Antibodies to listeriolysin O reflect the acquired resistance to Listeria monocytogenes in experimentally infected goats.

We induced experimental listeriosis in goats by two sequential oral inoculations of Listeria monocytogenes serovar 1/2a at 8 months' interval. Immunoblot analysis with the goat sera demonstrated listeriolysin O (LLO) as the principal protein antigen of L. monocytogenes. Pre-existing antibodies to LLO were, depending on their initial level, associated with either mild clinical symptoms of short duration or the total absence of clinical symptoms. Similarly, the presence and development of such antibodies corresponded with the disappearance pattern of L. monocytogenes from the gastrointestinal tract. These findings suggest that an association exists between antibodies to LLO and acquired resistance to Listeria infections.