Chapter Three - Aeromonas

Abstract

Aeromonas species are Gram-negative, rod shaped, non-spore forming, oxidase-positive, and facultatively anaerobic bacteria. Aeromonas are divided into two groups namely the non-motile psychrophilic aeromonads and the motile mesophilic aeromonads. These bacteria are commonly found in freshwater reservoirs, soil and agricultural produce. Aeromonas have also been isolated from the gastrointestinal contents of fish, reptiles, amphibia and higher vertebrates. Aeromonads have been documented as being involved in both intestinal and extraintestinal human infections. There are a number of virulence mechanisms possessed by Aeromonas, in particular the ability to be an avid biofilm former. In addition, many extracellular enzymes produced by Aeromonas are known to enhance its virulence and pathogenicity, including nucleases, cytolytic toxins, staphylolysin, lipases, sulphatases, lecithinase and amylase. Numerous epidemiological studies suggest that people become colonized by Aeromonas from contaminated drinking untreated water systems. However, the possible role of potable water implicated in the transmission of infections from Aeromonas is still under discussion. When it comes to controlling the numbers of Aeromonas, it has been found that for clinical and environmental strains of A. hydrophila, A. sobria, A. caviae and A. veronii, the mesophilic aeromonads are generally more susceptible to chlorine and monochloramine than the Enterobacteriaceae and pseudomonads