Automobile air conditioning systems (ACS) might be considered an extreme environment for many microorganisms. Organisms surviving and proliferating in these systems may be presented with temperature changes ranging from subzero to over 140°F, water activity from saturation to dryness and a nutrient complexity including varying levels of hydrocarbons. Microbial communities develop in ACS and sometimes proliferate to the extent of massive colonization and production of objectionable odors.

In a few instances microorganisms emanating from ACS have been associated with hypersensitivity pneumonitis and other allergic reactions. Previously we demonstrated that foam insulation and glues, in particular, on ACS insulations were colonized by fungi such as Aspergillus, Aureobasidium, Cladosporium, and Penicillium. Such fungi often are implicated in colonization of similar substrates in buildings categorized with the sick building syndrome.

A total of 42 ACS from the United States, Europe and Central America have been examined by cabin air sampling culture swab, direct microscopy or a combination of these techniques.