Aeromonas is a genus of gram-negative, facultative anaerobic, rod-shaped bacteria that morphologically resemble members of the family Enterobacteriaceae. 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 and wound infections, with or without bacteremia. 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 and even amputation. Although some potential virulence factors have been identified, their precise roles are unknown. Aeromonas species cause:
There is literature on this subject, but many papers have not adequately studied the causal role of the Aeromonas strain 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, 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.
Aeromonas species are endosymbionts of Hirudo medicinalis, a species of leech that is FDA-approved for use in vascular surgery 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 and sepsis.
Respiratory infection
Aeromonas species have also been associated with pneumonia 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 bacteremia and death.
Antimicrobial therapy
Aeromonas species are resistant to penicillins, most cephalosporins, and erythromycin. Ciprofloxacin 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, air, gas; and -monas|monas, unit, monad; gas monad. Members of the genus Aeromonas can be referred to as aeromonads.
