Antibiotic substances in natto of several strains of natto bacteria were observed.
Antibiotic activity of natto was attributed partly to the substance(s) in the alkaline ether extract, partly to the substances in the volatile fraction of the acidic ether extract and mainly to the substance(s) of the non-volatile fracton of the acidic ether extract of natto.
A crystaline substance like dipicolinic acid was isolated from the non-volatile fraction.
The production of dipicolinic acid was surmised to be one of specific characters of natto bacteria.