Environmental Attributes Influencing the Distribution of Burkholderia pseudomallei in Northern Australia

Abstract

Factors responsible for the spatial and temporal clustering of Burkholderia pseudomallei in the environment remain to be elucidated. Whilst laboratory based experiments have been performed to analyse survival of the organism in various soil types, such approaches are strongly influenced by alterations to the soil micro ecology during soil sanitisation and translocation. During the monsoonal season in Townsville, Australia, B. pseudomallei is discharged from Castle Hill (an area with a very high soil prevalence of the organism) by groundwater seeps and is washed through a nearby area where intensive sampling in the dry season has been unable to detect the organism. We undertook environmental sampling and soil and plant characterisation in both areas to ascertain physiochemical and macro-floral differences between the two sites that may affect the prevalence of B. pseudomallei. In contrast to previous studies, the presence of B. pseudomallei was correlated with a low gravimetric water content and low nutrient availability (nitrogen and sulphur) and higher exchangeable potassium in soils favouring recovery. Relatively low levels of copper, iron and zinc favoured survival. The prevalence of the organism was found to be highest under the grasses Aristida sp. and Heteropogon contortus and to a lesser extent under Melinis repens. The findings of this study indicate that a greater variety of factors influence the endemicity of melioidosis than has previously been reported, and suggest that biogeographical boundaries to the organisms’ distribution involve complex interactions.

Soil Nutrient Depletion Is Associated with the Presence of Burkholderia pseudomallei

“…The negative association between soil organic matter and the presence of B. pseudomallei is consistent with two previous environmental studies in northern Australia (15) and Northeast Thailand (30), which showed that the level of organic carbon was negatively associated with the presence of B. pseudomallei.…”

“…In contrast, two cross-sectional studies in the natural environment in northern Australia and Northeast Thailand found that the presence of B. pseudomallei was negatively associated with the level of iron in soil (14, 15), and a recent modeling study and an experimental field study suggested that the presence of B. pseudomallei was not associated with soil acidity (1, 12).…”

“…Furthermore, both negative and positive correlations between the presence of B. pseudomallei and soil salinity have been reported (1, 12, 15). Land use can affect the biodiversity of organisms in soil (16), but there is currently no information on the association between the presence of B.…”

Burkholderia pseudomallei in a lowland rice paddy: seasonal changes and influence of soil depth and physico-chemical properties

“…reported that a higher soil pH 6.05, a low water holding capacity, and low iron were associated with the presence of B. pseudomallei in soil from paddy fields in north east Thailand in the rainy season, whereas a high concentration of manganese correlated with the presence of the organism in the dry season 20 . More recently, workers in both Thailand and Australia have reported an association between sandy, nutrient-depleted soil and the presence of B. pseudomallei 14, 15 , contrasting with earlier reports of an association with soils enriched with organic matter from animal waste 12 .…”

“…also found B. pseudomallei to be negatively associated with soil organic matter content, concluding that B. pseudomallei may thrive in nutrient-depleted soils 15 . The data regarding iron are conflicting – the organism has been associated with both low 14, 15, 20 and high 9, 16, 17 levels of iron in natural environments, whilst iron enhanced the growth of B. pseudomallei in soil microcosms under laboratory conditions 35, 41 . B. pseudomallei is known to produce a siderophore and has other mechanisms that enable it to acquire iron.…”