Burkholderia pseudomallei causes a life-threatening meliodiosis (also called Whitmore’s disease). It is glanders (caused by B. mallei) like disease in animals and humans.
It affects humans and animals (rats, rabbits, and guinea pigs). Melioidosis is also called ‘Vietnamese time-bomb disease’ because of its long latent period (it can reactivate many years after the primary infection). This organism can be used as a potential biological warfare agent, so CDC has grouped B. pseudomallei and B. mallei as category B bio-threat agents.
- Aerobic, nonfermentative (they do not use carbohydrates as a source of energy or degrade them through metabolic pathways other than fermentation) gram-negative bacilli.
- It is Gram-negative bacilli that typically exhibit a bipolar or safety pin appearance.
- It is a member of the family Burkholderiaceae, which includes other genera (Cuprivvidus, Lautropia, Pandoraea, and Ralstonia). More than 87 species of Burkholderia have been identified. Other medically important species are Burkholderia cepacia, Burkholderia gladioli, etc.
- Burkholderia pseudomallei is a saprophyte of soil and water and is spread to humans and animals through direct contact with contaminated sources.
Burkholderia is a saprophyte of soil and water. People acquire this infection mostly through
- inhalation of contaminated dust or water droplets
- ingestion of contaminated water, and
- contact with contaminated soil, especially through skin abrasions.
Person-to-person transmission can occur but rarely.
Known virulence factors are:
- Polysaccharide capsule
- Type III secretion system
Meliodiosis is predominantly a disease in tropical climates, especially in Southeast Asia (Thailand, Vietnam, Cambodia, Laos, Malaysia, Myanmar) and northern Australia.
The incubation period is not clearly defined but may range from 2 days to many years. Most infections are asymptomatic or present as a self-limited, flu-like illness. It shows various signs and symptoms, from localized abscesses to disseminated infections with CNS manifestations. If not treated, the mortality rate is approximately 95% in patients with acute disease.
Acute Localized Infection: Infection is localized as a nodule and results from inoculation through a break in the skin. A patient generally presents with:
- Localized pain or swelling
Pulmonary Infection: This form of the disease can produce a clinical picture of mild bronchitis to severe pneumonia. Commonly seen signs/symptoms are:
- Chest pain
- High fever
Acute Bloodstream Infection: Patients with underlying illnesses such as HIV, renal failure, and diabetes may develop this type of infection. The symptoms generally include:
- Respiratory distress
- Abdominal discomfort
- Joint pain
Chronic Suppurative Infection: Chronic melioidosis is a disseminated infection that involves various organs of the body such as joints, viscera, skin, brain, liver, lungs, bones, and spleen.
Sample depends on the site of infection. Sputum and purulent discharge from the lesion are commonly used.
Microscopy and Staining
B. pseudomallei is a Gram-negative bacillus that typically exhibits a bipolar or safety pin appearance, which is better appreciated when stained with methylene blue.
It is an obligate aerobe that grows in various media, e.g. nutrient agar, blood agar, and MacConkey agar. Colonies are typically rough and corrugated, similar to the colonies of Pseudomonas stutzeri. Ashdown’s medium is used as a selective medium, where it produces wrinkled purple colonies.
Important properties that differentiate it from Pseudomonas stutzeri include
- Gelatin liquefaction positive
- Utilizes arginine
- Positive for intracellular poly-β-hydroxybutyrate (PHB).
Latex agglutination test: Culture can be confirmed by latex agglutination test using specific antisera.
Rapid agglutination tests for detecting B. pseudomallei antigen in urine are available.
Antibodies against B. pseudomallei can be detected and measured in blood.
Presently, optimal therapy for meliodosis remains controversial. Burkholderia spp. can express resistance to various antibiotics, so devising effective treatment options may be problematic. CDC recommends intravenous antimicrobial therapy for a minimum of 2 weeks followed by 3-6 months of oral
antimicrobial therapy. Intravenous therapy consists of ceftazidime administered every 6–8 hours or meropenem administered every 8 hours. Oral antimicrobial therapy consists of trimethoprim-sulfamethoxazole taken every 12 hours or amoxicillin/clavulanic acid (co-amoxiclav) taken every 8 hours.
References and Further Readings
- Procop, G. W., & Koneman, E. W. (2016). Koneman’s Color Atlas and Textbook of Diagnostic Microbiology (Seventh, International edition). Lippincott Williams and Wilkins.
- Image source: By Gavin Koh – Own work, CC BY-SA 4.0, ttps://commons.wikimedia.org/w/index.php?curid=4975784
- Melioidosis. Centers for Disease Control and Prevention.