ASSESSMENT OF THE LUNG MICROBIOTA IN HEALTHY DOGS AND DOGS WITH CANINE IDIOPATHIC PULMONARY FIBROSIS: IMPACT OF BREED AND DISEASE.

Purpose of the study: The lung microbiota (LM) corresponds to all the bacteria residing in the lung. In man, the LM has been widely studied in chronic lung disease including idiopathic pulmonary fibrosis (IPF). In IPF, the LM is suspected to play a causal role in the disease and has been associated with the disease severity and outcome. In dogs, so far, the LM has been described exclusively in healthy experimental beagles. Canine idiopathic pulmonary fibrosis (CIPF) is a disease that affects dogs of the West Highland white terrier (WHWT) breed. This study aimed to describe the LM in client-owned healthy dogs from different types of breeds, as well as in dogs affected with CIPF. Methods used: Thirty-eight healthy dogs were recruited and categorized into 4 groups: shepherd dogs (S), brachycephalic dogs (Br), terrier dogs (T) and WHWTs (H-WHWTs). Eighteen CIPF WHWTs (CIPF-WHWTs) were also included. CIPF was confirmed either by chest scanner, or by histopathological examination of the lung or both. Bronchoalveolar lavage was performed in all dogs and an aliquot of bronchoalveolar lavage fluid (BALF) was stored at -80°C until analysis. After DNA extraction from BALFs, PCRs targeting the V1-V3 region of the 16S rDNA were performed and amplicons sequenced. Taxonomical assignation based on the SILVA database and microbiota community analyses were done with MOTHUR v1.40 with an OTU clustering distance of 0.03. The bacterial load was calculated by quantitative PCR targeting the V2-V3 region of the 16S rDNA. Summary of results: The bacterial load was not different between groups (P=0.135). Analysis of the molecular variance showed significant difference between CIPF-WHWTs and the S group (P=0.0007) but no differences were shown between the other groups. Bacterial richness was higher in H-WHWT (mean (interquartile range) = 507.6 (439.8-575.8)) than in S (290.4 (247.7-360.4)) and T (273.8 (228.3-393.9)), P=0.001 and 0.002 respectively, but there were no significant differences between the other groups for the richness, and for the evenness and the α-diversity. The relative abundance of the genus Brochothrix was significantly higher in H-WHWTs and C-WHWTs compared with other groups (P<0.05). In each group, specific genera were found as indicators of discrimination. The more discriminant genera were Chryseobacterium in S, Delftia, in Br, Bacteroidales_ge in T, Prevotella_9 in H-WHWTs and Lactobacillus in CIPF-WHWTs. Spearman correlation between all the genera and the dog’s status (healthy or CIPF) indicated that 66 and 7 genera were respectively positively and negatively correlated with CIPF including Brochothrix (r=0.6; P<0.0001), Hydrogenohpilus (r=0.5; P