First Description of Oral Microbiota in Domestic Cats Affected by Oral Squamous Cell Carcinoma

Oral squamous cell carcinoma (OSCC) accounts for the majority of feline oral neoplasms and carries a poor prognosis; however, the oral microbiome in affected cats remains poorly characterized. This study aimed to preliminarily describe the oral bacterial communities of cats with OSCC and compare them with those of clinically healthy cats using DNA amplicon sequencing. Oral swabs were collected from cats with OSCC, including tumor surfaces, tumor cut surfaces, and clinically normal mucosa distant from the tumor (<i>n</i> = 20 total samples), and from the gingival margin of healthy cats (<i>n</i> = 12). DNA was extracted and full-length 16S rRNA gene sequencing was performed to assess microbial composition and diversity. Cats with OSCC exhibited significant alterations in oral microbiota compared with healthy controls, including reduced alpha diversity, distinct beta-diversity clustering, and consistent taxonomic shifts. Healthy cats displayed a relatively conserved core microbiome dominated by <i>Porphyromonas</i> spp., <i>Bacteroides</i>, Pasteurellaceae, <i>Helcococcus</i>, and <i>Moraxella</i>. In contrast, OSCC-associated samples showed increased relative abundances of anaerobic and disease-associated taxa, including <i>Filifactor villosus</i>, <i>Bacteroides pyogenes</i>, <i>Odoribacter denticanis</i>, <i>Porphyromonas circumdentaria</i>, and members of the Pasteurellaceae. These findings provide the first description of the oral microbiota associated with feline OSCC and demonstrate exploratory microbial differences between health and disease.