Evaluation of population genetic structure and horizontal gene transfer for the human pathogen Burkholderia pseudomallei

Burkhofderia pseudomallei is a soil-dwelling saprophyte and the cause of melioidosis. Multilocus sequence typing (MLST) of266 Thai B. pseudoma/lei isolates (83 soil and 183 invasive) defined 123 sequence types (STs). Invasive isolates were over-represented in the 10 largest clones, and there was'! significant difference in the classification index between environmental an~ disease isolates, confirming that genotypes were not distributed rando~1ly between the two samples. MLST profiles for 158 predominantly invasive isolates from northem Australia contained a similar number of STs (96) as the Thai invasive isolates, but noú ST was found in both populations. This analysis revealedú strong genetic differentiation on the basis of geographical -isolation, and a significant differentiation on the basis of virulence potential. The presence and distribution of five genomIc islands described for B. pseudomallei K96243 was investigated in natural populations. 111 silico analysis of 10 B. pseudoma/lei genome sequences demonstrated variable presence of these regions, together with evidence for micro-evolutionary changes that generates Gl diversity. Their presence was assessed in environmental (83) and invasive (103) B. pseudoma/lei isolates using peR. Positivity ranged from 12% for a prophage-like island (GJ 9), to 76% for a metabolic island (GJ 16). The presence of each of the five GIs did no! differ between environmental and disease-associated isolates. There was no reproducible association between the individual or cumulati ve presence of five Gis and clinical features in 103 patients with melioidosis. BUl'kho/deria thailandensis is a non-pathogenic soil saprophyte which is highly related to B. pseudomallei. MLST of a collection aLB. fhai/clI7dcnsis isolates demonstrated t\.\lO clusters. One cluster contained three isolates (one each from France, the U.S. and Cambodia), and the second larger cluster contained isolates from Thailand, Vietnam and Laos. eBURST analysis indicated that the larger cluster formed a single clonal complex, while all three strains of the small cluster were singletons.EThOS - Electronic Theses Online ServiceGBUnited Kingdo