Bacterial community structures in air conditioners installed in Japanese residential buildings

Abstract

The bacterial community structures in fourJapanese split-type air conditioners were analyzedusing a next-generation sequencer. A variety ofbacteria were detected in the air filter of an airconditioner installed on the first floor. In the evaporatorof this air conditioner, bacteria belonging to thegenus Methylobacterium, or the family of Sphingomonadaceae,were predominantly detected. On theother hand, the majority of bacteria detected in the airfilters and evaporators of air conditioners installed onthe fifth and twelfth floors belonged to the familyEnterobacteriaceae. The source of bacteria belongingto the family Enterobacteriaceae may have beenaerosols generated by toilet flushing in the buildings.Our results suggested the possibility that the bacterialcontamination in the air conditioners was affected bythe floor level on which they were installed. The airconditioner installed on the lower floor, near theground, may have been contaminated by a variety ofoutdoor bacteria, whereas the air conditioners installedon floors more distant from the ground may have beenless contaminated by outdoor bacteria. However, thesesuppositions may apply only to the specific split-typeair conditioners that we analyzed, because our samplesize was small