This organism is capable of producing cytotonic enterotoxins, Alt and Ast, as well as the cytotoxic enterotoxin (Alt). Enterotoxins are toxic proteins that specifically affect the intestinal lining. Cytotonic enterotoxins more specifically change the morphology of the cell, but do not kill the cell. For example, they are able to lyse red blood cells, destroy tissue culture cell lines, evoke a fluid secretory response in ligated intestinal loop models, and induce lethality in mice. In contrast, cytotoxic enterotoxins result in cell death.

Alt is composed of a single polypeptide chain with 368 amino acids. This enterotoxin is homologous to the Alt enterotoxin in E. coli. Ast is a heat-stable cytotonic enterotoxin, having the least significant effect on fluid secretion compared to Alt and Act. It is also a single polypeptide chain made up of 636 amino acids.

Act, the pore-forming cytoxic enterotoxin contributes the greatest to fluid secretion out of the three toxins. In fact, it is so significant that the amount of Act secreted is most strongly related to the extent of tissue damage in the host. Thus, the more bacteria present at the site of injury, the greater the infection. However, out of all infections caused by Aeromonas hydrophila, Act is only secreted about 50% of the time while Alt and Act are secreted in 100% of infections. In intestinal infections, Act is most closely related to the symptomatic presence of bloody diarrhea. In other sites of infections, this enterotoxin can be lethal at certain doses. As an aerolysin toxin, it is able to kill host cells by forming discrete channels in the plasma membranes of host cells. Since this toxin is able to kill tissues, especially in wound infections, it can cause the formation of gas gangrene which can be fatal to the host. The formation of gas gangrene in Aeromonas hydrophila is not common, but has been reported several times in clinical reports. The genus Clostridium more frequently causes the formation of gas gangrene. As dangerous as this particular infection can be, it is not very common.

It is possible that a strain of Aeromonas hydrophila with the Act, Alt, and Ast genes deleted could serve as a potential vaccine in the future.

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