Alicia M. Mohr

Background Previous preclinical studies have demonstrated sex-specific alterations in the gut microbiome following traumatic injury or sepsis alone; however, the impact of host sex on dysbiosis in the setting of postinjury sepsis acutely is unknown. We hypothesized that multicompartmental injury with subsequent pneumonia would result in host sex-specific dysbiosis. Methods Male and proestrus female Sprague-Dawley rats (n = 8/group) were subjected to either polytrauma (PT) (lung contusion, hemorrhagic shock, cecectomy, bifemoral pseudofracture), PT plus 2-hours daily restraint stress (PT/RS), PT with postinjury day 1 pseudomonas aeruginosa pneumonia (PT + PNA), PT/RS with pneumonia (PT/RS + PNA), or naive controls. Fecal microbiome was measured on days 0 and 2 using high-throughput 16S rRNA sequencing and QIIME2 bioinformatics analyses. Microbial α-diversity was assessed using Chao1 (number of different unique species) and Shannon (species richness and evenness) indices. β-diversity was assessed using principal coordinate analysis. Significance was defined as p < 0.05. Results All groups had drastic declines in the Chao1 (α-diversity) index compared to naïve controls (p < 0.05). PT + PNA and PT/RS + PNA resulted in different β-diversity arrays compared to uninfected counterparts (PT, PT/RS) (p = 0.001). Postinjury sepsis cohorts showed a loss of commensal bacteria along with emergence of pathogenic bacteria, with blooms of Proteus in PT + PNA and Escherichia-Shigella group in PT/RS + PNA compared to other cohorts. At day 2, PT + PNA resulted in β-diversity which was unique between males and females (p = 0.004). Microbiome composition in PT + PNA males was dominated by Anaerostipes and Parasuterella whereas females had increased Barnesiella and Oscillibacter . PT/RS males had an abundance of Gastranaerophilales and Muribaculaceae . Conclusions Multicompartmental trauma complicated by sepsis significantly diminishes diversity and alters microbial composition towards a severely dysbiotic state early after injury, which varies between males and females. These findings highlight the role of sex in postinjury sepsis and the pathobiome which may influence outcomes after severe trauma and sepsis. LEVEL OF EVIDENCE Not applicable – basic science