Interaction of Listeria monocytogenes and influenza in an animal model.

This study was designed to investigate the effects of viruses in the pathogenesis of Listeria monocytogenes. The organisms used in this study were: Listeria monocytogenes Type 1 isolated from a local fatal case; Mouse adapted influenza A/PR8/34 (HONI); Streptococcus pneumoniae Group B (U.M. Med. Ctr.) and poliovirus Type 2 MEF--G3M2. Balb-C mice were inoculated intraperitoneally with one LD50 of Listeria monocytogenes. Ten days later, the survivors were challenged intransally with 10 LD50 of influenza virus and observed for 14 days. Another set of Balb-C mice was inoculated intranasally with one LD50 of influenza virus and the survivors challenged 14 days later intraperitoneally with 10 LD50 of Listeria monocytogenes. Controls consisted of similar inoculation and challenge methods in mice using Streptococcus pneumoniae and polio virus with Listeria monocytogenes and influenza virus. Cross protection was observed only between Listeria monocytogenes and influenza virus. Cellular immunity may play a role in this interaction. This findings seem to agree with reports from others who showed cross protection between Listeria monocytogenes and other intracellular bacteria and parasites.