Distribution of Burkholderia pseudomallei in Northern Australia, a Land of Diversity

Abstract

ABSTRACTBurkholderia pseudomalleiis a Gram-negative soil bacillus that is the etiological agent of melioidosis and a biothreat agent. Little is known about the biogeography of this bacterium in Australia, despite its hyperendemicity in the northern region of this continent. The population structure of 953 AustralianB. pseudomalleistrains representing 779 and 174 isolates of clinical and environmental origins, respectively, was analyzed using multilocus sequence typing (MLST). Bayesian population structure and network SplitsTree analyses were performed on concatenated MLST loci, and sequence type (ST) diversity and evenness were examined using Simpson's and Pielou's indices and a multivariate dissimilarity matrix. Bayesian analysis found twoB. pseudomalleipopulations in Australia that were geographically distinct; isolates from the Northern Territory were grouped mainly into the first population, whereas the majority of isolates from Queensland were grouped in a second population. Differences in ST evenness were observed between sampling areas, confirming thatB. pseudomalleiis widespread and established across northern Australia, with a large number of fragmented habitats. ST analysis showed thatB. pseudomalleipopulations diversified as the sampling area increased. This observation was in contrast to smaller sampling areas where a few STs predominated, suggesting thatB. pseudomalleipopulations are ecologically established and not frequently dispersed. Interestingly, there was no identifiable ST bias between clinical and environmental isolates, suggesting the potential for all culturableB. pseudomalleiisolates to cause disease. Our findings have important implications for understanding the ecology ofB. pseudomalleiin Australia and for potential source attribution of this bacterium in the event of unexpected cases of melioidosis.