Retrospective Study of Bacteremia Caused byAlistipesSpecies in Japan, 2016–2023

The clinical characteristics of Alistipes bacteremia remain insufficiently described. Therefore, here, we retrospectively analyzed 13 cases of Alistipes bacteremia at a tertiary care center to evaluate their clinical and microbiological characteristics. Ten patients were aged ≥ 65 years, and seven were female. Nine patients had comorbidities, including seven with solid tumors or hematological malignancies. Eleven patients presented with gastrointestinal symptoms. The isolates included four Alistipes finegoldii , four Alistipes onderdonkii , three Alistipes putredinis , two Alistipes indistinctus , and one Alistipes ihumii isolates. Ten available strains exhibited low minimum inhibitory concentrations against β-lactam/β-lactamase inhibitors and metronidazole, whereas they exhibited high minimum inhibitory concentrations for penicillin, ceftriaxone, and minocycline. Several strains harbored antimicrobial resistance genes, including adeF , tet (Q), cfxA3 , cfxA4 , and erm (G). Twelve patients received β-lactam/β-lactamase inhibitors, and two elderly patients with solid tumors developed septic shock and died. Alistipes species can translocate from the gastrointestinal tract into the bloodstream, leading to severe infections.