Antibiotic Resistance and Movement of Animals between Farms have Facilitated the Spread of MRSA in Danish Pigs

Nov. 13, 2018

Washington, DC - November 13, 2018 - During the last decade, a new form of the bacterium known as methicillin-resistant Staphylococcus aureus (MRSA) has become widespread in the Danish pig population from where it spreads to people, resulting in an increasing number of human infections.

In a new study published today in mBio Danish and U.S. researchers have shown that the current surge of MRSA in pigs is caused by expansion of 3 successful lineages, which are particularly resistant to antibiotics that are used to treat sick pigs. The study also revealed that pig movements have facilitated the spread of these lineages.

Marc Stegger, who co-led the study, says: ”Our study shows that there were many different MRSA lineages present in the Danish pig population 10 years ago, but none of them were very successful. At some point, 3 of these lineages began to spread quite fast, and it is those lineages that are responsible for the high rate of positive pig farms that we see today.”

The other co-leader of the study, Jesper Larsen, continues: ”The 3 lineages are particularly well adapted to a life in a pig farm. Besides being methicillin-resistant, they are also resistant to those antibiotics that are used most frequently in Danish pig production.”

The results also show that the same lineages are responsible for the increasing number of infections, particularly in pig farmers but also in people with no contact with pigs.

“This spread to people without pig contact is worrisome, because it might affect elderly and immune-compromised individuals who have a higher risk of developing serious and even life-threatening infections,” says Jesper Larsen.

Raphael Sieber, first author of the article in mBio, analyzed whether animal movements could explain the rapid spread of MRSA in the Danish pig population. ”The results show that movement of animals has played an important role in the dissemination of MRSA between pig farms in Denmark. But it’s important to stress that our findings don’t rule out other ways of transmission, for example via people or through the environment,” says Sieber.

Anders Rhod Larsen, leader of the National Reference Laboratory for Staphylococci in Denmark, sums up: ”On the positive side, the study demonstrates the value of monitoring MRSA and other antibiotic-resistant bacteria in food animals and humans. But from a public health perspective, it shows the importance of finding new ways to reduce the prevalence and spread of antibiotic-resistant bacteria in food animals.”

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Author: ASM Communications

ASM Communications
ASM Communications staff.