Abstract
Background: Emergence and spread of antibiotic resistance has become a global health threat
and is often linked with overuse and misuse of clinical and veterinary chemotherapeutic agents.
Modern industrial-scale animal feeding operations rely extensively on veterinary
pharmaceuticals, including antibiotics, to augment animal growth. Following excretion,
antibiotics are transported through the environment via runoff, leaching, and land application of
manure; however, airborne transport from feedyards has not been characterized.
Objectives: The goal of this study was to determine the extent to which antibiotics, antibiotic
resistance genes (ARG), and ruminant-associated microbes are aerially dispersed via particulate
matter (PM) derived from large scale beef cattle feedyards.
Methods: PM was collected downwind and upwind of ten beef cattle feedyards. Upon extraction
from PM, six veterinary antibiotics were quantified via LC-MS/MS, ARG were quantified via
targeted qPCR, and microbial community diversity was analyzed via 16S rRNA amplification
and sequencing.
Results: Airborne PM derived from feedyards facilitated dispersal of several veterinary
antibiotics, and microbial communities containing ARG. Concentrations of several antibiotics in
airborne PM immediately downwind of feedyards ranged from 0.5-4.6 μg/g of PM. Microbial
communities of PM collected downwind of feedyards were enriched with ruminant-associated
taxa, and were distinct when compared to upwind PM assemblages. Furthermore, abundance of
genes encoding resistance to tetracycline antibiotics was significantly greater in PM collected
downwind of feedyards as compared to upwind.