Antagonism of lactic acid bacteria from goats' milk against pathogenic strains assessed by the 'sandwich method'

Lactobacilli isolated from goats' milk were tested for their inhibitory effects toward Lisleria monocytogenes and Staphylococcus aureus growth. Most of them were antagonistic against these pathogens, as demonstrated by a classical well-diffusion method and a more sensitive deferred technique, named the 'sandwich method'. Inhibitory zones, which were largely reduced in the presence of buffered and sugar-limited medium, were not affected by protease treatment. On the contrary, a few streptococci exhibited inhibitory activity toward L. monocytogenes . Large zones of inhibition were observed, independently of the culture medium and sensitive to protease action, indicating the presence of proteinaceous antimicrobial compounds (bacteriocins). Therefore, the simple sandwich method was sensitive enough to discriminate between antagonistic activities supported by either acid production or bacteriocin action.