A Comparison of the Oral Microbiota in Healthy Dogs and Dogs with Oral Tumors.

The aim of this study was to further describe the oral microbiota of healthy dogs by DNA shotgun sequencing and compare those to dogs with oral tumors. Oral swabs (representative of all niches of the oral cavity) were collected from healthy dogs (n = 24) and from dogs with different oral tumors (n = 7). DNA was extracted from the swabs and shotgun metagenomic sequencing was performed. Only minor differences in microbiota composition were observed between the two groups. At the phylum level, the Bacteroidota, Proteobacteria, Actinobacteriota, Desulfobacterota and Firmicutes were most abundant in both groups. Observed Operational Taxonomic Units-OTUs (species richness) was significantly higher in the healthy patients, but there was no significant difference in the Shannon diversity index between the groups. No significant difference was found in beta diversity between the groups. The core oral microbiota consisted of 67 bacterial species that were identified in all 24 healthy dogs. Our study provides further insight into the composition of the oral microbiota of healthy dogs and in dogs with oral tumors.

Correlation between Targeted qPCR Assays and Untargeted DNA Shotgun Metagenomic Sequencing for Assessing the Fecal Microbiota in Dogs.

DNA shotgun sequencing is an untargeted approach for identifying changes in relative abundances, while qPCR allows reproducible quantification of specific bacteria. The canine dysbiosis index (DI) assesses the canine fecal microbiota by using a mathematical algorithm based on qPCR results. We evaluated the correlation between qPCR and shotgun sequencing using fecal samples from 296 dogs with different clinical phenotypes. While significant correlations were found between qPCR and sequencing, certain taxa were only detectable by qPCR and not by sequencing. Based on sequencing, less than 2% of bacterial species (17/1190) were consistently present in all healthy dogs (n = 76). Dogs with an abnormal DI had lower alpha-diversity compared to dogs with normal DI. Increases in the DI correctly predicted the gradual shifts in microbiota observed by sequencing: minor changes (R = 0.19, DI < 0 with any targeted taxa outside the reference interval, RI), mild-moderate changes (R = 0.24, 0 < DI < 2), and significant dysbiosis (R = 0.54, 0.73, and 0.91 for DI > 2, DI > 5, and DI > 8, respectively), compared to dogs with a normal DI (DI < 0, all targets within the RI), as higher R-values indicated larger dissimilarities. In conclusion, the qPCR-based DI is an effective indicator of overall microbiota shifts observed by shotgun sequencing in dogs.