The human body plays host to many microbes, and the communities that these microorganisms form are known as microbiomes. There are some fungi, or yeast that are normal parts of the skin microbiome. Researchers have now identified an antimicrobial molecule made by yeast that live on human skin. They determined that it had powerful effects against Staphylococcus aureus, a bacterium that has many forms, some of which are harmful while others can cause serious infection. This work may help create new drugs to treat staph infections, which are becoming increasingly resistant to antibiotics. The findings have been reported in Current Biology.
It's been estimated that around 33% of poeple carry S. aureus bacteria in their nose, which is where these microbes tend to live. Usually, these microbes stay there harmlessly. But around 2% of people carry Methicillin-resistant Staphylococcus aureus (MRSA), which has the potential to cause serious illness, if it gets into cells to cause an infection.
Malassezia is a yeast that is often found on human skin, and it can take up fats from the skin to generate fatty acids. These hydroxy fatty acids, which are made from lipids on human skin, have antibacterial effects. The fatty acids act like a detergent and can rip the membranes of staph bacteria open, killing the bacterial cells.
When the staph levels got very high, however, the antimicrobial effect was overcome, and the staph was eventually able to evade the effects of the bacterial fatty acids, and survive them.
The researchers took note of these fatty acids by studying human skin samples from volunteers; they do not have this antimicrobial impact when the yeast is grown in the lab.
"I think that's why in some cases we may have missed these kinds of antimicrobial mechanisms, because the pH in the lab wasn't low enough. But human skin is really acidic," explained first study author Caitlin Kowalski, a postdoctoral researcher at the University of Oregon.
Kowalski noted that Malassezia yeast often dominates the human skin microbiome. And though it has been associated with dandruff and eczema, it's usually a harmless part of the skin microbiome. It is so tailored to the skin environment that it won't produce fatty acids unless it has access to oils from the skin.
There is still a lot to learn about the skin microbiome, added Kowalski. The gut microbiome is known to modify or produce certain molecules, but we don't know much about the bioactive compounds that are made by the mirobes on skin.
Additional work showed that resistant bacteria had acquired a mutation in a stress response gene. Mutations like this have been found in staph strains collected from infected patients. It highlights how a bacteria can use its interactions with the environment, or other microbes, to gain resistance to drugs.
Sources: University of Oregon, Current Biology
