Valutazione del rischio microbiologico sulle salme dei santi Ambrogio, Gervaso e Protaso

When first discovered, the three skeletons were considered to be in a good state of conservation. The first notice of discoloration putatively caused by molds was reported in 1985. In March 2018, a cultural heritage conservation organization claimed that the relics were under microbiological attack; the following summer, the assessment of the potential microbiological risk to the conservation of the relics was entrusted to the University of Milan. The aim of our work was to evaluate whether the chromatic alterations on the relics were due to a microbiological attack and to evaluate the viability of cells. Twenty-nine samples of discolored and non-discolored bone areas were collected using a non-invasive fungi tape strip. Additionally, a sample of what appeared to be green threads, taken from the pillow of one of the Saints, was studied. All samples were stained to label bacteria (green fluorescence), fungi (blue fluorescence) and the metabolically-active microbial community (red fluorescence). After staining, samples were observed by epifluorescence and confocal microscopy. An extremely low number of cells on tape samples was detected by epifluorescence and confocal microscopy. Both the discolored and non-discolored areas showed the same number of cells. No red fluorescence was observed on any of the adhesive tape samples, showing that the few cells were quiescent. The microscopic analysis of the material seemingly made of green thread revealed that the filamentous structures were not microbial in origin. In conclusion, it was proved that at the time of sampling the relics were not under microbial attack. Nevertheless, it is recommended to carefully monitor thermohygrometric conditions to preserve the relics of the three saints from any future microbiological attack.