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

BACKGROUND

Natto consumption has been associated with improved cardiovascular and survival outcomes. variant ( var. ) is essential for soybean fermentation in natto production. Recently, several cases of var. bacteremia have been reported, although the contribution of var. remains unclear. This study assessed the prevalence and clinical impact of var. in bacteremia.

METHODS

This retrospective cohort study analyzed medical records of patients with positive blood cultures at Tenri Hospital from 1 April 2016 to 31 March 2023. True bacteremia required portal-of-entry or, for intra-abdominal/abscess, 2-physician adjudication; if no portal, 2 or more same-day blood culture-positive sets. Genetic testing confirmed var. through specific mutations in the and genes.

RESULTS

Of 4634 positive blood cultures, 70 (1.5%) were identified as , with 69 (99%) classified as var. . Of these, 25 cases (36%) were confirmed as true bacteremia. The primary diagnoses included intra-abdominal infections, pneumonia, and urinary tract infection. The median patient age was 79 years, with 9 being women. The median Pitt bacteremia score was 0 (interquartile range: 0-1). Seven patients (28%) required urgent surgery or endoscopic procedures, while 4 (16%) died within 30 days.

CONCLUSIONS

Most blood strains isolates were var. . This bacteremia carried significant severity, with a 16% 30-day mortality rate and 28% requiring urgent interventions. Clinicians should not dismiss var. , a probiotic strain, as harmless.