YERSINIA
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| GRAM STAINING |
YERSINIA PESTIS
Yersinia Pestis: Causative agent of plague.
General characterstics
Gram negative bacilli or coccobacilli, with rounded ends, convex or parallel sides. Non motile. Capsule present when grown at 37ºC. Bipolar staining (safety pin appearance) with methylene blue or giemsa stain.
Pleomorphic when grown in unfavourable conditions (nutrient agar with 3% sodium chloride). Grow on ordinary media. Colonies are dark brown on blood agar because of absorption of haemin. On Maconkey agar NLF colonies are produced. Optimum temperature 27ºC Liquid media- granular deposit and surface pellicle. Shows stalactite growth if a drop of sterile oil/gheebroth is allowed to float on broth and the medium is not disturbed growth hangs down from oil/ghee into the liduid medium which looks like stalactites.
Catalase: Positive
Oxidase, Urease, and Indole: Negative
- Fraction-1 or F1: heat labile protein envelope antigen ⇒ antiphagocytic
- V and W antigens: always produced together ⇒inhibits phagocytosis andintracellular killing,
- Pesticin 1 (bacteriocin), fibrinolysin ,coagulase : inhibits strains of Y.enterocolitica and Y. Pseudotuberculosis and E.coli
- Plague toxin (endotoxin -LPS and Murinetoxin)Ability to synthesize purine
Pathogenesis
Causative agent of plague. It is a zoonotic disease. Rodents are the natural reservoirs. It is transmitted through a bite of an infected rat flea (Xenopsylla species), but can also be transmitted by air (especially during pandemics of thE disease). Rat fleas become infected after taking blood meals from septicemic animals. Y. pestis grows in the midgut and eventually blocks the proventriculus, starving the flea for blood. The insects attempt to feed more often but end up giving back infected blood into the wound. Rat flea can’t fly. It jumps to a height of <2 feet, usually biting on the legs of humans.
Laboratory Diagnosis
Specimen
- For pneumonic plague Sputum /Bronchial wash/ tracheal aspirate,
- For septicemic plague - blood.
- For bubonic plague - Aspirate or biopsy of bubo.
Culture: Exudates/other specimen cultured on blood agar. Perform biochemical testing for identification of the isolate. Blood culture can be done in septicemic cases.
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| Yersinia enterocolitica growing on C.I.N. Agar |
YERSINIA ENTEROCOLITICA
Causative agent of gastroenteritis, mesenteric lymphadenitis and septicaemia. Laboratory diagnosis is by isolation of organism from blood, lymph node, feces, food or soil or by serology using tube agglutination test. Cold enrichment often helps. The organism is motile at 25°C but non motile at 37°C.
YERSINIA PSEUDOTUBERCULOSIS
Causative agent of pseudotuberculosis (a zoonosis). Causes mesenteric lymphadenitis and erythema nodosum especially in young males. Diagnosis is by serology using tube agglutination test (for antibody detection). This organism is motile at 25°C but non motile at 37°C and hydrolyses urea and has relatively poor growth on MaConkey agar.
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