SALMONELLA IS A LEADING BACTERIAL FOODBORNE PATHOGEN BOTH IN THE UNITED STATES AND GLOBALLY. DESPITE EFFORTS TO REDUCE SALMONELLA DURING POULTRY SLAUGHTER AND PROCESSING A NUMBER OF OUTBREAKS OCCUR EACH YEAR THAT ARE ATTRIBUTED TO POULTRY AND POULTRY-RELATED PRODUCTS. IN ADDITION TO THE OBVIOUS IMPACTS ON PUBLIC HEALTH SALMONELLA CONTAMINATION RESULTS IN SIGNIFICANT ECONOMIC LOSSES FOR THE POULTRY INDUSTRY.A KEY LIMITATION IN SALMONELLA SURVEILLANCE HAS BEEN THE ISOLATION AND SUBSEQUENT CHARACTERIZATION OF A SMALL NUMBER OF ISOLATED SALMONELLA COLONIES. THIS APPROACH DOES NOT REFLECT THE ENTIRE POPULATION RATHER LEADS TO THE MOST ABUNDANT SEROTYPES BEING IDENTIFIED AND THESE MAY NOT ALWAYS HAVE A HIGH ASSOCIATION WITH HUMAN ILLNESS. FURTHER THEIR ABUNDANCE CAN MASK LESS DOMINANT SEROTYPES THAT ARE FREQUENTLY ASSOCIATED WITH HUMAN ILLNESS. CRISPR-SEROSEQ DEVELOPED WITH USDA-NIFA SEED FUNDING IS A TOOL THAT REVEALS ENTIRE SALMONELLA POPULATIONS IDENTIFYING SEROTYPES THAT CONSTITUTE AS LOW AS 0.003% OF THE SALMONELLA POPULATION. THIS TRANSFORMATIVE TOOL CAN NOW BE USED TO ADDRESS CRUCIAL QUESTIONS IN FOOD SAFETY AND POULTRY. IN THIS PROPOSAL WE WILL BE USING CRISPR-SEROSEQ TO INVESTIGATE TWO IMPORTANT ISSUES: 1) HOW SALMONELLA SEROTYPE POPULATIONS FLUCTUATE WITHIN THE LIFETIME OF A BROILER BREEDER FLOCK AND HOW DYNAMIC ARE SALMONELLA POPULATIONS IN POULTRY IN THE SOUTHEAST (PRODUCERS OF OVER A QUARTER OF OUR NATION'S BROILER CHICKENS). THIS INFORMATION WILL BE USED TO DEVELOP MODELS THAT FORECAST SALMONELLA SEROTYPES PATTERNS. 2) REVEALING BIASES IN SEROTYPE GROWTH UNDER DIFFERENT SELECTIVE ENRICHMENT CONDITIONS AND REDUCING THIS BIAS BY IMPROVING EARLY DETECTION OF SALMONELLA FROM PRE-ENRICHED CULTURES. COLLECTIVELY THESE APPROACHES WILL IMPROVE OUR UNDERSTANDING OF SALMONELLA ECOLOGY AND ENABLE DEVELOPMENT OF TARGETED IMPLEMENTATION OF SEROTYPE-SPECIFIC SALMONELLA MITIGATION STRATEGIES.SALMONELLA SEROTYPE KENTUCKY IS THE TOP SEROTYPE FOUND IN US POULTRY BUT HAS A LOWER ASSOCIATION WITH HUMAN ILLNESS THAN SEROTYPES SUCH AS ENTERITIDIS OR INFANTIS. THERE ARE TWO GENETIC LINEAGES OF KENTUCKY I AND II. THE 'DOMESTIC' IS KENTUCKY-I WHEREAS KENTUCKY-II IS A FOUND FREQUENTLY OUTSIDE OF THE US WHERE IT HAS A HIGHER ASSOCIATION WITH HUMAN ILLNESS AND IS RESISTANT TO IMPORTANT ANTIBIOTICS USED IN HUMAN THERAPY (EG. CIPROFLOXACIN). WE HAVE ALREADY FOUND SOME CASES OF KENTUCKY-II IN US POULTRY FLOCKS AND IN THIS STUDY WE WILL SURVEY NATIONAL AND REGIONAL POULTRY SAMPLES TO SEE WHETHER KENTUCKY-II IS INCREASING AND IF SO AT WHAT RATE. CHALLENGE EXPERIMENTS WILL BE PERFORMED AS A RISK ASSESSMENT STUDY.COMPLETION OF THE PROPOSED RESEARCH WILL PROVIDE A VALUABLE FRAMEWORK THAT CAN EASILY TRANSLATED TO OTHER FOOD ANIMAL SYSTEMS WHERE SALMONELLA IS A PROBLEM (EG. CATTLE SWINE) AND OTHER AGRICULTURAL SYSTEMS WHERE IMPROVED SALMONELLA DETECTION IS KEY TO REDUCING OUTBREAKS (EG. FRESH PRODUCE).