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

L Manivanh,O Ribolzi,Y Buisson,O Kounnavongsa,R Phetsouvanh,J Silisouk,J -L Maeght,D A B Dance,P N Newton,E Rochelle-Newall,K Xayyathip,I Elliott,A Pierret,M Vongsouvath,G Lacombe,S Rattanavong

doi:10.1038/s41598-017-02946-z

Abstract

Melioidosis, a severe infection with the environmental bacterium Burkholderia pseudomallei, is being recognised increasingly frequently. What determines its uneven distribution within endemic areas is poorly understood. We cultured soil from a rice field in Laos for B. pseudomallei at different depths on 4 occasions over a 13-month period. We also measured physical and chemical parameters in order to identify associated characteristics. Overall, 195 of 653 samples (29.7%) yielded B. pseudomallei. A higher prevalence of B. pseudomallei was found at soil depths greater than the 30 cm currently recommended for B. pseudomallei environmental sampling. B. pseudomallei was associated with a high soil water content and low total nitrogen, carbon and organic matter content. Our results suggested that a sampling grid of 25 five metre square quadrats (i.e. 25 × 25 m) should be sufficient to detect B. pseudomallei at a given location if samples are taken at a soil depth of at least 60 cm. However, culture of B. pseudomallei in environmental samples is difficult and liable to variation. Future studies should both rely on molecular approaches and address the micro-heterogeneity of soil when investigating physico-chemical associations with the presence of B. pseudomallei.

Highlights

Burkholderia pseudomallei, the causative agent of the disease melioidosis, is an environmental bacterium that is widespread in soil and water in endemic areas, most notably Southeast Asia and northern Australia[1, 2]
In this study we investigated the seasonal changes in the presence of B. pseudomallei at different depths and places within the same rain-fed lowland rice field and attempted to correlate these with a range of physicochemical parameters in an effort to identify factors that may account for the small-scale variation in the distribution of B. pseudomallei within the environment
Melioidosis is being increasingly recognised as a significant public health problem both worldwide[3] and in Laos since the organism was first isolated from soil and the first human cases were described just over a decade ago[23, 24]

Summary

Introduction

Burkholderia pseudomallei, the causative agent of the disease melioidosis, is an environmental bacterium that is widespread in soil and water in endemic areas, most notably Southeast Asia and northern Australia[1, 2]. The incidence of melioidosis varies across endemic areas and this is thought, at least in part, to relate to the uneven distribution of B. pseudomallei in the environment, which varies on both a large (e.g. regional/national) and a small (e.g. within a single field) scale[6,7,8]. In this study we investigated the seasonal changes in the presence of B. pseudomallei at different depths (from near the surface to 90 cm below the surface) and places within the same rain-fed lowland rice field and attempted to correlate these with a range of physicochemical parameters in an effort to identify factors that may account for the small-scale variation in the distribution of B. pseudomallei within the environment

Methods

Results

Conclusion