Pathogen and antibiotic resistant bacterial colonization of a newly established broiler house

Conventional commercial broiler production involves the rearing of more than 20,000 broilers in a single confined space, atop bedding material such as pine shavings or rice hulls, for approximately 6.5 weeks.  This environment is known for harboring pathogens and antibiotic resistant bacteria, but studies have focused on previously established houses.  A concerted effort by the broiler industry has involved the scaling back of antibiotic use on-farm, but this has only been a recent occurrence.  In the current study, a set of three naïve houses were followed from inception through 11 broiler flocks and monitored for ambient climatic conditions, bacterial pathogens, and antibiotic resistance.  Within the first 3 weeks of the first flock cycle, nearly 90% of litter samples were positive for Salmonella, whileCampylobacter was culture negative but polymerase chain reaction positive.  Tetracycline resistance increased through the first 2 flocks and remained at 10⁶ genomic units per g of litter.  The influence of intra-house location was minor with only watering lines influencing pathogen levels.  Antibiotic resistance genes reflected a population quickly dominated by resistance genes; however, Escherichia coliand pathogen isolates did not reflect this phenotypically, most likely representing antibiotic resistant commensal organisms.  Additionally, the presence of background tetracycline resistance in naïve rice hulls, albeit at 1000 x’s less concentrated levels, represents the presence of antibiotic resistance genes in the environment prior to the introduction of chickens to a farm.  This study represents a first of its kind view into the time required for bacterial pathogens and antibiotic resistance to colonize and establish in naïve broiler houses.