Unique microbial profiles and severity-associated alterations in the peritoneal fluid of children with acute appendicitis

Background

Intra-abdominal abscesses (IAA) after appendectomy for acute appendicitis (AA) result from residual bacteria in the abdominal cavity. However, the microbiota of the peritoneal fluid (PF) in children with AA has not been well-characterized, particularly through culture-independent methods. This study aimed to characterize the PF microbiota using next-generation sequencing.

Methods

This observational study prospectively enrolled 21 pediatric AA patients (simple appendicitis [SA], n = 11; complicated appendicitis [CA], n = 10) who underwent appendectomy. PF and appendiceal lumen samples were collected, and their microbiota was analyzed using 16S rRNA amplicon sequencing.

Results

The most abundant bacterial genera in the PF microbiota were Bacteroides, Parvimonas, Prevotella, Streptococcus, Blautia, and Fusobacterium, each exhibiting an average relative abundance of ≥5 %. Redundancy analysis revealed a significant correlation between serum C-reactive protein levels and the composition of the PF microbiota (P = 0.011). In addition, nine bacterial genera showed significantly higher relative abundances in SA than in CA. The microbiota of the PF and appendiceal lumen differed regarding alpha- and beta-diversity and the average relative abundance of 19 bacterial genera.

Conclusion

The PF microbiota exhibits a unique composition distinct from that of the appendiceal lumen. Furthermore, it demonstrates alterations associated with the severity of AA, reflecting both the degree of inflammatory response, as indicated by serum CRP levels, and pathological severity, as defined by the distinction between SA and CA. These findings provide new insights into the pathogenesis of postoperative IAA.