Prevalence and Clinical Impact of Bacillus subtilis var. natto Bacteremia

Overview

This retrospective study identified that nearly all Bacillus subtilis strains isolated from blood cultures were the natto variant, with 36% representing true bacteremia cases. These infections had significant clinical severity, including a 16% 30-day mortality and 28% requiring urgent surgical or endoscopic intervention.

Background

Bacillus subtilis var. natto is a key bacterium used in fermenting soybeans to produce natto, a traditional Japanese food with noted cardiovascular and survival benefits. Despite its probiotic reputation, recent reports have linked B. subtilis var. natto to bacteremia, especially in elderly or immunocompromised patients. Differentiating this variant from other B. subtilis strains requires genetic testing due to limitations of routine microbiological methods. Understanding its prevalence and clinical impact is important given natto's increasing global consumption.

Data Highlights

Key Findings

• Of 70 B. subtilis blood isolates, 99% were genetically confirmed as B. subtilis var. natto.
• True bacteremia was confirmed in 36% of B. subtilis var. natto cases, indicating clinical infection rather than contamination.
• Primary infection sites included intra-abdominal infections, pneumonia, and urinary tract infections.
• The median patient age was elderly (79 years), with a low median Pitt bacteremia score, suggesting mild to moderate severity at presentation.
• Despite low initial severity scores, 28% required urgent invasive interventions, and 16% died within 30 days, indicating significant clinical impact.
• Genetic markers in bioF and bioW genes reliably identified B. subtilis var. natto strains, differentiating them from other B. subtilis subspecies.

Clinical Implications

Clinicians should recognize that B. subtilis var. natto, despite being a probiotic strain associated with natto consumption, can cause significant bloodstream infections, particularly in elderly patients. Positive blood cultures for B. subtilis var. natto should not be dismissed as contaminants, and appropriate evaluation and management are warranted. Genetic testing can aid in accurate identification to guide clinical decisions.

Conclusion

Bacillus subtilis var. natto constitutes the vast majority of B. subtilis bacteremia cases in this Japanese cohort and is associated with notable morbidity and mortality. Awareness of its pathogenic potential is essential for timely diagnosis and treatment.

References

1. Study Authors/2024 -- Prevalence of Bacillus subtilis Strains from Blood Cultures Linked to Traditional Japanese Fermented Soybeans Natto