Буркхольдерия маллеи: сипаттамасы және қасиеттері

Species of bacterium

Burkholderia mallei is a Gram negative, bipolar, aerobic bacterium, a human and animal pathogen of genus Burkholderia causing glanders; the Latin name of this disease (malleus) gave its name to the species causing it. It is closely related to B. pseudomallei, and by multilocus sequence typing it is a subspecies of B. pseudomallei. B. mallei evolved from B. pseudomallei by selective reduction and deletions from the B. pseudomallei genome. Unlike B. pseudomallei and other genus members, B. mallei is nonmotile; its shape is coccobacillary measuring some 1.5–3.0 μm in length and 0.5–1.0 μm in diameter with rounded ends.

Wilhelm Schütz and Friedrich Löffler first isolated B. mallei in 1882. It was isolated from an infected liver and spleen of a horse. This bacterium is also one of the first to be identified containing a type VI secretion system which is important for its pathogenicity. In 1885, the German Botanist and Bacteriologist, Wilhelm Zopf (1846–1909) gave the pathogen its binomial name, after analyzing samples of the bacterium. He further refined his observations with the pathogen in 1886.

Most organisms within the Burkholderiaceae live in soil; however, B. mallei does not. Because B. mallei is an obligate mammalian pathogen, it must infect a host mammal to live and to be transmitted from one host to another.

B. mallei is very closely related to B. pseudomallei, being 99% identical in conserved genes when compared to B. pseudomallei. B. malllei has about 1.4 Mb less DNA than B. pseudomallei.

The genome of B. mallei was sequenced in the United States by The Institute of Genomic Research. The size of the genome is smaller than that of B. pseudomallei. The B. mallei sequence revealed a chromosome of 3.5 mega base pairs (Mb) and a 2.3 Mb "megaplasmid". Many insertion sequences and phase variable genes were also found.

Both B. mallei and B. pseudomallei can be cultured in a laboratory; nutrient agar can be used to grow the bacteria. When grown in culture, B. mallei grows in smooth, grey, translucent colonies. In a period of 18 hours at 37 °C, a B. mallei colony can grow to about 0.5–1.0 mm in diameter. B. mallei culture growth on MacConkey agar is variable. Many microbiologists are unfamiliar with B. mallei and as a result it has frequently been misidentified as a Pseudomonas species or as a contaminant in a culture. B. malleis ability to live within the host cell makes developing a vaccine against it difficult and complex. The vaccine would need to create a cell mediated immune response, as well as a humoral response to the bacteria in to be effective in protecting against B. mallei. In regards to a vaccine against B. mallei, the closeness of B. mallei to B. pseudomallei may make it possible that a vaccine developed for either type would be effective against the other. Lipopolysaccharide isolated from B. mallei demonstrated significantly lower biological activity as compared to the LPS from Escherichia coli, in agreement with the lower degree of acylation of its lipid A: the major forms of B. mallei lipid A were penta and tetraacylated, whereas classical lipid A from E. coli was hexaacylated. In addition, lipid A from B. mallei contains 4 amino 4 deoxyarabinose residue in almost half of the molecules, which would partially neutralize the negative charge of the phosphate groups necessary for the interaction with the positively charged amino acids of TLR4. At the same time, lipid A acyl chains in B. mallei were on the average longer (14–16 carbon atoms) than those in E. coli (14 carbon atoms), yet LPS from B. mallei appeared to be a weaker activator. B. mallei may employ LPS with low biological activity to evade proper recognition by the TLR4/MD 2 complex of innate immune system, dampening the host immune response and increasing the risk of bacterial dissemination.

Burkholderia mallei has been eradicated in the United States and most Western countries, but still affects animals in Africa, Asia, the Middle East, Central America, and South America.

Bukrholderia mallei and B. pseudomallei have a history of being on a list of potential biological warfare agents. The Centers for Disease Control and Prevention classifies B. mallei as a category B critical biological agent.

In March 2000, one of the first cases since the 1940s of glanders in the United States occurred in a young microbiologist working for the U. S. Army Medical Research Institute for Infectious Diseases. The researcher had type 1 diabetes and had been working with B. mallei for about two years, but he did not always wear gloves while conducting his research. The researcher experienced enlargement of the lymph nodes and a fever which lasted for 10 days even with antibiotic treatment. In the following weeks, the researcher experienced fatigue, rigors, night sweats, and loss of weight. The next month, his symptoms seemed to disappear after treatment with clarithromycin, but after the medication was stopped, the symptoms reappeared. After conducting multiple tests on cultures from the researcher's blood and a biopsied portion of a liver abscess, the bacterium was identified as B. mallei. Once it was established what infected the researcher, another course of antibiotics was given (imipenem and doxycycline) with 6 months of treatment. After a year, the researcher made a full recovery. This incident also showed how a cut or skin abrasion is not absolutely necessary to contract the disease, as the researcher had no recollection of any cut or accident while working in the laboratory. The case was significant as it showed the difficulty that microbiology laboratories have in identifying bioweapon agents and the potential consequences if measures are not taken to prepare for an actual biological attack. The Japanese used B. mallei in their biological warfare research units. The most notable and notorious unit, Unit 731, used the bacterium to conduct experiments on live human subjects. However, the Japanese did not end up creating a biological weapon out of B. mallei. They did actually use B. mallei to test its effectiveness in contaminating water supplies, and the results of these tests were successful. The Russians' biological weapons program also took an interest in B. mallei and conducted field tests with it. Some of the researchers from the program were actually infected and killed by it during the course of their research. It has been suggested that the Soviet Union eventually used B. mallei during their war in Afghanistan against the mujahideen.