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Campylobacter
in Poultry Processing
Omar A. Oyarzabal Department of Poultry Science Auburn University |
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Introduction
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| Campylobacters
are Gram-negative bacteria with curved, rod-shaped cells and polar flagella.
The unique spiral shape of the cell and the motility due to the flagella
are useful characteristics to identify Campylobacter with phase
contrast or dark field microscopy. Campylobacters grow at 42°C and
require low oxygen and a relatively high concentration of carbon dioxide
in the environment. Campylobacter jejuni and C. coli
are the species most commonly isolated from human gastroenteritis and
from food sources. Several closely related species (C. coli, C.
fetus, and C. upsalienis) may also cause disease in human but their
incidence is rare. Arcobacters, a group of bacteria related to Campylobacter, are seldom discussed in the US. Although Arcobacter has been linked to human disease, it appearance is not as important as campylobacters. We do not understand the epidemiology of Arcobacter as much as the epidemiology of Campylobacter. In addition, the methodology for isolation of Arcobacter is time consuming and therefore clinical laboratories and food microbiology laboratories do not actively search for it. The Centers for Disease Control and Prevention (CDC), in collaboration with other organizations, such as State Health Departments, has been reporting the level of Campylobacter infections in humans through sentinel sites located across the US. Although recent reports by CDC proclaim that the incidence of bacterial foodborne pathogens is declining, Campylobacter is still the second most common bacterial pathogen after Salmonella in humans, with an incidence of 12.6 cases every 100,000 people for the year 2003. Many more cases go undiagnosed and therefore unreported. |
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Clinical Features of the Infections
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Campylobacter produces isolated cases, with very
few outbreaks. An outbreak is defined as two or more similar cases having
the same source of infection. The most consistent and prominent feature
of Campylobacter infection is diarrhea, sometimes bloody. The
bloody diarrhea indicates that Campylobacter is an invasive
pathogen that infiltrates the lining of the small intestine. Other typical
symptoms of C. jejuni infections include fever, nausea and
vomiting, abdominal pain, headache, and muscle pain. Most of the Campylobacter
infections are mild, do not require hospitalization and may be self-limited.
However, few C. jejuni infection can be severe and life threatening.
Death is more common when other diseases (e.g., cancer, liver disease,
immunodeficiency diseases) are present. It has been estimated that 500
persons die each year due to complications with Campylobacter infections.
Some strains of C. jejuni have also been incriminated in the
production of Guillian-Barré syndrome, an acute neuromuscular
paralysis, and Reiter syndrome, a reactive arthropathy. |
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Sources of Campylobacters
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Campylobacters
live in the intestinal tract of healthy cattle, pigs and poultry.
Campylobacters have been also isolated from pets and occasionally
from streams, lakes and ponds. In commercial broiler chickens, campylobacters
multiply without producing any disease to the chickens. The contamination
of chicken meats with these pathogenic bacteria may occur when chickens
are processed to convert them in human food. The first large baseline
study of bacterial pathogens on poultry carcasses (years 1994-1995)
revealed an incidence of 88% of Campylobacter bacteria with
no apparent seasonal variation. Although figures from the most recent
baseline study (years 1999-2000) have not been published, current
scientific data indicate that there is still a high incidence of campylobacters
in processed chicken carcasses.
Studies show that close to 20% of Campylobacter strains isolated from humans are genetically related to the strains isolated from poultry meats. These findings suggest that poultry meat is an important reservoir of campylobacters for humans. Yet, large Campylobacter outbreaks are not associated with raw poultry, but are associated with drinking unpasteurized milk or contaminated water. Other identified food vehicles include undercooked meats, mushrooms, cheese, shellfish, and eggs. |
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Contamination and Survival in Foods
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| Food becomes contaminated with intestinal material during processing.
C. jejuni grows poorly on properly refrigerated foods, but
survives refrigeration and grows on contaminated foods left out at room
temperature. Campylobacter is sensitive to heat and common
disinfection procedures. Pasteurization of milk, adequate cooking of
meat and poultry and chlorination of water will destroy the organism.
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Isolation of Campylobacters from Food
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| In
the laboratory, campylobacters are presumptively identified by looking
at the cell shape and motility with a phase contrast or a dark filed
microscope. Positive results with catalase, oxidase and latex agglutination
tests are used to confirm isolates to the genus level. Most of the times,
these are the only tests used to confirm isolates as Campylobacter
spp. The confirmation of isolates to the species level requires performing
biochemical and physiological tests, such as hippurate hydrolysis and
sensitivity to antibiotics. Unlike Salmonella or Escherichia coli, Campylobacter and Arcobacter do not metabolize sugars and therefore few tests are available for species confirmation. Besides, the few available tests required trained personnel to avoid subjectivity and are time-consuming to perform. Few commercial laboratories offer a rapid identification system based on physiological and biochemical techniques for species identification. New molecular tests, such as the polymerase chain reaction technique, are replacing the laborious physiological tests for identification of Campylobacter isolates. Yet, these molecular techniques can be run only in few dedicated laboratories. Several methods, including enrichment and plate media, have been developed for the isolation of Campylobacter from commercial poultry carcasses. However, Campylobacter isolation methods have always been discussed when attempting to understand the meaning of the counts and incidence reported in the literature. The U. S. Department of Agriculture Food Safety and Inspection Service (USDA FSIS) has requested the National Advisory Committee on Microbiological Criteria for Foods to evaluate the methodologies used in the 1994-1995 and the 1999-2000 baseline studies. To date, no performance standard for Campylobacter has been established by USDA FSIS. The collection of samples for Campylobacter studies in processing plant is done using the standard carcass rinse technique. Because of the large number of Campylobacter cells present per ml of carcass rinse, direct plating can be used to report the results in counts (CFU per ml of rinse). If the sample is enriched, the results are reported as positive or negative for Campylobacter. Both counts and positive/negative results are used to calculate the incidence (percentage positive) of campylobacters from a series of carcass samples. |
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Incidence and Control of Campylobacters in Chicken Carcasses
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| In
general, there is a continuous decline in the number of campylobacters
on commercial poultry carcasses from evisceration to immediately after
the chiller. Campylobacter counts post-evisceration (pre-wash)
are generally in the range of 2.5 to 3.7 log CFU per ml of carcass rinse.
This range is typically found when sampling different processing plants
or the same processing plant at different times. The washing systems used during processing, some of which are called inside-outside bird washers (IOBW), may help reduce the number of Campylobacter spp. on carcasses. However, the reduction may not be of significance, or achieved consistently. In addition, the percentage of Campylobacter positive samples following the IOBW remains generally the same as pre-IOBW samples. In general, IOBWs reduce Campylobacter counts up to 0.7 log CFU/ml. The effectiveness of an IOBW to reduce Campylobacter, as well as other bacterial pathogens, depends greatly on the water volume/pressure and the level of chlorine in the water. These variables may be difficult to control consistently in commercial processing environments. The addition of an antimicrobial system, such as trisodium phosphate (TSP) or acidified sodium chlorite (ASC), to the washes produces a reduction of 1-1.7 log CFU/ml in the number of Campylobacter counts. The combined used of IOBWs and chemical sprays have been found effective to remove visible fecal contaminations and to allow for a continuous online processing of commercial broiler carcasses. Although these washes and spray systems reduce Campylobacter spp., in some instances there have been no differences in the numbers of Campylobacter positives between pre-chill and post-chill samples. Some chemical interventions are now being applied after chilling with successful reduction of Campylobacter. Applying chemicals after the chiller may have the advantage of using cold shock to potentiate the killing effect of the chemical. The chiller is also a processing step that may account for the decrease in the number of Campylobacter. There appears to be a consistent reduction in Campylobacter counts due to the chilling process. However, a large number of post-chill carcasses are still positive for Campylobacter after enrichment. The chiller usually accounts for 0.8-1.3 log CFU/ml reduction in the number of Campylobacter, and 0 to 20% in the reduction of carcasses positive to Campylobacter. It is logical to believe that if the number of Campylobacter contaminating the carcasses pre-chill is still large, chances are the chilling process will not be able to significantly reduce the number of Campylobacter and/or the incidence of positive carcasses. We do not still understand the extent of contamination that carcasses may be subjected to in the chiller tank, if such a contamination exits. The impact of the washing system, an antimicrobial application system and the chiller considered altogether account for a reduction of approximately 1.8 log CFU/ml of Campylobacter counts. Carcasses that undergo through this series of processing steps right after evisceration have a consistent reduction in the percentage of positive Campylobacter samples post-chill. However, if the level of Campylobacter spp. coming with the carcasses to the chiller tank is too high, the standard chilling process does not considerably reduce the level of contamination. Although several intervention strategies and changes in processing have been incorporated to comply with the requirements brought about by HACCP regulations, a single intervention step would require a consistent reduction capability of up to a 3.7 log CFU/ml, with minimal impact on the organoleptic characteristics of the final product. The alternative approach, based on the use of several barriers or hurdles applied at different processing steps, is more currently used and appears to be more realistic for the control of Campylobacter spp. in poultry carcasses. Besides the control measures at different stages of food processing, an important step in preventing and controlling campylobacteriosis is to adequately cook all poultry products. The most reliable method to ensure adequately cooking is to use a cooking thermometer. Research institutions must continue to work together with the poultry industry to collect critical epidemiological information on how Campylobacter survives and transmits in foods. Improving our understanding of key epidemiological issues related to Campylobacter transmission in foods will certainly improve our chances of success in controlling this pathogen. Finally, we have to continue our efforts on the development of intervention technologies that can be applied at different stages during processing to reduce or eliminate the incidence of Campylobacter in poultry meat. |
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Supported by: Non-Assistance Cooperative Agreement #FSIS-C-33-2003, Development of a Virtual Library for Small and Very Small Meat and Poultry Processors | ||
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