Research

Laboratory for Molecular Typing

Research

Molecular subtyping and virulence characterization of Listeria monocytogenes olecular subtyping and virulence characterization of Listeria monocytogenes

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Transmission electron micrograph at 70,000X magnification of L. monocytogenes.
(From Crandall, A.D., 1997, Ph.D. Thesis, Rutgers University)

Listeria monocytogenes is a foodborne pathogen capable of causing serious invasive disease in animals and in humans. The frequency of human listeriosis is estimated to be ~ 5 cases/million population with mortality rates of ~ 20%. An estimated 1,700 cases of clinical listeriosis occur annually in the U.S., resulting in ~550 deaths. Only very few, genetically distinctive, L. monocytogenes strains have currently been linked to human outbreaks, strongly suggesting that not all strains of this species are equally virulent and/or equally capable of being transmitted from animals or foods to humans. The Food Safety Laboratory uses population genetic approaches to study the diversity of L. monocytogenes isolates from animals, foods and humans to test the hypotheses that L. monocytogenes strains differ in their abilities to be transmitted along the food chain as well as in their human pathogenic potentials. We also hypothesize that the presence of specific alleles of virulence-associated genes, specifically actA, leads to differences in pathogenic potentials. The long-term objective of our work is to enhance the safety of the food supply through an improved understanding of: (i) the ecology of L. monocytogenes strains and their transmission along the food chain; and (ii) virulence differences and host specificities among L. monocytogenes strains. Our specific research objectives are to: (i) characterize animal, food, and human L. monocytogenes isolates to determine specific features of strains responsible for sporadic human cases and epidemic outbreaks. These studies will also lead to the development of a pathway model for transmission of different L. monocytogenes strains along the food chain and will identify specific markers for strains with unique pathogenic potentials; (ii) test unique actA alleles in an isogenic background for effects on virulence and cytopathogenicity. This will help us to define the molecular basis for the unique pathogenic potentials of specific L. monocytogenes strains (particularly those causing human epidemic outbreaks); (iii) establish the utility of different molecular markers for differentiating L. monocytogenes strains and determine the relationships of these markers to serotypes; and (iv) characterize specific clonal groups of L. monocytogenes that are atypical for L. monocytogenes and that may have attenuated human virulence.

The Food Safety laboratory has also taken the leadership in developing a model system for a L. monocytogenes research, surveillance and extension program in the Northeastern US. Participants in this program include the New York State Department of Health, the New York State Veterinary Diagnostic Laboratory, New York State Department of Agriculture and Markets as well as health departments in other regions and states including New York City and Connecticut. Through these collaborations we have developed an integrated surveillance program for human, animal, and food L. monocytogenes isolates. This program is designed to integrate research, surveillance and extension. Currently, L. monocytogenes isolates from human, foods and animals are collected and characterized by molecular subtyping (including automated ribotyping and Pulsed Field Gel Electrophoresis). We already have assembled a collection of more than 300 human and more than 200 animal and food L. monocytogenes isolates. This collection will help us to address the research questions outlined above and will also allow us to monitor the emergence of new L. monocytogenes strains and antibiotic resistance trends among L. monocytogenes isolates. This program has significantly contributed to the detection and tracking of the human listeriosis outbreak linked to the consumption of hot dogs and deli meats produced at the Bil Mar plant, MI.

Most of the current research in Dr. Wiedmann’s laboratory focuses on studying Listeria monocytogenes as a model system for bacterial pathogens that can cause disease in both humans and animals. L. monocytogenes is a foodborne pathogen capable of causing serious invasive human and animal disease, including abortion, septicemia, meningitis and meningoencephalitis.Among humans, immunocompromised persons and neonates are particularly at risk of listerial infections.An estimated 1,200 to 1,700 cases of clinical listeriosis occur annually in the U.S., resulting in a total of about 350 to 550 deaths.Due to its severe consequences, listeriosis is a major public health concern. L. monocytogenes is also commonly found in nature and in food processing environments and has the ability to survive for extended time periods outside animal hosts. Thus, control of this organism represents a serious challenge for the food industry.

Specific research projects in Dr. Wiedmann's laboratory are targeted (i) at understanding differences among distinct L. monocytogenes strains in abilities to cause human and animal disease; (ii) at understanding the role of stress response systems (and specifically alternative sigma factors) in the ability of L. monocytogenes to survive in foods and to cause disease; (iii) to develop and apply improved molecular typing methods for L. monocytogenes to help to detect and track human and animal listeriosis cases and to track sources of L. monocytogenes in food plants and on farms; and (iv) to better understand the evolution of virulence in L. monocytogenes.Research projects utilize cutting edge molecular biology and pathogenesis approaches (including tissue culture and animal studies).Our basic studies on the biology and pathogenesis of L. monocytogenes are also supported by a collection of more than 1000 human, animal and food isolates of this bacterium.Characterization of these isolates will allow us to gain further insight into the evolution of this important human and animal pathogen.

Research in Dr. Wiedmann’s laboratory is conducted in collaboration with other universities, private industry and federal and state agencies. For example, through collaboration on molecular fingerprinting of L. monocytogenes with the New York State Department of Health and other health departments, our research group recently contributed to the detection of a large multistate outbreak of human listeriosis cases which was ultimately linked to consumption of contaminated hot dogs and deli meats. Control of Listeria in RTE Seafoods

“Control Strategies for Listeria monocytogenes in Food Processing Environments”

Funded under the National Food Safety Initiative in 2000 by the Cooperative State Research, Education and Extension Service of USDA, Project Number 00-51110-9768

The goal of this project is to integrate research, extension, and teaching efforts to develop, evaluate, and deliver science-based outreach programs for improved control strategies to help the food industry control the food borne pathogen Listeria monocytogenes. This organism has the ability to grow well at refrigeration temperatures and in many types of food processing plant environments. Strategies to prevent post-processing contamination of Ready-to-Eat (RTE) foods are essential to prevent consumers from becoming ill from these products.

Our specific hypothesis is that improved environmental control strategies and sanitation procedures can significantly reduce L. monocytogenes contamination of RTE food products. We are using the RTE seafood industry as a model system to: (i) evaluate sensitive molecular sub-typing methods for L. monocytogenes to identify contamination sources and track the spread of environmental contamination in the processing plant, and to (ii) develop science-based intervention and control strategies utilizing specific sanitation procedures, employee training, and in-plant monitoring using molecular sub-typing.

Three specific training programs were developed for this project to help processing plants establish and implement improved science based L. monocytogenes control programs. These training programs are designed for use in the plant, to train employees who conduct specific activities that are integral to the successful implementation of a program, to reduce and prevent Listeria monocytogenes contamination of RTE seafood products. The following questions areaddressed in these training programs…

What is Listeria monocytogenes?

Why is Listeria monocytogenes a concern for a food processing plant?

Where can you find Listeria in a processing plant?

How does Listeria spread throughout a plant?

How does one control Listeria contamination in a processing plant?

What do plant employees need to do to control and prevent L. monocytogenes contamination?

What types of cleaning and sanitation procedures are required?

How does a plant prevent cross contamination within their processing facility?

Each of the three training programs consists of a set of PowerPoint slides that can be used by management to train their employees. Each slide is accompanied by an extensive set of “speaker notes” designed to help plant management deliver an effective training program. These training programs are available on-line. Please click on the training program of interest to view the material on-line or download each presentation to your computer.

These training programs were designed by Ken Gall, NYSG Seafood Specialist, in collaboration with Doris Hicks of the University of Delaware and Cornell University, New York Sea Grant, University of Maryland Sea Grant, Virginia Tech, Louisiana State University, the National Food Processors Association and the National Fisheries Institute.