Antigenic secreted proteins fromHaemophilus paragallinarum. A 110-kDa putative RTX protein

Regulation of chicken immunity-related genes and host response profiles against Avibacterium paragallinarum pathogen challenge

Infectious coryza (IC) is a well-recognised and commonly encountered upper respiratory tract disease in chickens. The aim of this study was to monitor aspects of the immune response of chickens infected with Avibacterium paragallinarum. Gene expression profiling of 30 genes was carried out for 11 chicken nasal area samples belonging to four groups, including one non-infected control group. For this purpose, 30 biomarker transcripts were selected for comparative gene expression analysis and were analysed by real-time PCR using TaqMan(®) assays. The biomarkers included three reference genes. The reference genes were used to normalise the results in a relative quantification approach. The gene expression changes of the 27 biomarker transcripts (genes of interest) were quantified between all treated groups in six pair-wise comparisons. It was concluded from the data that immune response initiation is via TLR4, which leads to a Th2 dominant type response. Furthermore, TLR4 results in signalling via the MyD88-dependent pathway, resulting in early onset of NF-kβ leading to the production of inflammatory cytokines. This work provides an informative outlay of immune response initiation upon infection with this pathogen.

Identification of iron-acquisition proteins of Avibacterium paragallinarum

When Avibacterium paragallinarum reference strain 0083 (serovar A) was grown in an iron-restricted culture medium, the expression of the 60, 68 and 93 kDa outer membrane proteins increased as compared with normal media. Sera of chickens experimentally infected with Av. paragallinarum recognized these iron-restriction induced proteins, suggesting their expression in vivo. The three outer membrane proteins were identified as transferrin receptor and iron transport proteins by mass spectroscopy and a search in sequence databases. As these proteins have been reported to be regulated by the Fur protein in many bacteria, we investigated, through molecular methods, the presence of the fur gene in Av. paragallinarum. A candidate fur gene of Av. paragallinarum was amplified by polymerase chain reaction using complementary primers to conserved regions of fur gene sequences from members of the Pasteurellaceae family. The nucleotide sequence of the cloned gene, from ATG to TAA stop codon, was 453 base pairs in length and the deduced amino acid sequence showed 94% identity with Fur sequences of Actinobacillus pleuropneumoniae and Haemophilus ducreyi. The Av. paragallinarum deduced Fur protein (17.8 kDa) amino acid sequence contains the N-terminal helix-turn-helix DNA-binding domain and the two iron-binding sites in the C-terminal end, typical of other described Fur proteins. The study of iron-restriction-induced proteins and the mechanism regulating their expression could lead to an understanding of the responses of Av. paragallinarum to survive in an iron-restricted environment on host mucosal surfaces.

Identification and characterization of complete RTX operons in Moraxella bovoculi and Moraxella ovis

To determine if Moraxella bovoculi (M. bovoculi), a recently characterized coccoid Moraxella that was isolated from the eyes of calves affected with infectious bovine keratoconjunctivitis (IBK), and Moraxella ovis (M. ovis), originally isolated from sheep with conjunctivitis, possessed genes encoding RTX proteins, genomic DNA was amplified with oligonucleotide primers targeting RTX operon genes of Moraxella bovis (M. bovis). Complete classical RTX operons composed of RTXCABD genes closely linked to a putative secretion accessory protein encoding gene (tolC) were identified in M. bovoculi and M. ovis and were designated mbvCABDtolC and movCABDtolC, respectively. These genes were closely related to M. bovis mbxCABDtolC. Polyclonal rabbit antiserum against the carboxy terminus of M. bovoculi MbvA neutralized hemolytic activity of both M. bovoculi and M. ovis; this antiserum did not neutralize the hemolytic activity of M. bovis. M. bovoculi and M. ovis possess genes that encode proteins related to pathogenic factors of M. bovis.

Haemophilus paragallinarumsecretes metalloproteases

Haemophilus paragallinarum secretes metalloproteases into different culture media lacking serum. Secreted proteins, concentrated by precipitation with 70% ammonium sulphate ((NH4)2SO4) or methanol, displayed proteolytic activity at >100 kDa molecular mass in 10% polyacrylamide gels co-polymerized with porcine gelatin (0.1%). They were active in a broad pH range (4–9); pH 7.5 being the optimum. Protease activity was inhibited by 20 mmol EDTA/L and reactivated by calcium. The proteolytic activity was heat-stable at 40, 50, and 60 °C, but its activity diminished at 70 °C or higher. Secreted proteins partially degraded chicken immunoglobulin G (IgG) and cross-reacted with a polyclonal serum against a high molecular mass protease secreted by Actinobacillus pleuropneumoniae. Extracellular proteases could play a role in infectious coryza caused by H. paragallinarum.Key words: pathogenicity, secreted protein, infectious coryza.

Virulence of the nine serovar reference strains of Haemophilus paragallinarum

The virulence of the reference strains of the nine currently recognized Kume serovars of Haemophilus paragallinarum was investigated. The capacity of the H. paragallinarum strains to cause the typical clinical signs of upper respiratory tract disease associated with infectious coryza in unvaccinated, nasal-challenged chickens was assessed. Differences in virulence were assessed by means of a standardized scoring system for clinical signs. All nine strains were pathogenic to chickens, producing typical clinical signs of infectious coryza. The highest clinical signs score was obtained for serovar C-1 (1.72), while the lowest clinical signs score was obtained for serovar C-4 (0.32). Our results indicate that virulence differences exist among the serovars of H. paragallinarum.