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Viable Airborne and Deposited Microorganisms inside the Historical Museum of Crete

ABSTRACT  
 
Measurements of viable ambient microbial levels and of microbial deposits on surfaces were performed in the Historical Museum of Crete for a period of two years. The concentrations of airborne microbes in museum rooms showed a considerable variability, which is mainly related to indoor activities (such as the number of visitors), the regulation of the indoor environmental conditions and air exchange rate, the chemical composition and conservation treatment of the exhibits, as well as the cleaning and storage conditions. An enrichment of acid producing bacteria, heterotrophic bacteria, and autotrophic chemolithotrophic bacteria was encountered indoors. A considerable decrease of the measured viable microbes was measured after the deployment of photocatalytic ionizers in the different indoor sites ranging from 5.5 % to 76 %. The use of photocatalytic ionizers improved the air quality by reducing mainly the presence of acid producing bacteria, which may cause the deterioration of cultural heritage objects. The microbial colonization on 24 different painting materials and surfaces of model essays, without the use of any preservation treatment, was examined for an exposure period of 18 months. The results from the bacterial deposition on paintings showed a gradual colonization, specific to the materials and surfaces, in concentrations ranging from 10 to 300,000 CFU cm-2. Although airborne fungi were measured in the exhibition rooms (yearly average concentration: 143 ± 115 CFU m-3), no growth of fungi could be detected on the majority of the used painting materials of the model essays. Very slow fungal surface colonization could be only determined on tempera, charcoal, wax pastel, and carton board in low concentrations ranging from 70 to 200 CFU cm-2.