Salmonella spp. are Gram-negative microorganisms. Currently, there are over 2500 serovars of Salmonella. Salmonella enterica subspecies enterica serovar Gallinarum biovar Gallinarum (SG) and biovar Pullorum (SP) are two non-flagellated biovars causative of two different avian systemic diseases, fowl typhoid and pullorum disease, respectively. It is believed that the absence of flagella induces low production of pro-inflammatory interleukins, reducing inflammatory responses in intestinal epithelium and favoring systemic infection. Flagellin, the main flagellar protein, has the capacity of stimulating the TLR-5 and consequently to trigger the production of pro-inflammatory cytokines and chemokines which induce a rapid inflammation on the intestinal mucosa, reducing the severity of systemic infection. In a previous study carried out by this research group (FAPESP: 2007/59233-3), a SG mutant strain capable of expressing flagella (SG Fla+) was produced. SG Fla+ is less pathogenic and can also induce inflammation in the intestinal mucosa of birds. However, it was noticed that SG Fla+, although capable of expressing flagella, trends to stop its production after two or more consecutive passages in vitro, becoming phenotypically aflagellated (SG Fla-). This study aims to assess the importance of the flagella in the pathogenesis of SG, phenotypes SG Fla+ and SG Fla- comparing to the SG wild type strain.
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