Infection beats skin defense mechanism

Interestingly, USA300 now constitutes almost 98 percent of skin and soft tissue infections in hospitals, significantly surpassing the infectious rates of other bacterial strains. The sudden surge of USA300 in North America has puzzled scientists, as an increase in virulence could not fully elucidate the reason behind its vast replacement of other bacterial species. Instead, scientists looked into the reasons behind how this species was transmitted from community to community at an astonishingly efficient rate.

The answer was found on the palm of their hands. Researchers from University of North Carolina School of Medicine discovered that the chunk of unique genes in USA300 conferred a certain robustness to the strain that allowed it to survive on skin for a longer period than normal.

Typically, our skin possesses certain physical and immunological traits that allow us to fight infectious diseases before they enter our bodies.

First and foremost, the epidermis of our skin serves as a tight barrier that keeps bacteria, fungi, and viruses out of our bodies. While the infectious agents continue to spread around our skin, another of our defense mechanisms, sweat, can create an adverse and rather acidic environment for the infections. Additionally, molecules like arginine contribute to our inflammatory response.

Arginine, one of the twenty standard amino acids, is converted to orthinine and then to polyamines, an

end product that is crucial in the tissue regeneration process. While polyamines are found in almost all living organisms, S. aureus is ironically very susceptible to the compound, and is easily killed at physiological concentrations of polyamine.

This susceptibility was not observed in USA300, however, allowing the strain to survive longer periods on the skin

and spread to other locations. They gained this ability by expressing a unique protein called Spm/Spd acetyltransferase, an enzyme that acetylates polyamines to suppress their function.

USA300 circumvents our defenses in another fundamental way. The cluster of genes identified in this species may confer tolerance against the acidity of our skin. Typically, the pH of our skin is around 5, due to the lactic acid we produce in sweat. However, USA300 may produce ammonia that neutralizes the acid, creating a more hospitable environment for the strain.

Unfortunately, due to lapses in hand washing regulation and enforcement, the spread of disease continues to sicken patients within the walls of hospitals. Don’t let these bacteria scare you though; washing your hands is the most effective way to prevent the transmission of infections—even USA300!