Purification of a surface-specific soluble antigen from Listeria monocytogenes.

A complex antigenic preparation obtained from Listeria monocytogenes serovariant 4b by freeze-pressing, centrifugation, and gel filtration treatment was studied by crossed immunoelectrophoresis, with the aim of preparing an antigenic fraction that could be used to investigate the serological response to listeric infection. Of 17 immunoprecipitates revealed in the soluble extract, one of three major antigens (designated antigen 2) was shown to be a strong antigen in humans or rabbits infected with L. monocytogenes serovariant 4b. A monospecific antiantigen 2 serum was obtained and used to prepare a serologically homogeneous antigen by immunoadsorption. Antigen 2, most probably located on the bacterial surface, is common to all serovariants of L. monocytogenes and to Listeria grayi and is not shared by the main bacterial species known to have common antigens with L. monocytogenes.