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The broiler slaughter poses a risk for the contamination of chicken meat with human pathogenic Salmonella spp. and Campylobacter spp. It is not yet sufficiently clear which slaughterhouse-specific factors influence this contamination. In the present study, the contamination of the carcasses is examined at two German slaughterhouses with different operating structures. The aim was to identify sources for cross-contamination within a flock and between consecutively slaughtered flocks.
In this study, neck skin, scalding water, caecum and slaughter line samples were taken during and after the slaughter of 11 broiler batches. The neck skin samples were collected at four different stages of slaughter: immediately after defeathering, after evisceration, after the inside-outside washer and after cooling of carcasses. As general hygiene parameters the aerobic colony count and the number of Enterobacteriaceae of the neck skin and scalding water samples were determined. For each neck skin, scalding water and caecal content sample a semiquantitative determination of Campylobacter numbers (modified according to ISO 10272-3:2010) and Salmonella numbers (ISO/TS 6579-2: 2012 (E)) was performed. For the swab samples of the slaughter line a qualitative detection of Salmonella spp. and Campylobacter spp. was carried out. Confirmed isolates were typed by sequencing the flaA gene (Campylobacter spp.) or by macrorestriction analysis by Pulsed field gel electrophoresis (Salmonella spp.).
The results of the present study indicate that contamination of carcasses occured especially after the slaughter of Salmonella- or Campylobacter-positive broiler flocks. In both slaughterhouses low Salmonella numbers from 0.14 to 260 MPN/g (slaughterhouse A) or from 0.14 to 470 MPN/g (slaughterhouse B) were detected in the positive caecal content and neck skin samples. The median MPN value of Campylobacter spp. in the neck skin samples was 3.4 log MPN/g in slaughterhouse A and 2.4 log MPN/g in slaughterhouse B. The differences between the individual process steps in the number of Campylobacter spp. were not statistically significant. Depending on the slaughterhouse the evisceration, washing and chilling process steps showed different and partly significant impact on the general hygiene parameters.
Within each sample drawing one Salmonella serotype with matching PFGE profile (> 95% similarity) or one to four Campylobacter flaA types were detected. In both slaughterhouses usually only one Campylobacter flaA type or Salmonella serotype dominated at various sampling points. In flocks where Salmonella or Campylobacter were detected in the caecal samples, related genotypes were also detected on the carcasses. By sampling three consecutively slaughtered flocks in slaughterhouse B, the same Campylobacter flaA types were partly detected in all three flocks. As potential sources of cross-contamination, the scalding water, the picking fingers and the evisceration equipment were identified. More research and technological development in the process of scalding, defeathering and evisceration is needed to reduce the risk of contamination in broiler slaughter.