Altered gut microbial profile is a proponent of bacterial translocation in acute-on-chronic liver failure

Background: Gut dysbiosis is implicated in the pathogenesis of acute-on-chronic liver failure (ACLF) where alterations in gut microbiota (GM) pathogenicity have been proposed to lead to increased bacterial translocation (BT). Increased BT in association with gut barrier dysfunction may result in elevated circulating levels of bacterial-derived components. This in turn can potentiate a pro-inflammatory milieu with adverse clinical outcomes. We determined GM composition in faeces from ACLF patients, and measured circulating levels of whole blood (WB) bacterial DNA (bDNA) used as a surrogate for BT.Methods: Patients with ACLF (n=38) and decompensated cirrhosis (DC)(n=46) were compared to stable cirrhosis (SC) and healthy controls (HC)(n=32). Whole blood (WB) for bDNA and faecal samples for GM analysis were obtained concomitantly.After DNA extraction from faeces, GM analysis was performed by amplifying and sequencing the V4 region of the 16S rRNA gene using Illumina MiSeq platform. Operational taxonomic unit assignment was performed using Quantitative Insights Into Microbial Ecology. After DNA extraction from WB, real-time qPCR with a TaqMan probe targeting a 380bp region of bacterial 16S rRNA gene was used to quantify bDNA (in pg/mL (median (IQR))). Results: CLIF-SOFA scores (median (IQR)) were SC 4 (3-5); DC 5 (4-7); ACLF 9 (8-11); P<0.0001.Circulating WB bDNA levels in ACLF (7.03 (6.96); P=0.0001) were elevated significantly as compared to SC (2.78 (1.70)), but without significant differences in DC (4.51 (2.35)) (Fig.1). bDNA levels were also similar in HC (1.62 (0.93)) and SC. A significant difference in GM diversity measured by PERMANOVA where P<0.01 is significant was observed in ACLF (P=0.0011) and DC (P=0.0069) as compared to SC. No significant differences in GM diversity were detected between SC and HC (P=0.019), as shown in Fig.2A. A positive correlation was evident between potentially pathogenic Enterococcus in ACLF, with a relative decrease in fermentative Clostridiales (Fig.2B).Discussion: Significantly higher levels of circulating WB bDNA levels, a robust marker of gut BT, was found in ACLF as compared to SC and HC. Similarly, the GM of ACLF differed most markedly from that of SC and DC. We propose that this altered GM composition serves to drive BT in ACLF. Subsequent mechanistic insight from GM studies over the role of endotoxin tolerance, immuneparesis and infection susceptibility may lead to the identification of potential therapeutic targets in ACLF.