Antagonism of Foodborne Bacteria by Pseudomonas spp.: A Possible Role for Iron ¹

Antagonistic action of Pseudomonas spp. against foodborne spoilage and pathogenic bacteria was studied to determine mechanisms involved in the establishment of dominance by these organisms in food systems. Thirteen Pseudomonas strains from plant and food origin were tested for the ability to inhibit other Pseudomonas spp. on brain heart infusion agar using a bacteriocin screening assay. P. aeruginosa AA was the most active, inhibiting P. phaseolicola , P. pisi , P. putida , P. fluorescens , and P. fragi strains. When testing for antagonism against non-pseudomonads, four Pseudomonas spp. showed wide spectrum activity against a variety of gram positive and gram negative bacteria. Growth of most Pseudomonas spp. on an iron-deficient medium increased antagonism. In assays conducted in liquid media, inhibitory activity varied greatly as a result of the composition of the media. A minimal media extract from a P. aeruginosa AA culture significantly inhibited the growth of P. fluorescens and Staphylococcus aureus in milk.