2025 Volume 74 Issue 2 Pages 411-415
Streptobacillus notomytis is a pathogen that causes rat-bite fever, similar to Streptobacillus moniliformis, and has been identified as a new species in 2015. These two bacteria are difficult to differentiate using biochemical properties and mass spectrometry; therefore, genetic analysis is required. We encountered a case in which ingestion of food contaminated with rat excrement was suspected to cause arthritis and bacteremia, which were identified as S. notomytis by genetic analyses. A woman in her 70s was admitted to our hospital with pain in the knee joints and fever. Blood tests showed elevated inflammatory markers and computed tomography revealed fluid retention in the knee joints. On hospitalization day 4, a cloudy articular fluid culture was detected with filamentous gram-negative rods, which we suspected to belong to the genus Streptobacillus. We asked the clinical side to confirm contact history with rats and received information that her home was infested with rats. Blood culture was extended to 14 days, and gram-negative rods were detected on hospitalization day 9. Mass spectrometry identified S. moniliformis, but the score was low. It was identified as S. notomytis by 16S rRNA gene analysis. For mass spectrometry, the database for the genus Streptobacillus contains only S. moniliformis. Therefore, if the identification score is low, S. notomytis infection should be considered. Additionally, on suspecting S. notomytis based on morphology, it is important to extend the incubation period and confirm the animal contact history. In this case, these measures led to a successful diagnosis and treatment.
