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Contamination of chicken carcasses and the abattoir environment with Salmonella spp. and Listeria monocytogenes in Taiwan

Lin, Chih-Hsien (2021) Contamination of chicken carcasses and the abattoir environment with Salmonella spp. and Listeria monocytogenes in Taiwan. PhD thesis, Murdoch University.

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Abstract

Contaminated poultry and poultry products are the main food sources for human salmonellosis and listeriosis, with these contaminations predominantly occurring in abattoirs during the slaughtering and processing stages. Although poultry is the most commonly consumed meat in Taiwan, the epidemiological characteristics of contaminations during processing were not known prior to the studies described in this thesis.

A nationwide survey of 362 batches of broiler carcasses (1810 individual carcasses) processed at 45 abattoirs in Taiwan found that 56.4% (95% CI: 51.1-61.5) were positive for Salmonella. The results of a multivariable logistic regression analysis found that contamination was significantly associated with: season of sampling (warm season > cooler season, OR = 1.95; 95% CI: 1.2-3.2); location of the abattoir (southern region < northern region, OR = 0.45; 95% CI: 0.3-0.8); duration of scalding (scalding times longer than 90 seconds < shorter scalding times, OR = 0.2; 95% CI: 0.1-0.3); and bird type (commercial white broiler < Taiwan native chickens, OR = 0.21; 95% CI: 0.1-0.4).

Salmonella were detected in 156 of 622 samples (25.1%; 95% CI: 21.7-28.7) collected from a more intensive study undertaken at six abattoirs. The prevalence of Salmonella varied between sampling sites with 5.8, 17.6, 31.3 and 35.5% of cloacal swabs, environmental samples prior to processing, environmental samples during processing and carcass rinse samples, respectively, being positive. These 156 isolates represented 50 PFGE types. The presence of the same PFGE type at multiple stages during processing highlighted that the abattoir environment and intestinal contents are important sources of Salmonella in abattoirs. Listeria monocytogenes was not detected in any cloacal swabs (n = 120) or environmental (n = 256) samples collected before and during processing, but 28 of 246 (11.4%; 95% CI: 7.7-16.0) rinse samples collected from carcasses post-evisceration were positive. These 28 isolates represented 5 PFGE types, confirming the presence of cross-contamination during processing.

An intensive study undertaken at one abattoir on 12 consecutive processing days involving repeated sampling of chickens from 12 farms detected Salmonella in 83.3, 22.9, 35.4, 34.4, 19.8 and 21.9% of carcass samples at post exsanguination, post plucking, post evisceration, post inside-outside bird washer, post wash tank, and post air-chilling, respectively. Fifty-seven PFGE types were characterized from the 223 isolates, and confirmed that Salmonella-infected flocks are important sources of contamination in the abattoir resulting in subsequent cross-contamination of carcasses. Distribution biomaps were developed in combination with Salmonella PFGE profiles to identify potential sources of cross-contamination in the abattoir.

Overall a total of 968 isolates belonging to 33 serotypes of Salmonella were detected in the three studies, with S. Albany (30.9%), S. Enteritidis (16.5%), S. Schwarzengrund (9.7%), and S. Typhimurium (6.7%) being most frequently isolated. These results demonstrate that the Salmonella serotypes commonly isolated from chicken carcasses and the abattoir environment were also those frequently affecting humans in Taiwan, supporting the belief that contaminated chicken meat is one source of human salmonellosis. The 28 isolates of L. monocytogenes were serotyped as either 1/2a (82.1%) or 1/2b (14.3%), with one isolate non-typeable (3.6%). These serotypes were the same as those causing the majority of human listeriosis cases in Taiwan and other countries of the world.

It is concluded that the information obtained from this research can be used to assess control measures to minimize the contamination of chickens processed at abattoirs in Taiwan with potentially pathogenic bacteria.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): Veterinary Medicine
Supervisor(s): Robertson, Ian, Adams, Peter and Lin, J-H
URI: http://researchrepository.murdoch.edu.au/id/eprint/64239
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