Colonoscopy is a necessary item of physical examination for colorectal cancer. For high-risk groups, annual physical examination is the most effective way of early prevention; At present, a large amount of polyethylene glycol (PEG2000 - 4000) is often used as laxative and lubricant in colonoscopy. However, the widespread use of PEG may cause long-term and irreversible damage to intestinal microorganisms and bring great hidden dangers to health. The appendix has long been regarded as a redundant organ in evolution. The incidence of appendicitis ranks first in surgical acute abdomen. Traditionally, once acute appendicitis is diagnosed, it is usually treated with appendectomy. However, recent studies have revealed that appendectomy may be associated with psychiatric diseases, colorectal cancer, cardiovascular diseases and other diseases. The appendix is not only an important organ of the immune system, but also undertakes the function of storing and protecting intestinal microbes.. . This change may affect the function of the central nervous system through the microbe gut brain axis, and then pose a potential threat to the health and behavior of the host, such as increasing the risk of diseases such as Parkinson's disease. Based on this, this clinical trial aims to investigate (1) the changes of intestinal flora in the appendectomy population before and after colonoscopy in the process of polyethylene glycol intestinal preparation; (2) the differences between the changes of intestinal flora before and after colonoscopy in the appendicectomy population and the normal population in the process of flora recovery.

The human gut microbiota constitutes one of the densest microbial communities on Earth, encompassing a highly diverse assembly of microorganisms that perform metabolic, immune, and protective functions crucial to human health. The gastrointestinal microbiota is influenced by a variety of factors, including genetics, host physiological status (such as age, disease, and stress), and environmental conditions such as living environment and medication use. Among these numerous perturbing factors, iatrogenic interventions-particularly the bowel cleansing procedure essential before colonoscopy-exert a particularly significant impact on the gut microecosystem.

Current colonoscopy preparation involves the administration of large volumes of polyethylene glycol (PEG2000-4000) as a laxative and lubricant. Existing studies indicate that PEG use may markedly reduce microbial richness and diversity. Specifically, PEG ingestion can lead to aberrant proliferation of *Akkermansia* species, a reduction in Firmicutes, and an increased load and virulence gene expression of pathogens such as *Citrobacter*. Metabolically, PEG use may result in decreased dehydroxylation of primary bile acids and altered cholesterol metabolism, ultimately contributing to diarrhea, weight loss, disruption of lipid and energy metabolism, and intestinal inflammation. Thus, extensive use of PEG may cause long-term and irreversible damage to the gut microbiota, posing substantial risks to health.

The appendix, located at the base of the cecum, is an elongated, tubular structure protruding from the posterior wall of the cecum. As an integral component of the intestinal mucosal immune system, its lumen harbors rich biofilm structures that provide an "ecological sanctuary" for commensal bacteria, shielding them from the flushing effect of intestinal contents. Emerging research indicates that under physiological conditions, the appendix continuously receives and shelters specific microbiota from the proximal colon, particularly adherent members of the Firmicutes and Bacteroidetes phyla. When microbial dysbiosis occurs in the host-due to factors such as infection, antibiotic exposure, or bowel cleansing-the appendix can serve as a microbial reservoir, accelerating the process of microecological restoration. Therefore, the appendix is considered a "natural backup system" for the gut microbiota, and its integrity plays an irreplaceable role in resisting microbial disturbances and maintaining microecological resilience. Historically, appendicitis has ranked as the most common acute abdominal emergency, and once acute appendicitis occurs, traditional therapy often involves appendectomy. Extensive epidemiological evidence has shown that post-appendectomy populations have significantly elevated risks of *Clostridioides difficile* infection, colorectal cancer, Parkinson's disease, and depression. Metagenomic studies further reveal that appendectomized individuals exhibit reduced gut microbial diversity, persistently low abundance of short-chain fatty acid-producing genera (e.g., *Faecalibacterium* and *Roseburia*), diminished stability of microbial networks, and compromised resistance and resilience against external disturbances. These findings suggest that appendiceal loss may place the gut microecosystem in a state of "fragile equilibrium," wherein superimposing the strong perturbation of PEG-based bowel cleansing could induce more severe and persistent dysbiosis.

This study adopts a parallel-controlled, monitored clinical trial design, enrolling a total of approximately 10 participants. Eligible subjects must have previously undergone appendectomy or right hemicolectomy with appendectomy, be aged 18-75 years, be scheduled for colonoscopy, be generally healthy, and have no history of major organ diseases. Control subjects must be aged 18-75 years, have no history of appendectomy or right hemicolectomy with appendectomy, be generally healthy, and have no history of major organ diseases. Both groups must meet corresponding exclusion criteria, including: contraindications to colonoscopy (e.g., organic diseases such as cardiopulmonary insufficiency), inability to tolerate PEG laxatives, pregnancy, long-standing history of intestinal diseases, or antibiotic use within the past six months.

Fecal samples will be collected at multiple time points: before colonoscopy, at the first non-watery stool after colonoscopy, and at one month, three months, and six months post-colonoscopy. Metagenomic sequencing will be used to detect fecal gut microbial information, and bioinformatics analysis will be performed with a focus on: (1) the long-term effects of colonoscopy on the gut microbiota and the disturbance characteristics during gut microecological recovery following appendectomy; (2) designing microecological restoration probiotic formulations based on microbiome features; and (3) screening representative fecal samples for subsequent animal experiments.

This study will not use recruitment advertisements; participation is entirely voluntary. Subjects will be informed of potential risks during the experiment and will sign informed consent forms upon agreeing to join the study. Volunteers who consent to participate will complete a questionnaire to assess their intestinal health status and other health conditions and will be screened according to the aforementioned selection and exclusion criteria. Collected samples will be labeled with codes to ensure that no personally identifiable information is disclosed. Throughout the study, participants' identities will be kept confidential, with only codes and disease phenotypes visible. Subjects may withdraw from the study at any time.

This study will analyze the composition and structure of participants' gut microbiota, and subjects will be kept informed of the progress of the tests and analyses in a timely manner and will have access to their own relevant data.

Inclusion Criteria:

• Aged 18-75 years.

• Scheduled to undergo colonoscopy.

• Generally healthy without major organ diseases.

  1. For appendectomy group: history of appendectomy or right hemicolectomy (including appendectomy).
  2. For control group: no history of appendectomy or right hemicolectomy.

Exclusion Criteria:

• Allergy or intolerance to PEG laxatives.

• Pregnant or lactating women.

• Mental disorders.

• Use of antibiotics within 6 months prior to study enrollment.

  1. Contraindications to colonoscopy (e.g., severe cardiopulmonary insufficiency).
  2. For control group only: presence of organic diseases.

The research subjects were adult patients from the Department of Gastroenterology of Tongji Hospital in Wuhan, China, who were scheduled to undergo colonoscopy. Participants were recruited continuously from the outpatient department and voluntarily joined after signing a written informed consent form. The participants were divided into two cohorts based on their history of appendectomy: individuals with a history of appendectomy (appendectomy group) and those without an appendectomy (normal group). All participants received routine bowel preparation using polyethylene glycol and provided fecal samples regularly within 6 months. No experimental interventions were conducted.

Individual participant data collected during this trial, including fecal metagenomic sequencing data and questionnaire responses, will not be shared to protect participant privacy. Summary results will be disseminated through publication in peer-reviewed journals. As stated in the informed consent form, de-identified aggregate data may be made available for public query, but individual-level data will not be shared.