Objective To explore the dynamic changes of gut microbiota metabolites in septic patients following admission, as well as the correlations between these metabolites, the gut microbiota, and the prognosis of septic patients.

Methods A total of 119 fecal samples were collected from 23 septic patients, 16 non-septic patients admitted to the Emergency Intensive Care Unit (ICU), and 20 healthy controls at Zhongshan Hospital, Fudan University, from January to August 2019. The 16S rRNA gene sequencing technology was applied to analyze the microbiome, while ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was used for metabolomics research. The R software was used to analyze the gut microbiota and metabolite data. Based on 180-day survival status after admission, the sepsis group was divided into the survival group (n＝15) and the death group (n＝8) to analyze differential metabolites between the two groups. Spearman correlation coefficients were used to assess correlations between gut microbiota and metabolites.

Results In the first week of ICU stay, gut microbiota metabolites such as nicotinic acid, methylsuccinic acid, and glutaric acid were significantly lower in septic patients than in healthy controls (P＜0.05), whereas tryptophan, histidine, valine, and pyroglutamic acid were higher in septic patients (P＜0.05). The methylsuccinic acid and phenylacetic acid levels in the first week were lower in the death group than those in the survival group (P＜0.05), and the levels of methylsuccinic acid, phenylacetic acid, and glutaric acid were lower in the third week (P＜0.05). Further analysis indicated that methylsuccinic acid was closely associated with sepsis prognosis. These differential metabolites involved in metabolic pathways such as phenylalanine metabolism and β-alanine metabolism. Most differential amino acids were positively correlated with opportunistic pathogens but negatively correlated with normal gut microbiota. Conversely, metabolites such as nicotinic acid, phenylacetic acid, methylsuccinic acid, and glutaric acid were negatively correlated with opportunistic pathogens and positively correlated with normal gut microbiota.

Conclusions Significant dynamic changes occur in gut microbiota metabolites in septic patients, with methylsuccinic acid, phenylacetic acid, and glutaric acid potentially playing important roles in determining patient prognosis.