This week is World Antibiotic Awareness Week and USDA’s Agricultural Research Service (ARS) remains committed to using a “One Health” approach in conducting research that will identify solutions to help prolong the usefulness of a very precious resource—antibiotics. For example, ARS research includes understanding how common production practices might impact antimicrobial resistance and understanding whether certain animal pathogens may be a public health concern. Methicillin-resistant Staphylococcus aureus (MRSA) is one bacteria type that is a public health concern because of its resistance to some antibiotics which can make it difficult to treat. MRSA has been found in livestock – mainly in swine. One particular MRSA strain, called ST5, has raised additional public health concerns because it is a major cause of human infections globally.
To address these public health concerns, ARS conducted research to determine whether production practices like using in-feed zinc as an antidiarrheal agent contribute to the emergence and spread of MRSA in U.S. swine populations, and if ST5 bacterial isolates from swine and from humans are genetically related.
ARS data demonstrated that applying zinc in feed does not play a role in the prevalence of livestock-associated MRSA ST5 in the U.S. swine population. More importantly, ARS found that ST5 isolates from agricultural sources are genetically distinct and separate from clinical MRSA ST5 isolates obtained from human clinical settings. Specifically, isolates from agricultural sources were found to be extremely similar to each other within farms and lacked genes typically carried by human isolates. Collectively, ARS data indicate that livestock-associated MRSA and clinical MRSA ST5 isolates are genetically distinct and transmission and/or genetic exchange between them is not currently occurring based on the findings in this study.
ARS researchers are continuing to build on these results to further determine the distribution and impact of livestock-associated-MRSA ST5 outside of the livestock setting. As we celebrate World Antibiotic Awareness Week, we remain committed to a “One-Health” approach to prevent, not just react to, complex public and animal health issues. The information gained from these studies is important to our overall understanding of animal pathogens, and any potential risks to public health.
