Archaeological medicinal earths as antibacterial agents: the case of the Basel Lemnian sphragides

Abstract

This paper presents the scientific investigation of three Lemnian sphragides (terra sigillata, stamped earth), a famed medicinal clay in antiquity, dated to the sixteenth–seventeenth centuries, and presently in the Museum for the History of Pharmacy, University of Basel. The three specimens are compared with clays from the purported locality of its extraction, at Kotsinas, NE Lemnos, Greece. The study suggests a local origin for the Basel samples; it also demonstrates, for the first time, that the three Lemnian sphragides have a significant antibacterial effect against Staphylococcus aureus, a common Gram-positive pathogen, but have no such effect against Pseudomonas aeruginosa, a Gram-negative microorganism. Clay samples from the purported locality of extraction showed no antibacterial effect against S. aureus. Subsequent analysis with ultra-performance liquid-chromatography mass spectrometry (UPLC-MS) revealed the presence of organic constituents in one sphragis which were absent from a sample of modern clay. A fungal secondary metabolite is proposed here as the active ingredient but other factors may also play a role. The ongoing investigation into the bioactivity of some medicinal clays might aid in the re-evaluation of Belon's statement included at the start of this paper, namely, that the Lemnian earth worked only because people in the past wished it to work.

Bridging the Gaps: Bole and Terra Sigillata as Artefacts, as Simples and as Antibacterial Clays

“…Lemnian Earth 700.18 (yellow grey) contained 66% montmorillonite, 18.1% illite, 6.9% quartz, 9% albite. Of the three, it is 700.17 that is most the similar to 01405, being kaolinite-rich [15]. It is noteworthy that the medicinal earths examined in this study are essentially smectite free.…”

“…This is because as archaeological artefacts they have a long history of use and associated efficacy. Our work over the last few years has been dedicated to the investigation of the antibacterial properties of some medicinal earths of the Aegean, like Samian Earth [33] and Lemnian Earth [15,16]; also clay-iron oxides composites (miltos) [26], as well as alunogen and alunite with kaolinite minerals [34]. For example, we demonstrated that antibacterial properties of Samian Earth may have been attributed to its smectite being naturally enriched in Boron [33].…”

“…A third sample of Lemnian Earth 700.4 (white) (Figure 1h) contained 65.2% dolomite, 9.9% illite, 17.3% kaolinite, and 7.6% quartz [15]. Sample 700.4 is similar to 01277 despite the latter being more yellow than white; this is presumably on account of small quantities of jarosite and possibly of trace amounts of goethite, the abundance of which is below the detection limit of the method.…”

“…This was the red earth 01405, which is presumed be an Armenian bole. We have compared this bioactive sample with bioactive earths from Lemnos (Figure 1i,j) [15,16]. Lemnian Earth 700.17 (red) contained 37.6% kaolinite, 41% illite, 17.7% quartz, and 3.8% hematite.…”

“…Our work over the past twenty years and on the purported place of its extraction, in Kotsinas in the north-east of Lemnos, has resulted in sampling local deposits of sedimentary clays and the waters of local springs [13,14]; the latter seem to have played a role in the 'preparation' of the earth, at least as hinted by the visitors to the island in the Ottoman period [14]. In the last three years we have also undertaken analysis and preliminary (qualitative) antibacterial testing of pellets of Lemnian Earth (sphragides) from the collection of the Pharmacy Museum of the University of Basel [15] (see also Figure 1h,j). More recently, quantitative assessment of the same samples showed that two of the three artefacts were antibacterial against both Gram-negative and Gram-positive pathogens, but the third was mildly so and against only one of the two bacteria tested [16].…”