The Majority of Bacillus subtilis Strains Isolated From Blood Cultures Were Derived From Traditional Japanese Fermented Soybeans Natto: A Single-center Retrospective Study

Category	Detail
Condition	Bacillus subtilis var. natto bacteremia
Key Mechanisms	B. subtilis var. natto is a probiotic strain essential for natto fermentation, identified by specific bioF and bioW gene mutations; can cause bloodstream infections especially in elderly or immunocompromised patients
Target Population	Primarily elderly patients (median age 79) with intra-abdominal infections, pneumonia, or urinary tract infections
Care Setting	Hospital inpatient setting with blood culture diagnostics and infectious disease specialist adjudication

99% of B. subtilis blood isolates were identified as B. subtilis var. natto by genetic testing
36% of B. subtilis var. natto isolates represented true bacteremia cases with significant clinical severity
B. subtilis var. natto bacteremia had a 16% 30-day mortality rate and 28% required urgent surgical or endoscopic intervention

Use genetic testing targeting bioF and bioW gene mutations to accurately identify B. subtilis var. natto
Do not rely solely on MALDI-TOF MS for differentiation between B. subtilis and B. subtilis var. natto
Confirm true bacteremia by clinical adjudication including portal-of-entry identification or multiple positive blood cultures

Treat confirmed B. subtilis var. natto bacteremia with effective antibiotics
Consider urgent surgical or endoscopic interventions when indicated by infection severity
Do not dismiss B. subtilis var. natto as a harmless probiotic in bloodstream infections

Monitor patients closely for clinical progression given the potential for severe outcomes and mortality
Assess for underlying infection sources such as intra-abdominal infections, pneumonia, or urinary tract infections

Elderly and immunocompromised patients consuming natto may be at increased risk for bacteremia
B. subtilis var. natto bacteremia can lead to significant morbidity and mortality despite probiotic origin

Elderly patients with B. subtilis var. natto bacteremia identified from blood cultures

Effective antibiotic therapy is critical; 28% required urgent invasive procedures; mortality remains significant at 16% within 30 days

Perform genetic confirmation of B. subtilis var. natto in blood culture isolates for accurate diagnosis
Evaluate clinical context and portal of entry to distinguish true bacteremia from contamination
Recognize that probiotic strains like B. subtilis var. natto can cause serious bloodstream infections
Implement prompt and appropriate antimicrobial treatment and surgical intervention when necessary
Maintain vigilance in elderly or immunocompromised patients with recent natto consumption presenting with signs of infection