Golden staph lives quietly in millions of noses until it finds an opening
A large share of people carry Staphylococcus aureus in their nostrils or on their skin without ever noticing. The same golden-coloured bacterium is among the five most common causes of hospital infections. Penicillin once cured it reliably, but by the end of the 1940s resistance had already spread through its populations.
The name joins Greek for grape-cluster berry with Latin aureus, golden, describing both how the round cells bunch under a microscope and the large yellow colonies they form on blood agar. The Scottish surgeon Alexander Ogston named the genus in 1880 after spotting clustered bacteria in pus from an abscess he was operating on. In 1884 the German scientist Friedrich Julius Rosenbach distinguished S. aureus from its paler relative, then called Staphylococcus albus. Before the 1940s, most infections with it were fatal.
Estimates of carriage vary. One puts long-term carriers at 21 to 30 percent of people; another describes roughly half the population as carriers, some continuously and others on and off. Because it lives harmlessly in the nose, gut lining and skin but can turn dangerous when barriers are breached, biologists class it as a pathobiont. It ranges from causing pimples and boils to pneumonia, endocarditis and sepsis, and it builds stubborn biofilms on medical implants.
Its genome changes quickly thanks to mobile elements such as plasmids, transposons and bacteriophages, which pass new traits between cells. Yet it also has brakes. A restriction system called Sau1 chops up foreign DNA, allowing exchange within a lineage but blocking it between the ten dominant human lineages. Mutations that disable its master virulence regulator, AGR, can make strains fitter, a trade that swaps lower virulence for greater drug resistance.
The cost is large. In the United States, MRSA infections alone are estimated at over 3.2 billion dollars a year and nearly 20,000 deaths, more than HIV/AIDS, Parkinson's disease or homicide. Around 500,000 hospital patients there contract staphylococcal infections annually, and each MRSA case adds roughly 6 to 11 days to a hospital stay.
Source: Staphylococcus aureus
