Mouths, enemies and spit
Our mouths are teeming with inhabitants of the most diverse origin. Bacteria and fungi for one, but all sorts of various-sized peptides too, each of which carry out various tasks. In fact, our mouths are like a metropolis, with its underlying complexity of continuous bonds and exchanges between its individuals and compartments. As in any society, things need to be kept balanced and regulated to avoid unrest and chaos. Likewise, the bacteria and fungi that nestle down in the nooks and crannies of our mouths must not be left to multiply unrestrained, which would only bring about a full-blown infection. This is why Nature has provided our saliva with an assortment of antimicrobial peptides, just in case things get out of hand. Histatins are antimicrobial peptides found in primate saliva. One histatin, called histatin 5 or Hst5, specifically fights off infections by Candida albicans, a yeast naturally harboured in our mouths. Hst5 does this by using crossing - unscathed - the yeast's membrane to reach the cell's cytoplasm. Hst5 then goes on to meddle with the yeast's ion homeostasis, gradually leading it to its death.
