Yersinia

Yersinia is a genus of Gram-negative, non-spore-forming, facultatively intracellular bacteria in the family Yersiniaceae. Members are typically rod-shaped and can be motile at lower temperatures, with motility differing among species. The genus includes several human pathogens, most notably Yersinia pestis, the agent of plague, and the enteric pathogens Yersinia enterocolitica and Yersinia pseudotuberculosis.

Natural reservoirs are small mammals, and transmission to humans occurs via fleas for Y. pestis and via contaminated food or water and contact with animals for other species.

Virulence factors include a plasmid-encoded type III secretion system with Yop effector proteins, a F1 capsule antigen, and the Pla protease. These factors promote survival in macrophages and tissue invasion; plasmids and lipopolysaccharide contribute to immune evasion.

Clinically, plague caused by Y. pestis can present as bubonic, septicemic, or pneumonic forms and is a public health concern. Y. enterocolitica and Y. pseudotuberculosis typically cause gastroenteritis and mesenteric adenitis, sometimes mimicking appendicitis.

Diagnosis relies on culture on selective media, Gram stain, serology, and molecular methods such as PCR. Treatment depends on species and disease but commonly includes aminoglycosides (e.g., streptomycin, gentamicin), doxycycline, or fluoroquinolones; plague requires rapid antibiotic therapy and public health measures.

Prevention focuses on rodent and flea control, safe food handling, and surveillance. There is no widely used general human vaccine for Yersinia species; vaccines have been developed for high-risk groups in limited settings. The genus is named after Alexandre Yersin, who described the plague bacillus in 1894.