The Salmonella virulence protein PagN is a potential promoter of bacterial escape from the Salmonella-containing vacuole to host cytosol

International audienceSalmonella Typhimurium is a facultative intracellular entero-pathogen that remains a risk to public health worldwide. The tools and strategies allowing it to invade and survive within host cells are numerous. Nowadays, it is the only pathogen known to invade host cells using either a trigger or a zipper mechanism, respectively depending on the Type 3 secretion system-1, mainly encoded on Salmonella pathogenicity island-I, and on the two invasins Rck (1) and PagN (2, 3). Intracellularly, Salmonella are contained in a Salmonella-containing vacuole (SCV), whose maturation results in an acidic environment which is poor in divalent cations. Nevertheless, in the last decades, several studies gave some evidences for a Salmonella escape from the early SCV, leading to cytosolic hyper replication of the pathogen (4). As PagN expression was previously shown to be dependent on acidic pH and low divalent cation concentration (2), we explored the potential role of PagN in the escape of the SCV

The YfgL Lipoprotein Is Essential for Type III Secretion System Expression and Virulence of Salmonella enterica Serovar Enteritidis

Salmonella enterica, like many gram-negative pathogens, uses type three secretion systems (TTSS) to infect its hosts. The three TTSS of Salmonella, namely, TTSS-1, TTSS-2, and flagella, play a major role in the virulence of this bacterium, allowing it to cross the intestinal barrier and to disseminate systemically. Previous data from our laboratory have demonstrated the involvement of the chromosomal region harboring the yfgL, engA, and yfgJ open reading frames in S. enterica serovar Enteritidis virulence. Using microarray analysis and real-time reverse transcription-PCR after growth of bacterial cultures favorable for either TTSS-1 or TTSS-2 expression, we show in this study that the deletion in S. enterica serovar Enteritidis of yfgL, encoding an outer membrane lipoprotein, led to the transcriptional down-regulation of most Salmonella pathogenicity island 1 (SPI-1), SPI-2, and flagellar genes encoding the TTSS structural proteins and effector proteins secreted by these TTSS. In line with these results, the virulence of the ΔyfgL mutant was greatly attenuated in mice. Moreover, even if YfgL is involved in the assembly of outer membrane proteins, the regulation of TTSS expression observed was not due to an inability of the ΔyfgL mutant to assemble TTSS in its membrane. Indeed, when we forced the transcription of SPI-1 genes by constitutively expressing HilA, the secretion of the TTSS-1 effector protein SipA was restored in the culture supernatant of the mutant. These results highlight the crucial role of the outer membrane lipoprotein YfgL in the expression of all Salmonella TTSS and, thus, in the virulence of Salmonella. Therefore, this outer membrane protein seems to be a privileged target for fighting Salmonella

The role of type I interferons (IFNs) in the regulation of chicken macrophage inflammatory response to bacterial challenge

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Antimicrobial Resistance Analysis of French Isolates of Enterococcus cecorum

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