Burkholderia pseudomallei and Melioidosis
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Direct answer
Burkholderia pseudomallei is a motile, oxidase-positive Gram-negative bacillus that causes melioidosis, an infection acquired from soil and surface water in endemic tropical regions. It produces pneumonia, localised abscesses and septicaemia, and it is a major cause of severe infection in people with diabetes. Intrinsic resistance to several antibiotics means treatment is prolonged and starts with intravenous ceftazidime or meropenem.
What you must remember
- Morphology: motile Gram-negative bacillus that shows bipolar staining on Wayson or Giemsa stain.
- Habitat: soil and surface water in endemic regions, with entry through skin injury, inhalation or ingestion, and cases reported across parts of India.
- Risk factors: diabetes mellitus is the commonest predisposing condition, with alcohol excess, chronic kidney disease and chronic lung disease also recognised.
- Clinical forms: acute pneumonia is the commonest form, alongside localised abscesses in liver, spleen, prostate or skin, acute septicaemia and chronic pulmonary disease that mimics tuberculosis.
- Diagnosis: culture on Ashdown's selective medium, identification by biochemical tests or mass spectrometry, with PCR and serology as support.
- Intrinsic resistance: the organism is resistant to aminoglycosides and polymyxins, so these drugs are avoided.
- Intensive therapy: intravenous ceftazidime or meropenem for 10 to 14 days.
- Eradication therapy: an oral regimen such as co-trimoxazole with doxycycline or amoxicillin-clavulanate for at least 12 weeks.
Approach to suspected melioidosis
Melioidosis is easy to miss because it mimics tuberculosis and ordinary pneumonia. The steps follow the usual sequence from suspicion to a complete treatment course.
- Suspect: consider melioidosis in a patient with diabetes who has pneumonia or an abscess after exposure to soil or water in an endemic region.
- Sample: send blood, sputum, pus and urine for culture before antibiotics are changed, because early samples give the best yield.
- Identify: grow the organism on Ashdown's medium and confirm it with biochemical tests, mass spectrometry or PCR, working under biosafety level 3 precautions.
- Treat intensively: give intravenous ceftazidime or meropenem for 10 to 14 days to control the acute infection and any septic spread.
- Eradicate: continue oral co-trimoxazole with doxycycline or amoxicillin-clavulanate for at least 12 weeks to prevent relapse.
- Drain and follow up: abscesses are drained and the patient is monitored for relapse, since latent infection can reactivate years later.
Where the exam tries to catch you
Melioidosis questions test staining, drug choice and the length of therapy.
- Trap: believing safety-pin staining confirms melioidosis Correct: both Yersinia pestis and B. pseudomallei show bipolar safety-pin staining, so the stain cannot separate them and confirmation needs culture and identification.
- Trap: choosing gentamicin for intensive treatment Correct: the organism is intrinsically resistant to aminoglycosides, so ceftazidime or meropenem is preferred.
- Trap: stopping co-trimoxazole once fever settles after two weeks Correct: the eradication phase lasts at least 12 weeks, because early cessation allows relapse.
Frequently asked questions
Why is ceftazidime preferred in the intensive phase of melioidosis?
Ceftazidime is preferred in the intensive phase of melioidosis because Burkholderia pseudomallei is susceptible to it and it treats the acute infection effectively. Meropenem is an alternative in severe disease, while aminoglycosides are avoided because of intrinsic resistance.
What is the most common clinical form of melioidosis?
Acute pneumonia is the commonest clinical form of melioidosis, and it may progress to septicaemia with multiple abscesses. Localised abscesses in the liver, spleen, prostate or skin, and chronic pulmonary disease resembling tuberculosis, also occur in Burkholderia pseudomallei infection.
Why is diabetes linked to melioidosis?
Diabetes mellitus is the commonest predisposing condition for melioidosis, because hyperglycaemia impairs neutrophil function and allows the organism to disseminate. Alcohol excess, chronic kidney disease and chronic lung disease are other recognised risk factors for this infection.
Why does eradication therapy in melioidosis last so long?
Eradication therapy lasts at least 12 weeks because Burkholderia pseudomallei can persist in tissues and cause relapse if treatment is stopped early. Oral co-trimoxazole combined with doxycycline or amoxicillin-clavulanate is a commonly used regimen per current guidance.
How is Burkholderia pseudomallei identified in the laboratory?
Burkholderia pseudomallei is identified by culture on selective medium such as Ashdown's agar, followed by biochemical identification or mass spectrometry. PCR and serology support the diagnosis, and the culture work is done under biosafety level 3 precautions.