Burkholderia bacteria - good, bad or both?


CORVALLIS - A species of bacterium common in soil and water called "Burkholderia cepacia" (B. cepacia) is being championed by agricultural scientists as a non-chemical means of fighting plant infections.

Environmental scientists have shown that B. cepacia can also remove hydrocarbon contaminants from ground water and soil.

But physicians worry that if B. cepacia becomes widely used as a microbial pesticide and environmental clean up agent, it may pose a risk to human health.

Jennifer Parke, a plant pathologist at Oregon State University, is collaborating with a group of international medical specialists to help them better understand the biology of the extraordinarily versatile, but enigmatic B. cepacia.

"Found in the natural environment, in soil, pond water, under your fingernails, this is one organism that seems to be able to do it all," said Parke, who conducts research on B. cepacia as a microbial pesticide on crop seedlings.

With at least five known sub-populations of B. cepacia, the strains used in agriculture to fight fungal diseases in plants have mostly been from one sub-population, explained Parke. The B. cepacia bacteria found fatal to cystic fibrosis patients have mostly been from another sub-population. But the cases are not cut and dry. Cystic fibrosis is an inherited disease that impairs lung functions and makes them susceptible to bacterial infections.

B. cepacia has shown promise as a natural pesticide for crops because it can out-compete plant diseases, produce antibiotics and perhaps boost a plant's own defenses, said Parke. Three strains of B. cepacia are registered by the EPA. for use as microbial pesticides and others are being considered, she said. With an ability to metabolize a broad range of organic compounds as energy sources, B. cepacia has been harnessed for use in cleaning up toxic contaminants in soil and groundwater as well.

In the 1980s came three outbreaks of B. cepacia-induced lung infections in cystic fibrosis patients in Europe and North America. The international medical community raised a red flag on the impending potential widespread use of B. cepacia in the environment.

"A dialogue was badly needed between specialists in plant and human diseases," said Parke.

In November 1998, Parke co-organized an international symposium "Burkholderia cepacia: Friend or Foe?" as part of the American Phytopathological Society annual meeting. Chief among the scientists' concerns was developing a way to be able to distinguish between the harmful human pathogenic and useful strains of B. cepacia. Until this happens, Parke said government regulators will not allow further use of the bacteria as a microbial pesticide or bioremediation tool.

Medical scientists also worry that strains of B. cepacia could change from more benign strains to more lethal strains after they are released into the environment.

"B. cepacia has a huge genome, which may mean it can mutate and adapt to change quickly," said Parke.

Parke is optimistic that modern molecular genetic technology will ultimately help distinguish between the harmful strains and useful strains, allowing use of some strains in agriculture and environmental clean up.

"Promising new methods should aid in the rapid and reliable determination of risk associated with individual strains of B. cepacia and may lead to the discovery of the factors responsible for human infection," she said.

Parke also feels that the medical establishment may be overly cautious about the potential for natural populations of B. cepacia to cause fatal outbreaks in humans.

"There has been no proof that B. cepacia outbreaks in humans have come from anywhere but other humans," she said. "There's no evidence that the patients are getting the disease from the environment. But if the release of strains for biocontrol or clean up of toxic wastes is perceived as a danger, then we had better look more carefully at the safety of the naturally occurring populations as well."

Parke is collaborating with her medical colleagues to determine population levels of B. cepacia in soil, plants and streams and to screen them for factors known to be involved in human diseases.