Exposure to traffic-related air pollution and bacterial diversity in the lower respiratory tract of children.

Christine Niemeier-Walsh,Atin Adhikari,Tiina Reponen,Patrick H Ryan,Nicholas J Ollberding,Jaroslaw Meller

doi:10.1371/journal.pone.0244341

Abstract

BackgroundExposure to particulate matter has been shown to increase the adhesion of bacteria to human airway epithelial cells. However, the impact of traffic-related air pollution (TRAP) on the respiratory microbiome is unknown.MethodsForty children were recruited through the Cincinnati Childhood Allergy and Air Pollution Study, a longitudinal cohort followed from birth through early adolescence. Saliva and induced sputum were collected at age 14 years. Exposure to TRAP was characterized from birth through the time of sample collection using a previously validated land-use regression model. Sequencing of the bacterial 16S and ITS fungal rRNA genes was performed on sputum and saliva samples. The relative abundance of bacterial taxa and diversity indices were compared in children with exposure to high and low TRAP. We also used multiple linear regression to assess the effect of TRAP exposure, gender, asthma status, and socioeconomic status on the alpha diversity of bacteria in sputum.ResultsWe observed higher bacterial alpha diversity indices in sputum than in saliva. The diversity indices for bacteria were greater in the high TRAP exposure group than the low exposure group. These differences remained after adjusting for asthma status, gender, and mother’s education. No differences were observed in the fungal microbiome between TRAP exposure groups.ConclusionOur findings indicate that exposure to TRAP in early childhood and adolescence may be associated with greater bacterial diversity in the lower respiratory tract. Asthma status does not appear to confound the observed differences in diversity. These results demonstrate that there may be a TRAP-exposure related change in the lower respiratory microbiota that is independent of asthma status.

Highlights

For many years it was believed that the lungs were sterile due to the limitation of characterizing bacterial communities through culture-dependent methods [1]
The diversity indices for bacteria were greater in the high Traffic-related air pollution (TRAP) exposure group than the low exposure group
No differences were observed in the fungal microbiome between TRAP exposure groups

Summary

Introduction

For many years it was believed that the lungs were sterile due to the limitation of characterizing bacterial communities through culture-dependent methods [1]. Aggregates of elemental carbon nanoparticles are common components of urban PM [22,23] and are retained by lung tissue [22] They have the capacity to induce pulmonary oxidative stress [24] and to stimulate proinflammatory cytokine release from airway cells [25]. The airway microbiota may interact with the innate and adaptive arms of the host’s mucosal immune system in the respiratory tract (e.g., by activating tolerogenic dendritic cells) and influence regulatory T and B cell induction and differentiation in the lung and respiratory tract. This interaction can be critically important in maintaining immune tolerance. The impact of traffic-related air pollution (TRAP) on the respiratory microbiome is unknown

Methods

Discussion

Conclusion