December 12, 2013
Researchers Find Staph Bacteria Deep Within The Nose, In Inverse Relationship With C. Pseudodiphtheriticum
April Flowers for redOrbit.com - Your Universe Online
Staphylococcus aureus, which is a major bacterial cause of disease, has been found in previously overlooked sites deep within the nose, according to a new study from Stanford University School of Medicine.
"About one-third of all people are persistent S. aureus carriers, another third are occasional carriers and a remaining third don't seem to carry S. aureus at all," said David Relman, MD, the Thomas C. and Joan M. Merigan Professor and a professor of medicine and of microbiology and immunology. Relman, who is also chief of the infectious disease section at Veterans Affairs Palo Alto Health Care System, collaborated with Miling Nan, PhD, a graduate student in Relman's lab at the time the experiments were performed.
"The nose has been long known to be a primary reservoir of S. aureus," Relman said. S. aureus is also abundant on the skin, with a special affinity for the armpits and groin. The vast majority of the time, however, it does little or no harm to its host. Relman adds that no one has figured out if it is serving any positive purpose.
However, if the skin is compromised – for example, by a wound or a medical incision or catheter placement — S. aureus can enter the bloodstream and cause serious, or even life-threatening, problems such as sepsis, pneumonia or infection of heart valves. Nearly half of all strains of S. aureus are resistant to a family of antibiotics that include methicillin. More than 80,000 severe methicillin-resistant S. aureus infections, as well as more than 11,000 related deaths, occurred in the United States alone in 2011. There were also a much higher number of less-severe infections.
"Not everyone who carries S. aureus gets sick," Relman said. "When they're out walking the streets and otherwise healthy, attempts to rid them of their S. aureus are not necessary, and even sometimes futile. But once a carrier enters a hospital with an underlying illness or a weakened immune system or a high likelihood of undergoing skin-penetrating procedures, S. aureus carriage is a major liability."
There are existing regimens for eliminating S. aureus on people's skin or in their noses, but they are rigorous and somewhat tedious, and it can take only a matter of weeks or months before the bacteria repopulate those who are susceptible. The new study, published in Cell Host & Microbe, offers a possible reason why.
Twelve healthy subjects were recruited for the study, which was funded in part by a National Institutes of Health (NIH) Pioneer Award. They were brought to a Stanford ear, nose and throat clinic run by Peter Hwang, MD, professor of otolaryngology. The team used special instrumentation, which allowed them to guide tiny swabs to precise locations within the nose. Three specific areas were sampled. The first location, the anterior naris, was the most accessible, making it also the most well-studied. The anterior naris is a relatively dry, skin-like patch of tissue located near the nostril. The middle meatus was the second location - a warmer, wetter, mucus-producing fold found about midway up the nasal cavity. The sphenoethmoidal recess, the third site, is situated deep within the cavity near the roof of the nose and, like the middle meatus, warm, wet and mucosal.
The presence or absence of S. aureus at one nasal site was found to be typically correlated with its presence or absence at the other two. The researchers suggest that one implication of their findings: If a person's anterior naris is carrying the bacteria, the upper mucosal areas probably are, too. This deeper infection could explain why efforts to banish S. aureus have so often proven short-lived. Current decolonization procedures focus largely on the bacteria on the anterior naris—leaving deeper reservoirs intact.
Three additional key findings were made. The first discovery was that the relative abundance of S. aureus was inversely related to that of another bacterial species, C. pseudodiphtheriticum. If one bacteria was found at high levels, the other was present at low levels or absent all together. a research associate in Relman's lab, Sunje Pamp, PhD, put the two bacterial species on an agar plate to scrutinize this relationship further, and found that C. pseudodiphtheriticum strongly blocked the growth of S. aureus.
C. pseudodiphtheriticum most likely produces and secretes something — perhaps a protein, or possibly a small molecule — that is responsible for the failure of S. aureus to thrive. Pamp said that if such a substance could be identified, it could provide clues to the development of new compounds to prevent or treat S. aureus infections.
The second key finding was that microbial communities in those patients who harbor S. aureus differed in other ways from those in patients who don't. The researchers say that this means S. aureus could alter its environment to make it more or less hospitable to other microbes. Another possibility is that different microbial communities are more or less hospitable to colonization by S. aureus. If this is the case, based on resident nasal microbes, it might be possible to predict which patients are most likely at high risk of a S. aureus infection - even if they're not currently carrying it — and monitor and treat them accordingly. Such procedures could be avoided for patients found to be at a lower risk.
The third finding involves the middle meatus and the sphenoethmoidal recess—the two deeper, wetter mucosal regions of the nose. In these areas, microbial communities were similar to each another, but quite distinct from the one inhabiting the more accessible and better-studied outer site, the anterior naris, suggesting that currently routine methods of sampling the nasal cavity for microbe-research purposes may be yielding skewed results.