Overview


Characteristics

  • Enterobacteria, but grow more slowly and at lower temperatures than other enterobacteria
  • Gram negative, non-spore forming, facultative anaerobes - rods or colibacilli
  • Non-lactose fermentors
  • Facultative intracellular pathogens
  • Show bipolar staining in Giemsa-stained smears from animal tissue
  • Pathogenic strains identified by serotyping and biotyping


Pathogenesis

  • Y. enterocolitica and Y. pseudotuberculosis enter the intestinal mucosa via M cells of the Peyer's patches
  • Engulfed by macrphages in the mucosa
  • All three invasive species are facultative intracellular organisms and grow inside macrophages
  • Plasmid and chromosomal-encoded virulence factors required for survival and multiplication in macrophages
  • Survive in phagolysosomes and do not interfere with degranulation or lysosomal fusion
  • Resistant to macrophage killing mechanisms
  • Antiphagocytic proteins secreted by the organisms interfere with host neutrophils
  • Y. pestis is more invasive than the other species and also possesses and antiphagocytic capsule and a plasminogen activator which aids systemic spread; endotoxin also contributes to its pathogenicity
  • Transport within macrophages to mesenteric lymph nodes
  • Replication in lymph nodes and development of necrotic lesions, with neutrophil invasion
  • The bacteria destroy the macrophages causing septicaemia


Clinical infections

  • Yersinia enterocolitica
    • Pathogen of animals and humans
    • Found in intestinal tract and oral cavity of animals, eg. pigs, leading to infection of humans via contaminated carcasses
    • Enterocolitis in man which lasts 2-3 weeks or develops into a chronic form
    • Enteric disease in farmed deer
    • Ileitis, gastroenteritis, mesenteric adenitis
    • Pathogenicity related to a heat stable enterotoxin


Diagnosis

  • Yersinia species grow on blood agar and MacConkey agar at room temperature.
  • Y. pseudotuberculosis and Y. enerocolica are motile, unlike Y. pestis
  • Biochemical tests to identify particular species
  • Specific fluorescent antibody staining of lymph node aspirates to identify Y. pestis


Control

  • Control Y. pestis by controlling rodent population and flea control of cats
  • Control of other Yersinia species difficult due to their ubiquity


Treatment

  • Euthanase or isolate animals suspected of Y. pestis infection; Streptomycin, doxycycline, gentamicin or chloramphinol
  • Long-acting tetracyclines, trimethoprim-sulphonamides, aminoglycosides and chloramphicol effective against Y. pseudotuberculosis and Y. enterocolica