A novel combination of bacteriocins produced by Streptococcus uberis strain 42

Streptococcus uberis is a common and persistent cause of bovine mastitis, and new approaches to control these infections need to be identified. One such approach may be the application of bacteriocins. The best-known example is the well-characterised bacteriocin nisin, produced by Lactococcus lactis, which has activity against a wide range of gram-positive bacteria including mastitis-causing pathogens such as S. uberis. Nisin A is the active ingredient in two commercial products currently in use for the prevention of mastitis. Although nisin A has been utilised for mastitis control, it is not always effective and, in particular, there have been reports of resistance development. A potential solution would be to use a cocktail of bacteriocins having combined synergistic inhibitory activity against mastitis pathogens. Our research has involved investigation of some of the impressive array of bacteriocin-like inhibitory substances (BLIS) produced by S. uberis that are active in vitro against mastitis pathogens. This has resulted in the identification and characterisation of two very different bacteriocins. The first is a 3030 Da lantibiotic, nisin U, which differs in eight amino acid residues from nisin A. The second is a novel 7050 Da bacteriocin named uberolysin, belonging to the newly emerging class of cyclic bacteriocins. Uberolysin has a broader spectrum of activity than nisin U and, unlike nisin U, causes lysis of susceptible cells.