The interweaving roles of mineral and microbiome in shaping the antibacterial activity of archaeological medicinal clays

Research output: Contribution to journalArticlepeer-review


  • G. E. Christidis
  • C. W. Knapp
  • D. Venieri
  • I. Gounaki
  • E. Photos-Jones

Colleges, School and Institutes


Ethnopharmacological relevance
Medicinal Earths (MEs), natural aluminosilicate-based substances (largely kaolinite and montmorillonite), have been part of the European pharmacopoeia for well over two millennia; they were used generically as ‘antidotes to poison’.

Aim of the study
To test the antibacterial activity of three Lemnian and three Silesian Earths, medicinal earths in the collection of the Pharmacy Museum of the University of Basel, dating to 16th-18th century and following a prescribed methodology (see graphical abstract). To assess and prioritize the parameters which drive their antibacterial activity, if present.

Materials and Methods
The medicinal earths are characterised chemically (ICP-MS), mineralogically (both bulk (XRD) and at the nano-sized level (TEM-EDAX)); their organic load (bacterial and fungal) is DNA-sequenced; their bioactivity (MIC60) is tested against Gram-positive, S. aureus and Gram-negative, P. aeruginosa. The bioactivities (MIC60) of natural clays from Lemnos, N Aegean, and Melos, SW Aegean, spiked with Al, Fe, Ti, and B are also tested against the same pathogens for purposes of comparison.

Not all MEs are antibacterial. Of the three Lemnian Earths, only two are antibacterial against both pathogens; of the Silesian Earths only one is mildly antibacterial and against Gram-negative pathogen, only. The bioactivity of the two Lemnian Earths is driven by a fungal component, Talaromyces spp, a fungus of the family of Trichocomaceae (order Eurotiales), historically associated with Penicillium. This fungus was not found in the natural Lemnos clays examined here. Comparable bioactivity with that of the two Lemnian Earths can be obtained from kaolinitic/smectitic clays spiked with B or Al.

It is not known whether archaeological medicinal earths were used as antibacterials, over and above as absorbants of toxins. Nevertheless, some display antibacterial properties which appear to have their origins in an organic (fungal) load.


Original languageEnglish
Article number112894
JournalJournal of Ethnopharmacology
Early online date26 Apr 2020
Publication statusE-pub ahead of print - 26 Apr 2020


  • Medicinal earths, Lemnian, Silesian, Bioactivity, Talaromyces spp, Mineral, Nanoparticle, Antimicrobial resistance