Aeromonas hydrophila is a bacterium that is extremely common in freshwater. This species is thought to cause foodborne disease and infections of wounds, among other diseases. The exact mechanisms of the virulence were not known as of 2011.
Part of the Aeromonadaceae family, cells of A. hydrophila are shaped like rods. They are Gram negative, which means that the cells appear reddish after a common staining process in microbiology called the Gram stain, which helps identify bacterial species on the basis of the thickness of their cell wall. Aeromonas hydrophila can live in environments that have oxygen present, but they also thrive without oxygen. Some bacteria produce spores, which are tough, dormant cells, to survive harsh environments, but A. hydrophila does not.
Widely present in water sources, A. hydrophila lives in rivers, lakes and even in seawater. The species also can be found in sewage and in drinking water sources. Inside water storage and water piping, it can form biofilms, which are like sticky layers of bacteria on a surface, and they are difficult to remove. Summer temperatures increase the rate of growth of the bacteria, so the warm months of the year show a higher rate of A. hydrophila infection compared with cooler months.
As of 2011, Aeromonas hydrophila was not definitively known to cause foodborne or waterborne illness. It is present, however, in the feces of many people who have diarrheal disease and who do not appear to be suffering from any other gastrointestinal pathogen. Artificial attempts at infection of volunteers with large numbers of the bacteria, on the other hand, have not resulted in disease. Symptoms of illness that are associated with the species range from bloody, loose stools to very watery diarrhea.
Various virulence properties are part of Aeromonas hydrophila's genetic makeup. Some of these properties are toxins that attack cells or attack blood. These are thought to play a role in the gastrointestinal disease. Young children and people who have weak immune systems are most at risk of developing the foodborne or waterborne form of A. hydrophila infection. The illness usually resolves itself without the need for treatment, and very few people experience a serious episode that leads to blood poisoning.
The types of food that may contain A. hydrophila cells are primarily fish and shellfish. Beef, lamb and poultry can also contain the bacteria. Scientist believe, however, that as the species is so common that not all of the strains of the species are capable of causing disease.
For people who have open wounds, swimming in or exposing the wound to water that has Aeromonas hydrophila in it can result in wound infections. Swallowing water while swimming can also cause gastrointestinal illness. Other forms of possible infections include cellulitis, meningitis and colitis, along with respiratory infections. Antibiotics are capable of treating all of these forms of disease.