Dominance of Lactobacillus plantarum strains in grass silage as demonstrated by a novel competition assay

An assay was developed for assessing the competitive ability of potential Lactobacillus plantarum silage inoculants. This assay was based on the ability of the test inoculant to outcompete a standard strain ( Lact. plantarum DCU101) co-inoculated at the same rate of 5 × 10⁵ colony forming units g^-1 of grass. Total populations of Lact. plantarum were enumerated with a selective medium and Lact. plantarum DCU101 was identified with a strain-specific DNA probe. The DNA probe was based on a small (2.2 kb), cryptic, indigenous plasmid which was cloned into pAT153, a multicopy cloning vector. Seven Lact. plantarum strains, six of which were isolated from well-preserved grass silages, were used to inoculate laboratory scale silos, and variation in strain dominance was monitored over the 14 d ensilage period.