-2 was performed to verify the presence of this gene in E. ictaluri