Walker occupancy has an impact on changing airborne bacterial communities in an underground pedestrian space, as small-dust particles increased with raising both temperature and humidity.

Torahiko Okubo,Shigeru Kamiya,Hiroyuki Yamaguchi,Takako Osaki,Akira Uemura,Eriko Nozaki,Shinji Nakamura,Junji Matsuo,Kouhei Sakai,Mizue Matushita

doi:10.1371/journal.pone.0184980

Torahiko Okubo, Shigeru Kamiya + Show 8 more

Open Access

https://doi.org/10.1371/journal.pone.0184980

Copy DOI

Journal: PloS one	Publication Date: Sep 18, 2017
Citations: 10	License type: CC BY 4.0

Affiliation: Hokkaido University, Kyorin University, Juntendo University

Abstract

Although human occupancy is a source of airborne bacteria, the role of walkers on bacterial communities in built environments is poorly understood. Therefore, we visualized the impact of walker occupancy combined with other factors (temperature, humidity, atmospheric pressure, dust particles) on airborne bacterial features in the Sapporo underground pedestrian space in Sapporo, Japan. Air samples (n = 18; 4,800L/each sample) were collected at 8:00 h to 20:00 h on 3 days (regular sampling) and at early morning / late night (5:50 h to 7:50 h / 22:15 h to 24:45 h) on a day (baseline sampling), and the number of CFUs (colony forming units) OTUs (operational taxonomic units) and other factors were determined. The results revealed that temperature, humidity, and atmospheric pressure changed with weather. The number of walkers increased greatly in the morning and evening on each regular sampling day, although total walker numbers did not differ significantly among regular sampling days. A slight increase in small dust particles (0.3–0.5μm) was observed on the days with higher temperature regardless of regular or baseline sampling. At the period on regular sampling, CFU levels varied irregularly among days, and the OTUs of 22-phylum types were observed, with the majority being from Firmicutes or Proteobacteria (γ-), including Staphylococcus sp. derived from human individuals. The data obtained from regular samplings reveled that although no direct interaction of walker occupancy and airborne CFU and OTU features was observed upon Pearson's correlation analysis, cluster analysis indicated an obvious lineage consisting of walker occupancy, CFU numbers, OTU types, small dust particles, and seasonal factors (including temperature and humidity). Meanwhile, at the period on baseline sampling both walker and CFU numbers were similarly minimal. Taken together, the results revealed a positive correlation of walker occupancy with airborne bacteria that increased with increases in temperature and humidity in the presence of airborne small particles. Moreover, the results indicated that small dust particles at high temperature and humidity may be a crucial factor responsible for stabilizing the bacteria released from walkers in built environments. The findings presented herein advance our knowledge and understanding of the relationship between humans and bacterial communities in built environments, and will help improve public health in urban communities.

Highlights

Humans spends over 90% of their time in indoor environments such as houses, offices, schools, hospitals, restaurants, and other public spaces such as underground pedestrian walkways [1,2,3]; these environments should be maintained in a clean state without air pollution
The features and rate of bacterial shedding from individuals could be reflected in the bacterial community structures of built environments; they may serve as markers for estimating healthy indoor air conditions
Samples were collected from the center of the walkway (Fig 1B, red star marked on the map) on May 2, June 1, and July 5 (8:00 h to 20:00 h), and July 15 (5:50 h to 7:50 h / 22:15 h to 24:45 h), which correspond to the larger temperature changes in a year, an optimum period for assessing the effect of temperature or humidity on changing the amount of dust particles or bacteria with bacterial flora dynamics at the pedestrian space

Summary

Introduction

Humans spends over 90% of their time in indoor environments such as houses, offices, schools, hospitals, restaurants, and other public spaces such as underground pedestrian walkways [1,2,3]; these environments should be maintained in a clean state without air pollution. Air pollution of indoor environments with human pathogens can hinder individual health by spreading or exacerbating disease [8,9,10]. The features and rate of bacterial shedding from individuals could be reflected in the bacterial community structures of built environments; they may serve as markers for estimating healthy indoor air conditions. Building ventilation systems and sanitation can influence the community structure of indoor air bacteria, the abundance of human-derived bacteria is more than two-fold greater in human occupied indoor environments than unoccupied areas [12,13,14]. It is clear that human occupancy influences bacterial communities in indoor air, it is not known whether the movement of individuals (e.g., walking) has an impact on these communities

Methods

Results

Discussion

Conclusion