Assessment of lung microbiota in healthy dogs: impact of breed and living conditions.

The lung has been recognized to host a diverse, low biomass bacterial population, identified as the lung microbiota (LM). In human chronic lung diseases (CLDs), the LM is altered compared with that of healthy patients. However, whether alterations are a cause or a consequence of the disease is still unclear. In dogs, the LM has been described mostly in healthy experimental beagles. However, in a previous work from our team, an impact of the living conditions and/or of the breed was suspected between healthy beagles and West Highland white terriers (WHWTs). Recent studies in mice and horses showed modifications in the LM according to the living conditions. These modifications in the LM could predispose individuals to certain CLDs. So, we aimed to assess the breed impact and the influence of living conditions, either experimental or domestic, on the LM, in healthy dogs.
Healthy dogs were sampled, for a total of 48 dogs, and categorized into 5 groups: experimental Beagle (EB), Shepherd (S), Terrier (T), Brachycephalic (Br) and WHWT dogs, a breed with high susceptibility for canine idiopathic pulmonary fibrosis (CIPF). Bronchoalveolar lavage fluid (BALF) was obtained under anaesthesia in each dog. After DNA extraction from BALFs, a PCR targeting the V1-V3 region of the 16S rDNA was performed. Amplicons were then sequenced on a MiSeq Illumina sequencer. Taxonomical assignation and microbiota community analysis were done with MOTHUR V1.40 with an OTU clustering distance of 0.03.
Results showed that the bacterial load was higher in EB dogs (p<0.0001). The AMOVA results indicated differences between EB group compared with S and T groups (p<0.005). Significant differences in relative abundances at the family and the genus level were found. The genus Hydrogenophilus was higher in EB and the genera Brochothrix, Limnohabitans, Parabacteroides and Curvibacter were higher in WHWT compared with other groups (p<0.05). In each group, specific genera were found as indicators of discrimination (p<0.05). Bacterial richness was higher in WHWT than in EB, S and T groups (p<0.001), but there were no significant differences for the evenness and the α-diversity between groups.
Our study demonstrated an effect of the living conditions on the LM. Breed differences were also shown. This LM modifications might be related to breed susceptibility to lower respiratory diseases, such as CIPF in WHWTs and need to be considered in future analyses on the role of LM disturbances in diseases.