Microorganisms are ubiquitous in the environment; they are present wherever there is water.1 They are highly versatile in their nutritional requirements for growth, which can be met by raw materials used to make water-based coatings in their wet stage. The metabolisms of the microbes (bacteria, yeast and molds) pose a potential threat to many industries where water is being used in product manufacture or in process.
In the paint industry it is primarily bacteria, and sometimes yeast, that are responsible for wet-stage spoilage of paint product. Microbial spoilage can be observed as a foul odor, gelation, settling, curdling and blackening.2 Identified groups of organisms responsible for spoilage of wet-stage paint are normally found in water and soil, as well as in natural raw materials like clay, pigments, TiO2, etc. These microorganisms are mainly members of the Enterobacteraceae family, such as the Citrobacter, Enterobacter and Escherichia species, and Pseudomonadaceae, especially Pseudomonas spp. being the most frequently encountered contaminants. Later spoilage with anaerobes such as Desulfovibrio spp. give badly infected products a characteristic odor and in many cases discoloration.3