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Enterobacterales

Raoultella ornithinolytica

Encapsulated, non-motile Gram-negative bacilli

Identification & Growth

Identification

  • Similar to Klebsiella but ornithine decarboxylase positive with growth at 10 °C

Growth Conditions

  • MacConkey, mucoid colonies; 35–37 °C, 18–24 h

Clinical Significance

  • Catheter-related bacteremia, urinary and biliary infection; histamine formation in fish

Intrinsic Resistance

  • Ampicillin and amoxicillin have no activity (chromosomal beta-lactamase)

Bench Alerts

  • Often reported as Klebsiella — the distinction matters in outbreak investigation

Clinical Notes

Clinical presentations

  • Causes urinary tract infections, bacteremia, and wound infections, mainly in immunocompromised patients.
  • Associated with histamine (scombroid) poisoning via histidine decarboxylase production in improperly stored fish.
  • Can cause cholangitis and biliary infections in patients with biliary tract obstruction.

Specimens and collection

  • Blood, urine, and bile are relevant specimens depending on the suspected clinical site.
  • In suspected histamine poisoning, correlate with detailed dietary history, as diagnosis is predominantly clinical.
  • Blood cultures should be drawn before empiric antibiotic therapy in suspected bacteremia.

Epidemiology and at-risk populations

  • Found in aquatic environments, soil, and plants, being an occasional colonizer of the human gastrointestinal tract.
  • Hospitalized patients with invasive devices and hepatobiliary comorbidities have increased risk of invasive infection.
  • Previously classified as Klebsiella ornithinolytica, which is relevant for interpreting historical epidemiologic data.

Resistance and therapeutic implications

  • Can acquire extended-spectrum beta-lactamases and carbapenemases, similar to other Enterobacterales.
  • Phenotypic and molecular resistance mechanism testing is recommended for sterile-site isolates.
  • Antimicrobial therapy should be guided by individualized susceptibility testing, without predictable class-wide susceptibility.

Bench and reporting notes

  • Positive ornithine decarboxylase is a key biochemical feature for differentiation from Klebsiella spp.
  • MALDI-TOF is the preferred method for precise species identification within the Raoultella genus.
  • In the context of fish-related food poisoning, correlate isolation with dietary history in the report, though diagnosis remains clinical.

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 Raoultella ornithinolytica in the lab?

Raoultella ornithinolytica is identified through similar to klebsiella but ornithine decarboxylase positive with growth at 10 °c.

What are the intrinsic resistances of Raoultella ornithinolytica?

This organism is naturally resistant to ampicillin and amoxicillin have no activity (chromosomal beta-lactamase). These drugs should not be reported as susceptible.

Where is Raoultella ornithinolytica commonly found?

It is typically associated with catheter-related bacteremia, urinary and biliary infection; histamine formation in fish.

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