As controlling C. jejuni infection on the farm is complex and difficult to achieve, it has been suggested that there should be a greater focus on prevention of cross contamination at the processing plant, or decontamination of carcasses following processing (Corry and Atabay, 2001).Plant automation has increased the number of birds a plant is able to process, which in turn has increased the potential for contamination (Arnold and Silvers, 2000). Plants typically deal with 12,000 birds per hour and run continually, stopping only to clean and disinfect machinery. Poultry are eviscerated without opening the carcass and skin is typically not removed. Feathers are loosened by submerging carcasses in warm water, the temperature of which is usually between 50°C and 60°C. Plucking machines have rubbery fingers attached to rotating disks, and plucking is aided by spraying water on to the carcass while the feathers are removed. The most important contamination control step is the wash before chilling. The carcass should be thoroughly washed inside and out at this point, as microbial contamination of meat is typically a surface phenomenon (Corry and Atabay, 2001).
Many studies on Campylobacter sp. within processing plants have now been completed and cross contamination of C. jejuni negative flocks is frequently found (Allen et al., 2007). A recent systematic review identified 1,716 papers when using the search terms „Campylobacter‟, „chicken‟ and „processing‟ (Guerin et al., 2010). Results from many of the papers appear contradictory, and total concentrations of Campylobacter sp. vary greatly
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between studies. In part this variation is due to the different enumeration and isolation techniques used (Bai et al., 2014) or sampling sites chosen (Baré et al., 2013, Luber and Bartelt, 2007). Other factors effecting Campylobacter sp. cell numbers include slaughter processing methods, prevalence within the flocks before slaughter (Guerin et al., 2010) and season that the sampling took place (Jore et al., 2010, Kovats et al., 2005, Meldrum et al., 2005). Although studies show great variability, some conclusions are able to be drawn. It has been noted by several researchers that Campylobacter sp. numbers typically reduce following the scalding and chilling stages of processing (Rosenquist et al., 2006, Duffy et al., 2014, Guerin et al., 2010). There was also a trend of increased Campylobacter sp. prevalence following the defeathering process (Guerin et al., 2010), which occurs directly after scalding. A study of E. coli, Campylobacter sp. and Coliforms showed that the scalding process reduced the bacterial load on the production line from an initial mean value of 4.7 log CFU/ml of rinse fluid to 1.8 log CFU/ml rinse fluid at the post scald stage, increasing back to 3.7 log10 CFU/ml rinse fluid following plucking (Berrang and Dickens, 2000). The primary cause of this increase is an escape of gut contents when carcasses passed through the defeathering machine (Berrang et al., 2011).
Carcass chilling, one of the final stages of processing, can be carried out in two ways: air or, in the USA, water cooling (Demirok et al., 2013). Both methods provided a reduction in
Campylobacter sp. numbers (Rosenquist et al., 2006), although the water tanks used during
water cooling represent a major cross contamination risk (Guerin et al., 2010). The use of water treatments such as chlorine or gamma radiation has been shown to be effective in reducing bacterial contamination of the chill water (Corry and Atabay, 2001), however there is low consumer acceptance of these interventions (MacRitchie et al., 2014) and they are currently not used within the EU.
Following processing, carcasses are typically either refrigerated or frozen before sale. Freezing has been shown to reduce Campylobacter sp. numbers significantly (Wassenaar, 2011). This effect is so consistent that freezing of Campylobacter sp. contaminated poultry has become one of the main infection reduction strategies in countries such as Iceland (Tustin et al., 2011). Chilling, compared to freezing, allows greater Campylobacter sp. survival, although an overall reduction is still observed during storage. Chicken breast inoculated with C. jejuni and stored at 4°C showed a 1-2 log decline in CFU over 17 days (Blankenship and Craven, 1982).
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Figure 1-8 Flow diagram of slaughter process indicating potential contamination and C. jejuni release points
The diagram shows the main points of the poultry slaughter process. A brief description of the temperature the processing stage is carried out at, it‟s potential to increase/decrease or spread C.
jejuni, and the net increase or decrease in C. jejuni numbers is shown. The colour of the boxes
indicates the temperature the carcasses are at during the stage, with red being hottest, yellow indicating a mid-point, and blue being the coolest temperature in the process.
1.4.2.1 Cross contamination within the processing plant
During processing there are several points where cross contamination may occur. Several researchers have suggested that cross contamination is possible within processing factories, and food chain persistence is well recognised in other bacterial foodborne pathogens such as L. monocytogenes (discussed in Section 1.1.5.3). A study by Berghaus et al. (2013) showed that 63.6% of flocks leaving farms during their study tested positive for
Campylobacter sp.. Following processing 87.3% were positive, suggesting cross
contamination occurred during this study. Allen et al. (2007) typed Campylobacter sp. strains isolated from chickens prior to slaughter and throughout the processing plant. They observed that the strains found on carcasses did not correlate closely with the strains found in the caeca prior to slaughter, again highlighting the potential for cross contamination and
Campylobacter sp. persistence within the food chain. During this study Campylobacter sp.
were isolated from aerosols, particles and droplets throughout the processing plant, although not in chilled storage areas, hinting at a possible cross contamination method (Allen et al., 2007).
In contrast, a study by (Elvers et al., 2011) found that the strains identified on the birds entering the processing plant, remained predominant throughout the processing procedure. This was also observed by Kudirkiene et al. (2011), who found that one genotype was predominant from farm to end of slaughter. Although these studies suggest that
Campylobacter sp. strains are not able to persist for extended periods within processing
plants, there is still the potential for short term persistence. An assessment of the transfer of
Campylobacter sp. from positive to negative flocks was carried out by processing Campylobacter sp. negative flocks directly after positive flocks had been slaughtered.
Several strains were isolated from previously negative flocks, and results showed that the isolates were of the same type as those found in the positive flocks (Elvers et al., 2011). Taken together these studies highlight that Campylobacter sp. are able to persist within food processing plants and contaminate other carcasses and the environment.
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