''Aeromonas'' is a genus of

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

facultative anaerobic A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. Some examples of facultatively anaerobic bacteria are '' Staphylococc ...

, rod-shaped bacteria that morphologically resemble members of the family

Enterobacteriaceae Enterobacteriaceae is a large family (biology), family of Gram-negative bacteria. It was first proposed by Rahn in 1936, and now includes over 30 genera and more than 100 species. Its classification above the level of family is still a subject ...

. Most of the 14 described species have been associated with human diseases. The most important pathogens are '' A. hydrophila'', '' A. caviae'', and '' A. veronii'' biovar ''sobria''. The organisms are ubiquitous in fresh and brackish water. They group with the gamma subclass of the Proteobacteria. Two major diseases associated with ''Aeromonas'' are

gastroenteritis Gastroenteritis, also known as infectious diarrhea and gastro, is an inflammation of the gastrointestinal tract including the stomach and intestine. Symptoms may include diarrhea, vomiting, and abdominal pain. Fever, lack of energy, and dehydra ...

and wound infections, with or without

bacteremia Bloodstream infections (BSIs), which include bacteremias when the infections are bacterial and fungemias when the infections are fungal, are infections present in the blood. Blood is normally a sterile environment, so the detection of microb ...

. Gastroenteritis typically occurs after the ingestion of contaminated water or food, whereas wound infections result from exposure to contaminated water. In its most severe form, ''Aeromonas'' spp. can cause necrotizing fasciitis, which is life-threatening, usually requiring treatment with

antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention o ...

and even amputation. Although some potential virulence factors (e.g. endotoxins,

hemolysin Hemolysins or haemolysins are lipids and proteins that cause lysis of red blood cells by disrupting the cell membrane. Although the lytic activity of some microbe-derived hemolysins on red blood cells may be of great importance for nutrient acqu ...

enterotoxin An enterotoxin is a protein exotoxin released by a microorganism that targets the intestines. Enterotoxins are chromosomally encoded or plasmid encoded exotoxins that are produced and secreted from several bacterial organisms. They are heat labi ...

s, adherence factors) have been identified, their precise roles are unknown. ''Aeromonas'' species cause: * Diarrheal disease in otherwise healthy individuals * Wound infections * Opportunistic systemic disease in immunocompromised patients

Caution about differential diagnosis

If automated machines are not using the most updated database, ''

Elizabethkingia meningoseptica ''Elizabethkingia meningoseptica'' is a Gram-negative, rod-shaped bacterium widely distributed in nature (e.g. fresh water, salt water, or soil). It may be normally present in fish and frogs; it may be isolated from chronic infectious states, as ...

'' may be mistaken for ''A. salmonicida''.

Association with human diarrhea and human intestinal infections

Literature exists on this subject, but many papers have not adequately studied the causal role of the ''Aeromonas'' strain(s) that were isolated from the cases that were studied. The presence of an ''Aeromonas'' strain in a fecal specimen does not prove or even imply that the strain was causing the diarrhea. Gastrointestinal disease in children is usually an acute, severe illness, whereas that in adults tends to be chronic diarrhea. Severe ''Aeromonas'' gastroenteritis resembles

shigellosis Shigellosis is an infection of the intestines caused by ''Shigella'' bacteria. Symptoms generally start one to two days after exposure and include diarrhea, fever, abdominal pain, and feeling the need to pass stools even when the bowels are emp ...

, with blood and leukocytes in the stool. Acute diarrheal disease is self-limited, and only supportive care is indicated in affected patients.

Wound infection

Wound infections are the second-most common type of human infection associated with ''Aeromonas''. They are associated with penetrating wounds or abrasions that place the wound in contact with fresh water or soil.

Medicinal leeches

''Aeromonas'' species are endosymbionts of ''

Hirudo medicinalis ''Hirudo medicinalis'', the European medicinal leech, is one of several species of leeches used as "medicinal leeches". Other species of ''Hirudo'' sometimes also used as medicinal leeches include '' H. orientalis'', ''H. troctina'', and '' H. ...

'', a species of

leech Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular segmented bodie ...

that is

FDA The United States Food and Drug Administration (FDA or US FDA) is a federal agency of the Department of Health and Human Services. The FDA is responsible for protecting and promoting public health through the control and supervision of food s ...

-approved for use in

vascular surgery Vascular surgery is a surgical subspecialty in which diseases of the vascular system, or arteries, veins and lymphatic circulation, are managed by medical therapy, minimally-invasive catheter procedures and surgical reconstruction. The specialty ...

such as skin grafts and flaps. ''Aeromonas'' aides leeches in digesting blood meals. ''H. medicinalis'' used after surgery has led to ''Aeromonas'' infections, most commonly with ''A. veronii''. This can present as a local cellulitis, though can progress to subcutaneous

abscess An abscess is a collection of pus that has built up within the tissue of the body. Signs and symptoms of abscesses include redness, pain, warmth, and swelling. The swelling may feel fluid-filled when pressed. The area of redness often extends b ...

and

sepsis Sepsis, formerly known as septicemia (septicaemia in British English) or blood poisoning, is a life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage is follo ...

Respiratory infection

''Aeromonas'' species have also been associated with

pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severity ...

after near-drowning events, especially in fresh water. Most commonly, this has been reported with ''A. hydrophila'', though the ability of clinical laboratories to correctly identify species of ''Aeromonas'' has been limited. ''Aeromonas'' pneumonia due to episodes of near-drowning are frequently complicated by

and death.

Antimicrobial therapy

''Aeromonas'' species are resistant to

penicillin Penicillins (P, PCN or PEN) are a group of β-lactam antibiotics originally obtained from ''Penicillium'' moulds, principally '' P. chrysogenum'' and '' P. rubens''. Most penicillins in clinical use are synthesised by P. chrysogenum using ...

s, most

cephalosporin The cephalosporins (sg. ) are a class of β-lactam antibiotics originally derived from the fungus ''Acremonium'', which was previously known as ''Cephalosporium''. Together with cephamycins, they constitute a subgroup of β-lactam antibiotics ...

s, and

erythromycin Erythromycin is an antibiotic used for the treatment of a number of bacterial infections. This includes respiratory tract infections, skin infections, chlamydia infections, pelvic inflammatory disease, and syphilis. It may also be used duri ...

Ciprofloxacin Ciprofloxacin is a fluoroquinolone antibiotic used to treat a number of bacterial infections. This includes bone and joint infections, intra abdominal infections, certain types of infectious diarrhea, respiratory tract infections, skin infec ...

is consistently active against their strains in the U.S. and Europe, but resistant cases have been reported in Asia.

Etymology

The name ''Aeromonas'' derives from:
Greek ''aer, aeros'' (ἀήρ, ἀέρος), air, gas; and ''-monas, monas'' (μονάς), unit, monad; gas(-producing) monad. Members of the genus ''Aeromonas'' can be referred to as aeromonads (''viz.'' trivialisation of names).