B. Faraon1,2, B.H. Pollock3, B. Kreiswirth4, J. Mediavilla4, A. Alarhayem5, T. Perdomo2, P. Rhee2, A. Ramirez5, R. Jardine2, B. Rollins2, L. Hiraldo2, K. Wong2, N. Chidiebere2, S.M. Cohn2 1CUNY School of Medicine, New York, NY, USA 2SBH Health System, Department Of Surgery, Bronx, NY, USA 3University Of California – Davis, Department Of Public Health Sciences, Sacramento, CA, USA 4Hackensack Meridian Health, Center For Discovery & Innovation, Nutley, NJ, USA 5Banner Health, Phoenix, AZ, USA
Introduction: The human appendix is thought to have some immune function based on its association with substantial lymphatic tissue. The appendix has been proposed to serve as a “safe house” for commensal bacteria, providing support for bacterial growth and potentially facilitating re-inoculation of the colon if the contents of the intestinal tract are purged following exposure to a pathogen. We performed a pilot prospective cohort study to identify microbiological factors that impact the severity and outcomes of adults with acute appendicitis.
Methods: Patients aged ≥15 years who underwent appendectomies, right colectomies, or subtotal colectomies at our institution were included. Patients were excluded if they received preoperative antibiotics within one week before surgery, had known immunodeficiency disorders, or metastatic cancer. Rectal swabs were obtained under anesthesia. Immediately after the appendectomy, an aerobic swab of the appendix lumen and biopsy of the mucosa were performed. Microbiological culturing and 16S/18S/ITS amplicon sequencing were performed to examine the diversity of bacterial and fungal species.
Results: Over 8 months (September 2023 to May 2024) 35 nonconsecutive patients underwent appendix microbiome analysis. Twenty-three patients had acute appendicitis (5 were perforated), and 12 underwent appendectomy as part of a colectomy or as an incidental procedure (these were treated as controls). Twenty-one bacterial species were identified in the appendix and rectum. The organisms in the appendix lumen were similar to those in the appendiceal biopsy. These microbes were typically also found on the rectal swab. There were few differences in the microbial profile seen in patients with perforated and nonperforated appendicitis or between those patients with acute appendicitis and controls. Strikingly, E. coli was found in 17/23 (74%) of patients with acute appendicitis but in only 3/12 (25%) controls.
Conclusion: We did not find evidence to support the theory that bacteria in the appendix are in any way different from those of the rectum during acute illness, but the difference in the presence of E. coli between the appendicitis cases and the controls raises the question whether “normal” appendices are commonly colonized with pathogens.