Inducer bacteria, unique signal peptides, and low-nutrient media stimulate in vitro bacteriocin production by Lactobacillus spp. and Enterococcus spp. Strains.

Bacteriocins (BCN) are antimicrobial peptides that provide potential to control bacterial infections in a variety of applications. We previously reported on three class IIa BCN molecules produced by Lactobacillus salivarius B-30514 (OR-7), Enterococcus faecium B-30746 (E 50-52), and Enterococcus durans/faecium/hirae B-30745 (E-760). These BCN are notably effective against a wide array of pathogenic bacteria. To commercially apply such BCN, adequate quantities must be produced and harvested. We determined that a combination of host producer synthesized signal peptides (SP) in the presence of both producer and inducer bacteria grown in a dilute fermentation medium enabled marked increases in the synthesis of BCN. These SP contained 24-30 amino acid residues with sizes ranging from 2095 to 3065 Da having the unique terminal carboxyl sequence of VKGLT. The inducer bacterial isolates used were Lactobacillus acidophilus B-30510 and Lactobacillus crispatus B-30884. We used a nutrient-limited medium of 10% brucella broth (containing 0.01% glucose) to enhance BCN production. Using the combination of these above three parameters enabled us to reproducibly harvest at least 200 mg of BCN/L of the spent fermentation broth. This information can be used to assist in the production of BCN.