Summary
This study assesses the persistence of antibiotic resistance genes (ARGs) in a cattle backgrounding environment (i.e. the entirety of environment surrounding the cattle, not just where they physically reside) prior to and two years following the operation’s cessation in Bowling Green, Kentucky. Measuring over the unit’s feeding versus grazing areas, the study finds that higher concentrations of bacteria and ARGs in the feeding and watering area indicate that nutrient supply from concentrated fecal deposition plays a significant role in propagating these bacterial genes. ARG concentrations were reduced in the two years following removal of cattle, but not statistically significantly. Strengths of the study include controlling for soil nutrient levels and yearly sampling time point variations. Although the qPCR test has its strengths, a limitation is the near impossibility of measuring all ARGs in a given ecosystem, leaving room for selection bias. Implications of these findings include a need to reduce concentrations of animals during feeding and watering as it promotes bacterial transmission. Additionally in reference to post-cessation, once ARGs are present, they could persist in the soil environment for years even in the absence of animals. As the rate of demand for animal products grows, sharp increases in antibiotic use in food animals are expected. The antibiotic traces found in animal manure have potential future implications for human and animal health, given their ability to enrich antibiotic resistant bacterial pathogens.
Confined animal feeding operations can facilitate the spread of genes associated with antibiotic resistance. It is not known how cattle removal from beef cattle backgrounding operation affects the persistence of antibiotic resistance genes (ARGs) in the environment. We investigated the effect of cessation of beef cattle backgrounding operation on the persistence and distribution of ARGs in the beef cattle backgrounding environment. The study was conducted at a pasture-feedlot type beef cattle backgrounding operation which consisted of feeding and grazing areas that were separated by a fence with an access gate. Backgrounding occurred for seven years before cattle were removed from the facility. Soil samples (n = 78) from 26 georeferenced locations were collected at the baseline before cattle were removed, and then one year and two years after cattle were removed. Metagenomic DNA was extracted from the soil samples and total bacterial population (16S rRNA), total Enterococcus species and class 1 integrons (intI1), and erythromycin (ermB and ermF), sulfonamide (sul1 and sul2) and tetracycline (tetO, tetW and tetQ) resistance genes were quantified. Concentrations of total bacteria, Enterococcus spp., class 1 integrons, and ARGs were higher in the feeding area and its immediate vicinity (around the fence and the gate) followed by a gradient decline along the grazing area. Although the concentrations of total bacteria, Enterococcus spp., class 1 integrons and ARGs in the feeding area significantly decreased two years after cattle removal, their concentrations were still higher than that observed in the grazing area. Higher concentrations over two years in the feeding area when compared to the grazing area suggest a lasting effect of confined beef cattle production system on the persistence of bacteria and ARGs in the soil.