Aeromonas
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 (e.g. endotoxins, hemolysins, enterotoxins, adherence factors) have been identified, their precise roles are unknown. "Aeromonas" species cause: Caution about differential diagnosis. If automated machines are not using the most updated database, "Elizabethkingia meningoseptica" 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, 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", 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" (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).