Megaplasmid Dissemination in Multidrug-ResistantSerotypes from Backyard and Commercial Broiler Production Systems in the Southeastern United States.

Abstract

Over the past decade, there has been a rise in U.S. backyard poultry ownership, raising concern for residential area antimicrobial-resistant (AMR)contamination. This study aims to lay the groundwork to better understand the persistence of AMRin residential broiler production systems and make comparisons with commercial systems. Ten backyard and 10 commercial farms were sampled at three time points across bird production. Both fecal ( = 10) and environmental (soil, = 5, litter/compost, = 5, feeder, and waterer swabs, = 6) samples were collected at each visit on days 10, 31, and 52 of production for backyard farms and days 10, 24, and 38 of production for commercial farms. AMRwas characterized phenotypically by broth microdilution and genotypically by whole-genome sequencing. Overall,was more prevalent in commercial farm samples (52.31%) over backyard farms (19.10%). Kentucky (sequence type (ST) 152) was the most common serotype found in both backyard and commercial farms. Multidrug-resistant (MDR, resistance to ≥3 or more antimicrobial classes) isolates were found in both production systems, while ciprofloxacin- and nalidixic acid-resistant and intermediate isolates were more prevalent in commercial (33%) than backyard samples (1%). Plasmids that have been associated with MDR were found in Kentucky and Infantis isolates, particularly IncFIB(K)_1_Kpn3 megaplasmid (Infantis). Our study emphasizes the need to understand the selection pressures in disseminating megaplasmids in MDRin distinct broiler production systems.