A newly developed Escherichia coli isolate panel from a cross section of U.S. animal production systems reveals geographic and commodity-based differences in antibiotic resistance gene carriage

Abstract

There are limited numbers of Escherichia coli isolate panels that represent United States food animal production. The majority of existing Escherichia coli isolate panels are typically designed: (i) to optimize genetic and/or phenotypic diversity; or (ii) focus on human isolates. To address this shortfall in agriculturally-related resources, we have assembled a publicly-available isolate panel (AgEc) from the four major animal production commodities in the United States, including beef, dairy, poultry, and swine, as well as isolates from agriculturally-impacted environments, and other commodity groups. Diversity analyses by phylotyping and Pulsed-field Gel Electrophoresis revealed a highly diverse composition, with the 300 isolates clustered into 71 PFGE sub-types based upon an 80% similarity cutoff. To demonstrate the panel’s utility, tetracycline and sulfonamide resistance genes were assayed, which identified 131 isolates harboring genes involved in tetracycline resistance, and 41 isolates containing sulfonamide resistance genes. There was strong overlap in the two pools of isolates, 38 of the 41 isolates harboring sulfonamide resistance genes also contained tetracycline resistance genes. Analysis of antimicrobial resistance gene patterns revealed significant differences along commodity and geographical lines. This panel therefore provides the research community an E. coli isolate panel for study of issues pertinent to U.S. food animal production.