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Não fermentadores

Pseudomonas aeruginosa

Slender Gram-negative bacilli

Identification & Growth

Identification

  • Oxidase-positive, non-fermenter (TSI K/K), grows at 42 °C
  • Pyocyanin (blue) and pyoverdine (green fluorescent) pigments; grape-like odour

Growth Conditions

  • MacConkey agar: lactose-negative, flat colonies with an irregular edge and metallic sheen
  • Selective cetrimide agar; 35–42 °C, 18–24 h

Clinical Significance

  • Ventilator-associated pneumonia, catheter-associated UTI, otitis externa, burn-wound infection and cystic fibrosis

Intrinsic Resistance

  • Ampicillin, amoxicillin-clavulanate, first- and second-generation cephalosporins, cefotaxime and ceftriaxone (EUCAST Expected Resistant Phenotypes v1.2)
  • Ertapenem, tetracyclines/tigecycline, SXT, chloramphenicol, nitrofurantoin

Bench Alerts

  • Ertapenem is NEVER an option — do not report
  • Under current BrCAST/EUCAST criteria, several combinations only carry the I and R categories (increased exposure)
  • Resistance can emerge during therapy — repeat culture in cases of clinical failure

Clinical Notes

Clinical presentations

  • Causes ventilator-associated pneumonia, burn wound infections, malignant otitis externa, and catheter-associated urinary infections.
  • Is a chronic airway pathogen in cystic fibrosis patients, with biofilm formation and a mucoid phenotype.
  • Bacteremia in neutropenic patients may present with ecthyma gangrenosum.
  • Causes endophthalmitis, contact lens-associated keratitis, and osteochondritis following puncture wounds through footwear.

Specimens and collection

  • Sputum or tracheal aspirate should be collected before initiating or adjusting antibiotics in hospital-acquired pneumonia.
  • Serial blood cultures are indicated when bacteremia is suspected, especially in febrile neutropenic patients.
  • Wound swab should be supplemented with deep tissue biopsy when invasive infection is suspected.
  • Sputum culture in cystic fibrosis patients should use selective media to differentiate mucoid and non-mucoid morphotypes.

Epidemiology and at-risk populations

  • Relevant opportunistic pathogen in patients with cystic fibrosis, neutropenia, extensive burns, and prolonged mechanical ventilation.
  • Thrives in moist hospital environments, including faucets, humidifiers, and respiratory therapy equipment.
  • Is a leading cause of healthcare-associated infection with significant impact on ICU mortality.

Resistance and therapeutic implications

  • Has intrinsic resistance to multiple antimicrobial classes and multiple acquired mechanisms, including efflux, OprD porin loss, and beta-lactamase production.
  • Carbapenemase-producing strains (VIM, IMP, NDM) and multidrug/extensively drug-resistant strains require combination therapy guided by susceptibility testing.
  • Ceftazidime-avibactam and ceftolozane-tazobactam are options for MDR strains without metallo-beta-lactamase production.
  • Susceptibility testing should include multiple classes due to phenotypic variability among clinical isolates.

Bench and reporting notes

  • Colonies with a characteristic grape-like odor and blue-green pigment (pyocyanin) suggest presumptive identification on plate inspection.
  • Positive oxidase test and growth at 42°C aid differentiation from other non-aeruginosa Pseudomonas species.
  • Phenotypic or molecular carbapenemase detection should be performed on carbapenem-resistant isolates to guide therapy and infection control.

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 Pseudomonas aeruginosa in the lab?

Pseudomonas aeruginosa is identified through oxidase-positive, non-fermenter (tsi k/k), grows at 42 °c, pyocyanin (blue) and pyoverdine (green fluorescent) pigments; grape-like odour.

What are the intrinsic resistances of Pseudomonas aeruginosa?

This organism is naturally resistant to ampicillin, amoxicillin-clavulanate, first- and second-generation cephalosporins, cefotaxime and ceftriaxone (eucast expected resistant phenotypes v1.2), ertapenem, tetracyclines/tigecycline, sxt, chloramphenicol, nitrofurantoin. These drugs should not be reported as susceptible.

Where is Pseudomonas aeruginosa commonly found?

It is typically associated with ventilator-associated pneumonia, catheter-associated uti, otitis externa, burn-wound infection and cystic fibrosis.

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