067: MRSA in agriculture and zombie epidemiology with Tara C. Smith

Tara C. Smith discusses her work uncovering ties between agriculture and methicillin-resistant Staphylococcus aureus (MRSA). Her studies have found MRSA on and around pig farms, on animal handlers, and even in packaged meat in the grocery store. She also talks about using zombies as an allegory for infectious disease outbreak preparedness.

Links for this episode

Tara C. Smith website

Aetiology Blog on Science Blogs Network

Outbreak News Interview with Smith on her work communicating the science around vaccines and fighting anti-vaccine sentiments.

Smith’s collected writings on Ebola and emerging infectious diseases

Zombie Infections: Epidemiology, Treatment, and Prevention in the British Medical Journal

History of Microbiology tidbit: Thomas Jukes’ 1968 Letter to the British Medical Journal and 1997 Recollections in Protein Science.

Julie’s biggest takeaways:

MRSA transitioned from primarily hospital-acquired to community-acquired infections in the 1990s. In the early 2000s, MRSA strains associated with livestock farming emerged in Europe. Smith’s group was the first to identify agriculture-associated MRSA strains in the United States.

Tara found MRSA on the very first farm in which she and her colleagues looked for MRSA.

The MRSA strain ST398 appears to have originated in people as MSSA then moved to livestock, where the strain acquired some antibiotic resistance related genes. This is because zoonotic diseases are a two-way street and microbes can pass from people to animals, as well as passed from animals to people.

Many factors may contribute to MRSA contamination of consumer meat products: for one, MRSA in farms is aerosolized and the same may be true in meat processing facilities. People can also be colonized and spread from workers to products. It’s likely a mixture of strains from farms and strains from people working in the packing plants.

Farms that raise animals without antibiotics were not positive for MRSA. Processing these animals at plants where conventional animals are raised creates potential for cross-contamination, however.

Prophylactic and treatment applications of antibiotics are still allowed for livestock, but antibiotics used for growth promotion purposes were phased out in January 2017.

Featured quotes:

“I was in Iowa, the #1 pig-producing state. We started looking for MRSA + found them on the very 1st farm we sampled”

“When we think of zoonotic diseases, usually we think of microbes that come from animals to people, but there can be bidirectional transmission. It’s definitely not just a one-way street

“That it doesn’t cause disease in pigs made S. aureus invisible to people studying its epidemiology for quite a while”

“Our biohazard people probably hated us because we had pounds and pounds of meat products we were checking” for MRSA

"S. aureus is definitely not the only one - there’s lots of bacteria that are affected by use of antibiotics on farms”

“Everything zombies now is a virus!”