Aeromonadales

Aeromonadales is an order of Gram-negative, non-spore-forming, rod-shaped bacteria within the class Gammaproteobacteria. The order comprises two families, Aeromonadaceae and Plesiomonadaceae, with the genera Aeromonas and Plesiomonas representing the best studied groups.

Ecology and metabolism: They are widespread in aquatic habitats, especially freshwater and brackish environments, but can also be found in soil and on animals. Members are chemoorganotrophic and facultatively anaerobic. They are typically oxidase-positive, catalase-positive, motile by polar flagella, and capable of glucose fermentation. They are adapted to a range of temperatures, which supports their presence in diverse environments.

Clinical and pathogenic relevance: Several species are opportunistic human pathogens, notably Aeromonas hydrophila and Aeromonas veronii, implicated in gastroenteritis, wound infections, and septicemia, particularly in immunocompromised individuals. Plesiomonas shigelloides is another human pathogen associated with gastroenteritis. In aquatic animals, Aeromonas species are linked to fish diseases. Virulence factors include toxins, hemolysins, and secretion systems, though pathogenic potential varies by species and strains.

Taxonomy and research: Modern classification relies on 16S rRNA gene sequencing and genomic data; the arrangement within Gammaproteobacteria reflects phylogenetic relationships rather than solely phenotypic traits. The group is of interest for environmental microbiology, fish health, and public health due to its environmental ubiquity and occasional pathogenicity.