Abstract: Antibiotics are commonly used in the dairy industry to prevent and treat disease in dairy cattle. Previous research has shown that manure from treated cattle influences the soil microbial community and functioning of ecosystems. Increase use of antibiotics has also led to an increase in antibiotic resistance in the environment showing that there is a need for alternative treatments. One alternative that has recently been introduced is a product called AHV. AHV mode of action is to inhibit quorum sensing in disease causing bacteria and inhibits biofilm formation. The effects of AHV, if excreted into the environment, is unknown. We compared two antibiotics that are commonly used in the dairy industry and the AHV product. For 11 weeks, weekly additions of the antibiotics and AHV product were added to soil collars located at two field sites, one in North Carolina and one in eastern Washington. There were high and low concentrations of solutions. Soil respiration measures we measured weekly. At the end of the field experiment, samples were taken of DNA sequencing and community analysis of bacterial and fungal communities, microbial biomass, and substrate induced respiration. qPCR was also performed to analyze chances in the fungal: bacterial ratios. Results show that AHV impacts both the bacterial and fungal community at the WA site and also impacts the fungal community in NC site. Results also show that at the NC site the active microbial biomass decreased with all of the antibiotic and AHV treatments. However at WA site Low AHV concentration showed an increase in active microbial biomass while the higher concentration showed a decrease. Fungal:bacterial ratios were also impacted by AHV and the antibiotics at both high and low concentrations. These results have shown that the impacts of AHV are similar to antibiotics if unmetabolized products are excreted out into the environment. The impacts may also be land-use dependent. Further studies need to be done to see what the exact impact of unmetabolized AHV is the soil microbial community.
