Incidence of Listeria monocytogenes in Silage and Its Subsequent Control by Specific and Nonspecific Antagonism

Silage samples representing approximately 10% of Vermont's dairy farms were tested for the presence of Listeria species. Listeria innocua was isolated from 15.3% of the silage samples, while Listeria monocytogenes was isolated from 2.9% of the examined samples. As silage pH increased, the incidence of Listeria increased concomitantly. Seventy-eight mesophilic lactic acid bacteria, indigenous to silage, were screened for specific and nonspecific antagonism against four L. monocytogenes indicator strains. Most of the silage isolates demonstrated nonspecific inhibition via lactic acid production against the L. monocytogenes indicator strains. None of the indigenous silage isolates tested in this survey demonstrated specific antagonism via production of bacteriocinogenic compounds.