Biogeography of Burkholderia pseudomallei in the Torres Strait Islands of Northern Australia

Abstract

It has been hypothesized that biogeographical boundaries are a feature of Burkholderia pseudomallei ecology, and they impact the epidemiology of melioidosis on a global scale. This study examined the relatedness of B. pseudomallei sourced from islands in the Torres Strait of Northern Australia to determine if the geography of isolated island communities is a determinant of the organisms' dispersal. Environmental sampling on Badu Island in the Near Western Island cluster recovered a single clone. An additional 32 clinical isolates from the region were sourced. Isolates were characterized using multilocus sequence typing and a multiplex PCR targeting the flagellum gene cluster. Gene cluster analysis determined that 69% of the isolates from the region encoded the ancestral Burkholderia thailandensis-like flagellum and chemotaxis gene cluster, a proportion significantly lower than that reported from mainland Australia and consistent with observations of isolates from southern Papua New Guinea. A goodness-of-fit test indicated that there was geographic localization of sequence types throughout the archipelago, with the exception of Thursday Island, the economic and cultural hub of the region. Sequence types common to mainland Australia and Papua New Guinea were identified. These findings demonstrate for the first time an environmental reservoir for B. pseudomallei in the Torres Strait, and multilocus sequence typing suggests that the organism is not randomly distributed throughout this region and that seawater may provide a barrier to dispersal of the organism. Moreover, these findings support an anthropogenic dispersal hypothesis for the spread of B. pseudomallei throughout this region.

Unprecedented Melioidosis Cases in Northern Australia Caused by an Asian Burkholderia pseudomallei Strain Identified by Using Large-Scale Comparative Genomics

“…The isolates from Cambodia with these shared STs are not genetically related to the isolates of the same ST from Australia but rather are the result of homoplasy (7). Less clear is the ST-89 overlap, which has been described in a B. pseudomallei isolate from a melioidosis patient from the Torres Strait Islands of Australia and in a Thai environmental isolate (43). Further review of the strains involved suggests that incorrect provenance likely accounts for this overlap, with the ST-89 strain listed as being from Thailand, while it is more likely to actually be an Australian strain (44).…”

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

“…Recently, five clinical isolates from islands in the Torres Strait region of Queensland were shown to overlap STs from the Northern Territory (STs 109, 255, 468, 470, and 594) (23). Although these STs have not yet been isolated from the environment in the Torres Strait and the travel history of these patients to the Northern Territory was not ascertained, the highly recombinogenic nature of the B. pseudomallei genome means that overlapping STs between geographically distinct regions is an eventual inevitability.…”

Draft Genome Sequences of Burkholderia pseudomallei and Staphylococcus aureus, Isolated from a Patient with Chronic Rhinosinusitis

“…Burkholderia pseudomallei is a Gram-negative soil- and water-associated pathogen causing melioidosis ( 1 ). In our region, B. pseudomallei is more commonly found in tropical parts of Australia ( 2 ). Burkholderia spp.…”

“…In silico MLST analysis ( http://bpseudomallei.mlst.net ) determined a novel ST, B. pseudomallei ST1381. The alleles were as follows: ace ( 8 ), gltb ( 1 ), gmhd ( 3 ), lepa ( 2 ), lipa ( 1 ), nark ( 2 ), and ndh ( 1 ). An oxacillinase gene, bla OXA-59 , was identified in B. pseudomallei .…”