Genome fingerprinting by pulsed-field gel electrophoresis of isolates of Burkholderia pseudomallei from patients with melioidosis in Thailand

A total of 95 isolates of Burkholderia pseudomallei from 53 sporadic cases in Thailand were examined by pulsed-field gel electrophoresis. Digestion of genomic DNA of all isolates by NcoI generated a macrorestriction pattern similar to that of B. pseudomallei which cannot assimilate l-arabinose. Analysis using restriction enzymes SpeI and AvrII demonstrated greater sensitivity than NcoI digestion in the differentiation of B. pseudomallei and could be used for epidemiological groupings. Four cluster groups were evident among 37 isolates tested and the majority of isolates within each cluster displayed more than 65% similarity. Furthermore, multiple isolates from 18 and 35 patients with single and recurrent episodes of melioidosis, respectively, were examined. All patients with a single episode yielded genetically identical isolates and four of 35 patients with recurrent episodes were infected with strains of different genotypic patterns from the primary isolate(s). Hence, most repeated episodes of infection in melioidosis are as a result of the original infecting strains.