Changes in Oral Microbial Diversity in a Piglet Model of Traumatic Brain Injury

The dynamic changes in the oral microbiome in response to disease has led to significant interest in utilizing microbiome analysis as a potential diagnostic and prognostic biomarker. Oral dysbiosis has been linked to the progression of neurological diseases such as Alzheimer's and Parkinson's diseases, however, no studies have been conducted to evaluate microbiome changes in traumatic brain injury (TBI). This study aimed to examine the changes in the oral microbiome structure during the acute stage of TBI in a clinically translational pig model. Landrace piglets (4-5 weeks old, male) underwent either a controlled cortical impact surgery (TBI, n=6) or sham surgery (Sham, n=6). TBI was confirmed by magnetic resonance imaging 1 day post-TBI. Oral swabs of the inside of upper and lower lips, both cheeks, and under the tongue were collected to sample the oral mucosa pre-surgery and 1, 3, and 7 days post-surgery (PS). Bacterial DNA was extracted and the V3-V4 region of 16s rRNA gene was amplified and sequenced using an Illumina NovaSeq platform. Alpha-, beta-diversity, and oral microbial composition at the phylum (P), family (F), genus (G), and species (S) level were examined using Qiime2 plugins. Mixed effects ANOVA was used to compare differences between the groups and time points. Significant time effects were identified in several alpha-diversity indexes during the acute stage of TBI: The number of observed features, Faith's Phylogenetic Diversity, Shannon Index, and Pielou's Evenness. However, no group effects were found between TBI and Sham groups, except for Faith's Phylogenetic Diversity. Faith's Phylogenetic Diversity showed group and time-by-group effects including a significant difference between groups at 7 days PS. In both TBI and Sham groups, beta-diversity was significantly different between time points and distinct microbial patterns were observed between TBI and Sham groups at 1, 3, and 7 days PS, with the most apparent difference at 7 days PS. Changes in oral microbial composition did not differ between TBI and Sham groups at any taxonomic level (P, F, G, and S), while significant time effects were found in several microbial taxa. Interestingly, significant time-by-group effects were found in P_Proteobacteria, F_Leptotrichiaceae, F_Micrococcaceae, and G_Rothia. In conclusion, species diversity as measured by Faith's Phylogenetic Diversity was lowest at 7 days PS in TBI group compared to Sham group, and TBI and Sham groups showed significant differences in beta-diversity. With respect to individual microbial taxa, the oral microbial composition was not significantly different between the two groups during the acute stage of TBI. Future studies are needed to investigate further changes in oral microbiome during the chronic stages of TBI. © FASEB.