• 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:

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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