Antibiotic-resistant strain on MRSA found in pigs is capable of rapidly spreading to humans

A new study found that a highly antibiotic resistant strain of the superbug, methicillin resistant Staphylococcus aureus (MRSA), which has emerged in pigs and other livestock over the last 50 years, has the potential to adapt to human hosts.

The study, published in the journal eLife, was led by Marta Matuszewska, a PhD candidate at the Intercollegiate Faculty of Biotechnology UG & MUG in Gdańsk, Poland, and Gemma Murray, PhD, of the Wellcome Sanger Institute in Hinxton, England. Matuszewska and Gdańsk focused their study on the MRSA strain CC398 which is commonly found in pigs in Europe, most likely due to widespread antibiotic use, according to the authors.

“Historically high levels of antibiotic use may have led to the evolution of this highly antibiotic resistant strain of MRSA on pig farms,” said Murray.

According to the study, the ability for CC398 to be transferred from livestock to humans is associated with three mobile genetic elements in the MRSA genome. These genetic elements give the MSRA the characteristics that allow it to be antibiotic-resistant and able to invade the human immune system. For their experiment, researchers reconstructed the evolutionary history of two of these genetic elements named Tn916 and SCCmec.

The study’s results showed that Tn916 and SCCmec are present in CC398 even when it jumps to humans. In addition, researchers found another genetic element that allowed CC398 to invade the human immune system known as φSa3, repeatedly disappeared then reappeared in human-associated CC398 and livestock-associated CC398.

Although cases of CC398 associated with livestock represent a small portion of cases of CC398 in humans, researchers said that these cases are increasing, and the issue should be taken seriously.

“Understanding the emergence and success of CC398 in European livestock - and its capacity to infect humans - is vitally important in managing the risk it poses to public health,” said Lucy Weinert, PhD, of the University of Cambridge’s department of veterinary medicine and senior author of the paper.