Antilisterial Activity of a Broad-Spectrum Bacteriocin, Enterocin LR/6 from Enterococcus faecium LR/6 Manoj Kumar & Sheela Srivastava Received: 8 July 2009 / Accepted: 29 October 2009 / Published online: 3 December 2009 # Springer Science+Business Media, LLC 2009 Abstract Enterocin LR/6, a purified bacteriocin, exhibited broad inhibitory spectrum both against related as well as some food-borne pathogens such as Listeria monocytogenes, Yersinia enterocolitica, Aeromonas sp., Shigella sp., and Bacillus licheniformis. In this investigation, we have focused on L. monocytogenes as the target organism, as it is not only an important pathogen but can also survive over a wide range of environmental conditions such as refrigeration temperature, low pH, and high-salt concentration. This allows the pathogen to overcome many food preservation and safety barriers and poses a potential risk to human health. The enterocin LR/6 showed a bactericidal action against L. mono- cytogenes and completely inhibited the growth on agar plates, supplemented with 200 AU/ ml of enterocin LR/6. The effectiveness of enterocin LR/6 in completely killing a population of acid-adapted (pH 5.2, 2 h) L. monocytogenes exposed to different temperatures (4–37 °C), pH (2.5–8.0), and osmotic (up to 30% NaCl) stress is reported here. This paper focuses on the key issue of killing of the acid-adapted L. monocytogenes cells under adverse environmental conditions. Keywords Acid adaptation . Enterocin LR/6 . Inhibitory spectrum . Listeria monocytogenes Introduction The antimicrobial proteinaceous molecules referred as bacteriocins, produced by lactic acid bacteria (LAB) and active against taxonomically related bacteria, have been considered as promising biopreservative [1, 2]. Bacteriocins have been classified into four classes (class I, II, III, and IV) based on their genetic and biochemical characteristics [3]. Among the bacteriocins active toward Listeria, the lantibiotic nisin has been widely studied and is currently used in many countries as a preservative in food products. Another group of antilisterial peptides produced by some LAB forms a subclass of bacteriocins, the class IIa [1]. Although several bacteriocins from LAB have been characterized to date, their use as Appl Biochem Biotechnol (2010) 162:698–706 DOI 10.1007/s12010-009-8851-1 M. Kumar : S. Srivastava (*) Department of Genetics, University of Delhi South Campus, New Delhi 110021, India e-mail: srivastava_sheela@yahoo.com