Prioritization of Microbial Research Needs for Fresh Produce in Canada

On March 19, 2008, the Bureau of Microbial Hazards (BMH), Health Canada hosted a working group meeting to prioritize microbiological research needs for fresh produce in Canada. The group reviewed the list of priority produce/pathogen combinations which had been developed by an expert FAO-WHO working group (Microbiological hazards in fresh fruits and vegetables, Expert Meeting Report, October 2007), and adapted the list to the Canadian context. The working group created the "Top 10" list of research needs and ranked all identified research topics into three categories (high, medium and low priority). The purpose of this document is to provide research institutions and other interested parties in Canada with the list of prioritized research needs.

Validating criteria for prioritization process

The following criteria were developed by an expert FAO-WHO working group (Microbiological hazards in fresh fruits and vegetables, Expert Meeting Report, October, 2007) and adapted to the Canadian context:

  • Probability/exposure and severity of disease
  • Size and scope of production/consumption
  • Diversity and complexity of the production chain and industry
  • Potential for amplification of foodborne pathogens through the food chain (i.e., fresh-cut produce)
  • Potential for control
  • Extent of international trade and economic impact
  • Consumer/Industry concerns and perceptions
  • Pressure Groups/Media Interest/Political Interest
  • Lab capability to detect pathogens of concerns

Prioritization Exercise

Using the criteria above, all identified research needs were placed into three categories, i.e., high (H), medium (M) or low (L).

  • H: Needs to be done
  • M: Nice to do
  • L: Not "important" enough to do

Top 10 Research Needs:

    1. Under what conditions can fertilizers derived from human/animal waste be safely employed for the production of produce (under temperate climate with a long winter)?
    2. What is the frequency and amount of pathogens introduced into the environment by use of manure-contaminated soil amendments and fertilizers?
    3. Efficacy of ageing/composting (taking into consideration our winter conditions): What is the survival rate of pathogens contained in fresh manure? Is there a need to establish the time of application (time-interval to wait before harvest)? What is potential for re-growth of pathogens?
    4. What are the factors affecting pathogen environmental loading and survival?
      • Adequacy of and compliance with composting procedures
      • Manure application scheduling during various phases of the growing cycle
      • Does the risk decrease if manure is applied to fields in the fall?
      • Can winter be considered a kill step for those pathogens?
      • Influence of timing and method of application on the survival of human pathogens from raw manure in different soils, under different climates
    1. How does irrigation water become contaminated?
    2. What influences the survival of pathogens in irrigation, ground, well, and surface water?
    3. What is the frequency and amount of pathogens introduced into the environment by water sources prior to and during various phases of the growing and harvest cycle?
    4. Does weather/time of the year play a role in pathogen survival in water and soil? (Contamination according to season)
    1. What is the evidence of internalization of pathogens into produce and how significant is this?
      • Is it a problem with crops other than tomatoes, apples and potatoes?
      • What are the best prevention methods?
      • Once pathogens infiltrate the product, how long will they survive/grow?
      • Can epidemiologically relevant numbers of pathogenic microorganisms infect a field crop via this route?
    2. Internalization
      • Pre-harvest: What is the risk of pathogen uptake by growing plants (leafy greens, tomatoes, fruits)
      • Post-harvest: Influence of processing parameters and how can one eliminate pathogens.
  1. What is the effectiveness of hand sanitizers and gloves on farms? (i.e., in the field, packaging house, re-packer and whole-sale level)
    • Effectiveness of hand sanitizers when hands are not washed first washed free of dirt/plant debris.
    • Effectiveness of hand wipes
    1. What is a better way of maintaining the conditions of flume water and rinsing water at packing establishments? Research to identify where pathogens are being introduced.
    2. What is the effectiveness of cleaning water in terms of reducing pathogen loads on produce?
      • Does water remove pathogens from product?
      • How much pressure needs to be applied?
      • How long does the product need to be in contact with the water?
      • How often should water be changed?
    1. Development of sampling protocols to facilitate efficient and reliable detection of pathogens?
    2. Sampling field crops: what, where, when, how much?
    3. Development of methods (fast and sensitive) for improving the timely detection of pathogens (bacteria, viruses, parasites) in or on fresh produce?
    4. Improvement of sample preparation (surface samplings vs low pH of mash, enrichment, background flora)?
    1. Research on interactions between pathogens, processed/stored plant tissue and the competitive microflorae.
    2. Research on survival and potential growth of pathogens on produce during the post-harvest process (handling, processing and/or distribution)
  2. What is the behaviour (survival/growth) of pathogens in fresh-cut produce from time of packaging to consumers?
  3. How many people are actually becoming sick from fresh fruits and vegetables in Canada?
    1. What are the specific foods?
    2. Where do they come from?
  4. Factors influencing attachment of pathogens to produce; why are some pathogens associated only with specific produce (i.e., tomatoes are associated with Salmonella, but not with E. coli. What intervention strategies could be developed?)

Overarching research question:

What is the mechanism of transference of human pathogens to fresh produce edible plant surfaces during growing, harvest post-harvest handling, processing and distribution operations,andwhat factors affect transference?

High Priority Research Needs (Not in the Top 10):

  • What types of microorganisms are in the agricultural environment? Can we link them to sources using, for example, PFGE (e.g., certain subtypes in ponds are associated with deer, human waste, or geese)? What are the sources of microorganisms, and how are they disseminated?
  • Are there specific time intervals or events after which well water sources should be tested?
  • Imported and domestic produce sampling surveys / surveillance studies
    • Surveillance studies (specific produce/pathogen combination);
    • Identify pathogenic and indicator organisms on Canadian produce; and,
    • Prevalence of pathogens on produce in Canada.
  • What can consumers do to reduce/remove pathogens from produce?

Medium Priority Research Needs:

  • Are some animals (livestock or wild) 'supershedders' and how relevant is this? (Quantify the problem and characterize the risks of wildlife in Canada. Birds and deer are the most important wild animals of concern in Canada. Identify ways to control them)
  • Are wild animals an important source of soil and produce contamination on ranches and farms? (Identify molecular types of pathogens)
  • What are the other vectors for transmission of pathogens in a real farm setting (e.g., insects, airborne dissemination, etc.)?
  • What are the prevalence rates and levels of pathogen (E. coli, Salmonella, norovirus, Giardia, Cryptosporidium) contamination of source water?
  • What is the risk associated with different irrigation delivery equipment? Is drip irrigation better than overhead; how much better?
  • Can E. coli be used as an indicator of irrigation water contamination and what is the significance of detection of E. coli in irrigation water?
  • Is there a need to develop better indicators for pathogens in produce and agricultural water?
  • What is the fate of human pathogens in soil (E. coli, Salmonella, viruses, parasites)?
  • Research on prior use of fields
    • What is the impact of prior field use?
    • How long is long enough to exceed life cycle of pathogen? What time intervals are needed before the land is used for the production?
    • What affects the length of life cycle of pathogen in field? Nutrients? Depth?
    • Does topography affect risk of produce contamination: water flooding, animals?
    • How do differences in growing ecology affect all of these factors? If a contamination event is suspected, what remedial actions/timeframes are appropriate?
  • What is the potential for farm workers to serve as a source of contamination for produce (education, personal hygiene)?
  • What mitigation strategies are available to reduce the risk of foodborne disease attributable to farm workers as a source of contamination, and what are the relative risk reductions that can be achieved by these mitigations?
  • What is the stress and post-stress behaviour of pathogens (bacteria, viruses, parasites) in fresh produce?
    • Performance of culture-based methods for isolation / detection
    • Can highly stressed cells "recover" in processed products?
    • Are there implications for infectivity?
  • What is the effectiveness of sanitizers in cleaning water?
    • If there is a high organic load, how effective is the sanitizer?
    • Which sanitizers work the best and how much is needed?
    • How do you monitor and control these sanitizers?
  • In the packing shed, when contaminated produce comes in the door - how likely is it that it will contaminate other produce, workers' hands, packing lines, dump tanks? What type of sanitation / preventative practices are required to control cross-contamination?
  • What is the influence of immediate post-harvest operations (e.g., vacuum cooling, removal of wrapper leaves, bulk storage, transportation, etc.) on the fate of pathogens?
  • Research on contamination levels of produce before and after washing.
  • Research on persistence and growth of pathogens in water.
  • Implications / risks associated with using water waste for fruit and vegetable crops.
  • What are the safety concerns of using contaminated water for pesticide applications?

Low Priority Research Needs:

  • How much is the evolution of EHEC towards 'superfitness' (better adapted) related to the environment and / or human hosts?
  • What is the microbiological risk associated with compost tea used in production?
  • Does the use of "green" fertilizer (i.e., composted plant waste) represent any significant risk in relation to increasing the likelihood that pathogenic micro-organisms will be present on fresh or fresh-cut produce?
  • What is the effectiveness of current biological and chemical decontamination processes, and is there a need for research?
  • Is there a need to do further research on a "kill step" to eliminate pathogens during processing (i.e., irradiation)?
  • What is the impact of size and composition of competitive microflorae in/on produce?
  • Is there a need to improve investigative methodology for outbreak traceback on-farm?
  • What is the behaviour (survival/growth) of pathogens in fresh-cut produce in the home? (What types of products, portions, single vs multiple use, consumer education; revised best before dates)
  • Is there increased risk of foodborne disease associated with further extending the shelf-life of fresh and fresh-cut produce?
  • What portion of the risk of foodborne illness associated with fresh produce is attributable to failure to maintain the cold chain?
  • What is the efficacy of produce washing at home? (Does water remove pathogens from product?)
  • Which produce sanitizers work the best and how much, if any, are needed?
  • Decontamination of seeds used to grow leafy greens (hydroponic).
  • Pathogen resistance or mutations due to use of sanitized and cleaning agents.

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