A rapid fluorescence assay for danofloxacin in beef muscle: effect of muscle type on limit of quantitation.

A simple, rapid fluorescence screening assay was applied to the analysis of beef muscle for danofloxacin at the U.S. tolerance level of 200 ng/g. Muscle samples were homogenized in acetic acid—acetonitrile, the resultant mixture centrifuged, and fluorescence of the supernatants was then measured. The significant difference between the fluorescence of control muscle sample extracts and extracts of samples fortified at 200 ng/g allowed for successful discrimination between the samples. Setting a threshold level at the average 200 ng/g fortified sample extract fluorescence —3cr allowed for identification of potentially violative samples. Successful analysis of a group of blind fortified samples over a range of concentrations was accomplished in this manner, without any false-negative results. The limits of quantitation for danofloxacin, as well as enrofloxacin, using this assay were determined in three types of beef muscle (hanging tenderloin, neck, and eye round steak), as well as in serum. Significant differences in limits of quantitation were found among the three different muscle types examined, with hanging tenderloin muscle providing the lowest value. This work not only shows the potential for use of the fluorescence screening assay as an alternative to currently used microbial or antibody-based assays for the analysis of danofloxacin in beef muscle, but also suggests that assays using beef muscle may vary in performance depending on the specific muscle selected for analysis. -w Fluoroquinolones (FQs) are a class of antibiotics displaying activity against a wide range of gram-positive and gram-negative bacteria, and are used in both human medical and veterinary applications. Use of FQs in food animals and the potential for residues that could lead to increased microbial resistance has led to some concern. Thus, efficient methods are needed to monitor the food supply to ensure that any residues, if present, are at a concentration below the U.S. Food and Drug Administration tolerance level. A large number of beef and dairy cows and steers are slaughtered annually in the United States, yet only a small percentage of these animals are identified as containing violative levels of antimicrobials. In 2005, for example, the number of violations was less than 1.5% of the animals selected by inspectors for testing (10). With such a low level of violations, rapid screening assays can be used to efficiently identify those relatively few samples that may contain problematic levels of antimicrobials, and then only these samples need be sent for further quantitative and confirmatory analysis. Such an approach can save a considerable amount of time, expense, and effort. Screening assays in use for the FQs typically involve either immunoassays, which necessitate obtaining the cor