pseudomallei [10]. There is extensive chromosomal synteny between B. thailandensis and B. pseudomallei, although some virulence-associated genes which are present in B. pseudomallei are absent in B. thailandensis [12]. Both

B. pseudomallei and B. thailandensis are able to invade and grow in a range of phagocytic AZD5153 and non-phagocytic cells, forming Cell Cycle inhibitor plaques or multinucleated giant cells [13, 14]. However, there is also evidence that the behaviour of B. pseudomallei and B. thailandensis differs in different cell lines. In A549 and human dendritic cells, B. pseudomallei has been shown to be more invasive than B. thailandensis, but there were no reported differences in the growth rate within cells. In contrast, in human macrophages, differences in intracellular growth rates have been reported [14]. Collectively, these findings have suggested that B. thailandensis could be used as a model to study certain aspects of the intracellular lifestyle of B. pseudomallei in cell culture systems [15]. The behaviour of B. oklahomensis in cell culture models is CX-6258 cell line not known. The value of whole animal or plant infection models, which use B. thailandensis or B. oklahomensis in place of B. pseudomallei, is much less clear. Isolates of B. thailandensis and B. oklahomensis that have been tested are considered to be highly attenuated or avirulent in BALB/c mice, with lethal doses for most isolates in excess of 107 cfu by the i.p. route [16]. However,

using intranasal challenge models, doses of greater than 104 cfu of B. thailandensis are reportedly able to kill mice and replicate B. pseudomallei disease phenotypes, although even in this model it is clear that B. thailandensis is much less virulent than B. pseudomallei [7]. There has been significant interest in the development of alternative infection models which avoid the use of mammals but also reflect the differences in virulence of species and isolates seen in mice. The Caenorhabditis elegans [17]

or tomato plant [18] infection models were not able to distinguish between B. pseudomallei and B. thailandensis, and in C. elegans, B. thailandensis was the most virulent Adenosine triphosphate [17]. Galleria mellonella (wax moth) larvae have previously been reported as susceptible to infection with B. pseudomallei, and a single B. thailandensis strain tested was reportedly less virulent [19]. This finding suggests that G. mellonella larvae may be a suitable host species for discerning differences in virulence. Our aim was to determine whether differences in the virulence of B. pseudomallei, B. thailandensis and B. oklahomensis isolates could be reliably determined in macrophage and G. mellonella larvae infection models. Results B. pseudomallei, B. thailandensis or B. oklahomensis are internalised with similar efficiencies into J774A.1 macrophages For this study we have selected a range of B. pseudomallei, B. thailandensis or B. oklahomensis isolates of known ancestry.