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Enterobacterales

Edwardsiella tarda

Motile Gram-negative bacilli

Identification & Growth

Identification

  • Strongly H₂S-positive, indole-positive, lactose-negative
  • Profile resembles Salmonella but is indole-positive

Growth Conditions

  • MacConkey and SS agar; 35–37 °C, 18–24 h

Clinical Significance

  • Gastroenteritis and wound infection linked to fresh water and fish
  • Bacteremia in patients with liver disease and hemochromatosis

Intrinsic Resistance

  • Colistin remains active; no relevant intrinsic beta-lactam resistance

Bench Alerts

  • In stool culture, H₂S-positive with indole-positive rules out Salmonella

Clinical Notes

Clinical presentations

  • Causes acute gastroenteritis associated with ingestion of raw or undercooked fish or seafood.
  • Can cause wound infections after exposure to contaminated fresh or salt water.
  • Severe cases include bacteremia, liver abscess, and extraintestinal infections in patients with chronic liver disease.

Specimens and collection

  • Stool specimen is indicated in gastroenteritis, with culture on selective media for enteric Enterobacterales.
  • Wound swab or aspirate should be collected when there is a history of aquatic exposure.
  • Blood cultures are indicated in patients with underlying liver disease and suspected bacteremia.

Epidemiology and at-risk populations

  • Found in aquatic environments and the gastrointestinal tract of fish and reptiles.
  • Patients with cirrhosis and iron overload have increased risk of severe invasive infection and liver abscess.
  • Recreational or occupational exposure to fresh/salt water and consumption of raw seafood are relevant exposure factors.

Resistance and therapeutic implications

  • Generally susceptible to fluoroquinolones, third-generation cephalosporins, and trimethoprim-sulfamethoxazole.
  • Individualized susceptibility testing is recommended, as acquired resistance has been sporadically reported.
  • Uncomplicated gastroenteritis is generally self-limited and does not routinely require systemic antimicrobial treatment.

Bench and reporting notes

  • H2S production on triple sugar iron agar may cause initial confusion with Salmonella; additional biochemical identification is needed.
  • MALDI-TOF provides reliable and rapid identification compared to manual biochemical panels.
  • Correlate with aquatic/dietary exposure history in the report to support the isolate's clinical significance.

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 Edwardsiella tarda in the lab?

Edwardsiella tarda is identified through strongly h₂s-positive, indole-positive, lactose-negative, profile resembles salmonella but is indole-positive.

What are the intrinsic resistances of Edwardsiella tarda?

This organism is naturally resistant to colistin remains active; no relevant intrinsic beta-lactam resistance. These drugs should not be reported as susceptible.

Where is Edwardsiella tarda commonly found?

It is typically associated with gastroenteritis and wound infection linked to fresh water and fish, bacteremia in patients with liver disease and hemochromatosis.

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