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Enterobacterales

Enterobacter cloacae complex

Gram-negative bacilli

Identification & Growth

Identification

  • Oxidase-negative, motile, ornithine-positive, lysine-negative, VP-positive
  • TSI A/A with gas

Growth Conditions

  • MacConkey agar, lactose-positive, 35–37 °C, 18–24 h

Clinical Significance

  • Ventilator-associated pneumonia, hospital-acquired UTI, catheter-related infection

Intrinsic Resistance

  • Ampicillin, amoxicillin-clavulanate, cefalotin, cefoxitin (chromosomal AmpC, EUCAST Expected Resistant Phenotypes v1.2)

Bench Alerts

  • Risk of AmpC derepression under third-generation cephalosporin therapy
  • Always report the natural resistance even when the zone appears susceptible

Clinical Notes

Clinical presentations

  • Causes diverse hospital infections: bacteremia, ventilator-associated pneumonia, urinary tract infection, and surgical wound infection.
  • Associated with bloodstream infection outbreaks related to contaminated intravenous solutions.

Specimens and collection

  • Blood cultures prior to starting empiric antibiotic therapy are essential in hospitalized patients with sepsis of undetermined origin.
  • Surgical wound specimens should be obtained by deep tissue biopsy or aspiration, avoiding low-accuracy superficial swabbing.

Epidemiology and at-risk populations

  • A predominantly nosocomial pathogen, associated with intensive care units and patients with invasive devices.
  • Included in CDC carbapenem-resistant Enterobacterales (CRE) surveillance due to its capacity to acquire carbapenemases.
  • The complex encompasses multiple genetically distinct species, whose differentiation impacts outbreak molecular epidemiology.

Resistance and therapeutic implications

  • Carries an inducible chromosomal AmpC beta-lactamase, with expected resistance to ampicillin, amoxicillin-clavulanate, and first/second-generation cephalosporins.
  • Derepressed mutants can emerge during third-generation cephalosporin therapy, leading to treatment failure despite initial susceptibility.
  • Cefepime and carbapenems are generally active against baseline AmpC production, but isolates with acquired carbapenemase require management guided by molecular confirmation.

Bench and reporting notes

  • Gram-negative rod, lactose-fermenting, oxidase-negative, motility-positive; complex-level identification is acceptable in routine practice, with species-level reserved for epidemiologic contexts.
  • The report should warn about the risk of emerging third-generation cephalosporin resistance during treatment, even with a low initial MIC.
  • EUCAST recommends caution when using third-generation cephalosporins for severe infections caused by this organism, due to AmpC derepression risk.

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 Enterobacter cloacae complex in the lab?

Enterobacter cloacae complex is identified through oxidase-negative, motile, ornithine-positive, lysine-negative, vp-positive, tsi a/a with gas.

What are the intrinsic resistances of Enterobacter cloacae complex?

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

Where is Enterobacter cloacae complex commonly found?

It is typically associated with ventilator-associated pneumonia, hospital-acquired uti, catheter-related infection.

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