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. 2022 Nov 13;10(11):2246.
doi: 10.3390/microorganisms10112246.

Bacterial Communities in Various Parts of Air-Conditioning Units in 17 Japanese Houses

Kensuke Watanabe  1 , U Yanagi  2 , Yoshiki Shiraishi  3 , Kazuhiro Harada  4 , Fumitoshi Ogino  4 , Koichiro Asano  3
Affiliations

Bacterial Communities in Various Parts of Air-Conditioning Units in 17 Japanese Houses

Kensuke Watanabe et al. Microorganisms. .

Abstract

HVAC systems have a significant impact on the indoor environment, and microbial contamination in HVAC systems has a significant effect on the indoor air quality. In this study, to gain a better understanding of the microbial contamination inside ACs, we used NGS to analyze the 16S rRNA gene of bacteria adhering to AC filters, cooling coils, fans, and air outlet surfaces. The five phyla in terms of the highest relative abundance were Proteobacteria, Firmicutes, Actinobacteria, Cyanobacteria, and Bacteroidetes. The surface of an AC filter provides a history of indoor airborne bacterial contamination, and of the 10 bacterial genera we detected with the highest abundance (in the following order: Pseudomonas > Staphylococcus > Paracoccus > Corynebacterium > Acinetobacter > Streptococcus > Methylobacterium > Enhydrobacter > Sphingomonas > Actinotignum) on the filter surface, the top 6 genera were Gram-negative bacteria. Furthermore, the seventh-most abundant genus adhering to the filter surface (Methylobacterium) was the second-most abundant genus on the cooling coil and fan, and the ninth-most abundant genus on the air filter (Sphingomonas) was the third-most abundant genus on the cooling coil. Various factors impact the bacterial flora inside AC units, including the location of the house, AC unit usage, and occupant activity.

Keywords: 16S rRNA gene; air conditioner; air filter; air outlet; bacteria; cooling coil; fan; next-generation sequencing; residential building.

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Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Figures

Figure 1
Figure 1
Location of sensors for measuring T and RH at air the conditioner air outlet (A), configuration of the ductless mini- split-type AC unit (B).
Figure 2
Figure 2
The quartile values of air temperature and relative humidity of living room and air conditioner air Outlet. Statistical significance was evaluated by Mann−Whitney U test. * p < 0.01, and ** p < 0.001.
Figure 3
Figure 3
Relationship between median temperature and median relative humidity.
Figure 4
Figure 4
Relative abundance of 2% or higher of bacterial genera for all samples from the 17 houses. A, C, F, and O corresponded to air filter, cooling coil, fan, and air outlet. Genus ANPR: Allorhizobium-Neorhizobium -Pararhizobium-Rhizobium.
Figure 5
Figure 5
Principal coordinate analysis (PCoA) of partial expansion of the unweighted UniFrac distance (A) and weighted UniFrac distance (B). A, C, F, and O corresponded to air filter, cooling coil, fan, and air outlet.
See this image and copyright information in PMC

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