Laboratory Studies
Pseudomonas aeruginosa and other Pseudomonas organisms are aerobic, nonfermentative, nonenterobacterial gram-negative bacilli. Obtain 2 sets of blood cultures (ie, aerobic and anaerobic bottles) from different sites before starting empiric antibiotics. The following laboratory results are helpful to confirm a pseudomonal infection:
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CBC counts revealing leukocytosis with a left shift and bandemia, which indicates possible presence of toxic granulations or vacuoles
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Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels, which may be elevated in infection
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Metabolic profile revealing any electrolyte abnormalities, degree of dehydration, and worsening renal function
The following additional studies may be indicated, depending on the site of infection:
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Culture of the purulent discharge helps diagnose suppurative otitis media or malignant otitis externa.
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Corneal scrapings and culture may reveal pseudomonal involvement.
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Culture of vegetations from patients with pseudomonal infectious endocarditis (IE) reveals high quantities of the organisms, although diagnosis is usually confirmed by a repeated blood culture.
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Sputum Gram stain and culture may be indicated to evaluate for respiratory infection. This is especially recommended in children who may be predisposed to such infections.
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Blood gas levels may reveal hypoxemia, with or without hypercarbia.
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Wound and burn cultures can be helpful to identify pseudomonal infections.
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Urinalysis with culture and sensitivity is helpful when evaluating for urinary tract infection (UTI). Although rare, sloughing of vesical membrane in the urine can indicate complications of pseudomonal infections.
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Obtain stool cultures in patients with diarrhea. Note, however, that pseudomonal organisms produce no toxins.
Diagnosis of glanders can be confirmed by isolating B mallei from blood, sputum, urine, or skin lesions. No serologic tests are available. Diagnosis of melioidosis can be confirmed by isolating B pseudomallei from the blood, urine, sputum, or skin lesions. Detecting antibodies to the bacteria in the blood is another method.
Imaging Studies
See the list below:
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Chest radiography
Patients with cystic fibrosis (CF) may have a small heart, depressed diaphragm, and increased anteroposterior chest diameter. Chest radiography may also reveal cyst formation, mucus plugging of dilated bronchi, generalized bronchiectasis, patchy atelectasis, peribronchial thickening, overaeration, or extensive peribronchial infiltration.
The classic presentation of bacteremic pseudomonal pneumonia includes rapid progression of radiographic findings. Chest radiography performed within 48-72 hours after initial fever onset reveals parenchymal involvement with interstitial and alveolar infiltrates. Cavitation appears after 48 hours.
Typical findings include (1) poorly-defined, hemorrhagic, often subpleural, nodular areas with a small central area of necrosis and (2) multiple, 2-mm to 15-mm, necrotic, umbilicated nodules with hemorrhagic parenchyma, representing the pulmonary component of an ecthyma gangrenosum (EG) skin lesion.
The typical progression of disease is from pulmonary vascular congestion to pulmonary edema to necrotizing bronchopneumonia.
Radiographs of patients with primary nonbacteremic pneumonia are similar to those from patients whose pneumonia is caused by Staphylococcus aureus. Among the common features are a diffuse bronchopneumonia (usually bilateral with distinctive nodular infiltrates with small areas of radiolucency) and pleural effusions; empyema or lobar consolidation is occasionally observed.
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CT scanning
A CT scan of the head may reveal a brain abscess. A CT scan of the surrounding soft tissue and osseous lesions is recommended in patients with malignant otitis externa to help define the intracranial and extracranial extent of disease.
Perform a CT scan of the abdomen as part of the workup for endocarditis, especially left-sided disease. Complications such as splenic abscesses require splenectomy before valvular replacement.
A CT scan of the chest is not usually indicated, except when respiratory failure requires better definition of chest involvement. With left-sided endocarditis, a CT scan of the chest also can reveal septic pulmonary emboli as a complication.
A CT scan of soft tissue and bone of skin infections may be required to exclude an abscess formation or osteomyelitis.
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MRI
Consider MRI of the head to evaluate a patient with a brain abscess. MRI of the head in a patient with left-sided endocarditis may show cerebritis and mycotic aneurysm.
A CT scan or MRI of the surrounding tissue of the site of infection may be needed to delineate abscess formation.
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Other studies
Echocardiography (ECHO) may reveal vegetations in endocarditis. However, because the yield is low, consider a transesophageal ECHO or repeat ECHO for highly suspicious cases.
Bone radiography or a nuclear study is helpful in diagnosing patients with suspected osteomyelitis.
Renal ultrasound may be helpful to evaluate patients with a suspected obstruction or abscess formation complicating a UTI.
A gallium WBC scan may help determine the extent of infection.
Other Tests
See the list below:
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To evaluate eye infections to determine the degree of corneal involvement, perform fluorescein staining and slit-lamp examination of the cornea.
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Patients who develop septic pulmonary emboli as a complication may require a ventilation-perfusion scan.
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A Wood light examination of a pseudomonal toe web reveals a green-white fluorescence from the elaboration of pyoverdin.
Procedures
See the list below:
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Needle biopsy or aspiration of the joint, possibly with fluoroscopic guidance, can be helpful in identifying the infectious organism. An open biopsy may be necessary, depending on disease extent.
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Lumbar puncture is indicated when CNS involvement is suspected. Workup of neonatal sepsis should include lumbar puncture, if indicated.
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Cardiac catheterization may reveal valvular involvement or vegetations.
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Quantitative cultures from bronchoalveolar lavage obtained by bronchoscopy helps distinguish infection from colonization.
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Thoracentesis may be indicated for patients who have pleural effusion.
Histologic Findings
See the list below:
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Histological findings of EG include edema, epidermal necrosis, and gram-negative rods on tissue gram stain.
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Few neutrophils in the sparse inflammatory infiltrate can also be seen.
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Erythematous papulopustules of pseudomonas folliculitis. Courtesy of Mark Welch, MD.
