Investigation into the prevalence and persistence of Listeria monocytogenes in Irish seafood: Possible roles for σB in environmental persistence

Abstract

L. monocytogenes is a robust bacterial pathogen capable of surviving in a wide range of environments including food processing facilities. This pathogen is of concern for the food processing industry particularly producers of Ready to Eat (RTE) food products such as smoked salmon and soft cheeses. The ability of this organism to overcome and survive under harsh conditions is partially due to the alternative sigma factor, σB. In a stressful environment, σB interacts with RNA polymerase to initiate transcription of the General Stress Response (GSR) regulon helping the bacterium to overcome the encountered stress. Developing surveillance programmes to determine the prevalence of L. monocytogenes in RTE processing facilities can provide information to assist producers to combat contamination by this pathogen. Characterisation of isolates collected during these types of studies can provide useful information regarding persistence of L. monocytogenes in the processing environment. This study aimed to conduct a surveillance programme to determine the occurrence of L. monocytogenes in Irish seafood facilities over the course of three years. We found that the overall occurrence was lower than that suggested for seafood facilities in other studies. We further aimed to characterise and investigate mechanisms leading to persistence of L. monocytogenes in processing environments using strains isolated during the surveillance study. Visible light has been shown to be a possible mechanism for controlling L. monocytogenes and here we demonstrate that blue light (460 – 470 nm) has an effect on the growth and survival of L. monocytogenes and this effect is dependent on the production of ROS. We also aim to characterise a possible P-type ATPase, Lmo0818 and its function in maintaining homeostasis of the cell. Results presented in this thesis highlight the prevalence of L. monocytogenes in Irish food processing facilities and the potential for novel treatment methods such as light to control this pathogen.