Bacillus subtilis Bacteremia from Gastrointestinal Perforation after Natto Ingestion, Japan

We report a case of Bacillus subtilis variant natto bacteremia from a gastrointestinal perforation in a patient who ingested natto. Genotypic methods showed the bacteria in a blood sample and the ingested natto were the same strains. Older or immunocompromised patients could be at risk for bacteremia from ingesting natto.

perforation was diagnosed, and a transverse colostomy and drainage were performed.After blood and pus cultures were collected, a course of intravenous meropenem (0.5 g every 8 h) was initiated.
We assessed whether blood and pus culture isolates and the isolate from natto the patient consumed (brand A) were the same strain, by using pulsed-field gel electrophoresis (PFGE), as previously described (7).To verify B. subtilis var.natto, we tested 2 brands (brands B and C) besides brand A that the patient reported consuming.PFGE revealed that the isolates detected from the blood and pus cultures were the same as the cultures of natto brand A that the patient consumed.Moreover, those isolates were the same as isolates from natto brand C (Figure ), suggesting that the blood and pus culture isolates were  (8).The most common known portal of entry for B. subtilis bacteria is the gastrointestinal tract, but often the site of entry is unknown, and bacteremia that has a gastrointestinal tract source is presumed to be related to natto ingestion (3)(4)(5)(6).However, B. subtilis var.natto was identified in only 2 prior cases, 1 that analyzed the draft wholegenome of each B. subtilis strain using next-generation sequencing ( 6) and 1 that used the biotin gene and the biotin requirement test (5).In our case, PFGE analysis revealed that the patient's isolate was B. subtilis var.natto that matched the natto brand he consumed.

RESEARCH LETTERS
We report a case of Bacillus subtilis variant natto bacteremia from a gastrointestinal perforation in a patient who ingested natto.Genotypic methods showed the bacteria in a blood sample and the ingested natto were the same strains.Older or immunocompromised patients could be at risk for bacteremia from ingesting natto.
Although B. subtilis bacteremia has been reported only in Japan thus far, the popularity of Japanese cuisine is increasing worldwide (9).Therefore, clinicians outside Japan should also be aware of B. subtilis bacteremia caused by natto consumption.
PFGE analysis revealed that the natto of brands A and B contained different bacterial strains.Many brands of natto are sold in Japan.Each brand uses different soybean cultivars, processing conditions (soaking, steaming, and fermentation), and B. subtilis var.natto strains (10).Therefore, a history of natto consumption alone might not be associated with the cause of B. subtilis bacteremia because eating natto is not uncommon among the population of Japan.
In conclusion, we report a case of B. subtilis bacteremia and secondary peritonitis resulting from gastrointestinal perforation in a patient who ingested natto.Our case and others in the literature indicate that older or immunocompromised patients who consume natto are at risk for serious infection from natto (4,6).Clinicians should advise patients in these risk groups to avoid eating natto or food products containing B. subtilis bacteria.

About the Author
Dr. Hashimoto is a physician at the Infection Control Center of Oita University Hospital.His main research interest is in microbiology.

Figure .
Figure.Pulsed-field gel electrophoresis patterns of restricted chromosomal DNA from Bacillus subtilis variant natto isolated from a case of bacteremia from gastrointestinal perforation after natto ingestion, Japan.B. subtilis strains were digested in Sfil enzyme.Lane M, CHEF DNA size marker (Bio-Rad, https://www.bio-rad.com) of Saccharomyces cerevisiae; lane 1, sample from blood; lane 2, sample from pus; lane 3, sample from natto brand A; lane 4, sample from natto brand B; lane 5, sample from natto brand C. Numbers at left indicate kilobases.