Bacteria which grow on the surface of such paintings might discolor the painting not only through their own pigments but also by excreting metabolic products. Heterotrophic bacteria can use organic compounds from the paint layer as growth substrates, producing acids, which cause discoloration of the paint or change its consistency. The bacterial contaminants isolated in the paint products included Bacillus sp. All isolates can grow in MSM medium with paint and cause some changes color, turbidity, acidity, decrease amount of paint and high to moderate growth of Bacillus sp.
