30. Yersinia spp. The causative agent of plague (Yersinia pestis). Morphology, biology, pathogenic factors. Pathogenesis and immunity. Microbiological diagnosis. Specific prophylaxis and therapy. Yersinia enterocolitica. General characteristics.
Topic 30 of 50 in the MU Plovdiv syllabus for Microbiology (Medicine, Years 2 and 3). The free AceMed note covers it in 15 sections, about 470 words (6 min of reading), with 30 flashcards.
In this note
Yersinia pestis
General Characteristics
Virulence Factors of Y. pestis
Epidemiology
Lab Diagnosis
Clinical Forms of Plague
Treatment
Prevention and Control
Yersinia enterocolitica
Pathogenesis
Virulence Factors
Diseases Caused
Diagnosis
Prevention
Comparison: Yersinia pestis vs Yersinia enterocolitica
General Characteristics
Family: Enterobacteriaceae
Shape: Gram-negative, small, ovoid rods
Motility: Non-motile
Capsule: Present at 37°C → protein capsule helps evade phagocytosis
Growth conditions: Facultative anaerobe
Staining: Bipolar staining seen with Giemsa or Wayson stain (safety pin appearance)
Temperature tolerance: Survives in cold, sensitive to heat
Culture: Forms rough colonies with scalloped edges and grainy appearance on nutrient agar
Biochemical:
Lactose (-)
Indole (-)
Citrate (-)
Catalase (+), Glucose (+)
Urease (-)
Epidemiology
Reservoir: Wild rodents (e.g., rats, squirrels)
Vector: Rat flea (Xenopsylla cheopis)
Transmission:
Bite of infected flea → most common route
Inhalation (droplets from infected person/animal) → pneumonic plague
Contaminated food/water (rare alimentary spread)
Geography: Still endemic in parts of Africa, Asia, South America
Lab Diagnosis
Specimens: Pus (buboes), blood, sputum (pneumonic), stool (rare)
