Yersinia enterocolitica and Yersinia pestis

Abstract

The genus Yersinia consists of 17 species, of which Y. enterocolitica, Y. pseudotuberculosis, and Y. pestis are pathogenic to humans. The former two are enteropathogenic and responsible for gastroenteritis, and the latter one is responsible for the plague. Y. enterocolitica and Y. pseudotuberculosis are transmitted through food, and pigs serve as the primary reservoir while Y. pestis infection is transmitted by fleabite, and rodents act as the intermediate host. All three pathogens carry chromosomal- and plasmid-encoded virulence factors, which are required for adhesion, invasion, and colonization of intestinal epithelial cells and lymph nodes, growth inside macrophages, macrophage apoptosis, and serum resistance. In Y. enterocolitica, chromosome-encoded virulence gene products include invasin, attachment invasion locus (Ail), siderophore (yersiniabactin), and an enterotoxin (Yst), which are important during initial colonization and invasion of intestinal M cells and enterocytes in the intestine. The pYV plasmid-encoded virulence factors include Yersinia outer membrane proteins (YOPs) that are responsible for bacterial virulence protein translocation by T3SS to the host cell cytosol and resist macrophage and neutrophil-mediated inhibition and serum resistance. Expression of YOPs is temperature-dependent and occurs mostly at 37 °C, which is critical for bacterial pathogenesis while inside a host. During passage through the digestive tract, bacteria invade M cells overlying Peyer’s patches, multiply in the lymphoid follicle, and are engulfed by macrophages. Y. enterocolitica is resistant to phagocytic killing by neutrophil, DC, and macrophages, and these cells help disseminate the organism to mesenteric lymph nodes, liver, and spleen.

Y. pestis causes the bubonic and pneumonic form of plague by colonizing the lymphoid tissues of the gastrointestinal and the respiratory tracts. The organisms acquired by either fleabite or aerosol are transported to the lymph nodes by macrophages where the bacteria survive and resist the killing by macrophages and neutrophils by producing several virulence factors: F1 (fraction 1 antigen) capsule, plasminogen activator (Pla), and low calcium response (Lcr) stimulon. In the bubonic form, the submaxillary lymph nodes are enlarged and appear as buboes. In this form, fever, chill, headache, and septicemia develop, and the mortality rate in untreated cases is 30–50%. In the secondary pneumonic phase, the bacteria disseminate to the respiratory tract and develop severe bronchopneumonia with bloody purulent sputum. This form of plague is highly contagious and invariably fatal, if not treated.