Aeromonas hydrophila
Aeromonas hydrophila is a heterotrophic, gram-negative bacterium, mainly found in areas where the climate is really warm.  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.  Aeromonas hydrophila was isolated from humans and animals until the 1950s.  This bacterium is the most well known of the six species of Aeromonas.  It is also very hard to kill, because it is a very resistant bacterium.  Aeromonas hydrophila is resistant to chlorine, refrigeration or cold temperatures (in fact Aeromonas hydrophila has been known to survive in temperatures as low as four degrees Celsius).

# Structure
Aeromonas hydrophila are Gram-negative straight rods with rounded ends(bacilli to coccibacilli shape).  They usually grow from .3 to 1 micrometer in width, and 1 to 3 micrometers 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.

# Pathology
Because of Aeromonas hydrophilas structure, it is very toxic to many organisms.  When it enters the body of its victim, it travels through the bloodstream to the first available organ.   It produces Aerolysin Cytotoxic Enterotoxin (ACT), a toxin that can cause tissue damage.  It is known as a pathogenic bacterium.  Aeromonas hydrophila, Aeromonas caviae, and Aeromonas sobria are all considered to be opportunistic pathogens, meaning they only infect hosts with weakened immune responses.  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 do not cause the diseases themselves.

### 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.

### Fish and amphibians
Aeromonas hydrophila is associated with diseases mainly found in fish and amphibians, because these organisms live in aquatic environments.  It is linked to a disease found in frogs called red leg, which causes internal, sometimes fatal hemorrhaging.  When infected with Aeromonas hydrophila, fish develop ulcers, tail rot, fin rot, and hemorrhagic septicaemia.  Hemorrhagic septicaemia causes lesions that lead to scale shedding, hemorrhages in the gills and anal area, ulcers, exophthalmia, and abdominal swelling.

### 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.  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.

### Outbreaks
Though Aeromonas hydrophila can cause serious diseases, there have never been serious outbreaks.  There was an outbreak inside the intestinal tract of lizards in Puerto Rico.  There were 116 different strains found in the lizards.  On May 1, 1988 there was a small Aeromonas hydrophila outbreak in California.  There were 225 isolates and 219 patients admitted in the hospital because of the bacterium.  Confidential Morbidity Report cards were used to report the cases of the bacterium to the local health departments.  Investigations were conducted, and reports were sent to the California department of health services for diagnosis and methods in treatment.

## Treatments
Though Aeromonas hydrophila is very resistant to the common methods used to kill most bacteria, it can be eliminated.  It can be killed using one percent sodium hypochlorite solution and two percent calcium hypochlorite solution.
Chemotherapeutic agents such as chloramphenicol, florenicol, tetracycline, sulphonamide, nitrofuran derivatives, and pyrodinecarboxylic acids are used to eliminate and control the infection of Aeromonas hydrophila.  Terramycin is placed in fish food during hatchery operations as another chemotherapeutic agent in preventing Aeromonas hydrophila.

## Anti microbial regimen
- Aeromonas hydrophila 
- 1. Diarrhea
- Preferred regimen (if not self-limiting, or if severe): Ciprofloxacin 500 mg PO bid.
- Alternate regimen: TMP-SMX 1 DS PO bid
- Note: High resistance to sulfa agents described in Taiwan and Spain
- 2. Skin and soft tissue infection
- 2.1 Mild infection
- Preferred regimen(1): Ciprofloxacin 500 mg PO bid
- Preferred regimen(2): Levofloxacin 500 mg qd
- 2.2 Severe infection or sepsis
- Preferred regimen(1): Ciprofloxacin 400 mg IV q8h
- Preferred regimen(2): Levofloxacin 750 mg IV q24h
- Note(1): For suspicion of water-based injury,empiric coverage for Vibrio doxycycline 100 mg bid, although flouroquinolones may also cover and vancomycin 15 mg/kg IV q12h with or without clindamycin or linezolid for inhibition of gram-positive toxin production
- Note(2): Alternatives to fluoroquinolones for Aeromonas coverage include carbapenems (ertapenem, doripenem, imipenem or meropenem), ceftriaxone, cefepime and aztreonam
- 3. Prevention
- Preferred regimen: Frequent recommendations include using a Cephalosporin (e.g.,cefuroxime,ceftriaxone or cefixime) OR a Fluoroquinolone (e.g.,ciprofloxacin or levofloxacin) during treatment with medicinal leeches
- Note (1): Duration of antibiotic use is 3-5 days, some recommend continuing until wound or eschar resolves
- Note (2): Aeromonas isolates from leeches have been described as uniformly susceptible to fluoroquinolones

## Preventing infection
It is ill-advised to transfer fish from hatchery to hatchery without any sanitation.  Hatchery workers should clean the fish, and check for bacterial infection between each operation.  To avoid contamination oxygen levels in fish should be maintained, and fish should always be handled gently, to avoid injury.  Prophylactic treatments can also be used when trying to prevent Aermonas hydrophila.  These treatments include disinfectants and Acriflavin.