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The biochemical characteristics of 213 isolates of Burkholderia pseudomallei from patients with melioidosis and 140 isolates from the soil in central and northeastern Thailand were compared. Whereas the biochemical profiles of all the clinical isolates were similar, all soil isolates from the central area and 25% of isolates from northeastern Thailand comprised a different phenotype. This was characterised by the ability to assimilate L-arabinose (100%), adonitol (100%), 5-keto-gluconate (90%) and D-xylose (84%), but failure to assimilate dulcitol (0%), erythritol (0%) and trehalose (10%). Compared with clinical isolates, these organisms had similar antibiotic susceptibility profiles and were also recognised by a specific polyclonal antibody against B. pseudomallei. As melioidosis is rare in central Thailand, but common in the northeast, this raises the possibility that this biochemical phenotype may be less virulent, or may even represent a different species.

Patients with melioidosis may present with recurrent infections after clinical resolution of their primary illness. Because there has been no satisfactory typing scheme for Pseudomonas pseudomallei, recrudescence could not be distinguished from reinfection. We determined the strain identity of primary and relapse isolates of P. pseudomallei from 25 patients with culture-proven melioidosis to answer whether secondary infections were due to the initial infecting strain or to the acquisition of a new strain. Fifty-four isolates were compared by the patterns of BamHI restriction digests produced after hybridization with a cDNA copy of Escherichia coli rRNA. Twenty-three patients had primary and relapse isolates with identical or highly similar ribotype patterns. The patterns of isolates from two patients were different; the primary and relapse isolates differed by a single fragment for one, and the other had identical primary and first-relapse isolates while the second-relapse isolate was markedly different. The results indicated that recurrent infection probably resulted from endogenous relapse in most of the melioidosis patients studied, although reinfection from an exogenous source was also possible in two cases.