Open Access Open Badges Research article

Molecular and virulence characteristics of an outer membrane-associated RTX exoprotein in Pasteurella pneumotropica

Hiraku Sasaki1*, Hiroki Ishikawa2, Toru Sato3, Satoshi Sekiguchi4, Hiromi Amao4, Eiichi Kawamoto1, Tetsuya Matsumoto2 and Kazuhiko Shirama3

Author Affiliations

1 Animal Research Center, Tokyo Medical University, Shinjuku, Tokyo, Japan

2 Department of Microbiology, Tokyo Medical University, Shinjuku, Tokyo, Japan

3 Department of Histology and Neuroanatomy, Tokyo Medical University, Shinjuku, Tokyo, Japan

4 Laboratory of Experimental Animal Science, Nippon Veterinary and Life Science University, 1-7-1 Musashino, Tokyo, Japan

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BMC Microbiology 2011, 11:55  doi:10.1186/1471-2180-11-55

Published: 17 March 2011



Pasteurella pneumotropica is a ubiquitous bacterium that is frequently isolated from laboratory rodents and causes various clinical symptoms in immunodeficient animals. Currently two RTX toxins, PnxIA and PnxIIA, which are similar to hemolysin-like high-molecular-weight exoproteins are known in this species. In this study, we identified and analyzed a further RTX toxin named PnxIIIA and the corresponding type I secretion system.


The RTX exoprotein, PnxIIIA, contains only a few copies of the RTX repeat-like sequence and 3 large repeat sequences that are partially similar to the outer membrane protein found in several prokaryotes. Recombinant PnxIIIA protein (rPnxIIIA) was cytotoxic toward J774A.1 mouse macrophage cells, whereas cytotoxicity was attenuated by the addition of anti-CD11a monoclonal antibody. rPnxIIIA could bind to extracellular matrices (ECMs) and cause hemagglutination of sheep erythrocytes. Binding was dependent on the 3 large repeat sequences in PnxIIIA. Protein interaction analyses indicated that PnxIIIA is mainly localized in the outer membrane of P. pneumotropica ATCC 35149 in a self-assembled oligomeric form. PnxIIIA is less cytotoxic to J774A.1 cells than PnxIA and PnxIIA.


The results implicate that PnxIIIA is located on the cell surface and participates in adhesion to ECMs and enhanced hemagglutination in the rodent pathogen P. pneumotropica.