Multi-laboratory validation of LC-MS/MS analyses of diagnostic samples including animal tissues and feeds for cereulide - 2025 Romano Vet-LIRN Project Summary/Abstract The Food and Drug Administration (FDA) Center for Veterinary Medicine (CVM) Office of Applied Science's Veterinary Laboratory Investigation and Response Network (Vet-LIRN) safeguards human and animal health by investigating potential animal food or drug contamination events. During investigation of suspected microbial or chemical contamination of animal foods/drugs, Vet-LIRN member laboratories can analyze animal diagnostic samples as well as animal food/drug products. Animal diagnostic sample testing provides additional insight beyond that obtained from traditional food testing laboratories. Diagnostic investigations require detection methods that are validated for biological samples (e.g., vomitus, urine, feces, blood, and tissues) in addition to the typical food matrices. Vet-LIRN laboratories can also provide surge capacity testing during large-scale outbreak situations. In such instances, analytical methods used and results reported by different laboratories must be comparable to guide sound decision-making by regulatory officials. The overall objective of this project is to increase the number of robustly validated analytical methods available to Vet-LIRN member laboratories to facilitate effective, coordinated analysis and reliable results. Specifically, we will perform multi-laboratory validation of a method to quantify cereulide, an emetic toxin produced by Bacillus cereus, which has been implicated in food poisoning of humans as well as animals. The method will first be validated in pet foods at the method-originating laboratory (UKVDL) and will then be expanded to include diagnostic samples such as feces, vomitus, serum, tissues, and other diagnostic samples. The method will be transferred to two other Vet-LIRN member laboratories. All participating laboratories will then complete a multi-laboratory blinded methods test (BMT) administered by a third party. Finally, the method will be disseminated to Vet-LIRN and its member laboratories via protocols.io. The project will improve human and animal health by increasing the number of shared, multi- laboratory validated testing methods available to Vet-LIRN laboratories to use during outbreaks or events of animal feed or drug contamination or adulterations.