Two important species are included in the Yersinia genus: Y. enterocolitica and Y. pestis. Y. enterocolitica is the most often encountered species of Yersinia in the lab. This bacterium is an invasive pathogen which can penetrate the gut lining and enter the lymphatic system and the blood. Infection, which is usually through ingestion of contaminated foods, can cause a severe intestinal inflammation called yersiniosis. Release of its enterotoxin can cause severe pain similar to that found in patients with appendicitis. Y. enterocolitica is easy to identify because it is able to grow in cold temperatures and is motile at room temperature. Antibiotic treatment can consist of aminoglycosides, chloramphenicol, or tetracycline.
Although not an enteric pathogen, Y. pestis is included hear because it causes the bubonic, pneumonic, and septicemic plagues. Human contraction of bubonic plague is usually through flea bites. Once inside the body, Y. pestis releases a toxin which inhibits electron transport chain function. Swelling of the lymph nodes, skin blotches, and dilerium are sometimes observed within a few days of infection. Untreated infections usually result in death within a week of initial infection. Although not common in the United States, the plague has historically been a deadly pathogen, inflicting Europeans in epidemic proportions during the fourteenth, fifteenth, and sixteenth centuries. A lack of sanitation allowed the plague to go unchecked killing tens of millions along the way. Fortunately, antibiotics such as streptomycin and gentamicin are effective in killing Y. pestis.