Lactocins are bacteriocins synthesised by Lactobacillus species that inhibit only other lactobacilli — narrow-spectrum antimicrobials in the competitive ecology of fermentations. Lactacin A, produced by Lactobacillus delbrueckii subsp. lactis strains JCM 1106 and 1107, has a narrow host range limited to closely related lactobacilli. Such strain-specific antimicrobials illustrate how starter cultures compete for dominance in mixed fermentations (yoghurt, cheese, sourdough), and they are studied as precision tools for controlling unwanted wild lactobacilli without broad-spectrum preservatives — though none is yet a mainstream food additive like nisin.