A case of community‐acquired pneumonia caused by Bacillus subtilis subsp. natto in an immunocompetent patient

A 70‐year‐old immunocompetent male with a history of insomnia presented with pneumonia and bacteremia caused by Bacillus subtilis. The patient took benzodiazepines and regularly consumed alcohol and natto (fermented soybeans). Initial antibiotic treatment was not effective, and bronchoalveolar lavage was performed. Bronchoalveolar lavage fluid (BALF) analysis revealed an increased lymphocytes fraction, and B. subtilis was detected in the BALF. Whole‐genome sequencing confirmed the congruence of the genetic sequences between the strain in the blood culture of the patient, BALF, and strain isolated from the consumed natto, confirming B. subtilis subsp. natto as the causative pathogen of pneumonia and bacteremia. Vancomycin followed by levofloxacin and systemic corticosteroid were used to treat the condition. This case highlights community‐acquired pneumonia and bacteremia caused by B. subtilis subsp. natto, particularly in individuals who consume natto. We report a rare case of pneumonia and bacteremia caused by Bacillus subtilis subsp. natto in an immunocompetent patient. B. subtilis subsp. natto is a gram‐positive spore‐forming bacteria and a subspecies of B. subtilis. Natto is a Japanese traditional food made by fermenting soybeans with B. subtilis subsp. natto which can produce nattokinase.