The occurrence and persistence of mixed biofilms in automobile air conditioning systems

Twelve automobile air conditioner systems from six manufacturers and three countries, selected mostly because of complaints of unpleasant odors in the passenger compartment, were examined for microbial growth by direct micros copy and enrichment culture. Mixed populations of fungi and bacteria (with occasional protozoa) were observed in biofilms in at least some of the comp onents from all used units. The aluminum heat exchanger fins from ten evapo rators demonstrated bacterial biofilms that yielded Methylobacterium mesoph ilicum. Penicillium viridicatum colonized components from four units. These bacteria and fungi were recoverable repeatedly from these units during 'dr y' storage of up to 27 months. This report associates a bacterial-fungal co mmunity with disagreeable air quality in some automobiles.