Scientists Investigate a Newly Emerging Staph Strain

Using genome sequencing and household surveillance, National Institutes of Health (NIH) scientists and their colleagues from Columbia University Medical Center and St. George's University of London have pieced together how a newly emerging type of Staphylococcus aureus bacteria has adapted to transmit more easily among humans. Their new study underscores the need for vigilance in surveillance of S. aureus.

A methicillin-resistant S. aureus (MRSA) strain known as livestock-associated (LA)-ST398 is a cause of severe infections in people in Europe who have close contact with swine, but the bacterium does not transmit well from person to person. More recently, a variant of LA-ST398 that presently is susceptible to methicillin has emerged as a significant cause of community-associated infections in several countries, including the United States, Canada and China. The new strain primarily infects the skin and soft tissue, but it can cause more severe disease.

Based on samples from 332 households in northern Manhattan, New York, scientists have determined that this new strain, named ST398-NM, efficiently transmits from person to personin contrast to the transmission characteristics of the livestock-associated strain.

By analyzing and comparing the genomes of LA-ST398 and ST398-NM, the study, led by Anne-Catrin Uhlemann, MD, PhD, at Columbia, charted several ways in which the bacterium has adapted to its hosts. For example, they learned that the human-adapted strain (ST398-NM) contains human-specific immune evasion genes, whereas the livestock-adapted strain does not. They also found that ST398-NM adheres well to human skin, thus increasing its ability to colonize and infect people.

The study authors say it is possible that the ST398-NM strain emerging in northern Manhattan could acquire genes making it resistant to methicillin. Scientists at the NIH National Institute of Allergy and Infectious Diseases and their colleagues plan to continue global surveillance of ST398, paying close attention to its molecular adaptations. Their work promises to inform the development of new diagnostic and surveillance strategies against this emerging pathogen.

This study on the human-adapted variant of ST398 strain complements a study that a different group of scientists published in mBio on Feb. 21. That study, also supported by NIH, focused on the evolution of the ST398 strain in livestock, including the effect of antibiotic use. Lance Price, PhD, and Paul Keim, PhD, at the Translational Genomics Research Institute in Flagstaff, Ariz., led that study with colleagues from around the world.