To investigate the composition and distribution characteristics of bacterial communities in different parts of household air conditioners (ACs) in Chengdu, providing a basis for effective contamination control.

Using convenience sampling, 15 households in Chengdu were selected, with the most frequently used household air-conditioning unit from each household included in the study. Microbial samples were collected using sterile swabs from four key components of the air-conditioning system, including the air outlet, filter screen, heat sink, and condensate tray, resulting in a total of 60 samples. All samples underwent 16S rRNA sequencing, followed by bioinformatics analysis to assess α-diversity, β-diversity, and bacterial community composition. One-way analysis of variance (ANOVA) and the Kruskal-Wallis rank-sum test were employed to determine whether there were differences in α-diversity, β-diversity, and phenotypes among the four components.

Through high-throughput sequencing, the 60 samples collectively yielded 52 bacterial phyla and 1 618 bacterial genera. The differences in the sobs index, Simpson diversity index, and Shannon diversity index, representing the α-diversity of the four components, were all statistically significant (F=12.392, P=1.981×10^-5; F=6.290, P=1.898×10^-3; F=8.294, P=3.479×10^-4). Proteobacteria, Firmicutes, and Actinobacteria were the three dominant phyla across all samples, with Methylobacterium, Rhodococcus, Pseudomonas, and Sphingomonas being the predominant genera. Six categories of potential pathogenic genera were detected: Pseudomonas, Acinetobacter, Staphylococcus, Bacillus, Corynebacterium, and Streptococcus. PCoA analysis revealed that the bacterial community composition of air outlet samples was similar to that of filter screen samples, while the composition of heat sink samples resembled that of condensate tray samples. The differences in bacterial community composition, i.e., β-diversity, among the four components were statistically significant (H=41.135, P=3.469×10^-10). BugBase phenotypic intergroup difference testing showed that the bacteria from the four components of household air conditioners exhibited statistically significant differences in biofilm formation (H=25.772, P=7.663×10-7), stress tolerance (H=14.933, P=1.538×10^-3), pathogenic potential (H=17.606, P=2.169×10^-4), and the proportion of Gram-positive bacteria (H=17.882, P=1.737×10^-4).

High-throughput sequencing revealed differences in bacterial community composition and the distribution of potential pathogenic bacteria across four components of household ACs from 15 households sampled in Chengdu. These findings suggest that differentiated cleaning and disinfection strategies should be implemented for different components to reduce the risk of bacterial exposure.