Microbiological characterisation of southern African medicinal and cosmetic clays

The effects of traditionally used medicinal and cosmetic clays in southern Africa on selected microorganisms were studied using microbiological media. The clay pH, microchemical composition, kind of associated microorganisms and antimicrobial activity of clays against test microorganisms were determined. The clays contained varying numbers of microorganisms which ranged from 0 up to 105 CFU/g. Clay pH ranged from 2.3-8.9. Neither Escherichia coli, nor other faecal coliforms were detected. Clays of pH value of <4 displayed antimicrobial activities. Clays which were active against test microorganisms had Na(2)O, Al(2)O(3), SiO(2), SO(3), CuO or Cl(2)O as major components. Microbial activity of clays was attributed mainly to low pH but cations such as Cu, Al, S or Cl and various anions might have contributed to the microbicidal effects. No antimicrobial activity was established for many of the clays commonly used in the treatment of common ailments of microbial origin.