Anaerobic bacteria are a significant component of the human microbiota, primarily found in higher concentrations in the upper respiratory tract (3:1), gastrointestinal tract (103:1), and female genital tract (10:1) compared to facultative anaerobic bacteria. They can also colonize oxygen-exposed areas like the skin, nose, mouth, and pharynx [1]. These bacteria provide protection against pathogenic bacteria by regulating the immune system, producing essential vitamins, and metabolizing bile acids. They also create oxygen-depleted environments and antimicrobial peptides to prevent pathogenic colonization, known as colonization resistance [2].

Infections caused by anaerobic bacteria occur when the mucosal barrier is disrupted, often due to factors like surgeries and tumors [3]. Anaerobic bacteremia accounts for 0.5 %–12 % of cases [4], with a noted increase in incidence since 1990 [5]. Anaerobic bacteremia carries a high mortality rate (10–60 %), dependent on underlying health conditions and appropriate antibiotic treatment. Adequate antibiotic therapy, surgical intervention, and debridement significantly enhance survival rates [6]. Notably, antibiotic resistance in anaerobic bacteria is on the rise, particularly against Bacteroides fragilis, the most frequently isolated microorganism in bacteremia [7].

The retrospective study's goals are to assess the frequency of anaerobic bacteremia over time and to analyze the species of isolated anaerobes and their antimicrobial susceptibilities.