Bacteriology of Anorectal Abscess and Anal Fistula: A Systematic Review of the Literature

Aim: A cryptoglandular anorectal abscess is a collection of purulent material around the anus, often leading to the development of an anal fistula after drainage. Although Escherichia coli and Bacteroides fragilis have been considered key bacteria in these conditions, recent evidence suggests the need to revisit this assumption. This work aimed to analyze the presence and role of bacteria in the development of anal fistulas following anorectal abscesses. Patients and Methods: A search was conducted using MEDLINE via PubMed, EMBASE, Cochrane Library, and Google Scholar. Articles reporting the microbiology of cryptoglandular anorectal abscesses and the resulting anal fistulas in human beings were included. The main outcome was to evaluate the presence of bacteria in cultures of anorectal abscesses or in patients who developed anal fistulas. Additional goals included identifying patient characteristics and assessing clinical outcomes on the basis of the isolated bacteria. Results: In total, 22 articles on anorectal abscesses and seven on anal fistulas met the inclusion criteria. Men were the most prevalent in both cases. Escherichia coli and the Bacteroides genus were the most isolated microorganisms in abscesses and fistulas, though inconsistently in the latter. Bilophila wadsworthia was newly isolated in abscesses, and Rothia sp. was notable in fistulas using new molecular techniques. Conclusions: Escherichia coli and Bacteroides sp. are involved in anorectal abscesses and anal fistula formation. Recently, using new technology non-well-known bacteria had been isolated involved in this clinical problem.