For a little background: There's a kind of mycobacteria (yep, that's spelled right) that exists in African swamps that gets onto the pincers of a biting waterbug. When people are bitten, the bacteria gets under their skin and creates an infection, which eventually (WARNING - ICKY PART) causes their skin to rot and slough off. It's basically a flesh-eating bug, like necrotizing fasciitis, and in the past, the only real treatment has been to amputate the affected limb. It's called Buruli ulcer, and it's nasty, and the people who get it don't do well. If they survive the infection and don't have the limb amputated, they have to have extensive and messy skin grafts to repair what are essentially open wounds.
One woman, however - a French humanitarian treating people in the Ivory Coast,
Dr. Lynda Williams comes in. She's a clay mineral geochemist, and was asked to help figure out just what about the green clays stops infections. I can't possibly do her talk justice here, but I can remember a few of the highlights: It seems that the antibacterial properties of the clays - which are mostly smectites - are linked not only to a specific size fraction of the clay minerals (~200 nanometers), but to trace minerals in the clays. She went through a complicated process of testing clays with interstitial water removed, and leached clay, and pH-adjusted clay; it turns out that in the French clays, the presence of iron had something to do with the antibacterial properties. (The clay leachates, which must have contained some iron, also killed bacteria, although they weren't effective after a certain time span. I think that Dr. Williams suggested that this might have something to do with the oxidation process the iron is undergoing - there was an Eh-pH diagram involved at one point.)
Not only do the French clays seem to kill Buruli ulcer, they also go after things like E. Coli and staph - with amazing results. One of the clay samples killed 100% of the E. Coli, and most of a particularly resistant staph strain. And these aren't the only clays that do this - some clay samples Dr. Williams received from undisclosed locations in the US do the same thing. (They have somewhat different chemical properties, however, which makes the puzzle even harder to piece together.) At any rate, she and her colleagues are still examining the clays, doing various kinds of geochemical analysis and SEM/TEM imaging to try and figure out the specific factor - or combination thereof - that makes them valuable as antibacterial agents.
And the best part? The clays are derived from altered volcanic rocks. That's right - volcanoes are saving lives! (Well, really indirectly and a long time after the fact.)*
I don't know about you all, but if I ever get a staph infection from a hospital visit, I'm definitely asking for a mud bath.