Unravelling the blood microbiome in healthy and febrile domestic cats via 16s rRNA metagenomics

The bacterial microbiome is defined as the collection of bacteria and their genomes, which can be either symbiotic, pathogenic, or commensal. In cats, the bacterial blood microbiome has been investigated in a small colony of healthy kittens. However, the clinical implications of resident circulating bacterial communities in healthy and diseased cats remain largely unexplored. The aims of this study were to evaluate and compare the blood bacterial microbiome in healthy and febrile cats.Genomic DNA samples purified from the blood of 300 domestic client-owned cats were analyzed via amplicon-based sequencing targeting the 16S rRNA variable V3-V4.High-quality sequencing reads were obtained from a total of 145 healthy cats, and 140 febrile cats. Comparisons between the blood of healthy and febrile cats revealed in both groups a dominant presence of Actinobacteria, followed by Firmicutes and Proteobacteria, and a lower relative abundance of Bacteroidetes. The bacterial composition was significantly different between healthy and febrile cats. Within the family taxonomic rank, the Faecalibacterium and Kineothrix (Firmicutes), and Phyllobacterium (Proteobacteria) experienced increased abundance in febrile samples. Whereas Thioprofundum (Proteobacteria) demonstrated a significant decrease in abundance. Furthermore, the bacterial composition and beta diversity within febrile cats revealed significant differences according to each affected body system (Oral/GI, systemic, skin, and respiratory) at both family and genus levels, except for the systemic and oral/gastrointestinal groups. Sex and age were not significant factors affecting the blood microbiome of febrile cats. Neither was sex in healthy cats, but age exhibited some influence on the blood-bacterial microbiome of healthy cats.Overall, the findings suggest that age, health status, and nature of disease are significant factors affecting blood microbiome diversity and composition in cats, but sex is not. This research expands the understanding of the role of microbial communities in healthy and febrile cats, setting the stage for future clinical applications.