Differences in microbiota profiles of simple and complicated pediatric appendicitis cases

This study aimed to identify the differences in microbial composition between simple appendicitis (SA) and complicated appendicitis (CA) in a limited sample size using culture and microbiota analysis. Appendix tissues and rectal swabs for microbiota analysis and conventional cultures were collected from patients. 16S rRNA regions were amplified using a DNA preparation kit with primers designed to target the V3-V4 region. Sixteen (41%) of the patients were classified as CA based on the histopathological analysis, and the rest as SA. The effect size was slightly greater in rectal swab samples than in appendiceal tissue samples. Based on the conventional culture, the most common aerobic bacteria were Escherichia , Klebsiella spp., and Enterococcus spp. A decrease in both Pseudomonadota and Bacteriodota phyla was observed in tissue samples, while a decrease in Bacteriodota and an increase in Pseudomonadota were observed in rectal samples. Differences in the relative abundance of Coprobacter and Hungatella were observed between CAT and SAT samples; however, no genus-level difference remained significant after ANCOM-BC2 multiple-testing correction. The most notable feature of the CAT group was the relatively higher presence of potential pathobionts. Bacteriodes and Roseburia showed higher relative abundance in the SA rectal (SAR) group. The genera Eubacterium and Clostridioides showed a significant increase in both the SAR and CA rectal (CAR) groups. Lower relative abundances of Parvimonas, Prevotella , and Dialister and a higher relative abundance of Tyzzerella were observed in CAR compared with controls, although these differences did not remain significant after multiple-testing correction. In the ANCOM-BC2 pairwise analysis, an unclassified genus within Enterobacteriaceae was significantly enriched in CAR compared with healthy controls (LFC = 3.56, q = 0.003). No statistically significant distinction was shown at the alpha and beta diversity levels between SA and CA cases. Our findings support previous studies on increased density and diversity at the phylum level in the CA group. The main limitations were the limited sample size and the use of pre-operative antibiotics. Microbiota profiling of appendiceal tissue and rectal swab samples may provide complementary information for understanding microbiota-associated patterns in appendicitis; however, the diagnostic or predictive utility of these microbial profiles requires validation in larger, independent cohorts using dedicated predictive modeling and diagnostic performance analyses.