Prevalence and genetic diversity of Burkholderia pseudomallei isolates in the environment near a patient's residence in Northeast Thailand

Background Burkholderia pseudomallei is the causative agent of melioidosis, a severe infectious disease in tropical regions. It is necessary to understand the risk of acquiring this infection from the environment. Methodology /Principal Findings The prevalence, concentration and genetic diversity of B. pseudomallei isolates collected from two sites in Buriram, Northeast Thailand were investigated. Forty-four environmental samples (18 from soil, 14 from rice rhizosphere, and 12 from water) were collected; of those 44 samples, 19 were collected from near a patient's residence and 25 from suspected exposure sites and compared with 10 clinical isolates of the patient. Quantitative culture was performed, and B. pseudomallei was identified using the latex agglutination test and matrix-laser absorption ionisation mass spectrometry. Genotyping was performed in 162 colonies from clinical (N = 10) and environmental samples (N = 152) using pulse-field gel electrophoresis (PFGE) followed by multi-locus sequence typing (MLST) of the clinical strain. B. pseudomallei was detected in 11 of the 44 environmental samples (1 from soil, 4 from rice rhizosphere, and 6 from water). The bacterial count in the positive soil sample was 115 CFU/g. The mean concentrations SDs of B. pseudomallei in the positive water and rhizosphere samples were 5.1 5.5 CFU/ml and 80 +/- 49 CFU/g, respectively. Six water samples with positive results were collected from a pond and water sources for drinking and daily use. All colonies isolated from the patient shared the same PFGE type (PT) indicating monoclonal infection of ST99. Although the 152 colonies from environmental isolates exhibited 25 PTs, none were identical to the patient's isolates. PT5 and PT7 were most common genotype among the environmental samples. Conclusions/Significance Diverse genotypes of B. pseudomallei were prevalent in the environment. However, the patient may have been infected with a low-density genotype. Intervention strategies for preventing B. pseudomallei infection are required. Author summary Burkholderia pseudomallei, an environmental bacterium, causes melioidosis, a serious but neglected infectious disease that is endemic in many tropical regions. Infection routes include inoculation, ingestion and inhalation. Several environmental sources serve as niches for persistence, providing a mechanism for further dissemination of the bacterium across distances, increasing the risk of human infection through repeated exposure or consumption. Understanding the exposure-relevant environmental sources and transmission routes is required to prevent and control the infection. The present study demonstrates several environmental samples, including those collected from soil and the rice rhizosphere as well as from various water sources, such as pond, rain, dug wells, and pump wells, from sampling points near the patient's residence were the reservoirs of B. pseudomallei with diverse genotypes. This suggests that the patient was exposed to B. pseudomallei multiple times. Thus, intervention strategies targeted at controlling environmental sources, preventing disease spread, and increasing education measures to reduce B. pseudomallei infection-related morbidity and mortality in Northeast Thailand are urgently required.