Plesiomonas shigelloides
Plesiomonas shigelloides characteristics
Plesiomonas shigelloides is a gram-negative bacillus that derived its name from the ancient Greek word plēsíon, which means “near” or “neighbour”, as it was considered near or related to the bacteria Aeromonas.
It is mostly found in freshwater, estuarine, or brackish water environments. It can be found in animals living in these environments, like fish, shrimp, shellfish, amphibians, reptiles, and vertebrates. It is mostly found in tropical waters but is increasingly reported from colder countries, especially in warmer months. In warmer temperatures, it could be found in seawater (and saltwater animals) as well.
Photo of the Mattole River estuary at the Pacific Ocean.
Wikipedia (Mattole Restoration Council - Mattole)
How do we get Plesiomonas shigelloides infection?
Most cases are associated with the consumption of raw or poorly prepared seafood, especially shellfish. Other types of contaminated foods, like chicken, could also be a source. It has also been reported to occur from the consumption of contaminated water.
Plesiomonas shigelloides symptoms
Diarrhoea: Plesiomonas has been associated with diarrhoea, which could be
Mild self-limiting watery diarrhoea (most common),
Severe bloody diarrhoea/ dysenteric colitis. or,
Chronic diarrhoea (>14 days duration)
Diarrhoea could be associated with abdominal pain, fever and vomiting. It is one of the commonest causes of travellers’ diarrhoea. Diarrhoea may last from 3 to 40 days.
A large number of Plesiomonas infections ( ~30%) are co-infection with other pathogens like rotavirus, Salmonella, Aeromonas, Vibrio parahaemolyticus.
Extraintestinal infection: Infections like sepsis and meningitis are usually seen in children or in immunocompromised people. Other infections rarely associated with this bacteria are –
osteomyelitis, septic arthritis,
endophthalmitis,
spontaneous bacterial peritonitis, pancreatic and splenic abscess, cholecystitis,
cellulitis,
epididymo-orchitis, salpingitis and
pneumonia.
Incubation period of Plesiomonas shigelloides is 1 - 2 days.
What are the risk factors for Plesiomonas shigelloides infection?
Diarrhoea
Consumption of uncooked/undercooked seafood, especially shellfish,
travel to south/southeast Asia,
HIV,
Children.
Extraintestinal disease
Old age,
underlying biliary disease,
immunocompromised state (HIV, cancer),
blood dyscrasia (sickle cell disease, thalassemia)
Plesiomonas shigelloides virulence factors
cytotoxic haemolysin,
iron acquisition systems, and
lipopolysaccharide
Plesimonas shigelloides laboratory identification
Plesiomonas shigelloides gram stain
Short Gram-negative rod.
Plesiomonas shigelloides culture
It is facultatively anaerobic, non–spore-forming, motile (polar flagella) bacilli.
On blood agar, it produces large grey, opaque, and convex, β-haemolytic colonies.
On Inositol Brilliant Green Bile Agar – pink colonies.
MacConkey agar – Non-lactose fermenting colonies.
Salmonella-Shigella agar may be inhibitory for some strains.
Plesiomonas shigelloides Treatment
Usually, diarrhoea is self-limiting; hence antibiotics may not be necessary. Supportive therapy with rehydration and nutrition should be sufficient.
Chronic diarrhoea, severe disease and extra intestinal disease may benefit from antibiotic therapy.
Plesiomonas shigelloides infection can be treated with azithromycin, ciprofloxacin (a fluoroquinolone), 3rd generation cephalosporin, carbapenems etc.
This organism is often resistant to amoxicillin and tetracycline.
Reference
Janda JM, Abbott SL, McIver CJ. 2016. Plesiomonas shigelloides revisited. Clin Microbiol Rev 29:349–374. doi:10.1128/CMR.00103-15.
Robert M. Kliegman, Aeromonas and Plesiomonas, Nelson Textbook of Pediatrics, 2020
Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases, 2020