Gram negative, rod-shaped, facultative anaerobes.
Two main groups, the first is the non-motile psychrophilic aeromonads, with optimal growth temperatures of 22–28 degree represented by Aeromonas salmonicida. The second much larger group contains the mesophilic motile aeromonads that have optimal growth temperatures of 30–37 degree.
Currently the genus contains 27 accepted and validated species.
Aeromonads are found ubiquitously in the environment, but are mainly associated with fresh or estuarine brackish water.
A. hydrophila -- a pathogen of fish, amphibians, reptiles, mammals, and an opportunistic pathogen of human.
The pathogenicity of Aeromonas is usually considered to be multifactorial: a number of virulence factors, including secretion systems, motility and adhesins, toxins, enzymes, quorum systems, iron acquisition and antibiotic resistance, have been identified, and metabolic adaptations may link with bacterial virulence.
Aeromonas are able to cause disease in many animal species but are mainly associated with infections in aquatic poikilothermic animals.
The psychrophilic species A. salmonicida subsp. salmonicida is a problem in aquaculture causing furunculosis, an infective bacteraemic and ulcerative disease of salmonid fish (salmon, trout) as well as several other economically important fish species such as turbot, or cod.
A. hydrophila and a
number of other motile aeromonad species can cause MAS (Motile Aeromonas septicaemia).
Aeromonads can cause a series of others infections in both reptiles and amphibians.
In humans, the mesophilic Aeromonas are mainly linked to gastroenteritis and wound infections, withmore than 85% of human clinical cases being caused
by three species, A. hydrophila, A. caviae and A. veronii biovar sobria.
In some instances (particularly in the young, elderly and other immunocompromised individuals), Aeromonas infections can range from superficial skin sequelae to more systemic infections including: cellulitis, bacteraemia, peritonitis and haemolytic–uraemic syndrome.
Genomes: ⇒ comparative pathogenomics ⇐
A. hydrophila ML09-119, 5024500 bp, NC_021290
A. hydrophila subsp. hydrophila ATCC 7966, 4744448 bp, NC_008570
A. salmonicida subsp. salmonicida A449, 4702402 bp, NC_009348
A. veronii B565, 4551783 bp, NC_015424
A. salmonicida subsp. salmonicida A449 5, 155098 bp, NC_009350
Seshadri R, et al., 2006. Genome sequence of Aeromonas hydrophila ATCC 7966T: jack of all trades. J Bacteriol 188(23):8272-82.
Reith ME, et al., 2008. The genome of Aeromonas salmonicida subsp. salmonicida A449: insights into the evolution of a fish pathogen. BMC Genomics 9:427.
Li Y, et al., 2011. Complete genome sequence of Aeromonas veronii strain B565. J Bacteriol 193(13):3389-90.
Schematic diagram showing the numerous structures that have been associated or implicated in the aeromonad pathogenesis process (From: Lowry R, et al., 2014. Aeromonas flagella and colonisation mechanisms. Adv Microb Physiol 65:203-56.).
Major virulence factors in Aeromonas:
Flp type IV pili
MSHA type IV pili
Tap type IV pili
Type I pili
Lateral flagella (A. salmonicida)
T3SS (A. salmonicida)
Location of virulence-associated genes in A. hydrophila:
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