INFECTIONS
December 24, 2010

Staph Prefers People

Scientists discover why staph bacteria prefer humans over other animals: it's all in the blood.

Scientists have long puzzled over the fact that staph infections seem to prefer humans over other animals. Even more perplexing, the bacteria can live peaceably within the nasal passages of some people, never causing harm, while it can cause a deadly infection in other people. Now, researchers are making big strides in understanding just why this is the case.

The bottom line is that not all hemoglobin is created equal.

Staphylococcus aureus (a.k.a. staph bacteria) need iron in order to multiply. Where do the bacteria get their iron? They "steal" it from the hemoglobin in the red blood cells of their hosts — but they much prefer to get it from humans over other types of critters.

In the current study, the research team purified hemoglobin from mice and humans and offered it to staph bacteria that were deprived of iron. The iron-hungry bacteria chose to bind themselves to a protein in the hemoglobin from humans instead of mice. While they were able to use mouse hemoglobin, it was just easier for them to use the stuff from humans. Next, the researchers studied a strain of mice who possessed both regular mouse hemoglobin and human hemoglobin and compared them to normal mice. As one would expect, staph bacteria preferred the mice with both kinds of hemoglobin — in fact, these mice had many times the number of bacteria living in them than regular mice did.

Do these findings have any relevance to understanding how staph infections work in humans? Absolutely. The bottom line is that not all hemoglobin is created equal.

The team is currently working on how the genetic sequence of hemoglobin varies in different people to lead to some being more susceptible to infection than others. By looking at samples from a DNA database at Vanderbilt University, where the current study was conducted, author Eric Skaar, Ph.D., M.P.H. and his team will be able to determine whether people who were infected with staph tend to have a certain genetic sequence.

Skaar told TheDoctor in an interview, "[i]f this were found to be the case, we could then begin screening for individuals that are at a high-risk for Staph infections based on their hemoglobin sequences. This is an exciting example of applying personalized medicine to infectious diseases in an effort to improve patient outcomes."

The study was published in the December 16, 2010 issue of Cell Host and Microbe.

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