Bacillus subtilis Bacteremia from Gastrointestinal Perforation after Natto Ingestion, Japan

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.

A rare case of Bacillus subtilis variant natto-induced persistent bacteremia with liver and splenic abscesses in an immunocompetent patient

Bacillus subtilis var. natto, a low-pathogenic bacterium used in the traditional Japanese food "natto" (fermented soybeans), has rarely been reported as a pathogen of infectious diseases in humans. Herein, we report the first case of persistent bacteremia caused by B. subtilis var. natto in an immunocompetent patient without any gastrointestinal involvement. A 53-year-old Japanese woman who had been consuming natto every day was admitted to our hospital with complaints of fever and chills. B. subtilis was isolated from blood cultures collected during the initial visit. Abdominal contrast-enhanced computed tomography (CT) showed multiple low-absorption areas in the liver and spleen. Treatment commenced with vancomycin; however, Bacillus sp. was re-detected in the blood culture on day 4 after treatment initiation. The blood culture on day 8 was negative. Subsequently, the treatment was switched to ampicillin-sulbactam and oral amoxicillin-clavulanic acid, and the patient recovered after 28 days of treatment from the time the blood cultures became negative. Contrast-enhanced CT of the abdomen at the end of treatment showed that the multiple low-absorption areas in the liver and spleen had disappeared. Later, the variant of the bacteria was identified as B. subtilis var. natto by DNA analysis. B. subtilis var. subtilis and B. subtilis var. natto cannot be distinguished using matrix-assisted laser desorption/ionization-time of flight mass spectrometry or 16S rRNA analysis. Biotin auxotrophy of B. subtilis var. natto is used to distinguish between the two variants.