Burkholderia pseudomallei

Source: Wikipedia, the free encyclopedia.

Burkholderia pseudomallei
Burkholderia pseudomallei colonies on
Ashdown's agar
showing the characteristic cornflower head morphology
Scientific classification Edit this classification
Domain: Bacteria
Phylum: Pseudomonadota
Class: Betaproteobacteria
Order: Burkholderiales
Family: Burkholderiaceae
Genus: Burkholderia
Species:
B. pseudomallei
Binomial name
Burkholderia pseudomallei
(Whitmore 1913)
Yabuuchi et al. 1993[1]
Synonyms

Bacillus pseudomallei Whitmore 1913
Bacterium whitmori Stanton and Fletcher 1921
Malleomyces pseudomallei Breed 1939
Loefflerella pseudomallei Brindle and Cowan 1951
Pfeiferella pseudomallei
Pseudomonas pseudomallei (Whitmore 1913) Haynes 1957

Burkholderia pseudomallei (also known as Pseudomonas pseudomallei) is a

bacterium.[2] It is a soil-dwelling bacterium endemic in tropical and subtropical regions worldwide, particularly in Thailand and northern Australia.[3] It was reported in 2008 that there had been an expansion of the affected regions due to significant natural disasters, and it could be found in Southern China, Hong Kong, and countries in America.[4] B. pseudomallei, amongst other pathogens, has been found in monkeys imported into the United States from Asia for laboratory use, posing a risk that the pathogen could be introduced into the country.[5]

Although it is mainly a soil-dwelling bacteria, a study performed by Apinya Pumpuang and others showed that Burkholderia pseudomallei survived in distilled water for 16 years, demonstrating that it is capable of living in water if a specific environment is provided.

CDC classifies it as a "Tier 1 select agent" with potential as a bioterrorism agent.[5] It infects other animals, most commonly livestock such as goats, pigs, and sheep, less frequently.[9] It is also capable of infecting plants in a laboratory setting.[10]

Burkholderia pseudomallei measures 2–5 μm in length and 0.4–0.8 μm in diameter and is capable of self-propulsion using

flagella. The bacteria can grow in a number of artificial nutrient environments, especially betaine- and arginine
-containing ones.

endotoxins. The role of the toxins identified in the process of melioidosis symptom development has not been fully elucidated.[11]

Identification

Burkholderia pseudomallei is not

blood agar, MacConkey agar, EMB, etc.). Ashdown's medium (or Burkholderia cepacia medium) may be used for selective isolation.[12]
Cultures typically become positive in 24 to 48 hours (this rapid growth rate differentiates the organism from
Gram-negative rod with a characteristic "safety pin" appearance (bipolar staining). On sensitivity testing, the organism appears highly resistant (it is innately resistant to many antibiotics including colistin and gentamicin) and that again differentiates it from B. mallei, which is in contrast, exquisitely sensitive to many antibiotics. For environmental specimens only, differentiation from the nonpathogenic B. thailandensis using an arabinose test is necessary (B. thailandensis is never isolated from clinical specimens).[13] The laboratory identification of B. pseudomallei has been described in the literature.[14]

The classic textbook description of B. pseudomallei in clinical samples is of an intracellular, bipolar-staining, Gram-negative rod, but this is of little value in identifying the organism from clinical samples.[14] Some[15] suggest the Wayson stain is useful for this purpose, but this has been shown not to be the case.[16]

Laboratory identification of B. pseudomallei can be difficult, especially in Western countries where it is rarely seen. The large, wrinkled colonies look like environmental contaminants, so are often discarded as being of no clinical significance.

mycobacteria) by bioMérieux has been shown to have superior yields compared to conventional blood culture media.[22]

Even when the isolate is recognized to be significant, commonly used identification systems may misidentify the organism as

Burkholderia cepacia or Pseudomonas aeruginosa.[23][24] Again, because the disease is rarely seen in Western countries, identification of B. pseudomallei in cultures may not actually trigger alarms in physicians unfamiliar with the disease.[25] Routine biochemical methods for identification of bacteria vary widely in their identification of this organism: the API 20NE system accurately identifies B. pseudomallei in 99% of cases,[26] as does the automated Vitek 1 system, but the automated Vitek 2 system only identifies 19% of isolates.[24]

The pattern of resistance to antimicrobials is distinctive, and helps to differentiate the organism from P. aeruginosa. The majority of B. pseudomallei isolates are intrinsically resistant to all aminoglycosides (via an efflux pump mechanism),[27] but sensitive to co-amoxiclav:[28] this pattern of resistance almost never occurs in P. aeruginosa and is helpful in identification.[29] Unfortunately, the majority of strains in Sarawak, Borneo, are susceptible to aminoglycosides and macrolides, which means the conventional recommendations for isolation and identification do not apply there.[30]

Molecular methods (

latex agglutination assay is widely used,[26] while a rapid immunofluorescence technique is also available in a small number of centres.[34]

Characteristics

Morphological, physiological, and biochemical characteristics of Burkholderia pseudomallei are shown in the Table below.

Test type Test Characteristics
Colony characters Size 2–5 μm in length and 0.4–0.8 μm in diameter
Type Round
Color Whitish
Shape Multiple
Morphological characters Shape Rod (Variable)
Physiological characters Motility +
Growth at 6.5% NaCl +
Biochemical characters Gram staining -
Oxidase +
Catalase +[35]
Oxidative-Fermentative
Motility +
Methyl Red
Voges-Proskauer
Indole -[36]
H2S Production -
Urease
Nitrate reductase +
β-Galactosidase
Hydrolysis of Gelatin +
Casein
Utilization of Glycerol +
Galactose +
D-Glucose +
D-Fructose +
D-Mannose +
Mannitol Variable

Note: + = Positive, – =Negative

Disinfection

Burkholderia pseudomallei is susceptible to numerous disinfectants, including

mercuric chloride, potassium permanganate, 1% sodium hypochlorite, 70% ethanol, 2% glutaraldehyde, and to a lesser extent, phenolic preparations.[37] B. pseudomallei is effectively killed by the commercial disinfectants, Perasafe and Virkon.[38] The microorganism can also be destroyed by heating to above 74 °C for 10 min or by ultraviolet irradiation.[39]

Medical importance

Main article: Melioidosis

Burkholderia pseudomallei infection in humans is called melioidosis or Whitmore's disease. It is spread though direct contact with water or soil that holds the bacteria. There have been few cases of transmission of the bacteria perinatally.[40] Its mortality is 20 to 50% even with treatment.[28]

Antibiotic treatment and sensitivity testing

Main article: Melioidosis treatment

The antibiotic of choice is

co-trimoxazole), they have been proven to be inferior in vivo for the treatment of acute melioidosis.[41] Disc diffusion tests are unreliable when looking for co-trimoxazole resistance in B. pseudomallei (they greatly overestimate resistance) and Etests or agar dilution tests should be used in preference.[42][43] The actions of co-trimoxazole and doxycycline are antagonistic, which suggests these two drugs ought not to be used together.[44]

The organism is intrinsically resistant to

Kanamycin is used to kill B. pseudomallei in the laboratory, but the concentrations used are much higher than those achievable in humans.[47]

Pathogenicity mechanisms and virulence factors

Burkholderia pseudomallei is an opportunistic pathogen. An environmental organism, it has no requirement to pass through an animal host to replicate. From the point of view of the bacterium, human infection is a developmental "dead end".[48]

Strains which cause disease in humans differ from those causing disease in other animals, by possessing certain

genomic islands.[49] It may have the ability to cause disease in humans because of DNA it has acquired from other microorganisms.[49] Its mutation rate is also high, and the organism continues to evolve even after infecting a host.[50]

Burkholderia pseudomallei is able to invade cells (it is an intracellular pathogen).[51] It is able to polymerise actin, and to spread from cell to cell, causing cell fusion and the formation of multinucleated giant cells.[52] It possesses a uniquely fusogenic type VI secretion system that is required for cell-cell spread and virulence in mammalian hosts.[53] The bacterium also expresses a toxin called lethal factor 1.[54] B. pseudomallei is one of the first Proteobacteria to be identified as containing an active type VI secretion system. It is also the only organism identified that contains up to six different type VI secretion systems.[55]

B. pseudomallei is intrinsically resistant to many antimicrobial agents by virtue of its

macrolides (BpeAB-OprB).[56]

Vaccine candidates

As of 2023[update] no vaccine had been licensed, although many had been evaluated in pre-clinical studies.[57][58]

Vaccine candidates have been suggested.

diaminopimelate (DAP) in rich media and auxotrophic for DAP, lysine, methionine and threonine in minimal media.[59] The Δasd bacterium (bacterium with the asd gene removed) protects against inhalational melioidosis in mice.[60]

Transformation

Burkholderia pseudomoallei can go through transformation. The bacteria is able to uptake a free plasmid using electroporation and the plasmid material will integrate into the host DNA when they are electrocompetent. An example is given by an experiment performed by Mack K. and Titball R. W., which showed that a Burkholderia pseudomallei 4845 was capable of transformation by electroporation, utilizing the incQ plasmid pKT230.[61]

References

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External links
Retrieved from "https://en.wikipedia.org/w/index.php?title=Burkholderia_pseudomallei&oldid=1215139508"