Monitoring, understanding and controlling listeria in food processing

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Leong, Dara
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University College Cork
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The objective of this study was to monitor, understand and help control Listeria monocytogenes and L. ivanovii in the food processing environment. As foodborne transmission has been identified as the primary route of human infection of L. monocytogenes, the contamination of foods during production poses a serious threat to public health. Although the incidence of listeriosis is relatively low, the mortality rate can be extremely high, especially in the immunocompromised. This work aimed to examine the prevalence of L. monocytogenes and ivanovii at the primary production stage and, through the typing of isolates, identify and subsequently examine persistent strains. A three year monitoring programme was conducted in 54 processing facilities which identified 86 distinguishable PFGE pulsotypes, 17 of which were seen to be persistent. The effect of management practices on the occurrence of L. monocytogenes was also examined. Separation of personal protective equipment in high and low risk areas, training being performed by management and the use of a power hose were seen to have an effect on L. monocytogenes occurrence and persistence. Challenge tests were also performed using varying methodologies on several types of food in order to establish whether the growth of L. monocytogenes was supported by these foods. Different methodologies were seen to affect the results in challenge tests performed in mushrooms while smoked salmon was seen to support L. monocytogenes growth regardless of methodology used. Finally, two closely related 1/2a L. monocytogenes strains isolated from smoked salmon were subjected to whole genome sequencing and their genomes were compared. The monitoring and examination of L. monocytogenes and L. ivanovii has been seen to reduce the occurrence in the food processing environment and therefore reduce the risk to public health.
Listeria , Persistence , Contamination , Food safety , Food processing
Leong, D. 2017. Monitoring, understanding and controlling listeria in food processing. PhD Thesis, University College Cork.