| Listeria monocytogenes is a causative agent of listeriosis and a deadly food-borne pathogen recognized as a significant public health problem in the United States. Prevention of food contamination as well as the development of efficient prevention and therapeutic strategies have been priorities for the food industry, regulatory agencies and the health research groups. Three specific aims were accomplished in efforts for the aforementioned in this study. The first aim was to evaluate a rapid molecular finger-printing technique, repetitive element sequence-based PCR (REP-PCR) for subtyping L. monocytogenes by comparing it to the gold standard method, pulse-field gel electrophoresis (PFGE). The results showed that the REP-PCR not only had good reproducibility but also provided a similar level of discriminatory ability as the PFGE. Since the REP-PCR is less expensive and more rapid than the PFGE, it could be considered as an alternative molecular typing method for L. monocytogenes.; The second aim was to investigate the subtypes of L. monocytogenes found on raw catfish fillets in three unrelated processing plants. Forty electrophoretic subtypes were distinguished from a total of 97 isolates. From this, 76 isolates were determined as plant-specific, 20 were non-plant-specific, 45 were single-seasonal-distributed and 52 were multi-seasonal-distributed. The results suggest that REP-PCR can be used in tracing the source(s) of contamination and monitoring the effectiveness of sanitation procedures in processing plants.; The third aim was to investigate the immunological responses of human brain microvascular endothelial cells (HBMEC) to L. monocytogenes at 4 hr post-infection using oligonucleotide human microarrays. The expression of 456 genes of HBMEC were significantly altered ( p<0.05). Of the 310 induced genes, many were involved in cell cycles, apoptosis/anti-apoptosis, transcription, and defense responses. Among the up-regulated genes, the induced mRNA levels of interleukin-8 and -15 were further confirmed by real-time RT-PCR. Both the cytokines were regarded as potent chemotactic factors for neutrophils, natural killer cells, and T-lymphocytes. These responses suggest that HBMEC is capable of recruiting cells of innate and adaptive immune responses during the early L. monocytogenes infection. |
