BackgroundLeptotrichia species are aerotolerant, Gram-negative fusiform bacteria. Cases of bacteremia caused by Leptotrichia trevisanii in immunocompromised patients have been rarely reported.Case presentationA 33-year-old female with systemic lupus erythematosus (SLE) was admitted to the department of rheumatology with bleeding from a mucosal ulcer. One month previously, she had visited our hospital and begun to receive methotrexate therapy, but mis-dosed for nearly 1month at home. Methotrexate toxicity resulted in a severe oral ulcer and bone marrow suppression. On day-7 of hospital admission, she developed a fever, and Gram-negative rods (Leptotrichia trevisanii) were detected in blood cultures. She was diagnosed with methotrexate poisoning followed by L. trevisanii bacteremia. After antibiotic and detoxification therapy, she recovered from bacteremia, and the oral ulcer and bone-marrow suppression improved obviously.ConclusionsThis is the first reported case of Leptotrichia trevisanii bacteremia in a SLE patient who took mis-dosed an immunosuppressant and had an oral mucosal lesion.