Sensitive and Specific Molecular Detection of Burkholderia pseudomallei , the Causative Agent of Melioidosis, in the Soil of Tropical Northern Australia

Abstract

Burkholderia pseudomallei, the cause of the severe disease melioidosis in humans and animals, is a gramnegative saprophyte living in soil and water of areas of endemicity such as tropical northern Australia and Southeast Asia. Infection occurs mainly by contact with wet contaminated soil. The environmental distribution of B. pseudomallei in northern Australia is still unclear. We developed and evaluated a direct soil B. pseudomallei DNA detection method based on the recently published real-time PCR targeting the B. pseudomallei type III secretion system. The method was evaluated by inoculating different soil types with B. pseudomallei dilution series and by comparing B. pseudomallei detection rate with culture-based detection rate for 104 randomly collected soil samples from the Darwin rural area in northern Australia. We found that direct soil B. pseudomallei DNA detection not only was substantially faster than culture but also proved to be more sensitive with no evident false-positive results. This assay provides a new tool to detect B. pseudomallei in soil samples in a fast and highly sensitive and specific manner and is applicable for large-scale B. pseudomallei environmental screening studies or in outbreak situations. Furthermore, analysis of the 104 collected soil samples revealed a significant association between B. pseudomallei-positive sites and the presence of animals at these locations and also with moist, reddish brown-to-reddish gray soils.

Seasonal variation of soil environmental characteristics affect the presence of Burkholderia pseudomallei in Khon Kaen, Thailand

“…The lower %WHC of the B. pseudomallei-positive soil in the rainy season agrees with the earlier finding on the presence of B. pseudomallei in sandy soil type (Palasatien et al, 2008). However, there was no correlation between the presence of B. pseudomallei and soil texture type in northern Australia (Kaestli et al, 2007).…”

“…In contrast, in Australia, most of B. pseudomallei were found in soil with high iron content (Kaestli et al, 2007). Iron is an essential element for bacterial metabolism but excessive concentration is toxic to bacteria (Weinberg 1989(Weinberg , 1990.…”

Morphological Alteration and Survival of Burkholderia pseudomallei in Soil Microcosms

“…21 Moreover, the growth-promoting effect of iron on B. pseudomallei reinforced the significant association between B. pseudomallei-positive sites and the soil being reddish gray or reddish brown, indicating its iron content and the presence of animals. 19 Red to reddishyellow loamy sand containing iron and iron-impregnated nodules has been reported in the melioidosis-endemic area of Nam Phong catena in northeastern Thailand. 34 Our results provide additional support of the findings of a soil survey in the Nam Phong and Muang Districts, Khon Kaen, conducted in 2009 that revealed a correlation between culturable B. pseudomallei and the presence of higher iron levels in the soil during the dry season compared with that during the rainy season.…”

“…The adaptations that facilitate the survival of B. pseudomallei in various environments, including water and soil, have been previously linked to the incidence or outbreaks of the disease. 19,32,33 In this study, sterile control soil microcosm models with or without the addition of salt or iron were established to evaluate the performance of B. pseudomallei grown in soil for up to 30 days compared with that on the first day of inoculation. The results obtained demonstrated the ability of B. pseudomallei to survive for extended periods in the control soil, the low-salinity soil, and the iron-containing soil (P < 0.05) (Figure 1).…”

“…17 The association of the presence of B. pseudomallei with that of iron and salt in water and soil has been demonstrated in endemic areas. 16,[18][19][20][21][22] These results may facilitate understanding of the ability of B. pseudomallei to adapt to soil in northeastern Thailand that has different environmental features, including high salinity and the presence of iron. The resilience exhibited by B. pseudomallei in endemic areas has resulted in a high risk of pathogen exposure.…”