The genetic analysis of the flp locus of Actinobacillus pleuropneumoniae
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ORIGINAL PAPER
The genetic analysis of the Xp locus of Actinobacillus pleuropneumoniae Tingting Li · Zhuofei Xu · Tengfei Zhang · Lu Li · Huanchun Chen · Rui Zhou
Received: 18 December 2010 / Revised: 12 July 2011 / Accepted: 27 July 2011 / Published online: 17 August 2011 © Springer-Verlag 2011
Abstract Actinobacillus pleuropneumoniae, one of the most important porcine respiratory pathogens, exhibits tight adherence to cell surfaces. The Flp pilus, which is assembled by the proteins encoded by the Xp (Wmbrial lowmolecular-weight protein) operon, may play an important role in the bacterial adherence. In this study, the Xp operons of twelve A. pleuropneumoniae serotype reference strains were sequenced and analyzed. The phenotypic diversity of Wmbriae was observed using transmission electron microscopy, and the adherence ability was tested against a porcine lung epithelial cell line. The complete Xp operon was identiWed in the reference strains of serotypes 1, 4, 5, 7, 12, and 13, consisting of 14 genes (Xp1-Xp2-tadV-rcpCAB-tadZABCDEFG). Fimbriae were observed protruding from the bacterial cell surfaces of these strains. In contrast, the Xp promoter was absent in serotypes 2, 3, 6, 9, and 11, and the Xp1 gene was truncated in serotypes 10 and 15. No pilus was observed on the surfaces of these strains. The piliated strains have higher eYciency of adhesion than the pilusnegative strains. Our data demonstrated that the Flp pili are involved in A. pleuropneumoniae adherence. The genetic diversity of the Xp operons among diVerent strains may contribute, at least in part, to the variation in virulence of Actinobacillus pleuropneumoniae.
Communicated by Sebastian Suerbaum. T. Li · Z. Xu · T. Zhang · L. Li · H. Chen · R. Zhou (&) Division of Animal Infectious Disease, State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural University, Wuhan 430070, People’s Republic of China e-mail: [email protected]
Keywords Actinobacillus pleuropneumoniae · The Xp operon · Adherence and colonization · Flp pili · Reference strains
Introduction Actinobacillus pleuropneumoniae is the etiologic agent of porcine pleuropneumonia, a highly contagious and fatal respiratory disease in pigs (Shope et al. 1964). This disease has caused great economic losses to the swine industry globally (Gottschalk and Taylor 2006). On the basis of their capsule, 15 serotypes of A. pleuropneumoniae have been recognized (Dubreuil et al. 2000; Blackall et al. 2002). Currently, many virulence factors involved in the infectious and pathogenic process of A. pleuropneumoniae have been reported (Haesebrouck et al. 1997; Bandara et al. 2003; Chiers et al. 2010) including extracellular toxins (Frey 1995), lipopolysaccharides (Jacques 2004), capsular polysaccharides (Jacques 2004), and membrane proteins (Frey 1995; Jacques 2004; Chung et al. 2007). The ability of diverse bacteria to adhere to host cell surfaces is an important property and a critical step for the colonization of environmental niches and the production
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