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Plesiomonas shigelloides

General characteristics

This is a Gram-negative, rod-shaped bacterium, which has been isolated from freshwater, freshwater fish, and shellfish and from many types of animals including cattle, goats, swine, cats, dogs, monkeys, vultures, snakes, and toads.

Most human P. shigelloides infections are suspected to be waterborne. The organism is mainly of tropical and sub-tropical origin. The organism may be present in unsanitary water, which has been used as drinking water, recreational water, or water used to rinse foods that are consumed without cooking or heating. The ingested P. shigelloides organism does not always cause illness in the host animal but may reside temporarily as a transient, non-infectious member of the intestinal flora. It has been isolated from the stools of patients with diarrhoea, but is also sometimes isolated from healthy individuals (0.2-3.2% of population).

It cannot yet be considered a definite cause of human disease, although its association with human diarrhoea and the virulence factors it demonstrates make it a prime candidate.

Disease symptoms

Gastroenteritis is the disease with which P. shigelloides has been implicated.

Most P. shigelloides strains associated with human gastrointestinal disease have been from stools of diarrheic patients living in tropical and subtropical areas. Infections are rarely reported in the U.S. or Europe, partly because of the self-limiting nature of the disease.

P. shigelloides gastroenteritis is usually a mild self-limiting disease with fever, chills, abdominal pain, nausea, diarrhoea, or vomiting; symptoms may begin 20-24 hours after consumption of contaminated food or water; diarrhoea is watery, non-mucoid, and non-bloody; in severe cases, diarrhoea may be greenish-yellow, foamy, and blood tinged; duration of illness in healthy people may be 1-7 days.

The infectious dose is presumed to be quite high, at least greater than one million organisms.


The pathogenesis of P. shigelloides infection is not known. The organism is suspected of being toxigenic and invasive. Its significance as an enteric (intestinal) pathogen is presumed because of its predominant isolation from stools of patients with diarrhoea. It is identified by common bacteriological analysis, serotyping, and antibiotic sensitivity testing.

Associated foods

Most P. shigelloides infections occur in the summer months and correlate with environmental contamination of freshwater (rivers, streams, ponds, etc.). The usual route of transmission of the organism in sporadic or epidemic cases is by ingestion of contaminated water or raw shellfish.


Total prevention is probably not possible, however avoiding raw shellfish and ingestion of surface water may reduce the risk.

Risk populations

All people may be susceptible to infection. Infants, children and chronically ill people are more likely to experience protracted illness and complications.


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