ANTIMICROBIAL SPECTRUM, STRUCTURE, PROPER TIES AND MODE OF ACTION OF NISIN, A BACTERIOCIN PRODUCED BY LACTOCOCCUS-LACTIS - REVIEW

Nisin is a 34 amino acid antibacterial peptide produced by certain str ains of Lactococcus lactis. This bacteriocin has found wide applicatio n as a food preservative owing to its non-toxic nature, its heat stabi lity at acidic pH, its inactivation by proteolytic enzymes in the dige stive tract and, especially, to its antimicrobial activity against a b road range of Gram-positive organisms, including food pathogens of con cern in food industry such as Clostridium botulinum and Listeria monoc ytogenes. However, the use of nisin has the limitation that its solubi lity and stability decrease progressively as the environmental pH incr eases. The two natural variants of nisin, named nisin A and nisin Z, a re ribosomally synthesized as 57 amino acid precursor peptides which a re subjected to further modifications. The mature peptide displays sev eral unusual features, such as the presence of dehydrated amino acids and lanthionine rings. Insertion of the peptide into the cytoplasmic m embrane of susceptible cells leads to the formation of pores, dissipat ing the membrane potential and pH gradients.