AGENDA AND PRESENTATION SUMMARIES
Sponsored by the APS Biological Control Committee
1998 Annual Meeting – Las Vegas
Ballroom C – 1-5 PM Monday, Nov. 9
1:00PM
Introduction
Jennifer Parke, Dept. of Crop and Soil Sciences, Oregon State University, Corvallis, Oregon
Burkholderia cepacia is a remarkably versatile bacterium. In this symposium we will bring together international experts to describe its ecology as a phytopathogen, biocontrol agent, and human pathogen, and discuss recent research findings in bacterial genetics that may provide insight into its evolutionary adaptability. We will learn the state-of-the art in differentiating between human pathogenic, plant pathogenic, and non-pathogenic strains, and establish a dialogue among plant pathologists, medical microbiologists, and regulatory experts with regard to the prudent use of
Burkholderia cepacia in agriculture.
1:10PM
B. cepacia as a phytopathogen
James Lorbeer and Norman Gundersheim, Dept. of Plant Pathology, Cornell University, Ithaca, New York
Burkholder in 1950 reported a soft rot of onion which he named sour skin . He described Pseudomonas cepacia as the causal agent of the disease. B. cepacia infects onion leaves and bulbs only when they are wounded. The leaf blade axil (junction of the leaf blade and sheath) is particularly susceptible when stab inoculated and kept moist. The bacterium can infect onion bulbs through succulent tissue of the neck wound created by the topping procedure at harvest. A bacterial disease of onions tentatively called bacterial canker appears to be caused primarily by B. cepacia. This disease affects the leaf blade axil area of onions growing under field conditions and often leads to sour skin symptoms in the bulbs.
1:30PM
B. cepacia as a biocontrol agent
Robert Lumsden, USDA-ARS, Beltsville, Maryland
Burkholderia cepacia is efficaceous for control of several soilborne disease problems. It has been successfully used for control of major soilborne disease problems caused by Pythium spp., Rhizoctonia solani, Fusarium spp., and others. Disease control has been demonstrated experimentally with B. cepacia for the past 25 years and was recently successfully registered with EPA and commercially developed. No adverse effects caused by B. cepacia have been reported during this long period of experimental and commercial use.
2:00 PM
B. cepacia as an agent of human disease
John LiPuma, Allegheny University of the Health Sciences, Philadelphia, Pennsylvania
Recovery of
Burkholderia cepacia from sputum culture from persons with cystic fibrosis (CF) was initially reported in the late1970s. Descriptions of clinical outcomes of respiratory tract colonization, including "cepacia syndrome", a condition characterized by severe necrotizing pneumonia and sepsis, soon followed. During the past decade a number of studies have helped to elucidate the epidemiology of
B. cepacia infection among CF patients. Many questions regarding specific virulence factors, pathogenesis and natural history remain unanswered, however.
2:30 PM
Human and environmental isolates of the B. cepacia complex: molecular taxonomy, epidemiology, and potential for virulence
John Govan, University Medical School, Edinburgh, Scotland and Peter Vandamme, Laboratorium voor Microbiologie, Gent, Belgium
In contrast to considerable information on the molecular and social epidemiology of
B. cepacia infection in humans, little is known about the organism’s virulence determinants.
B. cepacia appears to have a predilection for the respiratory tract. Pulmonary exacerbations due to
B. cepacia are associated with damaging inflammation and, in vitro, the bacterium’s lipopolysaccharide and lipopeptide haemolysin stimulate a potentially damaging cytokine and neutrophil response.
Click here to see an image illustrating the effect of a B. cepacia lipopeptide toxin on human erythrocytes. The organism is resistant to antimicrobial peptides (defensins) present in airways and to non-oxidative killing by neutrophils. A particular cause for anxiety in patients with cystic fibrosis is that clinical outcome in individual patients cannot be predicted even in epidemics when groups of patients are colonised by the same strain. Hypotheses to explain this unpredictable virulence include complex bacteria and host interactions which upset the balance between defensive and damaging consequences of the inflammatory response.
Recent taxonomic studies indicated that there is a marked heterogeneity amongst strains routinely identified as B. cepacia. Integrated genotypic and phenotypic analyses have shown that B. cepacia isolates, cultured from clinical or environmental sites, belong to at least five distinct genomic species or genomovars, referred to collectively as the B. cepacia complex. Following identification of distinguishing phenotypic characteristics, the name B. multivorans has been proposed for genomovar II, while genomovar V was identified as the recently described B. vietnamiensis, an organism thus far primarily isolated from the rice rhizosphere. The remaining three groups are referred to as B. cepacia genomovars I, III and IV pending differential phenotypic tests. All five groups and other Burkholderia species such as B. gladioli have been cultured from CF patients and environmental samples. A variety of species, some of which represent novel taxa, are regularly misidentified as B. cepacia; similarly, B. cepacia strains are regularly not recognized as Burkholderia strains.
3:25 PM
Break
3:35 PM
Genomic plasticity and metabolic diversity of B. cepacia
Thomas Lessie, Dept. of Microbiology, University of Massachusetts, Amherst, Massachusetts
More than thirty B. cepacia isolates, including representatives of all five of the genomovars defined by Vandamme et al, contained between two and four replicons with sizes in the range of 1 to 4 Mb. Analysis of spontaneous and transposon-generated mutants has revealed an underlying high frequency of genomic rearrangements which may complicate genetic analysis of B. cepacia. Click here for table showing size and number of replicons in B. cepacia isolates.
4:05 PM
Risk-assessment for registration of biopesticides
Janet Andersen, EPA, Washington, D.C.
Microbial pesticides, live and killed microbes sold to control pests, are registered by EPA’s Biopesticide and Pollution Prevention Division. Registration is undertaken to assure that regulated pest control products do not present unreasonable risks to those who may be exposed to them. This process typically includes toxicology tests performed on animals as surrogates for human risk. Toxicological tests are also typically performed on non-target plants and animals to assess risk to the environment. Unlike traditional pesticides, toxicology tests required for microbial pesticides are usually limited to short term high dose exposure, also known as acute tests. Also unlike traditional pesticides, pathogenicity must be assessed in the case of live microbial pesticides. Scientific literature may be used in the risk evaluation process where appropriate, and some tests may be waived if there is sufficient evidence that they are not necessary. One important aspect of the evaluation of microbial pesticides is the taxonomic relationship between known human, plant, or animal pathogens or toxin producers and the microbe being considered for registration. The taxonomic relationship between known human pathogenic and biocontrol strains of B. cepacia has become particularly important.
4:30 PM
Open discussion
David Gurian-Sherman (Moderator), EPA, Washington, D.C.
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