A rare case of lateral cervical cyst infection associated with Bacillus subtilis subsp. natto

Bacillus subtilis subsp. natto belongs to the Bacillaceae family and is used in "natto", a traditional Japanese food made from fermented soybeans. Recently, whole-genome sequencing has made it possible to distinguish B. subtilis from B. subtilis subsp. natto , and reports of infections caused by B. subtilis subsp. natto have been increasing and attracting attention. A 73-year-old male who frequently consumed natto was initially diagnosed with a lateral cervical cyst after aspiration of the cyst. The patient later complained of swelling and neck erythema. The cyst was re-aspirated and purulent fluid was obtained. Incision and drainage were performed, and antibiotics were administered. B. subtilis was identified twice following the diagnosis of the lateral cervical cyst infection, leading to the conclusion that B. subtilis was the causative organism. Whole-genome sequencing revealed that the strain of B. subtilis was identical to that found in the natto that he frequently consumed.