Non-typhoidal serotypes of Salmonella enterica remain important foodborne pathogens worldwide and the frequent emergence of epidemic strains in food-producing animals is a risk to public health. In recent years, Salmonella 4,[5],12:i:- isolates expressing only the first phase of the two flagellar antigens (FliC) have emerged and increased in prevalence worldwide. In Europe, the majority of 4,[5],12:i:- isolates belong to phage types DT193 and DT120 of Salmonella Typhimurium and pigs have been identified as the reservoir species. In this study, a number of pig-derived monophasic (4,[5],12:i:-) and biphasic DT193 isolates were characterised for phenotypes relating to virulence, to improve understanding of their ecological success. Additionally, their ability to invade a porcine intestinal epithelial cell line (IPEC-1) and stimulate a pro-inflammatory response from the host cells was investigated, to determine the infection biology of these strains. Monophasic and biphasic isolates were compared throughout, with the aim of identifying an explanation for the selective pressure behind the loss of flagellar phase variation. It was found that the panel of DT193 isolates possessed a heterogeneous repertoire of virulence-related phenotypes and genotypes. A number of isolates demonstrated the ability to form biofilms, however the optimum temperature and time for expression of this phenotype varied among the isolates, which may have implications for bacterial survival in the environment and in the host. Another variation was in the presence of sopE, the gene for an important SPI-1 secreted effector protein associated with virulence, in the genomes of the isolates. The 4,[5],12:i:- isolates exhibited comparable adhesion and invasion to that of the virulent S. Typhimurium isolate 4/74, suggesting that these strains may be capable of colonising the small intestine of pigs in vivo. Infection with 4,[5],12:i:- and biphasic DT193 isolates resulted in approximately the same level of TLR-5 (a flagellin receptor) and IL-8 (a pro-inflammatory chemokine) mRNA upregulation, except in the case of one 4,5,12:i:- isolate that elicited significantly greater upregulation of these genes. The monophasic variants also elicited similar levels of caspase activation and cytotoxicity to the phase variable DT193 isolates. These results suggest that monophasic Salmonella display a similar infection biology to phase variable S. Typhimurium during colonisation of the porcine intestinal tract. Consequently, failure of 4,[5],12:i:- isolates to express a second phase of flagellar antigen (FljB) is unlikely to hamper their pathogenicity during colonisation of the porcine intestinal tract in vivo.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:658120 |
| Date | January 2014 |
| Creators | Crayford, Georgina |
| Publisher | University of Liverpool |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://livrepository.liverpool.ac.uk/2014260/ |
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