What is it about?
Alistipes is a group of anaerobic bacteria that normally inhabits the human gut. Bloodstream infections caused by Alistipes are rare, and their clinical features and antibiotic resistance profiles are not well understood. We retrospectively analyzed 13 cases of Alistipes bacteremia identified at a tertiary care center in Japan between 2016 and 2023, representing 0.04% of all patients who underwent blood cultures. The median patient age was 72 years, and 10 of the 13 patients were older than 65. Seven patients had solid tumors or hematologic malignancies, and 11 experienced gastrointestinal symptoms. Five species were identified: A. finegoldii, A. onderdonkii, A. putredinis, A. indistinctus, and A. ihumii. Antimicrobial susceptibility testing showed low MICs for beta-lactam/beta-lactamase inhibitors and metronidazole, while MICs were high for penicillin, ceftriaxone, minocycline, and moxifloxacin. Resistance genes including adeF, tet(Q), cfxA3, cfxA4, and ermG were detected in several strains. Twelve patients received beta-lactam/beta-lactamase inhibitors; 11 recovered, and 2 patients with solid tumors died of septic shock.
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Why is it important?
Alistipes bacteremia is likely underdiagnosed due to the slow growth of these organisms and the limited coverage of current MALDI-TOF mass spectrometry databases — one strain identified as A. ihumii by 16S rRNA gene analysis could not be identified by mass spectrometry alone. This study provides the largest case series of Alistipes bacteremia to date and characterizes species-specific patterns of antimicrobial resistance, including reduced susceptibility to moxifloxacin in A. onderdonkii and to cefoxitin in A. indistinctus. These findings have direct implications for antibiotic selection in affected patients.
Perspectives
Alistipes species can translocate from the gastrointestinal tract into the bloodstream, particularly in patients with underlying malignancies, bowel obstruction, or perforation. Clinicians and clinical microbiologists should consider Alistipes as a potential cause of anaerobic bacteremia in elderly patients with gastrointestinal disease or cancer. Beta-lactam/beta-lactamase inhibitors and metronidazole are reasonable treatment options. Expanding MALDI-TOF mass spectrometry databases and performing molecular identification methods will help reduce the underdiagnosis of this emerging pathogen.
Dr Naoki Watanabe
Hirosaki University
Read the Original
This page is a summary of: Alistipes Bacteremia in Older Patients with Digestive and Cancer Comorbidities, Japan, 2016–2023, Emerging Infectious Diseases, April 2025, Centers for Disease Control and Prevention (CDC),
DOI: 10.3201/eid3104.241284.
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