History

Melioidosis is endemic in Southeast Asia and northern Australia and it was described earlier as glanders like disease. In 1911, the organism was first isolated from a young boy who was dying with pneumonia by a British pathologist Alfred Whitmore at Rangoon General Hospital, Burma. The term melioidosis was derived from two Greek words: “melis” (distemper of asses) and “eidos” (resemblance) and it was coined by Stanton and Fletcher in 1921. In endemic tropical regions, melioidosis is now recognized as a major cause of fatal septicaemia (Cheng and Currie, 2005). Usually, the disease is characterized by pneumonia and occasionally by multi organ abscesses in the patient with defined risk factors and with mortality rate of up to 40% (Jabbar and Currie, 2013).

About the organism

Burkholderia pseudomallei was initially classified under the species Pseudomonas as it exhibits similar culture and morphological characteristics and biochemical properties (Loveleena et al., 2004). Based on the 16S ribosomal RNA sequences, DNA-DNA homology values, cellular lipid and fatty acid composition, and phenotypic characteristics, seven species in Pseudomonas genus were transferred to the new genus Burkholderia (Yabuuchi et al., 1992). The bacterium has tendency to cause the disease after inhalation and this characteristic makes the pathogen to include in the Centers for Disease Control (CDC) list as a category B agent (Holden et al., 2004). B. pseudomallei is an environmental Gram-negative bacillus, motile, facultative intracellular bacterium (Cheng and Currie, 2005, Kespichayawattana et al., 2000).

Genome plasticity

The genome of the B. pseudomallei is composed of two chromosomes of 4.07 megabase pairs and 3.17 megabase pairs and encodes 3,460 and 2,395 coding sequences respectively. The large chromosome carries the core functions associated with the metabolism and cell growth where as the small chromosome carries most of the accessory functions associated with adaption and survival in different niches. The two chromosomes share a very little similarity except in rRNA clusters. The organism contains 42 insertion sequence elements and 26 pseudogenes. One of the most striking features of the genome is the presence of 16 genomic islands that constitute 6.1% of the genome (Holden et al., 2004). The comparative analysis of B. pseudomallei proteins with Ralstonia solanacearum produced highest number of orthologue matches whereas with more distant pseudomonads, produced fewer matches (Salanoubat et al., 2002).