Yersinia Bacteriology Notes

Cause of Disease in Rodents

  • Plague-like disease primarily affects guinea pigs, sometimes rats and other rodents; rare in other animals.
  • Pleomorphic nature; can appear as coccoid to bacilli (5 µm or more long).
  • Bi-polar staining possible.
  • Exhibits peritrichous flagella when cultured at 18-30ºC, absent at 37ºC.

Cultural Characteristics

  • Colonies are non-hemolytic, measuring 0.1 to 1.0 mm, and exhibit translucency and granularity.
  • Fermentation of glucose and some carbohydrates occurs but little to no gas is produced.

Virulence Factors

  • Envelope antigen (F1 antigen), made up of protein and carbohydrates, plays a critical role in virulence; also found in Yersinia pestis.
  • Infection primarily occurs through ingestion, with increased susceptibility in cold weather.
  • Significant swelling of mesenteric lymph nodes, characterized by caseous nodules and abscesses, particularly in Peyer's patches, liver, and spleen.
  • The presence of F1, V, and W antigens is crucial for virulence.

Genus Yersinia

  • Named after French bacteriologist Alexandre Yersin, who isolated Y. pestis in 1894 as the cause of plague.
  • Contains seven species, with Y. pseudotuberculosis being an important animal pathogen.
  • Y. enterocolitica commonly resides in the alimentary tracts of animals (carriers) and can infect humans.
  • Y. pestis is responsible for plague in humans, mainly affecting rodents, though can also infect dogs and cats.

Morphology and Staining

  • Yersinia may appear singly or in chains.
  • Gram-negative, non-acid fast, and non-capsulated organisms.
  • At 37ºC, flagella may be detached with antigens absent.

Cultural and Biochemical Features

  • Older colonies may have a raised center and opaque appearance compared to the peripheral area, showing radial striations.
  • Optimum growth temperature is 28ºC.
  • Yersinia does not produce urease, meaning it cannot break down urea.

Antigens

  • Encoded via plasmid, V and W antigens are also found in Y. pseudotuberculosis and Y. pestis.
  • Six serogroups based on thermos-stable O antigens L-VI and five H antigens (a to e).

Epizootiology and Pathogenesis

  • Infects diverse hosts: rodents, birds, and soil environments.
  • Associated with pneumonia and abortion in cattle.
  • Can cause abdominal and urinary disorders in cats.
  • Pseudotuberculosis is common in captive birds.
  • Guinea pigs may exhibit weight loss, diarrhea, and can die within 3 to 4 weeks of infection.

Disease Manifestations

  • Resembles Y. pseudotuberculosis in morphology and antigenic structure.
  • Heat-stable enterotoxin produced at 30ºC; disease can manifest pneumonically in colder climates, being both highly fatal and spreadable.
  • In rat populations, transmission usually occurs through flea bites (e.g., Xenopsylla cheopis).
  • The sylvatic form of plague can emerge in less inhabited areas.

Immunity

  • Live, avirulent cultures can confer immunity against virulent strains in guinea pigs.
  • Yersinia operates as a facultative intracellular parasite with significant cell-mediated immune responses.

Diagnosis

  • Differentiation from Y. pestis can be performed using a urease test and the bacterium's growth on deoxycholate-citrate agar.

Antimicrobial Susceptibility

  • Sensitive to chloramphenicol, nalidixic acid, streptomycin, sulfonamides, and tetracycline.

Human Disease Impact

  • Rare but severe cases can lead to fatal infections, mesenteric adenitis, or septicemia.
    • Septicemia: presence of bacteria in the blood; may or may not cause disease.

Yersinia enterocolitica

  • Ubiquitous presence but isolated in cases of alimentary disturbances in humans and chinchillas.
  • Found in healthy cattle and swine, isolated from contaminated meat, shellfish, and ice cream.
  • Has 34 O antigens, including 03 from pigs and common ones (03, 08, 09) from humans.
  • Causes disease symptoms like terminal ileitis, diarrhea, mesenteric adenitis, and can mimic appendicitis.

Yersinia pestis

  • The causative agent of bubonic plague or the Black Death in humans; fatal and highly contagious.
  • Primarily a rodent disease, with humans accidentally becoming infected.
  • In warm climates, the disease frequently presents in bubonic form, characterized by swollen lymph nodes (buboes).
  • Not typically associated with domestic animal diseases, and the organism thrives in fleas.