Low Prevalence of Penicillin Resistance in Staphylococcus chromogenes on Vermont Organic Dairy Farms

Antimicrobial resistance has become of increasing concern around the world in a wide range of industries and disciplines, as it has come to threaten our ability to treat and cure bacterial infections in humans and other animals. The impacts of this problem include welfare issues and economic losses, as well as risks to public and environmental health. Resistant bacteria can also spread through food products making this a significant One Health issue. Antimicrobial resistance has become especially important in the context of treating bovine mastitis in the dairy industry. In this project, we adapted a high throughput agar dilution antimicrobial susceptibility testing method following CLSI guidelines. The overall prevalence of resistance to penicillin among Staphylococcus chromogenes isolates collected from Vermont organic dairy farms was determined to be relatively low, 29% of 105 isolates screened. However, there is potential for even low resistance in this species to have a devastating effect on dairy farms due to the ability of bacteria to share genetic information through horizontal gene transfer. Steps can be taken to reduce the presence of resistant populations, such as testing the susceptibility of an individual infection to determine the best drug to treat the infection. Further research is also needed to determine alternative treatment options for bacterial infections, including mastitis, to reduce the overall use of antibiotics and the subsequent selection for resistance in future generations