A facultative psychrotrophic lactic acid bacterium isolated from fresh fish was identified as Carnobacterium piscicola on the basis of carbohydrate utilization, G + C content and 16S RNA analysis. Its bacteriocin, designated carnocin UI49, is produced during the mid-exponential phase of growth at temperatures between 15 degrees C and 34 degrees C. Carnocin UI49 is active against a large number of closely-related lactic acid bacteria including carnobacteria, lactobacilli, pediococci and lactococci. Furthermore, the bacteriocin has a bactericidic mode of action which results in lysis of sensitive cells. Maximum bactericidal activity is observed at 34 degrees C with a decrease in activity down to 15 degrees C where it is completely abolished.