Upper and lower respiratory tract microbiota in horses: bacterial communities associated with health and mild asthma (inflammatory airway disease) and effects of dexamethasone

Stephanie L Bond,Trevor Alexander,Renaud Léguillette,Edouard Timsit,Matthew Workentine

doi:10.1186/s12866-017-1092-5

Stephanie L Bond, Trevor Alexander + Show 3 more

Open Access

https://doi.org/10.1186/s12866-017-1092-5

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Abstract

BackgroundThe microbial composition of the equine respiratory tract, and differences due to mild equine asthma (also called Inflammatory Airway Disease (IAD)) have not been reported. The primary treatment for control of IAD in horses are corticosteroids. The objectives were to characterize the upper and lower respiratory tract microbiota associated with respiratory health and IAD, and to investigate the effects of dexamethasone on these bacterial communities using high throughput sequencing.ResultsThe respiratory microbiota of horses was dominated by four major phyla, Proteobacteria (43.85%), Actinobacteria (21.63%), Firmicutes (16.82%), and Bacteroidetes (13.24%). Fifty genera had a relative abundance > 0.1%, with Sphingomonas and Pantoea being the most abundant. The upper and lower respiratory tract microbiota differed in healthy horses, with a decrease in richness in the lower airways, and 2 OTUs that differed in abundance. There was a separation between bacterial communities in the lower respiratory tract of healthy and IAD horses; 6 OTUs in the tracheal community had different abundance with disease status, with Streptococcus being increased in IAD horses. Treatment with dexamethasone had an effect on the lower respiratory tract microbiota of both heathy and IAD horses, with 8 OTUs increasing in abundance (including Streptococcus) and 1 OTU decreasing.ConclusionsThe lower respiratory tract microbiota differed between healthy and IAD horses. Further research on the role of Streptococcus in IAD is warranted. Dexamethasone treatment affected the lower respiratory tract microbiota, which suggests that control of bacterial overgrowth in IAD horses treated with dexamethasone could be part of the treatment strategy.

Highlights

The microbial composition of the equine respiratory tract, and differences due to mild equine asthma ( called Inflammatory Airway Disease (IAD)) have not been reported
Horses were allocated on day 1 into one of three groups based on their bronchoalveolar lavages (BAL) cytology (IAD versus healthy) and random selection; IAD, Healthy dexamethasone group (DEX) and Healthy control group (CONTROL)
Six horses were classified as healthy based on their BAL cytology; three were randomly enrolled in the DEX group and received dexamethasone for 10 days and three were enrolled in the CONTROL group

Summary

Introduction

The microbial composition of the equine respiratory tract, and differences due to mild equine asthma ( called Inflammatory Airway Disease (IAD)) have not been reported. The objectives were to characterize the upper and lower respiratory tract microbiota associated with respiratory health and IAD, and to investigate the effects of dexamethasone on these bacterial communities using high throughput sequencing. Mild equine asthma ( known as Inflammatory Airway Disease [IAD]) affects up to 66% of the equine population [4]. Bond et al BMC Microbiology (2017) 17:184 with IAD, indicating that composition of the lower respiratory tract microbiota could contribute to the pathogenesis [9]. Microbial composition and diversity of the bronchial airways in humans with suboptimally controlled asthma has been associated with the degree of bronchial hyperresponsiveness, suggesting that lower airway bacterial communities play a role in asthma pathogenesis [12]. There is a need to comprehensively describe the bacterial communities present in health and disease as the overall composition of the bacterial communities, rather than the presence of individual species, is important in defining health and disease [12,13,14]

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