BackgroundAppendicitis remains a common surgical emergency in children. Empirical antibacterial treatment is indicated to reduce infective complications. We investigate the bacterial pathogens identified intra-operatively during appendectomies in children to guide empirical surgical antimicrobial prophylaxis options.MethodsA retrospective analysis of patients (< 18 years old) undergoing an appendectomy across a multisite London hospital (Nov 2019–March 2022) was undertaken. Patient-related outcomes including length of hospital stay (LOS), days of antibacterial therapy (DOT), intra-operative microbiology and post-operative radiology reports were interrogated.Results304 patients underwent an appendectomy during this period; 39.1% of patients had intraoperative samples cultured. Bacterial pathogens were found in 73/119 (61.3%) cases; the most common isolates beingEscherichia coli(42.0%),Pseudomonas aeruginosa(21.0%), milleriStreptococcus spp.(14.3%) andBacteroides fragilis(5.9%). Polymicrobial infection was common (32/73). Isolation ofPseudomonasspp.from intra-operative sampling was associated with a greater LOS (7.0 vs. 5.0 days; p = 0.011) but nil effect on the incidence of postoperative collections. Presence of milleriStreptococcus spp.was associated with longer LOS (7.0 vs. 5.0 day; p = 0.007), DOT (12.0 vs. 8.5 day; p = 0.007) but had no observed outcome on postoperative collections (29.4% vs. 18.6%; p = 0.330). 48% ofE. colipositive cultures were co-amoxiclav resistant and prolonged LOS compared to the non-resistant group (7.0 vs. 5.0 days; p = 0.040) but had no difference in post-operative collections (29.2% vs. 17.9%; p = 0.260).ConclusionA high proportion of children with appendicitis havePseudomonasspp.isolated, leading to a prolonged LOS. Evolving Enterobacterales resistance and the presence ofPseudomonasspp.necessitate extended antibacterial coverage for paediatric appendectomies with evidence of peritonitis.