Dr. Kathryn Boor - Short Biographical Sketch
Kathryn Boor is a Professor in the Department of Food Science. She studied at Cornell University (B.S. in Food Science), the University of Wisconsin (M.S. in Food Science) and the University of California, Davis (Ph.D. in Microbiology in 1994). She joined the Cornell faculty in 1994 and is a member of the Graduate Fields of Food Science, Microbiology and Environmental Toxicology. Kathryn has an extension/research appointment. She is the director of the Milk Quality Improvement Program. She serves as coordinator of the Cornell Food and Water Safety Program and as director of the Food Safety Graduate Training Program, including the USDA National Needs Development Program. Dr. Boor participates in the Infection and Pathobiology Program and in the Cornell Genomics Initiative. She also currently serves as the Secretary and Scientific Advisor of the New York State Cheese Manufacturers' Association. She served on the Board of Directors of the American Dairy Science Association and was the 1999-2000 President of the New York State Association for Food Protection. Dr. Boor is also a member of the Editorial Boards of the Journal of Food Protection and Applied and Environmental Microbiology.
ResearchOverview
Kathryn Boor’s research program focuses on determining factors that affect the presence and persistence of pathogenic and spoilage organisms in food products intended for human consumption. The specific goals of her research program are to identify and characterize bacterial systems that affect survival and transmission of foodborne microbes, including Listeria monocytogenes and spore-forming bacteria, throughout food systems. Her specific objectives are to integrate the tools of molecular biology and phenotypic microbiology to: (i) identify and characterize genetic factors that link the ability of bacteria to survive under various conditions, including in foods and in food processing environments, with their ability to cause human and animal disease; and (ii) rapidly identify and track spoilage and pathogenic bacteria in food systems. Research results associated with objective (i) have improved our understanding of specific cellular mechanisms that contribute to bacterial survival under widely varying environmental conditions. The latter objective directly links her research program with her extension program, in that projects undertaken are driven by current and future food industry needs. Dr. Boor’s major research accomplishments in tracking bacterial contaminants in food processing systems also have been used to generate focused educational opportunities for the dairy industry.
Background
Pathogenesis of foodborne diseases can involve complex interactions between a bacterial pathogen, a variety of environments and one or multiple host species. As a consequence, foodborne pathogens provide ideal model systems for studying bacterial cell adaptation, survival, and maintenance of virulence characteristics under widely varying conditions, including those not directly associated with a host. Pathogenesis of bacterial diseases transmitted from animals through foods to humans may encompass all or some of the following steps: (i) bacterial survival in animal feeds or in the animal’s environment (e.g., Listeria monocytogenes and Salmonella spp. are common environmental contaminants); (ii) establishment of clinical or subclinical infections in food animals; (iii) shedding of the organism into animal products used for human consumption (e.g., milk) or contamination of the product during slaughter (e.g., meat products); (iv) bacterial survival and/or multiplication under food processing and distribution conditions; and (v) infection of human hosts, including survival of gastric passage and establishment of enteric or systemic infections. Microbial survival under rapidly changing environmental conditions thus plays a key role in the pathogenesis of many foodborne diseases. To further illustrate, microorganisms causing human disease by the oral route must survive passage through the hostile and acidic environment of the stomach. Some intracellular foodborne pathogens such as L. monocytogenes must also survive inside eukaryotic vacuoles following bacterial invasion of the host cell. Defense systems of the host cell vacuole (e.g., reactive oxygen radicals, acidic pH) pose significant stresses on bacterial cells. Most foodborne pathogens also need to survive and multiply under stressful conditions (low pH, refrigeration temperatures) in foods.
Research in Dr. Boor’s laboratory addresses the hypothesis that bacterial stress-response systems provide a crucial link between bacterial survival under various environmental conditions and the ability of the organism to cause disease. One means by which bacterial cells respond to environmental changes is through rapid changes in gene expression patterns mediated through transcriptional regulatory proteins. The stress-responsive alternative sigma factors σB and RpoS transcribe genes contributing to bacterial survival under environmental stress conditions in Gram-positive and Gram-negative bacteria, respectively, therefore, Dr. Boor selected the σB and RpoS alternative sigma factors as key target proteins for investigating the survival of bacterial pathogens under various environmental conditions. An improved understanding of the ability of bacteria to sense, respond, and survive such rapid and extreme changes in environmental conditions through rapid changes in the regulation of gene expression will subsequently contribute to our understanding of factors that influence bacterial persistence and transmission in food systems.
RESEARCH ACCOMPLISHMENTS
Objective (i):
Identification and characterization of factors linking the ability of bacteria to survive under various conditions, including in foods and in food processing environments, with the ability of bacteria to cause human and animal disease.
• In collaboration with Dr. Martin Wiedmann, Dr. Boor’s research team has focused on the alternative sigma factor, σB, in Listeria monocytogenes. The collaborative team pioneered discovery of the functional characteristics of the L. monocytogenes sigma B protein; including identification of the regulon of genes controlled by sigma B; as well as some critical elements of the regulatory pathway that tightly control the activity of σB. A particularly exciting discovery was the identification of genetic linkages between the stress responsive sigma B and the ability of L. monocytogenes to invade host cells (i.e., σB contributions to inlA expression). Specifically, σB was identified as a positive direct regulator of virulence gene expression (inlA, inlB, bsh, prfA and others) in L. monocytogenes.
• Consumption of sufficiently high numbers of virulent strains of the Gram-negative Vibrio parahaemolyticus can cause gastroenteritis. Human infection with this pathogen is most frequently associated with the consumption of seafood, primarily raw or improperly cooked shellfish. Fortunately, not all strains of V. parahaemolyticus are pathogenic, however, distinguishing between virulent and non-virulent strains has been a technical challenge. In February 1996, the infection rate attributed to V. parahaemolyticus in Calcutta suddenly jumped to between 10 and 20 isolations each month. These cases marked the recognition of the emergence of a unique O3:K6 serotype which accounted for 50 to 80% of the strains isolated during this period. Multiple lines of evidence suggested that this unique V. parahaemolyticus O3:K6 strain became more prevalent not only in Calcutta, India, but also in Southeast Asian countries in approximately 1995. A V. parahaemolyticus O3:K6 strain with characteristics nearly identical to the clone identified in India and in Southeast Asia was associated with two outbreaks of gastroenteritis in the United States. The first outbreak occurred in Texas in July 1998 and involved more than 350 oyster consumers. A September 1998 outbreak in New York State was linked to shellfish harvested from Oyster Bay on Long Island. Following both outbreaks, the implicated harvesting areas were closed and all shellfish originating from those areas were recalled. Clinical isolates from infected individuals in both the Galveston Bay (Texas) and Oyster Bay outbreaks were identified as the O3:K6 Calcutta strain. To establish effective methods for distinguishing among V. parahaemolyticus strains, Dr. Boor’s lab applied and evaluated different DNA-based subtyping methods (Pulsed Field Gel Electrophoresis, ribotyping and DNA sequence analysis of tdh) and developed and evaluated PCR methods for the specific detection of the V. parahaemolyticus O3:K6 Calcutta clone. New methods were evaluated on oyster and shellfish samples and found to be effective. We also examined the survival and growth of selected V. parahaemolyticus strains and clonal groups under different environmental conditions, and characterized virulence and tissue culture cytopathogenicities of selected V. parahaemolyticus strains and clonal groups under different environmental conditions. The growth and survival characteristics of selected V. parahaemolyticus food and clinical strains were measured following exposure to acid, bile and salinity stresses. The cytotoxicities of acid-adapted and unadapted cells were determined (as measured by lactate dehydrogenase release) upon infecting human epithelial cells. Except for one of eight strains, relative cytotoxicities of unadapted stationary phase cells were 1.3 to 4.5 fold higher than those of adapted cells. The differences were statistically different (p<0.05) for six of eight strains. Thus, exposure to a mild acid (pH 5.5) impairs not only survival, but also cytotoxicity for stationary phase cells. While our work did not identify phenotypic characteristics unique and specific to O3:K6 strains, our PCR assay is highly effective at identifying the presence of very small numbers of these strains in seafood products.
• In collaboration with scientists in the Cornell College of Veterinary Medicine, Dr. Boor’s team completed a research project to develop improved detection methods for Mycobacterium avium subsp. paratuberculosis, which is an important pathogen in dairy cattle. Although controversial, some believe this organism to be a human food-borne pathogen responsible for Crohn’s disease. Plasmid- and phage-based firefly luciferase reporter constructs were evaluated as rapid detection systems for viable Mycobacterium avium subsp. paratuberculosis (MAP). A MAP strain bearing a luciferase-encoding plasmid was detectable at 100 cells / ml in skim milk and 1000 cells / ml in whole milk. Three luciferase-encoding mycobacteriophage were evaluated for detection of wild-type MAP. The best of these, phAE85, allowed detection of > 1000 cells / ml within 24 – 48 hours. Our work clearly demonstrated that luciferase reporters show promise for rapid detection of viable MAP.
• Dr. Boor’s research team determined the survival rates of E. coli O157:H7 in dairy fermentation systems, demonstrating the ability of this organism to persist as a post-pasteurization contaminant in commercial dairy products for periods of up to 35 days following initial contamination. This work scientifically disproved the commonly held, but not rigorously tested, belief in the dairy foods industry that starter cultures present in fermented dairy products would not allow the long-term persistence of pathogenic microbes in products with pH values below 4.6. This work received national attention, and was used recently by regulatory officials and other members of the dairy industry as supporting evidence for new rulings on dairy product safety in the 2005 National Conference on Interstate Milk Shipments (NCIMS) biennial meeting.
• Dr. Boor’s team cloned and sequenced a key gene responsible for regulating cellular responses to changes in environmental conditions (rpoS) in the Gram negative organism, E. coli O157:H7. As described above for a wild-type E. coli O157:H7 strain, survival characteristics were measured in dairy fermentations for an E. coli rpoS mutant strain, which lacks a functional sigma-S protein. This work demonstrated that the Gram negative RpoS general stress response system (orthologous to the σB system that we identified in the gram positive L. monocytogenes, as described above) clearly plays an important survival role when E. coli O157:H7 is faced with the moderately lethal conditions encountered in the presence of dairy starter cultures. As E. coli O157:H7 (or L. monocytogenes) is exposed to similar moderately lethal conditions upon ingestion by humans, this work builds toward identification of universal characteristics of bacterial survival systems that are not only important to survival in foods, and in the environment, but may also play a role in the ability of an organism to cause disease. In addition to providing valuable information regarding survival mechanisms of foodborne pathogens in dairy products, these studies may ultimately lead to strategies for the reduction of pathogens in food animal populations. Creation of strains lacking these functional proteins, which are likely to be virulence-attenuated, ultimately may provide biological material for future vaccine development.
Future Directions:
Dr. Boor’s team has the capacity to genetically manipulate bacteria, and particularly, L. monocytogenes strains, to study specific genetic and phenotypic characteristics. Further, her team has developed and applied effective gene expression monitoring tools, including Real Time PCR and microarray analyses. These methods will be applied to: (i) fully explore all contributions of sigma B to L. monocytogenes persistence in food production systems; (ii) identify sigma B-independent stress response mechanisms that contribute to L. monocytogenes survival and persistence; (iii) identify specific genetic features that enable some bacterial strains to be more problematic in food processing systems than others of the same species; and (iv) measure the extent to which bacterial virulence is affected by food matrices and food handling processes.
Objective (ii):
Rapid identification and tracking of spoilage and pathogenic bacteria in food systems.
• Dr. Boor’s team systematically collected and characterized Pseudomonas spp. and other strains associated with dairy product spoilage from NYS dairy processing plants, with the goal of establishing a rapid bacterial contaminant tracking system designed to identify and eliminate contaminant reservoirs, and thus, reduce dairy product spoilage. The genetic “fingerprints” generated from ribotyping were assembled into a database that is accessible on the World Wide Web. Ribotyping was also applied to track and determine the cause of bacterially reduced fluid milk shelf-life in a model dairy processing system with a sole raw milk source. When recommendations for shelf-life extension developed by Dr. Boor’s team were followed, fluid product shelf-life increased from 7 days to 21 days.
• Dr. Boor’s team worked with a group of NYS dairy farmers to determine the composition of bacteria present in seemingly random high bacteria counts (so-called “spikes”) in raw milk, with the goal of implementing specific control strategies targeting the sources of those bacteria. This work is of critical importance to dairy producers as farmers receive significant monetary incentives for producing milk with low bacterial counts. One “spike” can result in a severe economic penalty for a milk producer. We found that, in the absence of a significant and identifiable error in the milk handling, cooling or cleaning systems, the majority of high bacterial numbers result from the presence of “environmental” mastitis organisms such as Streptococcus uberis. Often, the animal shows no clinical symptoms of an infection, so it can be challenging to detect the presence of these organisms without standard bacterial culturing.
• In collaboration with Dr. Martin Wiedmann’s group, Dr. Boor’s team determined the prevalence of L. monocytogenes contamination in salmon processing plants and applied a fingerprinting system based on automated ribotyping to track the origins and the spread of L. monocytogenes strains in these operations.
• Dr. Boor’s group applied information learned from the smoked salmon processing research described above to track L. monocytogenes contamination in Latin-style cheese manufacturing operations in NYS. The Hispanic cheese industry is growing rapidly, but the industry is plagued by a high prevalence of L. monocytogenes in consumer products. Our work focused on identifying bacterial contamination reservoirs and developing specific strategies for reducing the risk of contamination.
• Dr. Boor’s group completed a comprehensive characterization of the bacteriological and chemical characteristics of milk produced on approximately 10% of randomly selected farms in New York State. This work identified specific microbiological parameters in need of improvement on a significant proportion of farms tested. Milk producers have used the results of this study to compare the quality of their own milk against the range of measurements found throughout the state. This work scientifically assessed the possibility of applying the results from any of the microbiological tests used in this study toward predicting the results of other microbiological tests. We found that no correlation exists among these tests. This finding implies that a processor must establish the most important microbiological criteria that will ensure their product shelf-life quality, then assess the presence of those specific organisms.
• Shelf-life characteristics of flavored milk products, which constitute the most rapidly growing segment of the NYS fluid dairy product market were measured. This work determined that while chocolate milks spoil faster than white milks processed in the same processing plant, the major spoilage organisms in both types of products are the same on a per product/per sampling period basis. Thus, chocolate milk ingredients do not appear to uniformly introduce novel microorganisms nor do chocolate products appear to support the growth of organisms that could not grow in unflavored milks.
Future Directions:
Dr. Boor’s team will continue to investigate the ecology and transmission of foodborne pathogens and spoilage organisms in food production systems. Current work focuses on identification of specific sources of Paenibacillus spp. and Bacillus spp. in fluid milk production systems.