Plesiomonadaceae

Plesiomonadaceae is a family of Gram-negative, facultatively anaerobic, rod-shaped bacteria within the class Gammaproteobacteria. The family comprises a single genus, Plesiomonas, with Plesiomonas shigelloides as its best-known species.

Taxonomy: It is placed in the order Enterobacterales, phylum Pseudomonadota. The type genus is Plesiomonas. Some classifications place Plesiomonadaceae near other enteric bacteria due to shared traits.

Biology: Members are Gram-negative, oxidase-positive, motile by a flagellum, non-spore-forming and facultatively anaerobic. They are generally non-lactose fermenters and may be curved or rod-shaped.

Ecology and clinical relevance: Plesiomonas species are found in aquatic environments worldwide, including freshwater and brackish habitats, and can be associated with fish and other aquatic animals. Plesiomonas shigelloides is the species most commonly isolated from human clinical samples and is recognized as a cause of gastroenteritis, presenting with diarrhea, abdominal cramps, and fever. Rarely, infections such as septicemia or wound infections occur in immunocompromised individuals.

Laboratory identification and treatment: Diagnosis is based on culture of clinical specimens followed by biochemical or molecular identification. Because antibiotic susceptibility varies, treatment decisions are guided by susceptibility testing; many infections are self-limiting, while severe cases require appropriate antimicrobial therapy.