Whole-genome sequencing to investigate a non-clonal melioidosis cluster on a remote Australian island.

Derek S Sarovich,Erin P Price,Stephanie N J Chapple,Matthew T G Holden,Mark Mayo,Bart J Currie,Sharon J Peacock

doi:10.1099/mgen.0.000117

Abstract

Melioidosis is a tropical disease caused by the bacterium Burkholderia pseudomallei. Outbreaks are uncommon and can generally be attributed to a single point source and strain. We used whole-genome sequencing to analyse B. pseudomallei isolates collected from an historical 2-year long case cluster that occurred in a remote northern Australian indigenous island community, where infections were previously linked to a contaminated communal water supply. We analysed the genome-wide relatedness of the two most common multilocus sequence types (STs) involved in the outbreak, STs 125 and 126. This analysis showed that although these STs were closely related on a whole-genome level, they demonstrated evidence of multiple recombination events that were unlikely to have occurred over the timeframe of the outbreak. Based on epidemiological and genetic data, we also identified two additional patients not previously associated with this outbreak. Our results confirm the previous hypothesis that a single unchlorinated water source harbouring multiple B. pseudomallei strains was linked to the outbreak, and that increased melioidosis risk in this community was associated with Piper methysticum root (kava) consumption.

Highlights

Burkholderia pseudomallei is a Gram-negative soil-borne bacterium and the aetiological agent of melioidosis, a disease endemic in northern Australia and South-East Asia that is becoming increasingly recognized elsewhere [1, 2]
Between March 1994 and June 1996, an unusual case cluster of nine melioidosis cases occurred in a remote island indigenous community in the Northern Territory, Australia [6]
pulsed-field gel electrophoresis (PFGE) was performed on the clinical isolates from the outbreak, with the resulting profiles showing that the majority of strains (7/9) were identical

Summary

Introduction

Burkholderia pseudomallei is a Gram-negative soil-borne bacterium and the aetiological agent of melioidosis, a disease endemic in northern Australia and South-East Asia that is becoming increasingly recognized elsewhere [1, 2]. These isolates comprised 12 clinical strains [5 with prior MLST data [11] and 1 environmental isolate from the community water supply (MSHR0491; previously typed by MLST [11])] and 6 additional environmental isolates derived from soil sampling conducted shortly following the outbreak.

Results

Conclusion