Aeromonas Hydrophila

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MICROBIOLOGY LEGEND

CYCLE 28 – ORGANISM 3

Aeromonas hydrophila

Aeromonas hydrophila is a heterotrophic, gram-negative, rod shaped bacterium, mainly found in areas with a warm climate. This bacterium can also be found in fresh, salt, marine, estuarine, chlorinated, and un-chlorinated water. Aeromonas hydrophila can survive in aerobic and anaerobic environments. This bacterium can digest materials such as gelatin, and hemoglobin. This bacterium is the most well known of the six species of Aeromonas. It is also highly resistant to multiple medications. Aeromonas hydrophila is resistant to chlorine, refrigeration and cold temperatures.

Structure Aeromonas hydrophila are Gram-negative straight rods with rounded ends (bacilli to coccibacilli shape) usually from 0.3 to 1 µm in width, and 1 to 3 µm in length. Aeromonas hydrophila does not form endospores, and can grow in temperatures as low as four degrees Celsius. These bacteria are motile by a polar flagella.

Aeromonas hydrophila - Gram stain Pathology

Thistle QA is a SANAS accredited organisation, No: PTS0001 Accredited to ISO guide 43 and ILAC G13 Certificate available on request or at www.sanas.co.za

P.O. Box 131375, Bryanston, 2074 Ground Floor, Block 5 Bryanston Gate, Main Road Bryanston, Johannesburg, South Africa www.thistle.co.za Tel: +27 (011) 463-3260 Fax: +27 (011) 463-3036 OR + 27 (0) 86-538-4484 e-mail : [email protected] Because of Aeromonas hydrophila’s structure, it is very toxic when it enters the body of its victim. It travels through the bloodstream to the first available organ and produces Aerolysin Cytotoxic Enterotoxin (ACT), a toxin that can cause tissue damage. Aeromonas hydrophila, Aeromonas caviae, and Aeromonas sobria are all considered to be opportunistic pathogens, meaning they only infect immunocompromised hosts. Though Aeromonas hydrophila is considered a pathogenic bacterium, scientists have not been able to prove that it is the actual cause of some of the diseases it is associated with. It is believed that this bacterium aids in the infection of diseases, but does not cause the diseases themselves.

Pathogenic mechanism It was believed that the pathogenicity of Aeromonas spp. is mediated by a number of extracellular proteins such as Aerolysin, lipase, chitinase, amylase, gelatinase, hemolysins and enterotoxins. However the pathogenic mechanisms of Aeromonas spp. is remain unknown. The recently proposed type III secretion system (TTSS) mediated pathogenic mechanism has been proven to play a pivotal role in Aeromonas pathogenesis.

The TTSS is specialized protein secretion machinery that export virulence factors delivered directly to host cells. These factors subvert normal host cell functions in ways that are beneficial to invading bacteria. In contrast to the general secretory pathway, type III secretion system is triggered when a pathogen comes in contact with host cells.

ADP-ribosylation toxin is one of the effector molecules secreted by several pathogenic bacteria, translocated through TTSS and delivered into the host cytoplasm which leads to interruption of NF-κB pathway, cytoskeletal damage and apoptosis. This toxin has been characterized in Aeromonas hydrophila (human diarrhoeal isolate), Aeromonas salmonicida (fish pathogen) and Aeromonas jandaei GV17, a pathogenic strain which can cause disease both in human and fish.

Occurrence of exposure Aeromonas hydrophila infections occur most during environmental changes, stressors, change in the temperature, in contaminated environments, and when an organism is already infected with a virus or another bacterium. It can also be ingested through food products that have already been infected with the bacterium, such as seafood, meats, and even certain vegetables such as sprouts.

Human diseases Aeromonas hydrophila is not as pathogenic to humans as it is to fish and amphibians. One of the diseases it can cause in humans is gastroenteritis. This disease can affect anyone, but it occurs most in young children and people who have compromised immune systems or growth problems. This bacterium is linked to two types of gastroenteritis.

Thistle QA is a SANAS accredited organisation, No: PTS0001 Accredited to ISO guide 43 and ILAC G13 Certificate available on request or at www.sanas.co.za

P.O. Box 131375, Bryanston, 2074 Ground Floor, Block 5 Bryanston Gate, Main Road Bryanston, Johannesburg, South Africa www.thistle.co.za Tel: +27 (011) 463-3260 Fax: +27 (011) 463-3036 OR + 27 (0) 86-538-4484 e-mail : [email protected] The first type is a disease similar to cholera, which causes rice-water diarrhea. The other type of disease is dysenteric gastroenteritis, which causes loose stools filled with blood and mucus. Dysenteric gastroenteritis is the most severe out of the two types, and can last for multiple weeks. Aeromonas hydrophila is also associated with cellulitis, an infection that causes inflammation in the skin tissue. It also causes diseases such as myonecrosis and eczema in people with compromised immune systems.

Treatments Aeromonas hydrophila can be eliminated using one percent sodium hypochlorite solution and two percent calcium hypochlorite solution. Antibiotic agents such as chloramphenicol, florenicol, tetracycline, sulfonamide, nitrofuran derivatives, and pyrodinecarboxylic acids are used to eliminate and control the infection of Aeromonas hydrophila.

References 1. http://en.wikipedia.org/wiki/Aeromonas 2. Hayes, John. "Aeromonas hydrophila." Oregon State University. 3. Arrow Scientific. "Aeromonas hydrophila."

Questions 1. What procedures would you follow to identify Aeromonas hydrophila in your lab? 2. What are the morphological characteristics of Aeromonas hydrophila? 3. Discuss the pathophysiology and treatment of Aeromonas hydrophila.

Thistle QA is a SANAS accredited organisation, No: PTS0001 Accredited to ISO guide 43 and ILAC G13 Certificate available on request or at www.sanas.co.za