Presence of Burkholderia pseudomallei in Soil and Paddy Rice Water in a Rice Field in Northeast Thailand, but Not in Air and Rainwater

Abstract

Environmental Burkholderia pseudomallei has been postulated to be aerosolized during ploughing and heavy rain, and could result in inhalational melioidosis. Here, we determined the presence of B. pseudomallei in soil, paddy field water (PFW), air, and rainwater samples in a single rice paddy field in Ubon Ratchathani, northeast Thailand. In 2012, we collected 100 soil samples during the dry season, 10 PFW samples during the monsoon season, 77 air samples during ploughing (N = 31) and heavy rains (N = 46), and 60 rainwater samples during 12 rain events. We found that 32 soil samples (32%), six PFW samples (60%), and none of the air and rainwater samples were culture positive for B. pseudomallei. Other soil bacteria were isolated from air and rainwater samples. Mean quantitative count of B. pseudomallei estimated from two culture-positive PFW samples was 200 colony forming units/mL. Our findings suggest that the risk of melioidosis acquisition by inhalation in Thailand might be low.

Figure 1.

Schematic diagram showing the sampled field, wind direction, and locations of air samplers during the dry season. The presence of Burkholderia pseudomallei in 100 equally spaced sampling points measuring 2.5 m by 2.5 m in a rice paddy field in Ubon Ratchathani was investigated during the dry season. The center point of each square was sampled for soil. The black arrow (top) indicates the direction of the prevailing wind. Orange pentagons represent the positions of SKC Air Samplers, the blue triangle represents the location of the Casella Slit Agar Sampler, and the green circle represents the location of the XMX 2L-MIL Bioaerosol Collector. This figure appears in color at www.ajtmh.org.

Figure 2.

Eight organisms with Burkholderia pseudomallei-like bacterial colonies isolated from air and rainwater samples in Ubon Ratchathani, Thailand. Bacterial colonies isolated from air samples using Casella Slit Agar Sampler: (A) Sphingobacterium thalpophilum, (B) Stenotrophomonas pavanii, (C) Delftia lacustris/tsuruhatensis, and using the XMX-MIL BioAerosol Collector: (D) Cupriavidus necator/brasiliensis. Bacterial colonies isolated from rainwater: (E) Ralstonia pickettii, (F) Burkholderia latens, (G) Burkholderia multivorans, and (H) Burkholderia ambifaria. This figure appears in color at www.ajtmh.org.