|PRODUCE AS A VECTOR FOR CAMPYLOBACTERIOSIS|
Campylobacter jejuni is a zoonotic organism present in the gastrointestinal tract of a large number of warm-blooded animals. Campylobacter jejuni and C. coli cause an estimated 2.4 million cases of human illness per year, of which 80% are foodborne, making it the leading cause of bacterial foodborne illness, even surpassing Salmonella as a diarrhea-causing pathogen (1, 11). Potential reservoirs of the organism include poultry, wild birds, cows, swine, sheep, horses, rabbits, rodents and domestic pets (12,15). As a fecal organism, C. jejuni is present in sewage (14), sewage effluents (8) and untreated waters (17). Soil, through which Campylobacter-contaminated water has passed, can also contain the organism. In a study of the survival of pathogens during mesophilic anaerobic digestion of animal manure (i.e. prior to sewage treatment), Kearney et al. (9) found that C. jejuni was remarkably resistant to treatment. The organism was approximately 13-times more resistant to anaerobic digestion than Salmonella typhimurium. Thus, C. jejuni represents a paradox (15). In spite of its "fragility", the organism can be found in the environment, particularly in water, and while it may not grow, it can survive. More information about the paradoxical behavior of C. jejuni can be found in an article authored by Solomon and Hoover (15).
C. jejuni is widely thought of as an environmentally-fragile organism, indicating that it would not persist for long periods of time on fruits and vegetables. It is sensitive to drying, acidity, freezing, salting, osmotic stress, oxygen (>5%), chemical rinses and disinfectants. C. jejuni does not grow below 30?C, is a poor competitor and is very sensitive to heat (D55C=1 min). Therefore, this susceptibility to a number of environmental conditions would suggest its survival in properly stored and processed foods is unlikely (12,15).
While the literature is sparse, it appears that C. jejuni may be a rare contaminant of produce. A recent review surveying pathogenic microorganisms associated with fresh produce indicates that C. jejuni was isolated only from retail mushrooms. Out of 200 mushroom samples, three (1.5%) were positive for C. jejuni (5,7). An United Kingdom study (11) indicated that imported unprepared whole lettuce (n = 151) obtained from retail outlets were free from Campylobacter, as well as being free of Salmonella and Escherichia coli O157:H7. In a study comparing the presence of C. jejuni on raw vegetables obtained from farmers' outdoor markets (n = 533) or supermarkets (n = 1031), only vegetables from the farmers' markets were positive, whereas supermarket samples were Campylobacter-free. The incidence of Campylobacter-contaminated vegetables averaged 1.7% (13). Vegetables from farmers' markets are more likely to be produced and stored under less sanitary conditions than vegetables obtained from supermarkets. To minimize microbial hazards, vegetables, especially those from farmers' markets, should be thoroughly washed and rinsed before eating.
Produce - An Uncommon Vehicle for Infection
Produce is not a common vehicle for Campylobacter enteritis, since few incidents in which vegetables have been involved have been reported. An outbreak of campylobacteriosis was shown to be due to ingestion of a cabbage-beef stew by school children in Germany. Since the stew was cooked, cross-contamination with C. jejuni was probably a major contributing factor to the outbreak (16). Similarly, cross-contamination of salad lettuce by raw chicken led to a small outbreak of campylobacteriosis in an Oklahoma restaurant in 1996 (2). Harris et al. (7) analyzed a number of dietary histories of individuals who had campylobacteriosis and determined that out of a number of vegetable items, only mushrooms were significantly associated with C. jejuni enteritis cases. A single outbreak of Campylobacter enteritis due to contaminated fruits or vegetables was reported for the period 1973-1987 (4) and another outbreak due to fruits or vegetables contaminated with Campylobacter was reported during 1989 (3). Details of these two outbreaks were not given.
Leafy vegetables and root crops irrigated with untreated water or grown in soils contaminated with Campylobacter would be expected to contain C. jejuni. The use of C. jejuni-contaminated water to wash produce or fruit may lead to depositing the organism on the surface of the product. Thus, the facts that waterborne outbreaks of campylobacteriosis occur (17) and that C. jejuni is present in sewage and water indicate that produce or fruit irrigated or washed with C. jejuni-contaminated water will allow the entrance of the organism into the food chain.
The Microbial Food Safety Research Unit (MFSRU) within the USDA/ARS Eastern Regional Research Center maintains a commitment to high quality basic and applied research on pathogenic bacteria to ensure a safe food supply. As part of this research program, the MFSRU addresses strategies to control and detect Campylobacter jejuni in food. Examples of research include:
Developing a multiplex PCR for the detection of Campylobacter jejuni and Campylobacter coli from pork, and characterization of isolates by PFGE and antibiotic resistance profiles
Determining growth and survival mechanisms of Campylobacter on chicken and pork under stress conditions
Evaluating the effect of competitive flora and temperature on growth/survival of Campylobacter
Determining the effect of stress on Campylobacter gene expression and on regulation of cellular composition and metabolism
Improving cultural methods to detect the variable morphological forms of Campylobacter
Sequencing plasmids from Campylobacter spp.
Determining the influence of processing steps on the incidence of Campylobacter on pig carcasses
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Author: James L. Smith, Ph.D. (James.Smith@ars.usda.gov)
Editor: Mark L. Tamplin, Ph.D.