[Resistance to infection with Listeria monocytogenes in normal and thymusless mice treated with ampicillin (author's transl)].

NMRI mice were infected intravenously with a sublethal dose of Listeria monocytogenes and divided into four groups. One group served as the control and the other three were treated with ampicillin beginning 4, 8 or 24 hours after infection. The animals were injected in the morning and in the evening each time with 4 mg ampicillin subcutaneously until a total dose of 48 mg was reached. As demonstrated by counting of the bacteria in the spleen, Listeria could multiply in the ampicillin treated mice in comparison to the control group at best delayed but the infection continued to persist for some days at a level of 10(3)-10(4) Listeriae per spleen independent from the starting point of the treatment. Eight days after the first infection all animals received a challenge dose of 10(4) Listeriae. Compared with the control animals the ampicillin treated mice had a clearly reduced immunity, even in the group in which ampicillin application had been started 24 hours after the primary infection. If the challenge infection was given at first after an intervall of six weeks between primary and secondary infection, only a reduced immunity was found. Furthermore, whereas spleen cells of mice 7 days after infection were able to transfer immunity to untreated recipients, spleen cells of ampicillin treated mice were unable to do so. Finally, an attempt was made to cure chronic listeric infection in thymusless nude mice by the application of high doses of ampicillin. The observation of a continuous infection in these animals showed that the T-cells played a primary importance in the elimination of the bacteria.