Lactobacillus plantarum UG1 isolated from dry sausage produced an antimicrobial substance that inhibited other strains of the genera Lactobacillus and Lactococcus, and some foodborne pathogens including Listeria monocytogenes, Bacillus cereus, Clostridium perfringens and Clostridium sporogenes. This antibacterial substance was inactivated by proteolytic enzymes and showed a bactericidal mode of action. Consequently, it was characterized as a bacteriocin, and was designated plantaricin UG1. This bacteriocin was stable in the pH range 4.5 to 7.0, partially inactivated by amylolytic enzymes and relatively thermostable. It was not affected by organic or lipolytic enzymes. Production of plantaricin UG1 was pH- and temperature-dependant and maximum yields were obtained in MRS broth cultures maintained at initial pH 6.5, and incubated at 25 degrees C to 30 degrees C, in the exponential to the early stationary growth phase of the producer organism. Ultrafiltration studies indicated that plantaricin UG1 has a molecular weight between 3 and 10 KDa. Curing experiments with L. plantarum UG1 resulted in the appearance of variants that lost bacteriocin production ability but were still immune to the bacteriocin. Plantaricin UG1 production appeared to be chromosomal encoded. Sensitive and insensitive Gram-positive bacteria adsorbed plantaricin UG1 irrespective of their susceptibility to it. In contrast, Gram-negative bacteria did not adsorb plantaricin UG1. The bactericidal action of plantaricin UG1 did not depend on the physiological state of the indicator culture and did not cause cell lysis. The resistance of two indicator strains to plantaricin UG1 has been studied.