The aim of this thesis was to investigate how two human pathogen sequence types of Campylobacter jejuni, ST-257 and ST-918, survive freezing in chicken fillets. Campylobacteriosis is the most reported zoonosis in the EU, with over 200,000 reported cases annually. Many cases are not reported and the true number of cases is estimated to nine million, with an estimated yearly cost of 2.4 billion euro. C. jejuni causes over 80% of the human infections and broilers are considered to be the major source of human exposure. Freezing reduces the concentration of bacteria and can be used as a post-harvest preventative measure. In this thesis, broiler meat was artificially contaminated and frozen together with meat juice, thereafter stored up to 49 days. The analysis of viable cells was made according to ISO 10272 part 2. Largest rate of decrease occurred the first two or four days after freezing and the rate of decrease flattened after approximately one week. ST-257 decreased by mean 1.6 to 2.0 log10 CFU/g in the meat and ST-918 decreased by 0.7-1.0 1.6 to 2.0 log10 CFU/g. The reduction in the juice was equal or larger to the reduction in the meat. ST-918 survived freezing to a greater extent than ST-257, indicating different abilities to stand the stress.
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