Edinburgh Napier University

  The food-borne pathogene Listeria monocytogenes has been considered a significant threat to human health worldwide. It mainly infects individuals suffering insuffecint immunity such as pregnant women. During pregnancy, L. monocytogenes is capable of causing a serious damage to the mother and the fetus. It can spread to different organs including the placenta via adaptation to interacellular lifestyle. To maintain pregnancy, the levels of the hormones progesterone and β-estradiol increase and reduction in hormone levels was proposed to be associated with fetal death and abortion. The objectives of this project therefore were to investigate the role of pregnancy hormones on the growth and virulence of L. monocytogenes, and to identify bacterial genes with possible roles in binding to pregnancy hormones. It was obsereved that the growth of L. monocytogenes in the presence of progesterone under anaerobic condition was affected by the action of the hormone and the effect was dose/time-dependent of exposure as increasing concentrations showed greater effect on the bacterial growth. Interestingly, bacterial growth was restored within 24 h of exposure to the hormone. In parallel, a Tn917-LTV3 insertion library was constructed and a number of mutants isolated that had reduced growth in the presence of β-estradiol were identified. However, reduction in growth was not microbiologically significant. Furthermore, bioinformatics analysis was performed to identify listerial genes with possible role in hormones degradation. It was observed that L. monocytogenes encodes for a protein that is possibly involved in steroid degradation; therefore, gene expression and a clear-deletion mutant were performed to test this hypothesis. This revealed no significant role of this protein in the growth restoration observed in the presence of progesterone. Also, the deleted gene was investigated of its ability to reduce NADPH in the presence of a possible substrate (progesterone, β-estradiol). This showed that this gene could possess an enzymatic activity toward pregnancy hormones. An attempt to purify this protein for further investigation was performed and protein expression in a soluble form was unsuccessful. The findings presented in this thesis represent an important view when considering the relation between pregnancy hormones and L. monocytogenes; however, further investigations of hormone-degrading proteins from L. monocytogenes are needed. This knowledge may form the basis of a therapy to protect pregnant individuals.