**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** COLIBACILLOSIS IS, ARGUABLY, THE MOST COMMON AND COSTLY DISEASE FOR THE POULTRY INDUSTRY WORLDWIDE, RESULTING IN MORTALITY AT THE FARM AND CARCASS CONDEMNATION AT SLAUGHTER. THE CAUSATIVE AGENT IS AVIAN PATHOGENIC E. COLI (APEC). FOR MANY YEARS, MOST STUDIES REPORTED THE MOST COMMON APEC SEROGROUPS ASSOCITED WITH DISEASE INCLUDED THE SEROGROUPS O1, O2 AND O78. THESE THREE SEROGROUPS WERE IDENTIFIED AS REPRESENTING OVER 90% OF ALL APEC ISOLATES, WITH COMMERCIAL VACCINES AVAILABLE SPECIFICALLY TARGETING THEM. IN A PRELIMINARY STUDY, USING RECENTLY COLLECTED ISOLATES (2018-2020), WE FOUND THAT ONLY 25 % OF ISOLATES WERE FROM SEROGROUP O2 OR O78, AND NONE OF THE ISOLATES WERE OF THE O1 SEROTYPE, INDICATING A SHIFT IN THE APEC CAUSING DISEASE IN MODERN POULTRY PRIDCUTION. THE GOAL OF THIS STUDY IS TO MONITOR THE APEC O SEROGROUPS THAT ARE CAUSING DISEASE AND CREATE A RAPID TOOL FOR SEROGROUP MONITORING THAT ALLOWS US TO BETTER PREDICT VULNERABLE FLOCKS AND IDENTIFY POTENTIAL STRATEGIES FORCOLLIBACILOSIS CONTROL AT THE FARM LEVEL. SPECIFICALLY, WE WILL: 1) BUILD AND CHARACTERIZE A COLLECTION OF AVIAN ESCHERICHIA COLI: APEC, AFEC (AVIAN FECAL E. COLI) AND LITTER E. COLI ISOLATES; 2) PERFORM MOLECULAR ANALYSIS OF THESE ISOLATES IN RELATION TO VIRULENCE. EPIDEMIOLOGICAL ANALYSIS OF OUR DATA WILL ALLOW US TO IDENTIFY NEW EMERGING STRAINS AND DEFINING TRAITS OF THE ENVIRONMENT AND THE HOST THAT POTENTIALLY LEAD TO E. COLI-ASSOCIATED DISEASE IN POULTRY. HAVING A BETTER KNOWLEDGE OF THE EMERGING SEROGROUPS ASSOCIATED WITH PRODUCTION AND DISEASE, WE WILL BE ABLE TO IDENTIFY NEW POTENTIAL TARGETS FOR COLLIBACILOSIS CONTROL AND DEVELOPMENT OF NON-ANTIMICROBIAL RELATED STRATEGIES.