To investigate the distribution characteristics of intestinal flora of patients with primary liver cancer by metagenome sequencing.

Fecal samples of 10 patients with primary liver cancer (primary liver cancer group) and 10 healthy people (healty control group) were collected from March to June 2019 in Beijing Youan Hospital, Capital Medical University and the general clinical information was recorded. According to the metagenome sequencing data, principal component analysis and diversity analysis were used to analyze the flora structure and species differences of the two groups of bacteria were also compared. Spearman correlation analysis was used to analyze the correlation between the abundance of Streptococcus parahaemolyticus, Streptococcus salivarius, Streptococcus mutans, Streptococcus_thermophilus, Haemophilus_parainfluenzae, Veillonella_sp._DORA_A_3_16_22, Veillonella_dispar, Akkermansia_sp._CAG.344, Akkermansia_muciniphila_CAG.154, Prevotella_sp._CAG.924 and Alistipes_sp._CAG.268 and serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), glutamyl transpeptidase (GGT), total protein, total bilirubin and alpha fetoprotein (AFP).

The analysis of beta diversity based on bray and jsd distance showed that the intestinal flora diversity of the two groups of subjects was statistically significant. The diversities of fecal flora in patients of primary liver cancer group were significantly lower than those of healthy control group, with significant differences (t = 5.402, P < 0.001; t = 5.248, P < 0.001). At genus level, the highest abundance was Bacteroides, followed by Prevotella, and the relative abundance were [34.94 (11.76, 56.02]% and [11.99 (1.29, 27.82]%, respectively; at species level, the highest abundance was Bacteroides vulgatus and Faecalibacterium prausnitzii, and the relative abundance were [1.55 (0.63, 3.90]% and [1.54 (0.53, 2.84]%, respectively. The abundance comparison at the species level of bacterial taxonomy showed that the distribution of 137 species in the healthy control group and the primary liver cancer group was statistically significant (all P < 0.05). In the primary liver cancer group, the abundance of Streptococcus_parasanguinis, Streptococcus_salivarius, Streptococcus_mutans, Streptococcus_thermophilus, Haemophilus_parainfluenzae, Veillonella_sp._DORA_A_3_16_22 and Veillonella_dispar were significantly increased, while the abundance of Akkermansia_sp._CAG.344, Akkermansia_muciniphila_CAG.154, Prevotella_sp._CAG.924 and Alistipes_sp._CAG.268 were significantly decreased. Correlation analysis found that Streptococcus_salivarius (r = 0.733, P = 0.020), Streptococcus_thermophilus (r = 0.867, P = 0.002) and Haemophilus_parainfluenzae (r = 0.721, P = 0.023) were significantly and positively correlated with serum ALT level. Akkermansia muciniphila was significantly correlated with serum AST (r = 0.646, P = 0.049), GGT (r = 0.762, P = 0.037) and total protein (r =-0.788, P = 0.010).

The diversity of intestinal flora in patients with primary liver cancer was significantly decreased, and the species abundance changed. There was a significant imbalance of intestinal flora. Specific differences in intestinal flora may be used as biomarkers for the early diagnosis of primary liver cancer.