Vibriões e curvos

Aeromonas hydrophila / caviae

Straight, motile Gram-negative bacilli

Identification & Growth

Identification

Oxidase-positive, resistant to the vibriostatic agent O/129, grows without NaCl
Beta-hemolysis on blood agar, indole-positive

Growth Conditions

Blood agar and MacConkey, 35 °C, 18–24 h

Clinical Significance

Gastroenteritis, cellulitis and fasciitis after fresh-water contact, bacteremia in patients with liver disease

Intrinsic Resistance

Multiple chromosomal beta-lactamases: ampicillin (and often cefalotin) inactive

Bench Alerts

May induce carbapenem resistance during therapy (chromosomal cephalosporinase plus carbapenemase)
An oxidase-positive, lactose-negative bacillus in stool culture should not be dismissed as flora

Clinical Notes

Clinical presentations

Acute gastroenteritis, generally self-limited, but which can present as prolonged diarrhea in children.
Skin and soft-tissue infection after wound exposure to fresh water, mud or aquatic animals, including cellulitis and, rarely, necrotizing fasciitis.
Bacteremia and sepsis in patients with chronic liver disease, hematologic malignancy or immunosuppression.

Specimens and collection

Stool culture on Aeromonas-selective medium (e.g. ampicillin agar) when there is specific clinical suspicion.
Wound and deep tissue material in soft-tissue infections, with direct Gram stain to guide initial empirical therapy.
Blood culture in patients with systemic signs, especially with underlying liver disease or neutropenia.

Epidemiology and at-risk populations

Environmental organisms of fresh, estuarine water and moist soil; associated with recreational or occupational exposure to these sources.
Medicinal leeches can carry Aeromonas, which is why antimicrobial prophylaxis is used during leech therapy.
Higher risk of invasive disease in cirrhotic and neutropenic patients and in trauma victims contaminated by water or mud.

Resistance and therapeutic implications

Intrinsic resistance to ampicillin via chromosomal beta-lactamase production, making it unsuitable as empirical monotherapy.
Fluoroquinolones, trimethoprim-sulfamethoxazole and third-generation cephalosporins are usually active, always confirmed by susceptibility testing.
EUCAST publishes breakpoints for Aeromonas spp.; use species-specific criteria when available in the current table.

Bench and reporting notes

Oxidase-positive, catalase-positive Gram-negative rod, motile via polar flagellum, growing well on MacConkey agar.
Differentiation between species (A. hydrophila, A. caviae, A. veronii) requires extended biochemical panels or MALDI-TOF; automated systems can misidentify the species.
Report stool isolation with clinical correlation, as it may represent colonization in asymptomatic carriers.

Sources

Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.

FAQ: Frequently Asked Questions

How to identify Aeromonas hydrophila / caviae in the lab?

Aeromonas hydrophila / caviae is identified through oxidase-positive, resistant to the vibriostatic agent o/129, grows without nacl, beta-hemolysis on blood agar, indole-positive.

What are the intrinsic resistances of Aeromonas hydrophila / caviae?

This organism is naturally resistant to multiple chromosomal beta-lactamases: ampicillin (and often cefalotin) inactive. These drugs should not be reported as susceptible.

Where is Aeromonas hydrophila / caviae commonly found?

It is typically associated with gastroenteritis, cellulitis and fasciitis after fresh-water contact, bacteremia in patients with liver disease.

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