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Enterobacterales

Morganella morganii

Gram-negative bacilli

Identification & Growth

Identification

  • Oxidase-negative, urease-positive, indole-positive, H₂S-negative, ornithine-positive

Growth Conditions

  • MacConkey agar, lactose-negative, no swarming; 35 °C, 24 h

Clinical Significance

  • Complicated UTI, wound infection, bacteremia in hospitalized patients

Intrinsic Resistance

  • Colistin/polymyxin B, nitrofurantoin, tetracyclines (EUCAST Expected Resistant Phenotypes v1.2)
  • Ampicillin, amoxicillin-clavulanate, cefalotin, cefoxitin (chromosomal AmpC)

Bench Alerts

  • Broad intrinsic-resistance profile — check before releasing the report
  • Imipenem breakpoints do not apply

Clinical Notes

Clinical presentations

  • Causes urinary tract and surgical wound infections, predominantly in the hospital or healthcare-associated setting.
  • Can cause severe bacteremia in elderly and immunosuppressed patients, often secondary to a urinary or biliary focus.

Specimens and collection

  • Urine culture and blood cultures should be obtained before starting empiric antibiotic therapy in a hospitalized patient with sepsis of urinary origin.
  • Deep surgical wound specimens should be preferred over superficial swabs for greater diagnostic accuracy.

Epidemiology and at-risk populations

  • It is predominantly a healthcare-associated pathogen, rarely causing infection in previously healthy community individuals.
  • Elderly patients, diabetics, and those with prolonged urinary catheterization constitute the main risk group.

Resistance and therapeutic implications

  • Carries an inducible chromosomal AmpC beta-lactamase, with expected resistance to ampicillin, amoxicillin-clavulanate, and first-generation cephalosporins.
  • It is intrinsically resistant to nitrofurantoin, tigecycline, colistin, and some narrow-spectrum agents used in UTI.
  • Derepressed AmpC mutants can emerge during third-generation cephalosporin therapy, compromising clinical response.

Bench and reporting notes

  • Gram-negative rod, urease-positive, but without swarming motility, which phenotypically differentiates it from Proteus mirabilis.
  • The report should state intrinsic resistance to nitrofurantoin, colistin, and tigecycline, regardless of the in vitro result.
  • Clinically flag the risk of treatment failure with third-generation cephalosporins due to AmpC derepression during prolonged therapy.

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 Morganella morganii in the lab?

Morganella morganii is identified through oxidase-negative, urease-positive, indole-positive, h₂s-negative, ornithine-positive.

What are the intrinsic resistances of Morganella morganii?

This organism is naturally resistant to colistin/polymyxin b, nitrofurantoin, tetracyclines (eucast expected resistant phenotypes v1.2), ampicillin, amoxicillin-clavulanate, cefalotin, cefoxitin (chromosomal ampc). These drugs should not be reported as susceptible.

Where is Morganella morganii commonly found?

It is typically associated with complicated uti, wound infection, bacteremia in hospitalized patients.

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