Identification of an antibiotic-producing bacterium from the human intestinal tract and characterization of its antimicrobial product.

An antibiotic-producing bacterium repeatedly isolated from human feces was characterized by standard bacteriological methods. The bacterium is a gram-positive bacillus possessing morphological and physiological features similar to those of Bacillus subtilis, except that it lacks temperature-resistant spore formation and has peritrichous flagella. The cell-free antibiotic produced by the organism in vitro was effective against some gram-negative and gram-positive bacteria and yeast in minimum inhibitory concentration and antibiotic disk assays. The 1,200-dalton antibiotic had an optimal activity against Proteus vulgaris within the pH range of 5.7 to 6.8. The activity was totally destroyed by digestion with pronase and trypsin but was resistant to pepsin, chymotrypsin, papain, and nuclease digestion. In addition, the antibiotic activity against P. vulgaris was stable between pH 3 to 9 and within the temperature range of 20 to 100 degrees C when tested in the fermentation medium. The activity was only partially retained by membrane filters which normally retain globular proteins of molecular weights between 500 to 10,000. Electrophoresis in phosphate buffer indicated that the activity against P. vulgaris had an isoelectric point of approximately 6.45. These properties are compatible with the antibiotic activity associated with a small peptide.