In Vitro Evaluation of <i>Thymus serpyllum</i> Essential Oil Against <i>Paracoccus marcusii</i> <scp>IBR3</scp> : A Potential Natural Protection Strategy for Historic Mural Paintings

Historic mural paintings are particularly vulnerable to biodeterioration caused by microbial colonization, which can lead to the degradation of the organic and inorganic components of wall surfaces. This study presents, to the best of our knowledge, the first identification of the Paracoccus marcusii IBR3 strain on a 19th-century mural painting from a private Italian villa. In vitro analyses revealed that strain IBR3 exhibits significant enzymatic activities, such as casein hydrolysis and calcium carbonate dissolution. These activities implicate the strain in the degradation of proteinaceous binders and mineral substrates, which are typical of mural artwork. As part of an environmentally sustainable conservation strategy, the antimicrobial activity of Thymus serpyllum essential oil was evaluated against strain IBR3 using in vitro tests, membrane integrity assays, and ATR-FTIR spectroscopy. The essential oil, chemically characterized by GC-MS, demonstrated promising biocidal efficacy. These findings suggest that T. serpyllum essential oil could serve as a non-toxic alternative for preserving and maintaining culturally significant wall paintings.