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Title: Enhanced Type III Secretion System activity contributes to the increased virulence of a Bordetella bronchiseptica lineage

Author
item BUBOLTZ, ANNE - PENN STATE UNIVERSITY
item Nicholson, Tracy
item WEYRICH, LAURA - PENN STATE UNIVERISTY
item STIBITZ, SCOTT - CBER/FOOD AND DRUG ADMIN
item HARVILL, ERIC - PENN STATE UNIVERSITY

Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2009
Publication Date: 9/1/2009
Citation: Buboltz, A.M., Nicholson, T.L., Weyrich, L.S., Harvill, E.T. 2009. Role of the Type III Secretion System in a Hypervirulent Lineage of Bordetella bronchiseptica. Infection and Immunity. 77(9):3969-3977.

Interpretive Summary: Bordetella bronchiseptica is a gram-negative respiratory pathogen that infects a wide-range of mammalian hosts, causing a variety of disease severities. The genetic changes that cause some strains to be more pathogenic than others are unknown. Here, we combine comparative genome analyses, a novel method of Bordetella allelic exchange, phylogenetics and a murine model of infection to determine bacterial factors that contribute to the differences in virulence caused by strains isolated from an asymptomatic host and diseased host. B. bronchiseptica strain 1289 is more virulent than strain RB50 in mice. Transcriptome analysis showed that type III secretion system (TTSS) related genes were more highly expressed by strain 1289 than strain RB50. We identified strains isolated from a wide-range of geographies that belonged to the same lineage as strain 1289 and determined that the TTSS contributed to the increased virulence of these strains as well, suggesting that the TTSS contributes to the increased virulence of this B. bronchiseptica lineage. These data provide a molecular basis for and are consistent with the view that B. bronchiseptica lineages appear to evolve to different levels of virulence, contributing to this species ability to cause a wide-variety of diseases in such a broad host range.

Technical Abstract: Bordetella bronchiseptica is a gram-negative respiratory pathogen that infects a wide-range of mammalian hosts, causing a variety of disease severities. The genetic changes that cause some strains to be more pathogenic than others is unkown. Here, we combine comparative genome analyses, a novel method of Bordetella allelic exchange, phylogenetics and a murine model of infection to determine bacterial factors that contribute to the differences in virulence caused by strains isolated from an asymptomatic host and diseased host. B. bronchiseptica strain 1289 is more virulent than strain RB50 in mice. Transcriptome analysis showed and qRT-PCR confirmed that type III secretion system (TTSS) related genes were more highly expressed by strain 1289 than strain RB50. Compared to strain RB50, the TTSS of strain 1289 caused more rapid cytotoxicity toward macrophages in vitro and contributed more to virulence in mice. Using MLST analysis, we identified strains isolated from a wide-range of geographies that belonged to the same lineage as strain 1289 (ST32). The TTSS was additionally found to contribute to the increased virulence of ST32 strains. Combined, our data suggest that the TTSS contributes to the increased virulence of a B. bronchiseptica lineage. These data provide a molecular basis for and are consistent with the view that B. bronchiseptica lineages appear to evolve to different levels of virulence, contributing to this species ability to cause a wide-variety of diseases in such a broad host range.