Burkholderia pseudomallei: Properties, Pathogenesis and Laboratory Diagnosis

Burkholderia pseudomallei causes a life-threatening disease known as meliodiosis (also called Whitmore’s disease). It is glanders (caused by B. mallei) like disease in animals and humans.

It affects both humans or animals (rats, rabbits, and guinea pigs). Meliodiosis is also called ‘Vietnamese time-bomb disease’ because of its long latent period (it can reactive many years after the primary infection). This organism can be used as a potential agent of biological warfare so CDC has grouped B. pseudomallei and B. mallei as category B bio-threat agents.

Properties

• Aerobic, nonfermentative (they do not use carbohydrates as a source of energy or degrade them through metabolic pathways other than fermentation) gram-negative bacilli.
• 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 the contaminated sources.

Pathogenesis

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.

Virulence Factors

Known virulence factors are:

• Polysaccharide capsule
• Type III secretion system
• Toxins
• Enzymes

Clinical Manifestations

Meliodiosis is predominantly a disease of 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 a wide range of signs and symptom which ranges from localized abscess to disseminated infections with CNS manifestations. The mortality rate is approximately 95% in patients with acute disease, if not treated.

Acute Localized Infection: Infection is localized as a nodule and results from inoculation through a break in the skin. Patient generally present with:

• Localized pain or swelling
• Fever
• Ulceration
• Abscess

Pulmonary Infection: This form of the disease can produce a clinical picture of mild bronchitis to severe pneumonia. Commonly seen signs/symptoms are:

• Cough
• Chest pain
• High fever
• Headache
• Anorexia

Acute Bloodstream Infection: Patients with underlying illness such as HIV, renal failure, and diabetes may develop this type of infection. The symptoms generally include:

• Fever
• Headache
• Respiratory distress
• Abdominal discomfort
• Joint pain
• Disorientation

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.

Laboratory Diagnosis

Sample

Sample depends on the site of infection. Sputum and purulent discharge from lesion is commonly used.

Microscopy and Staining

Gram-negative bacilli that typically exhibit a bipolar or safety pin appearance, which is better appreciated when stained with methylene blue.

Culture

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 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.

Antigen detection

Rapid agglutination tests for the detection of B. pseudomallei antigen in urine are available.

Serology

Antibodies against B. pseudomallei can be detected and measured in blood.

References and Further Readings

1. Procop, G. W., & Koneman, E. W. (2016). Koneman’s Color Atlas and Textbook of Diagnostic Microbiology (Seventh, International edition). Lippincott Williams and Wilkins.
2. Image source: By Gavin Koh – Own work, CC BY-SA 4.0, ttps://commons.wikimedia.org/w/index.php?curid=4975784