such as Chromobacterium violaceum, Vibrio parahaemolyticus, and Aeromonas hydrophila, associated with
serious and indolent wound infections.
56,91
The last can be cultured from natural bodies of water, as well as
from the mouths of domesticated aquarium fish, such as the piranha. Biologic control agents, such as guppy
fish bred in wells to control mosquito proliferation, can carry bacterial pathogens such as Pseudomonas.
One investigation sampled water, inanimate objects, and animals from freshwater environments in
California, Tennessee, and Florida. Bacteria isolated were predominantly gram-negative and included
Aeromonas hydrophila, Flavobacterium breve, Pseudomonas species, Vibrio parahaemolyticus, Serratia
species, Enterobacter species, Plesiomonas shigelloides, Bacillus species, Acinetobacter calcoaceticus, and
Alcaligenes denitrificans.
Wound Infections Due to Aeromonas species
Aeromonas hydrophila ("gas producing and water loving")is a gram-negative, facultatively anaerobic,
polarly flagellated, non-spore-forming, motile rod member of the family Vibrionaceae that commonly inhabits
soil, freshwater streams, and lakes. Aeromonas species are widely distributed and found at wide ranges of
temperature and pH. Three species (A. hydrophila, A. sobria, and A. caviae) have been associated with human
disease; there are seven or more distinct genotypes. A. hydrophila is pathogenic to amphibians, reptiles, and
fish. Soft tissue and gastroenteric human infections occur predominantly during the period from May to
November. Virulence factors elaborated by Aeromonas species include hemolysin, cytoxotin, enterotoxin,
chorera toxin-like factor, and hemagglutinins.
A wound, particularly of the puncture variety, immersed in contaminated water may become cellulitic within
24 hours, with erythema, edema, and a purulent discharge. The lower extremity is most frequently involved.
This usually occurs from stepping on a foreign object or being punctured under water. The appearance may be
indistinguishable from a typical streptococcal cellulitis, with localized pain, lymphangitis, fever, and chills.
Untreated or managed with antibiotics to which the organism is not susceptible, this may rarely progress to a
severe gas-forming soft tissue reaction, bulla formation, necrotizing myositis, or osteomyelitis. Appearance
similar to ecthyma gangrenosum caused by Pseudomonas aeruginosa has been reported in Aeromonas
septicemia.
Fever, hypotension, jaundice, and chills are common manifestations of septicemia. Additional clinical
manifestations include abdominal pain or tenderness, altered consciousness, acute renal failure, and
coagulopathy. In a manner analogous to the pathogenicity of virulent Vibrio species, the chronically ill or
immunocompromised host (chronic liver disease, neoplasm, diabetes, uremia, corticosteroid therapy,
extensive burns, etc.) is probably at greater risk of a severe infection and/or complication, such as meningitis,
endocarditis, or septicemia. Freshwater aspiration may result in Aeromonas hydrophila pneumonitis and
bacteremia. Infection has followed the bite of an alligator. A 15-year-old boy suffered A. hydrophila wound
infection after a bite from his pet piranha. For unknown reasons there is a marked preponderance of male
patients. This may represent the phenotypic variation of critical bacterial adhesins. Corneal ulcer caused by A.
sobria was reported following abrasion by a freshwater reed.
Gram's stain of the purulent discharge may demonstrate gram-negative bacilli, singly, paired, or in
short chains. Given the appropriate clinical setting (after a wound acquired in the freshwater environment),
this should not be casually attributed to contamination. Aeromonas hydrophila is generally sensitive to
chloramphenicol, aztreonam, gentamicin, amikacin, tobramycin, trimethoprim-sulfamethoxazole, cefotaxime,
cefuroxime, moxalactam, imipenem, ceftazidime, ciprofloxacin, and norfloxacin. In one case, culture of a
severe wound infection demonstrated the presence of two species, Aeromonas hydophila and A. sobria.
Notably, the latter was resistant to tetracycline in vitro. Initial therapy for a severe infection that includes an
aminoglycoside provides coverage against concomitant Pseudomonas or Serratia infection. As has been
demonstrated with Vibrio species, the first-generation cephalosporins, penicillin, and ampicillin, and
ampicillin-sulbactam are not efficacious, perhaps because of the production of a -lactamase by the organism.
Aeromonas species are capable of producing chromosomally encoded
-lactamases induced by -lactam
antibiotics. This leads to resistance to penicillins, cephalosporins, and monobactams. The
-lactamase
inhibitors, such as clavulanate, are not effective against these
-lactamases, so that amoxicillin-clavulanate
may not kill Aeromonas. Because of the microbiologic similarity of Aeromonas on biochemical testing to
