Perfis de contaminação e inactivação microbiana em azulejos

Abstract

One of the major challenges in the conservation of cultural heritage is the prevention and control of contamination caused by microorganisms.

The goals of the present study were the evaluation of methodologies for the characterization and quantification of the bioburden present in ancient ceramic tiles, and the estimation of the minimum dose of gamma radiation (Cobalt-60) necessary to inactivate the bioburden of these samples. Two ceramic tile panels were selected as case studies due to the evident signals of biodeterioration: the “Grande Panorama de Lisboa” (23 m length), of the beginning of the XVIII century, the most notable piece of the National Tile Museum and classified as National Treasure; and the panel “Quinta de Santo António” (XVIII century). The sampling, isolation and quantification of the bioburden present in the tiles were performed by the swab method followed by counting of colony forming units (CFU). The microorganisms isolated were phenotypically characterized by conventional techniques of microbiology in order to establish contamination patterns. Tile samples from the panel “Quinta de Santo António” were exposed to sub-lethal doses (1 to 4 kGy) of gamma radiation, and the bioburden of survival population evaluated both quantitatively and qualitatively.

In the analyzed panels, the estimate bioburden varied between 10²-10³ CFU/100 cm² of tile, consisting mostly of Gram positive rods (> 56%). The gamma rays irradiation indicated a decrease of the number of the microorganisms of approximately 25% for 4 kGy. However, the microbial load did not present an exponential inactivation kinetics. The obtained results suggest the potentiality of application of gamma radiation in the tile decontamination as a conservation treatment.