Yersinia species

1
Yersinia species

• Yersinia pestis
• Yersinia enterocolytica
• Yersinia pseudotuberculosis

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Plague mortality

• Plague has claimed millions of lives
• 6th century - killed 100 million
• 14th century - killed 25 million (1/4 of Europe)
• 1890s - killed 10 million (Asia)

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Yersinia pestis history

• Dr. Yersina identified the causative agent of
  plague in 1894
• Only sylvatic cases (400) of plague have been
  reported in the south-western US

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Morphology/Physiology

• Gram-negative, pleomorphic bacillus

• Facultative anaerobe
• Optimal growth at 28o C

• Facultative intracellular parasites

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Cell Cycle

• Mass of plaque bacteria forms in gut of infected
  flea
• Flea regurgitates uncapsulated organisms into
  bite on animal or human
• Most organisms destroyed by PMN, but some
  entering histiocytes survive
• Bacteria re-encapsulate and grow.
• Progeny is resistant to intracellular killing by
  PMN

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Symptoms

• Draining lymph nodes to become hot, swollen,
  hemorrhagic and painful (buboes)
• continued release of organisms causes septicemia
  and invasion of lungs (pneumonia)
• Circulating organisms cause subcutaneous
  hemorrhage (Black Death)
• Exhaled organisms infect others and cause
  (pneumonic plague)

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The different forms of plague

• Sylvatic
• In animals (rodents, rabbits, carnivores) only
• Bubonic
• Flea (bite) to humans
• Pneumonic
• Human (aerosol) to human

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Bubonic vs pneumonic plague
entry
flea-bite
inhalation

disease
buboes, hemorrhage, pneumonia
rapid pneumonia
flea exhalation
exhaled droplets
exit
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Virulence Determinants

• Calcium dependence at 37o C (lcr)
• Proteins V W
• Yops
• Envelope (F-1) antigen
• Coagulase and Fibrinogen Activator (fibrinolysin)

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V and W antigens

• Plasmid encoded proteins
• Part of the low calcium (lcr) regulated response
• Rapid proliferation leading to overwhelming
  septicemia

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Yersinia Outer Proteins (Yops)

• Plasmid encoded lcr controlled proteins (11)
• Cytotoxic
• Inhibit phagocyte migration, engulfment and
  intracellular killing
• Inhibit platelet aggregation

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F-1 Antigen

• Protein-polysaccharide complex
• Highly expressed in the mammalian host
• Not expressed in flea host
• Antiphagocytic
• Antibodies to F-1 are protective

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Coagulase and Fibrinolysin

• Plasmid encoded proteins
• Coagulase causes clotting and microthrombi
  formation
• Fibrinolysin promotes dissemination

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Diagnosis

• Examination of Buboes aspirate stained smears for
  bipolar staining
• Fluorescent-antibody
• Culture/identify organisms (hazardous)

15
Treatment and Prevention

• Streptomycin or tetracycline
• Hospitalization and strict isolation
• Minimize domestic rat population
• Control flea population

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Yersinia enterocolitica

• Gram-negative rod, motile
• Isolated from rodents, farm animals, cats and
  dogs
• Humans acquire infection via fecal-oral route
• Most common in Scandinavia and Western Europe

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Symptoms

• abdominal pain, diarrhea
• can mimic appendicitis
• swollen lymph nodes, fever
• can develop severe arthritis (HLA-B27)

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Diagnosis

• Isolation of organisms from feces, blood, or
  lymph node biopsy

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Treatment

• Septicemia - gentamicin or chloramphenicol
• Enteritis - self limiting and usually not treated

20
Yersinia pseudotuberculosis

• Animal pathogen
• Infects wild and domestic animals
• Causes necrotic lesions in the liver, spleen, and
  lymph nodes
• Infection via oral route from infected animal
  fecal material

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Symptoms

• abdominal pain, diarrhea
• can mimic appendicitis
• swollen lymph nodes, fever
• Rarely invades bloodstream or cause internal
  lesions
• May cause arthritis

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Treatment

• ampicillin, streptomycin, or tetracycline