Abstract: A biologically pure culture comprising a subcuticular bacteria isolated from A. gracillima and having bacillus morphology and antimicrobial activity is described. A sample has been deposited at American Type Tissue Culture (ATCC) on Apr. 14, 1998 under accession numbers 202111, 202112, or 202113. Mutants or derivatives thereof having the same antimicrobial activity as the culture are also described. Antimicrobial compositions including the biologically pure culture and methods of inhibiting the growth utilizing the biologically pure culture are also described. Finally, an antibiotic or antibiotic fraction derivable from the bacteria is also disclosed.