Abstract: The present invention relates to novel bacterial isolates and to their use s agents, or source of agents, antagonistic to growth of rot causing organisms. Particularly the present invention provides novel isolates of bacteria of species Pseudomonas fluorescens, Serratia liquefaciens, Serratia plymuthica, Bacillus subtilis, Bacillus pumilis and Bacillus polymyxa which are particularly effective in inhibiting the growth of organisms of the post-harvest disease causing fungi Botrytis cinerea and Alternaria brassicicola. Further provided are antibiotics derived from the Bacillus species.