Heterotrophic bacteria in an air-handling system

Abstract

Heterotrophic bacteria from structural surfaces, drain pan water, and the airstream of a well-maintained air-handling system with no reported building- related illness were enumerated. Visually the system appeared clean, but large populations of bacteria were found on the fin surface of the supply- side cooling coils (105 to 106 CFU cm-2), in drain pan water (105 to 107 CFU ml-1), and in the sump water of the evaporative condenser (105 CFU ml-1). Representative bacterial colony types recovered from heterotrophic plate count cultures on R2A medium were identified to the genus level. Budding bacteria belonging to the genus Blastobacter dominated the supply surface of the coil fins, the drain pan water, and the postcoil air. These data and independent scanning electron microscopy indicated that a resident population of predominantly Blastobacter bacteria was present as a biofilm on the supply-side cooling coil fins.