BackgroundProteusspp. are widespread in the environment and comprise a part of the normal flora of the human gastrointestinal tract. Only six species in this genus, includingProteus mirabilis, Proteus vulgaris, Proteus terrae, Proteus penneri, Proteus hauseri, andProteus faecis, have been isolated from human clinical specimens. However, there are no reports ofProteus alimentorumisolated from humans, and the clinical characteristics ofP. alimentoruminfection are unknown.Case presentationAn 85-year-old female patient with peritoneal cancer was hospitalized for complicated pyelonephritis and bacteremia caused byP. alimentorum.The patient received antimicrobial therapy and was discharged on day 7 of hospitalization. No recurrence was observed 14 days after the treatment. Various methods were used to identify theProteussp. Furthermore, the VITEK-2 GN ID card resulted in low discrimination betweenP. hauseriandP. penneri. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry showedP. hauseriwith a spectral score of 2.22 as the best match. Nevertheless, the pathogen was identified asP. alimentorumbased on genetic investigation using 16 S rRNA gene sequencing and biochemical tests.ConclusionProteus alimentorumis a human pathogen, and its infection has an excellent therapeutic response to antimicrobials based on antimicrobial susceptibility. Genomic methods may be helpful for the precise identification ofP. alimentorum.