Aeromonas hydrophilia
Lisa Guntly

Background:

Aeromonas hydrophilia is a rod-shaped bacterium natively found in freshwater environments. It is a gram-negative, heterotrophic bacterium with size ranging from .3-1 um in diamenter and 1.0-3.5 um in length. Other characteristics of A. hydrophila include its classification as oxidase positive, facultatively anaerobic, motile, and non-spore forming. The optimum growth temperature for A. hydrophila is 28 C but growth has been observed from 4 C to 37 C. A. hydrophila moves via a single polar flagella. As do many gram-negative bacteria, it uses fimbriae to attach to host cells and surfaces. Besides ingesting glucose, A. hydrophila can also ingest gelatin and hemoglobin. A. hydrophila is primarily known as a fish pathogen but can also be pathogenic in humans and amphibians due to a tissue damaging enterotoxin.



scanning electron micrographs of A. hydrophila

Fish Pathogen:

A. hydrophila is known to cause tail rot, fin rot, hemorrahagic septicemia, scale protrusion disease, and ulcer disease primarily in freshwater fish. However, there is some debate over the role of A. hydrophila as a fish pathogen. Some researchers believe it is a primary fish pathogen while others consider it only a secondary invader of already weakened fish. Environmental stress appears to be a likely inducer of disease outbreaks caused by A. hydrophila. Since A. hydrophila is naturally found in the fish gut, some stress or previously weakened state is usually necessary for a disease to develop. Proper care and optimal environmental conditions in hatcheries can help prevent outbreaks. A. hydrophila causes a related disease in the Xenopus species of frogs called red-leg disease.


Skin ulcer in a rainbow trout caused by A. hydrophila

Human Pathogen

A. hydrophila in humans is an opportunistic pathogen associated with blood infections, wound infections, and diarrhea. Reports of wound infections have become more common recently and can cause severe damage possibly requiring amputation. Wound infections can be classified into 3 categories: cellulitis, myonecrosis, and ecthyma. Cellulitis is the most frequently encountered type of infection and involves inflammation of skin tissue. Myonecrosis is more serious and less common, involving the formation of lesions that can require ampuation if not treated agressively. Ecthyma can occur after a blood infection becomes septic and is usually fatal. These diseases are rare in humans, occuring mainly in people with weakened immune systems, and can be prevented by taking proper care of wounds, especially by not washing wounds with lake or river water. A. hydrophila is also considered a cause of diarrhea in humans, usually found in young children and people with weakened immune systems. A. hydrophila is resistant to penicillin and penicillin derivatives but several other antibiotics can be used to treat infections.


           cellulitis infection                                          Myonecrosis

Sources

Aeromonas. 21 Aug. 2006. MicrobeWiki. 15 Mar. 2007.
http://microbewiki.kenyon.edu/index.php/Aeromonas

Aeromonas hydrophila. 14 June 2006. U.S. Food and Drug Administration – Bad Bug Book. 16 Mar. 2007. http://www.cfsan.fda.gov/~mow/chap17.html

Hayes, John. Aeromonas hydrophila. 15 Mar. 2007. http://hmsc.oregonstate.edu/classes/MB492/hydrophilahayes/

Material Safety Data Sheet – Infectious Substance. 23 Jan. 2001. Health Canada. 16 Mar. 2007. http://www.phac-aspc.gc.ca/msds-ftss/msds6e.html

*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.

 

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