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Molecular Epidemiology of Campylobacter Jejuni in Processed Cattle

Rajala-Schultz, Paivi; Gebreyes, Wondwossen; DeGraves, Fred
Ohio State University
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The long-term objective of our research is to reduce illness in human beings by focusing on the epidemiology of food-borne pathogens. The overall objective of this proposal is to demonstrate that the cattle population may serve as an important reservoir for sporadic cases of gastrointestinal illness in human beings caused by C. jejuni.Our central hypothesis is that current detection methods significantly underestimate viable C. jejuni concentrations in edible beef products. We believe this is due to the use of stringent culture-based methods that are routinely employed to grow C. jejuni; and due to viable, but nonculturable (VBNC) organisms that result from environmental stress associated with beef processing and storage methods. We also believe that C. jejuni strain-types proficient at surviving the cold and aerobic stress associated with beef processing and storage conditions will be available to infect human beings that eat undercooked beef products or to cross contaminate other food items and/or hands in the kitchen.

We intend to address these issues by evaluating carcass contamination with C. jejuni using molecular-based detection methods compared to traditional culture-based methods. An in vitro beef muscle inoculation model will also be used to evaluate C. jejuni survival kinetics, to allow the screening of a library of strain-types, and to allow the inclusion of strain-types that either die or become VBNC in response to environmental stress. C. jejuni strain-type survival will then be used as a predictor variable for strain-types previously reported to be associated with human illness. With the completion of this project we expect to demonstrate that specific strain-types of C. jejuni may survive in beef products at doses sufficient to cause sporadic human illness.

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NON-TECHNICAL SUMMARY: Campylobacter jejuni is considered the most common cause of bacterial gastroenteritis in human beings worldwide. The overall objective of this proposal is to demonstrate that cattle infected with C. jejuni are important sources of illness in human beings. We believe current detection methods underestimate C. jejuni concentrations in beef, as the organisms are difficult to grow in laboratories, and because bacterial stress associated with cattle processing may cause them to stop growing entirely. We also believe that some C. jejuni strains are good at surviving in beef products and therefore more likely to infect people. We intend to address these issues by using molecular detection methods that do not require organism growth. We will also evaluate a large number of C. jejuni strains that have been isolated from cattle, for their ability to survive in beef products, and evaluate whether they are related to strains associated with illness in people.

APPROACH: Our overall objective will be achieved through the following specific aims:

  1. To determine actual and apparent C. jejuni carcass contamination rates of cattle using molecular and culture-based quantitative diagnostic techniques.Total and viable C. jejuni contamination will be determined during cattle processing using C. jejuni specific real-time quantitative polymerase chain reaction (qPCR). Culturable organisms will be determined using culture-based methods, using media selective for Campylobacter followed by PCR for C. jejuni.
  2. To determine survival kinetics of C. jejuni strain-types isolated from cattle in an in vitro model that emulates the environmental stress associated with beef processing and storage conditions. An in vitro model will be used to allow kinetic modeling of C. jejuni survival under environmental stress conditions, to allow the screening of a library of C. jejuni isolates collected from infected cattle, and to allow the inclusion of strain-types that either die or become VBNC in response to environmental stress. An important goal is to identify strain-types that are capable of surviving in edible beef products under environmental stress conditions, including both culturable and nonculturable organisms.
  3. To use C. jejuni strain-type survival kinetics, under environmental stress conditions, as a predictor variable for strain-type representation in human isolates. These strain-types will be over-represented in C. jejuni isolates from human cases of disease, which will be assessed by comparing to human isolates that have been reported to a multi-locus strain-typing (MLST) data base available via the internet.
Funding Source
Nat'l. Inst. of Food and Agriculture
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Prevention and Control
Bacterial Pathogens