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Adapted from Graf (2015) writing in Aeromonas.

The genus Aeromonas

The genus Aeromonas consists of a group of bacterial species in the gamma subclass of the Proteobacteria (i.e., Gammaproteobacteria). Aeromonas is a Gram-negative, facultative anaerobic bacterium. Some of the members are associated with infections in humans, fish, and other animals, and are widespread in aquatic environments (Graf, 2015).

The genus Aeromonas is a fascinating group of organisms for a variety of reasons, including the complicated taxonomy, the controversy of causing infections in humans, and the wide range of hosts colonized. The history of bacteria now considered to be Aeromonas dates back to 1891, when these bacteria were linked to 'red leg' disease in frogs. It was over 50 years later when Proteus hydrophila, which later was reclassified to Aeromonas hydrophila, was described. During the 1980s DNA-DNA hybridization studies lead to the description of the main hybridization groups that included the species that are the most important fish and human pathogens, A. salmonicida, A. hydrophila, A. veronii and A. caviae. The advance of rRNA gene sequencing led to separation of the aeromonads from the Vibrionaceae as their own family. Over the years the interest in Aeromonas has increased as reflected by the increase in publications involving Aeromonas (Graf, 2015).

Perhaps the best-known diseases caused by aeromonads involve fish and are traditionally thought to be caused by non-motile (A. salmonicida) or motile (A. hydrophila) Aeromonas strains. However it is clear that an increasing number of other Aeromonas spp. have been shown to be able to cause disease in fish.

The role of Aeromonas spp. in causing disease in humans is perhaps the most controversial one, especially when it comes to the digestive tract illnesses such as diarrhoea. Current evidence for Aeromonas being a human pathogen focuses not just on gastrointestinal illnesses but also other infections that Aeromonas isolates have been associated with including injury or wound infections, nosocomial infections, septicaemia, respiratory tract infections and peritonitis.

While most research focuses on pathogenic associations of Aeromonas, some members of this genus are found in a number of different animals that are colonized in a benign or even beneficial manner. The best studied example of this is the digestive tract symbiosis of A. veronii and the medicinal leech and it was shown that Aeromonas can induce the normal development of the digestive tract in gnotobiotic zebrafish. In addition, Aeromonas spp. have been reported in mosquitoes and vampire bats, but the role in those organisms is less well understood.

As Aeromonas species are wide spread in water understanding the ecology, prevalence and factors influencing their abundance is important. Both results from classical culture-dependent studies and 16S rRNA gene studies are relevant (Graf, 2015).


Graf, J. (2015). Aeromonas. (Norfolk, UK: Caister Academic Press).

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