A ND M. J . C OV E NT RY . 1997. The effect of bacteriocin, piscicolin 126, on the growth of Listeria monocytogenes and cheese starter bacteria was investigated in milk and in Camembert cheese manufactured from milk challenged with 10 2 cfu ml −1 L. monocytogenes. In milk incubated at 30°C, piscicolin 126 added in the range of 512-2048 AU ml , and the viable count and acid production of these starter cultures in milk were not affected by the addition of 2048 AU ml −1 piscicolin 126. Camembert cheeses made from milk challenged with L. monocytogenes and with added piscicolin 126 showed a viable count of L. monocytogenes 3-4 log units lower than those without piscicolin 126. Inactivation of piscicolin 126 by proteolytic enzymes from cheese starter bacteria and mould together with the emergence of piscicolin 126-resistant isolates was responsible for the recovery of L. monocytogenes in the cheeses during ripening.

Elongation factor Tu (EF-Tu), the most abundant protein in Escherichia coli, is a guanine nucleotide-binding protein that in the 'on' state acts as a carrier of amino acyl-tRNA to the ribosome. Our knowledge of this essential component of translation has brought substantial progress in the past decade thanks to the co-ordinated application of biochemical, physico-chemical and genetic methods. Crystallographic analysis at 2.6 A resolution and site-directed mutagenesis have revealed structural and functional similarities between the guanine nucleotide-binding domains of EF-Tu and human H-ras p21 protein. The regulation of the expression of the two EF-Tu-encoding genes in E. coli, particularly that of tufB, has been shown to involve diverse mechanisms. Several aspects of the functions of EF-Tu in the elongation cycle have been reinvestigated, leading to new insights. These studies have emphasized the manifold aspects of the mechanisms regulating the activity of EF-Tu in the bacterial cell.

A novel peptide bacteriocin produced by the lactic acid bacterium Carnobacterium piscicola JG126 isolated from spoiled ham was purified and characterized. This bacteriocin, designated piscicolin 126, inhibited the growth of several gram-positive bacteria, especially the food-borne pathogen Listeria monocytogenes, but had no effect on the growth of a number of yeasts and gram-negative bacteria. Bactericidal activity was not destroyed by exposure to elevated temperatures at low pH values; however, bactericidal activity was lost at high pH values, especially when high pH values were combined with an elevated temperature. Piscicolin 126 activity was not affected by catalase, lipase, or lysozyme but was destroyed by exposure to a range of proteolytic enzymes. Piscicolin 126 was purified to homogeneity and was found to be a peptide having a molecular weight of 4,416.6 ؎ 1.9. A sequence analysis revealed that this compound is a cystibiotic (class IIa) bacteriocin containing 44 amino acid residues and one intrapeptide disulfide ring. Piscicolin 126 has regions of homology with some other bacteriocins obtained from lactic acid bacteria and is most closely related to sakacin P and pediocin PA-1 (levels of identity, 75 and 55%, respectively). Addition of piscicolin 126 to a devilled ham paste test food system inhibited the growth of L. monocytogenes for at least 14 days. Piscicolin 126 was more effective than two commercially available bacteriocin preparations tested in the same system. MATERIALS AND METHODS Materials. Chemicals and other products were obtained from the following suppliers. Growth media and agar were obtained from Oxoid, Basingstoke, United Kingdom. Catalase was obtained from Boehringer, Mannheim, Germany. ␣-Chymotrypsin, ␤-chymotrypsin, lipase, lysozyme, pepsin, trypsin, protease type I, protease type XIV, protease type XXIII, and ␣-cyano-4-hydroxycinnamic acid were obtained from Sigma Chemical Co., St. Louis, Mo. Nisin (as Nisaplin) was obtained from Aplin and Barrett, Trowbridge, United Kingdom. ALTA 2431 was obtained from Quest International, Sydney, New South Wales, Australia. Devilled ham paste was obtained from Master Foods, Sydney, New South Wales, Australia. Plasmid pGEM-T was obtained from Promega Corp., Madison, Wis. CM-Sepharose Fast Flow was obtained from Pharmacia Biotech, Uppsala, Sweden. 2-Mercaptoethanol was obtained from BDH,