After the study linking MRSA in livestock to antibiotic use from last week, MRSA makes another appearance in mBio, but this time the focus is on hospital-acquired infections. A human-specific, tetracycline-sensitive strain of Staphylococcus aureus (methicillin-sensitive S. aureus, or MSSA) is becoming an increasing problem in health care settings, and it is closely related to the MRSA strains called ST398, which favor livestock and farm workers.
Uhlemann et al. founded their study on one troubling observation: the emergence of this ST398 MSSA strain in households in Northern Manhattan, a region well-known for its low density of livestock farms. Unlike their livestock-associated relatives, however, MSSA isolates of the ST398 lineage are easily transmissible between humans, a fact that is making them problematic in hospitals. ST398 MSSA is also well-adapted to the human host, deploying a bevy of mobile genetic elements, surface adhesins, and the ability to adhere to cells in human skin called keratinocytes. The human ST398 MSSA is now apparently spreading independent of animal contact, causing conditions that range from soft tissue infections to invasive bloodstream infections, but it is also a benign resident of nasal tissues and household surfaces.