Detection of microorganisms and antibiotic resistance genes (ARGs) in the vicinity of swine barns and henhouses using conifer needles as passive samplers

Introduction. Characterizing airborne emissions of antibiotic resistance gene (ARGs) from livestock farming activities remains overlooked. Current air biosurveillance tools generally rely on active samplers, which are limited to snapshot measurements. Passive samplers could be integrated into long-term monitoring of bioaerosols emitted from agricultural buildings.

Objectives. Use conifer needles as long-term passive samplers to characterize airborne ARGs emitted from swine barns and henhouses.

Methods. Conifer needles from two rows of trees from two swine barns and two henhouses were collected. Air samples (240 m³) were also collected at these rows (25 to 180m apart), as well as at the fan exhausts, using an active sampler (SASS®4100). Each swine barn was visited five times and each henhouse, three times. The presence of 17 ARGs (related to tetracycline, erythromycin and sulfonamides) and one mobile genetic element (MGE), tnpA, was quantified in each sample by high-throughput PCR. The results were compared with data from air and needle samples collected at two control sites, sampled on the same days as the farms.

Results. The airborne concentrations of ARGs and MGEs at swine barns’ fans were 100–1,000 times higher than at control sites and returned to background levels by the second tree row. ARGs concentrations on needles were less distance-dependent and less variable than in the air, reaching 10–100,000 times control levels at the first row and remaining 1–10,000 times higher at the second row. Analyses of henhouse samples are ongoing.

Conclusion. Our study shows that conifer needles can passively accumulate bioaerosols originating from nearby pig farms and potentially other agricultural buildings, such as henhouses. Large-scale deployment of conifer needle sampling could be leveraged to identify and model emissions of antibiotic-resistant bacteria into the environment, ultimately helping to limit exposure to agricultural workers and surrounding populations.