yersinia

• Yersinia

  Genus made up of about 14 species, mainly environmental species
• Human pathogens of Yersinia

  • Y. pestis
  • Y. pseudotuberculosis
  • Y. enterocolitica
• Y. pestis

  Causes plague (disease primarily of rodents transmitted to humans by fleas)
• Y. pseudotuberculosis

  Causes mesenteric lymphadenitis and septicemic infections in immunocompromised individuals
• Y. enterocolitica


  Causes diarrhoea and mesenteric lymphadenitis
• Yersinia is zoonotic
• Yersinia pestis

  Causes plague also known as the black death, the scourge of the Middle Ages
• Yersinia pestis is one of the most virulent bacteria known with a strikingly low ID50 (i.e 1–10 organisms capable of causing disease)
• Concerns about possible bioterrorism exist regarding Yersinia pestis
• Transmission cycles of Yersinia pestis

  • Enzootic (sylvatic) cycle
  • Urban cycle
• Enzootic (sylvatic) cycle

  Transmission among wild rodents by fleas
• Urban cycle


  Transmission among urban rats by rat fleas
• Transmission to humans

  By bites of fleas
• Forms of plague

  • Bubonic
  • Septicemic
  • Pneumonic
• Bubonic plague


  Commonest form, results from the bite of an infected flea, symptoms include high fever with painful swollen regional lymph nodes (buboes)
• Septicemic plague


  Occurs when the bacteria spread to the bloodstream characterized by DIC and cutaneous hemorrhages
• Pneumonic plague

  Occurs secondary to bubonic plague or the septicemic form when organisms proliferate in the respiratory tract; can be a primary infection if the bacteria are inhaled
• Subsequent epidemic outbreaks can arise from the respiratory transmission of the organisms
• Fatality rate in pneumonic plague is high (essentially 100%—in untreated cases)
• Yops (Yersinia outer proteins)

  Group of virulence factors injected into the human cell and inhibit phagocytosis and cytokine production by macrophages and neutrophils
• Yersinia enterocolitica


  Most commonly isolated species of Yersinia
• Infection acquired through eating of contaminated food and water from excreta of household animals (swine, cats, and dogs)
• Yersinia enterocolitica survives cold temperatures; food refrigeration becomes an ineffective preventive measure
• Sepsis associated with the transfusion of contaminated packed red blood cells has been reported
• Clinical forms of Yersinia enterocolitica infection

  • Acute enteritis
  • Appendicitis-like syndrome
  • Arthritis
  • Erythema nodosum
• Yersinia pseudotuberculosis

  Pathogen primarily of rodents, particularly guinea pigs; also domestic animals
• Natural reservoirs of Yersinia pseudotuberculosis

  • Birds
  • Turkeys
  • Geese
  • Pigeons
• Disease caused by Yersinia pseudotuberculosis

  Characterized by caseous swellings called pseudotubercles, often fatal in animals
• Human infections of Yersinia pseudotuberculosis are rare and associated with close contact with infected animals, their faecal material or ingestion of contaminated drink or food
• Ingested organisms of Yersinia pseudotuberculosis

  Spread to mesenteric lymph nodes, producing a generalized infection that is usually self-limiting
• Clinical presentation of Yersinia pseudotuberculosis infection

  Includes septicemia accompanied by mesenteric lymphadenitis
• Yersiniae identification characteristics

  • Gram-negative
  • Short rod
  • Non-motile
  • No-spore-forming
• Bipolar staining


  Intense staining at each end of the bacillus with methylene blue/Giemsa/Wayson stains - “safety-pin” appearance
• Yersiniae can be isolated on routine culture medium eg blood agar, MacConkey agar
• Yersiniae can grow at 37°C but preferentially at 25°C - 30°C
• Cold enrichment

  Incubation of a stool sample at 4°C for 1 week increases the frequency of recovery of Y. enterocolitica
• Biochemical tests are used to differentiate between the species of Yersinia
• Treatment for Yersinia pestis

  Combination of streptomycin and a tetracycline such as doxycycline; levofloxacin can also be used
• Treatment for Y. enterocolitica and Y. pseudotuberculosis

  Enterocolitis and mesenteric adenitis do not require treatment; in cases of bacteremia or abscess, either trimethoprim–sulfamethoxazole or ciprofloxacin is effective