In a study reported this week in the journal Environmental Health Perspectives, researchers from the Department of Environmental Toxicology at Texas Tech University report detecting antibiotics and antibiotic resistance genes in particulate matter downwind from cattle feedyards.

The researchers set out to measure the extent to which antibiotics, antibiotic resistance genes (ARG), and ruminant-associated microbes are dispersed in the air via particulate matter (PM) derived from large scale beef cattle feedyards. They collected PM downnwind and upwind of ten beef cattle feedyards. They then extracted and quantified six veterinary antibiotics using liquid chromatography– tandem mass spectrometry (LC-MS/MS) quantified ARG using targeted qPCR and analyzed microbial community diversity using 16S rRNA amplification and sequencing.

The researchers found that airborne PM derived from feedyards facilitated dispersal of several veterinary antibiotics and microbial communities containing ARG, with concentrations downwind of the feedyards higher than those upwind. Concentrations of several antibiotics in airborne PM immediately downwind of feedyards ranged from 0.5 to 4.6 micrograms per gram (µg/g) or 0.5 to 4.6 parts per million of the PM. Microbial communities of PM collected downwind of feedyards contained ruminant-associated bacteria and were distinct when compared to upwind PM. They also found the  abundance of genes encoding resistance to tetracycline antibiotics was significantly greater in PM collected downwind of feedyards as compared to upwind.

As for the antimicrobials found, the ionophore Monensin was detected in 100 percent of PM samples downwind and upwind of feedyards, although in very low concentrations upwind. Downwind of feedyards, mean monensin concentration was 1,800 ± 370 ng/g (nanograms per gram, or parts per billion). Tylosin, a macrolide antibiotic, was detected in 80 percent of downwind PM samples downwind of feedyards with a mean concentration of 340 ± 92 ng/g PM, significantly lower than concentrations of monensin across all feedyards. Three tetracycline antibiotics (tetracycline, chlortetracycline, and oxytetracycline) were detected together in 60 percent of PM samples downwind of feedyards while oxytetracycline,  the most frequently detected of the three,  was detected in 100 percent of PM samples collected downwind of feedyards. Mean concentrations were 280 ± 170 ng/g PM tetracycline, 820 ± 220 ng/g oxytetracycline, and 970 ± 430 ng/g chlortetracycline.

The researchers also found six targeted tetracycline resistance genes were significantly more abundant in PM collected downwind of feedyards compared to upwind, and note that antibiotic resistance genes from beef cattle feedyards are of potential concern due to the possibility of lateral gene transfer among the bacterial community.

Noting that many feedyards are located in high-wind areas, the researchers conclude there is significant potential for widespread distribution of antibiotics, bacteria, and genetic material that encodes antibiotic resistance via airborne PM from feedyards.

View the abstract or complete article from Environmental Health Perspectives.