Microbiology · Enterobacterales
Yersinia !
- Bacterium
- Gram-negative
- Droplet
- For completeness
A genus with Y. pestis, which causes plague through rodent flea bites, and Y. enterocolitica, which causes diarrhea from pork.
Updated 2026-11-01
Also called: Yersinia pestis, Yersinia enterocolitica, plague bacillus
At a glance
- Gram
- Gram-negative
- Shape
- Coccobacillus; Y. pestis stains bipolar ("safety pin")
- Oxygen
- Facultative anaerobe
- Family
- Yersiniaceae
- Stain
- Giemsa or Wayson: dark staining at both ends
Morphology
- Gram-negative coccobacillus; Y. pestis non-motile, Y. enterocolitica motile at room temperature
- Non-lactose fermenters
- Y. enterocolitica grows in the cold (survives in refrigerated food and stored blood)
Transmission
- Plague: bites of infected rodent fleas, contact with animal tissues and, in the pneumonic form, respiratory droplets between people
- Y. enterocolitica: raw or undercooked pork, unpasteurized milk, untreated water
- Droplet (on top of standard) for pneumonic plague
Reservoir: Wild rodents and their fleas (Y. pestis); Pigs (Y. enterocolitica)
Vector: Rodent fleas (Y. pestis).
Isolation precautions
What the care team adds to standard precautions.
- Droplet
- Surgical mask within about a metre; single room.
Virulence factors
- F1 capsule and V and W antigens: resist phagocytosis
- Yop proteins injected through a type III secretion system: paralyze macrophages
- Rapid growth in lymph nodes (buboes) and blood
- Y. enterocolitica invades the terminal ileum and mesenteric nodes; iron overload (deferoxamine) raises the risk of sepsis
Diseases it causes
- Bubonic, septicemic and pneumonic plague Plague →
- Y. enterocolitica gastroenteritis with mesenteric adenitis that mimics appendicitis Acute (viral) gastroenteritis →
Clinical picture
- Bubonic plague: sudden fever and a very painful swollen node (bubo) near the bite
- Pneumonic plague: severe, contagious pneumonia, fatal without early treatment
- Y. enterocolitica: fever and right lower quadrant pain (pseudoappendicitis); later reactive arthritis or erythema nodosum
Diagnosis
- Plague: culture or stain of bubo aspirate, blood or sputum; rapid F1 antigen test
- Y. enterocolitica: stool culture on CIN agar (alert the lab), stool PCR
Treatment
Plague: immediate antibiotics with aminoglycosides (streptomycin or gentamicin), fluoroquinolones or doxycycline. Y. enterocolitica: most cases clear without antibiotics; severe cases get fluoroquinolones, trimethoprim-sulfamethoxazole or third-generation cephalosporins.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Rodent and flea control; not handling dead animals
- Antibiotic prophylaxis for contacts of pneumonic plague
- Cook pork through and use pasteurized milk
- Plague vaccine only for high-risk groups
Test yourself
Think of the answer, then tap the question to see it.
How is bubonic plague transmitted?
By the bite of infected rodent fleas or contact with infected animal tissue.
Which form of plague spreads between people, and which precaution does it need?
Pneumonic plague; it needs droplet precautions on top of standard.
Which gut infection mimics appendicitis and is linked to pork?
Yersinia enterocolitica infection (mesenteric adenitis and terminal ileitis).
What does Y. pestis look like on Giemsa or Wayson stain?
Coccobacilli staining darker at both ends, like a safety pin.
Related
Related conditions
← Back to the group: Enterobacterales
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Plague (WHO, 2026); About Plague (CDC, 2026); About Yersinia Infection (CDC, 2024).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.