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

Christidis, G.E. and Knapp, C.W. and Venieri, D. and Gounaki, I. and Elgy, C. and Valsami-Jones, E. and Photos-Jones, E. (2020) The interweaving roles of mineral and microbiome in shaping the efficacy of archaeological medicinal clays. Journal of Ethnopharmacology. ISSN 0378-8741

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    This paper addresses the antibacterial bioactivity of six samples of ‘stamped’ archaeological medicinal earths (Terra Sigillata, Lemnian and Silesian) in the collection of the Pharmacy Museum of the University of Basel, dating to 16th-18th century, and asks the question what makes some earths more antibacterial than others. We assess here the purported efficacy of these clays by examining the contribution to bioactivity of their constituent parts, i.e. the mineral, the elemental, the active nano-sized particles, as well as the organic component (derived from bacterial and fungal microbiome). The paper suggests that the organic component represents the key factor in driving the difference in antibacterial activity between the medicinal earths studied here. The presence of Talaromyces spp, a fungus of the family of Trichocomaceae (order Eurotiales), historically associated with Penicillium, has been identified in two of the three samples of Lemnian Earth. Of the three Silesian Earths, only one was bioactive and Aspergillus sp. was the fungus identified within. Differences in antibacterial action between MEs and natural clays appear to be driven by a fungal component; but natural clays spiked with boron or aluminium can be equally antibacterial without needing a fungal component. The response by microorganisms to growth-related stress by releasing secondary metabolites has potentially far-reaching implications for the bioactivity of clays, with (latent) medicinal applications.