Ecology and epidemiology of Burkholderia cepacia
Presented by Suzanne McKenzie Miller
Mentor: Jennifer Parke
Department of Crop and Soil Science, Oregon State University
Burkholderia cepacia is a genetically complex, metabolically diverse bacterium found in a range of environments, including soil, water, and the rhizosphere (the soil immediately surrounding a plant root). The B. cepacia complex includes strains used as biological control agents and in bioremediation projects. B. cepacia can also cause opportunistic, potentially fatal, infections in patients with cystic fibrosis. Patient-to-patient transmission of pathogenic B. cepacia has been documented; however, it is not known if human pathogenic strains are present in or acquired from the environment. This report describes a two-tiered effort to elucidate the relationship between human pathogenic and environmental strains of B. cepacia. First, work is underway to determine if it is possible to isolate potentially human pathogenic strains of B. cepacia from the environment. To date, 36 sites have been sampled comprising a wide range of bacterial habitats. Dilution plating on two selective media has yielded large numbers of putative B. cepacia colonies, especially from rhizosphere samples. Work is in progress to further identify these cultures using PCR-based techniques and traditional biochemical tests. These data will be compared with fingerprinting using DNA directly extracted from the 36 samples. A second part of the project is to create an assay to test the ability of human clinical strains to survive in the rhizosphere, a habitat known to support large populations of B. cepacia. Here 30 human pathogenic strains will be applied to pea seeds and grown at 20&Mac176;C, or applied to cucumber seeds and grown at 37&Mac176;C. Seven days after planting, serial dilutions from rhizosphere samples will be plated on selective media and their populations compared to those of strains known to colonize roots. Trials to establish seed type, temperatures, soil medium, water rates, optimal initial bacterial concentration and appropriate time points have been conducted. These studies should provide information which will contribute to our understanding of the ecology and epidemiology of B. cepacia.