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Não fermentadores

Acinetobacter baumannii complex

Gram-negative coccobacilli, difficult to decolorize

Identification & Growth

Identification

  • Oxidase-negative, catalase-positive, non-motile, non-fermenter
  • Grows at 44 °C (A. baumannii)

Growth Conditions

  • MacConkey agar: lactose-negative, mucoid, opaque colonies
  • Blood agar, 35 °C, 24 h; survives for prolonged periods on dry surfaces

Clinical Significance

  • ICU pneumonia, catheter and wound infection, hospital outbreaks

Intrinsic Resistance

  • Ertapenem, aztreonam, first- and second-generation cephalosporins (EUCAST Expected Resistant Phenotypes v1.2)
  • Fosfomycin and nalidixic acid

Bench Alerts

  • An XDR profile with carbapenem resistance is common in Brazil
  • Environmental reservoir — reinforce cleaning protocols and notify infection control
  • Ampicillin-sulbactam may retain activity through the sulbactam component

Clinical Notes

Clinical presentations

  • Causes ventilator-associated pneumonia, catheter-related bacteremia, and wound infections in critically ill patients.
  • Is a relevant agent in combat trauma and disaster-related infections, including soft tissue infection and osteomyelitis.
  • Can cause post-neurosurgical meningitis associated with external ventricular drains.

Specimens and collection

  • Tracheal aspirate or bronchoalveolar lavage should be collected to evaluate ventilator-associated pneumonia.
  • Blood cultures from peripheral sites and the catheter help differentiate device-related bacteremia.
  • Cerebrospinal fluid should be collected with strict aseptic technique in patients with ventricular drainage devices.

Epidemiology and at-risk populations

  • Survives for long periods on dry hospital surfaces, favoring cross-transmission and ICU outbreaks.
  • Patients with prolonged hospitalization, mechanical ventilation, and extensive broad-spectrum antimicrobial use are at highest risk.
  • Is classified by WHO as a critical priority pathogen due to carbapenem resistance.

Resistance and therapeutic implications

  • Carbapenem resistance mediated by class D carbapenemases (OXA-23, OXA-24/40, OXA-58) is endemic in many institutions.
  • Extensively drug-resistant (XDR) strains frequently leave polymyxins, tigecycline, or cefiderocol as remaining therapeutic options.
  • Colistin susceptibility testing requires broth microdilution methodology due to limitations of other methods.

Bench and reporting notes

  • Gram-negative, oxidase-negative, non-fermenting coccobacilli, frequently multidrug-resistant on initial screening.
  • Identification at the complex level (baumannii-calcoaceticus) is common in routine practice; exact species may require sequencing.
  • Carbapenem-resistant isolates should trigger contact precautions and hospital epidemiologic surveillance.

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 Acinetobacter baumannii complex in the lab?

Acinetobacter baumannii complex is identified through oxidase-negative, catalase-positive, non-motile, non-fermenter, grows at 44 °c (a. baumannii).

What are the intrinsic resistances of Acinetobacter baumannii complex?

This organism is naturally resistant to ertapenem, aztreonam, first- and second-generation cephalosporins (eucast expected resistant phenotypes v1.2), fosfomycin and nalidixic acid. These drugs should not be reported as susceptible.

Where is Acinetobacter baumannii complex commonly found?

It is typically associated with icu pneumonia, catheter and wound infection, hospital outbreaks.

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