Agarose/agar assay system for the selection of bacteriocin-producing lactic fermentation bacteria

The direct selection of bacteriocin-producing lactic fermentation bacteria was possible by plating diluted cultures of Pediococcus acidilactici on mixed agarose agar layers with the amount of each component incrementally adjusted to 1.2% (w/v). Between 0.5 and 1% agarose, the increased flexibility of the solidified support layer allowed its removal from Petri dishes without tearing and its smooth layering on the surface of 1.5% (w/v) standard agar medium seeded with Listeria innocua as the test organism. Selection of bacteriocin-producing clones was based on the size of inhibition zones visible in the bottom agar layer under colonies growing on the agarose/agar top layer. The lack of contact with the test organism permitted the transfer of superior clones from the surface of the agarose/agar layer directly into an appropriate nutrient medium.