Groundwater Seeps Facilitate Exposure to Burkholderia pseudomallei

Abstract

Burkholderia pseudomallei is a saprophytic bacterium which is the causative agent of melioidosis, a common cause of fatal bacterial pneumonia and sepsis in the tropics. The incidence of melioidosis is clustered spatially and temporally and is heavily linked to rainfall and extreme weather events. Clinical case clustering has recently been reported in Townsville, Australia, and has implicated Castle Hill, a granite monolith in the city center, as a potential reservoir of infection. Topsoil and water from seasonal groundwater seeps were collected around the base of Castle Hill and analyzed by quantitative real-time PCR targeting the type III secretion system genes for the presence of B. pseudomallei. The organism was identified in 65% (95% confidence interval [CI], 49.5 to 80.4) of soil samples (n ‫؍‬ 40) and 92.5% (95% CI, 83.9 to 100) of seasonal groundwater samples (n ‫؍‬ 40). Further sampling of water collected from roads and gutters in nearby residential areas after an intense rainfall event found that 88.2% (95% CI, 72.9 to 100) of samples (n ‫؍‬ 16) contained viable B. pseudomallei at concentrations up to 113 CFU/ml. Comparison of isolates using multilocus sequence typing demonstrated clinical matches and close associations between environmental isolates and isolates derived from clinical samples from patients in Townsville. This study demonstrated that waterborne B. pseudomallei from groundwater seeps around Castle Hill may facilitate exposure to B. pseudomallei and contribute to the clinical clustering at this site. Access to this type of information will advise the development and implementation of public health measures to reduce the incidence of melioidosis.

Biogeography of Burkholderia pseudomallei in the Torres Strait Islands of Northern Australia

“…Further sampling during the wet season, when there is generally a higher recovery of isolates (20), will aid in revealing more information about the environmental niche of B. pseudomallei in the Torres Strait; this activity is under way. While the environmental prevalence of the organism on Badu Island is apparently lower than that in Darwin and mainland Queensland (20,25), it is similar to that reported from the nearby Western Province, Papua New Guinea (PNG) (26).…”

“…Samples were processed as previously described (20). More specifically, water samples (50 ml) were transferred aseptically to an equal volume of double-strength Ashdown's broth (21) containing 15 g/liter tryptone (Oxoid, Australia), 5 mg/liter crystal violet, and 50 mg/liter colistin (Sigma, Australia) into 500-ml conical Pyrex culture flasks, which were sealed and then incubated at 37°C with agitation at 100 rpm for 24 h. Soil samples (10 g) were cultivated in sealed 70-ml specimen jars (Sarstedt, Germany) containing 50 ml of single-strength Ashdown's isolation broth under the same conditions as the water samples.…”

Burkholderia pseudomallei Genotype Distribution in the Northern Territory, Australia

“…1 Its ability to cause infection when inhaled makes it plausible that B. pseudomallei could be dispersed in severe weather events such as cyclones. This bacterium is also able to move in the water table 11 and presumably to track along waterways, to be transported in soil used for gardening, building and farming, and to live in the aerial parts of grasses. 12 In addition, B. pseudomallei has been isolated from the beak of a healthy bird, suggesting another possible mode of longdistance dissemination.…”

Survival, Sublethal Injury, and Recovery of Environmental Burkholderia pseudomallei in Soil Subjected to Desiccation

“…Tong et al (19) and Baker et al (24) have postulated that the low water content of dry-season soils reduces the persistence of B. pseudomallei, and the prevalence of the bacterium in soils in the wet season may be due to mobilization via the water cycle from other more favorable soil horizons (19,24). While these observations demonstrate that B. pseudomallei can be mobilized in water, our results indicate that B. pseudomallei can remain residual and viable in dry soil, an often-conjectured but not previously shown response.…”