Plesiomonas shigelloides: clinical, cultural and biochemical characteristics
Plesiomonas shigelloides: clinical, cultural and biochemical characteristics
  • Plesiomonas is derived from the Greek word where it means “neighbor”.
  • It indicates Plesiomonas has a close association with
  • It is included in the family Enterobacteriaceae.
  • P. shigelloides is the only species in the genus.

Classification of Plesiomonas shigelloides:

  • Kingdom: Bacteria
  • Phylum: Proteobacteria
  • Class: Gammaproteobacteria
  • Order: Enterobacteriales
  • Family: Enterobacteriaceae
  • Genus: Plesiomonas
  • Species: shigelloides

Clinical Significance of Plesiomonas shigelloides:

  • Plesiomonas shigelloides is present in surface waters and soil.
  • Different cold-blooded animals like frogs, snakes, turtles, lizards are infected by
  • By the ingestion of contaminated food, humans become infected with it.
  • Despite its less frequent recovery from human feces as compared to Aeromonas, Plesiomonas-induced gastroenteritis has been reported in children and adults.
  • In humans, Plesiomonas-related gastroenteritis is manifested as mild watery diarrhea.
  • In this condition, stools are free of blood and mucin.
  • In the immunosuppressed patients or persons having GI malignancies, severe colitis or a cholera-like illness may be seen.
  • The prevalence of this infection is more during the warm summer months and in the subtropical and tropical regions of the world.
  • It produces enteropathogenic enterotoxin.
  • It has caused illness after uncooked shellfish consumption.
  • It is also a cause of travelers’ diarrhea.
  • Extraintestinal infections have also been reported such as:
    • Septicemia
    • neonatal meningitis
    • cellulitis
    • septic arthritis
    • acute cholecystitis
  • Other reported cases are:
    • Postsplenectomy infection
    • Plesiomonas shigelloides-associated persistent dysentery
    • pseudomembranous colitis

 Laboratory diagnosis of Plesiomonas shigelloides:

  • P. shigelloides is a straight-to-rounded, short, Gram-negative bacteria.
  • Motile
  • Have lophotrichous flagella
  • grows well on sheep blood agar and most enteric media.
  • nonhemolytic on sheep blood agar
  • Grows at the incubation of 24 hours at 30°C- 35°C.
  • optimum  growth temperature is 30°C
  • Colony characteristics of Plesiomonas shigelloides:
    • average 1.5 mm in diameter
    • gray
    • shiny
    • smooth
    • opaque
    • slightly raised in the center.
  • Culture media for shigelloides:
    • MacConkey Agar
    • Deoxycholate Agar
    • Hektoen agar
    • xylose lysine deoxycholate Agar
  • Glucose fermentation takes place and appears as yellow in:
    • Kligler’s iron agar
    • triple sugar iron agar
  • Non-lactose fermenter in MacConkey agar and make confusion with Shigella spp
  • oxidase-positive
  • indole positive.
  • decarboxylates arginine, lysine, and ornithine
  • does not produce DNase or extracellular proteases
  • ferments inositol but not mannitol

Biochemical Characteristics of Plesiomonas shigelloides:

Hemolysis on sheep blood No haemolysis
Oxidase Positive
Motility Positive
DNase negative
Indole Positive
Voges-Proskauer negative
Decarboxylase test:  
Lysine positive
Ornithine positive
Arginine positive
Esculin test negative
Gas from Glucose fermentation negative
L-Arabinose  negative
Sucrose  negative
Mannitol negative
Inositol positive


Antibiotic Susceptibility of Plesiomonas shigelloides :

  • Resistant to penicillin, ampicillin, carbenicillin, and other β-lactamase susceptible penicillins.
  • susceptible to the aminoglycosides, chloramphenicol, tetracycline, trimethoprim-sulfamethoxazole and the quinolones, ciprofloxacin, and norfloxacin.


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