Biological and immunological properties of avirulent strain of Listeria innocua.

The strain isolated by Dr. J. H. Welshimer from plants has antigenic formula V (VI) IX; XV; XI; AB, C--serovar 6a, is non-haemolytic, produces lipase, and toxic factor Ei, is avirulent for adult mice, but causes encephalitis in sucklings. In organs of intravenously injected mice the strain persists and multiplies for 1-3 weeks. The protective effect against listerial infections in mice of this strain administered 2-14 days before challenge is dose depending. After 3 weeks induces resistance of guinea pigs to infection with Mycobacterium tuberculosis H37Rv measured by spleen weight and Feldman index. The hypersensitivity induced in animals is detectable by factor Ei and PPD or OT tuberculins using MIF method. A suspension of living cells of this strain injected intraperitoneally causes resistance to Mycobacterium kansasii in mice, measured by inhibition of loss of weight and decrease of the number of bacillus in their lungs.