Correlation between the gut microbiota characteristics of hosts with severe acute pancreatitis and secondary intra-abdominal infection

Abstract

Objective: The objective of the study is to investigate the changes in the composition of intestinal microecology in severe acute pancreatitis (SAP) patients with or without intra-abdominal infection and also to analyze the expression of antibiotic resistance genes to provide evidence for early warning of infectious diseases and the rational use of antibiotics.

Methods: Twenty patients with SAP were enrolled in the study. According to whether the enrolled patients had a secondary intra-abdominal infection, they were divided into two groups, each consisting of 10 patients. Stool specimens were collected when the patients were admitted to the emergency intensive care unit (EICU), and nucleic acid extraction was performed. Next-generation gene sequencing was used to compare the differences in intestinal microflora diversity and drug resistance gene expression between the two groups.

Results: The gut microbiota of patients in the infection group exhibited distribution on multiple clustered branches with some intra-group heterogeneity, and their flora diversity was compromised. The infected group showed an enrichment of various opportunistic bacteria in the gut microbiota, along with a high number of metabolic functions, stress functions to external signals, and genes associated with pathogenesis. Drug resistance genes were expressed in the gut microbiota of both groups, but their abundance was significantly lower in the non-infected group.

Conclusion: The intestinal microbiota of patients in the infection group exhibited distribution on multiple clustered branches with some intra-group heterogeneity, and their flora diversity was compromised. Additionally, drug resistance genes were expressed in the gut microbiota of both groups, although their abundance was significantly lower in the non-infected group.

Keywords: intensive care unit; intestinal microecology; intra-abdominal infection; metagenomic next-generation sequencing; severe acute pancreatitis.

Figure 1

Krona chart of microbial composition in the samples. (A) Microbial composition of fecal samples from infected patients; (B) Microbial composition of fecal samples from non-infected patients.

Figure 2

Cluster analysis of samples. (A) Cluster analysis of samples based on Bray–Curtis distance metric at the phylum level; (B) cluster analysis of samples based on Bray–Curtis distance metric at the family level; (C) stacked chart of the top 10 microbial compositions at the phylum level; (D) stacked chart of the top 10 microbial compositions at the family level.

Figure 3

PCA and NMDS results of species at different levels between the two groups. (A) Phylum-level PCA; (B) phylum-level NMDS; (C) class-level PCA; (D) class-level NMDS; (E) order-level PCA; (F) order-level NMDS; (G) family-level PCA; (H) family-level NMDS; (I) genus-level PCA; (J) genus-level NMDS; (K) species-level PCA; (L) species-level NMDS. In PCA analyses, the x-axis and y-axis denote the first and second principal components, respectively, with the percentages reflecting the contribution of each principal component. Each sample is represented by a point in the figure, with samples from the same group depicted in identical colors. In NMDS analyses, points in the figure represent samples, with the distance between points within the same group reflecting sample repeatability. The closeness of samples within a group indicates the variation in hierarchical distance among group samples. The distance between points signifies the level of dissimilarity among samples, with samples from the same group shown in the same color. An NMDS stress value below 0.2 denotes a meaningful graphical analysis.

Figure 4

Box plot showing species with statistical differences at the species level. The horizontal axis denotes sample grouping, while the vertical axis indicates the relative abundance of the corresponding species. A horizontal line signifies the presence of statistical differences between two groups; its absence suggests no statistical difference exists for that species between the groups. *p < 0.05, **p < 0.01.

Figure 5

Heatmap of microbes detected in patients at the species level.

Figure 6

Distribution of annotated genes (Unigenes) across databases. (A) KEGG; (B) eggNOG. (C) CAZy. In panel (A), the horizontal axis represents the number of annotated genes, while in panel (B,C) this role is assumed by the vertical axis. Conversely, the vertical axis in panel (A) and the horizontal axis in panel (B,C) depict the predicted levels of description, thereby illustrating the distribution of sample annotations across various functional categories.

Figure 7

Venn diagram illustrating resistance mechanisms and species across all samples. The right side of the Venn diagram displays species information at the phylum level, and the left side outlines resistance mechanisms. The large circle on the left shows the percentage of resistance genes in each species, sorted by resistance mechanism. In contrast, the right side depicts the proportion of resistance genes in each mechanism, linked to specific species. The color of each small circle represents the corresponding species and resistance mechanisms, with the scale indicating the number of resistance genes. The left side shows the total number of genes associated with a specific resistance mechanism, whereas the right side presents the overall count of resistance genes.

Figure 8

ARO distribution and abundance clustering heatmap. The horizontal axis represents the sample names, and the vertical axis on the right represents the names of the antibiotic resistance gene types (ARO).