Exploration of aerosolization of indoor bacterial communities in relation to antibiotic usage on swine farms

Airborne bacteria present on swine farms can adversely affect the health of pigs and livestock workers. However, many studies have intensively investigated the characterization of microbiota in pig feces and aerosol samples without considering the stepwise aerosolization process and the impact of antibiotic usage. This study aimed to comprehensively explore the bacterial communities of feces, surfaces, and bioaerosols during the aerosolization process and assess variations in bacterial resistance to antibiotic usage on swine farms. In this study, 32 samples were collected from six swine farms and categorized as high- or low-antibiotic-use farms based on the European Union’s defined daily dose for animals (DDDvet). Fecal samples had significantly higher alpha diversities, followed by aerosol and surface samples (p <0.05). However, no alpha diversity indices showed significant differences according to antibiotic usage. Beta-diversity analyses revealed significant differences between bioaerosols and fecal samples depending on antibiotic usage. Notably, Staphylococcus spp., Corynebacteria spp., and Enterococcus spp. were significantly more prevalent in bioaerosols from high-antibiotic-use farms than in fecal samples (p <0.05), indicating a potentially high level of antibiotic-resistant bacteria and the spread of antibiotic resistance among pigs and workers. For source tracking analysis, over 50 % of the aerosol samples contained bacteria from fecal and surface sources, contributing to the aerosol microbiome. These findings highlight that the aerosolization of fecal and surface particles within swine farms distinctly affects airborne bacterial communities. Our results showed that different antibiotic uses notably affected indoor bacterial communities and antibiotic resistance during stepwise aerosolization in swine farms. • High antibiotic use causes higher levels of bacteria in bioaerosols than in feces. • Aerosolization from feces to surfaces to aerosols promotes bacteria transmission. • Higher antibiotic usage increased the resistance of S. aureus and E. faecalis.