Abstract
Haemophilus parasuis is a commensal bacterium of the upper respiratory tract of healthy pigs. It is also the etiological agent of Glässer’s disease, a systemic disease characterized by polyarthritis, fibrinous polyserositis and meningitis, which causes high morbidity and mortality in piglets. The aim of this study was to evaluate biofilm formation by well-characterized virulent and non-virulent strains of H. parasuis. We observed that non-virulent strains isolated from the nasal cavities of healthy pigs formed significantly (p < 0.05) more biofilms than virulent strains isolated from lesions of pigs with Glässer’s disease. These differences were observed when biofilms were formed in microtiter plates under static conditions or formed in the presence of shear force in a drip-flow apparatus or a microfluidic system. Confocal laser scanning microscopy using different fluorescent probes on a representative subset of strains indicated that the biofilm matrix contains poly-N-acetylglucosamine, proteins and eDNA. The biofilm matrix was highly sensitive to degradation by proteinase K. Comparison of transcriptional profiles of biofilm and planktonic cells of the non-virulent H. parasuis F9 strain revealed a significant number of up-regulated membrane-related genes in biofilms, and genes previously identified in Actinobacillus pleuropneumoniae biofilms. Our data indicate that non-virulent strains of H. parasuis have the ability to form robust biofilms in contrast to virulent, systemic strains. Biofilm formation might therefore allow the non-virulent strains to colonize and persist in the upper respiratory tract of pigs. Conversely, the planktonic state of the virulent strains might allow them to disseminate within the host.Electronic supplementary materialThe online version of this article (doi:10.1186/s13567-014-0104-9) contains supplementary material, which is available to authorized users.
Highlights
Haemophilus parasuis is a Gram-negative bacterium and a commensal organism of the upper respiratory tract of healthy pigs
The heterogeneity among H. parasuis strains has been demonstrated by multiple methods, including multilocus sequence typing (MLST) which has shown a genetic lineage associated with polyserositis and another lineage associated with nasal colonization
We noticed that biofilm production was stronger in strains sensitive to serum compared to resistant strains (Additional file 1A, p = 0.059); in strains negative for vtaA group 1 genes compared to strains positive for these genes (Additional file 1B, p = 0.189); in strains belonging to MLST cluster C compared to strains belonging to MLST cluster A (Additional file 1C, p = 0.202), and in strains negative for the sialyltransferase gene lsgB compared to strains positive for lsgB (Additional file 1D, p = 0.228)
Summary
Haemophilus parasuis is a Gram-negative bacterium and a commensal organism of the upper respiratory tract of healthy pigs. It is the etiological agent of Glässer’s disease, a systemic disease characterized by polyarthritis, fibrinous polyserositis and meningitis, which causes high morbidity and mortality in piglets [1]. Some putative virulence factors have been reported [7,8] Those include the capsule [4], lipooligosaccharide (LOS) [9,10,11] and other genes involved in polysaccharide production, such as galE and galU, which have been associated with serum resistance and biofilm production [12]. Group 3 vtaA gene is highly conserved among invasive and non-invasive strains, whilst groups 1 and 2 vtaA genes were detected only in virulent strains
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