epiglucan and Actinobacillus-Infections

Actinobacillus pleuropneumoniae is the etiological agent of porcine pleuropneumonia, an economically important disease of pigs. The hfq gene in A. pleuropneumoniae, encoding the RNA chaperone and posttranscriptional regulator Hfq, is upregulated during infection of porcine lungs. To investigate the role of this in vivo-induced gene in A. pleuropneumoniae, an hfq mutant strain was constructed. The hfq mutant was defective in biofilm formation on abiotic surfaces. The level of pgaC transcript, encoding the biosynthesis of poly-β-1,6-N-acetylglucosamine (PNAG), a major biofilm matrix component, was lower and PNAG content was 10-fold lower in the hfq mutant than in the wild-type strain. When outer membrane proteins were examined, cysteine synthase, implicated in resistance to oxidative stress and tellurite, was not found at detectable levels in the absence of Hfq. The hfq mutant displayed enhanced sensitivity to superoxide generated by methyl viologen and tellurite. These phenotypes were readily reversed by complementation with the hfq gene expressed from its native promoter. The role of Hfq in the fitness of A. pleuropneumoniae was assessed in a natural host infection model. The hfq mutant failed to colonize porcine lungs and was outcompeted by the wild-type strain (median competitive index of 2 × 10(-5)). Our data demonstrate that the in vivo-induced gene hfq is involved in the regulation of PNAG-dependent biofilm formation, resistance to superoxide stress, and the fitness and virulence of A. pleuropneumoniae in pigs and begin to elucidate the role of an in vivo-induced gene in the pathogenesis of pleuropneumonia.

Topics: Actinobacillus Infections; Actinobacillus pleuropneumoniae; Amino Acid Sequence; Animals; Base Sequence; beta-Glucans; Biofilms; Electrophoresis, Polyacrylamide Gel; Host Factor 1 Protein; Molecular Sequence Data; Pleuropneumonia; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction; Swine; Swine Diseases; Virulence

We are developing a serotyping system for Actinobacillus suis based on its capsule (K) and lipopolysaccharide O-chain (O) structures. Previously, we have shown that less virulent strains of this swine pathogen express a (1→6)-β-D-glucan as both K- and O-chain polysaccharides and were serologically classified as K:1/O:1. Here, we show that representative A. suis strains with a high (H91-0380; serotype K:2/O:2) and intermediate (C84; serotype K:2/O:1) degree of virulence possess a capsule polysaccharide (K:2) composed of an O-acetylated diglycosyl phosphate repeat decorated with fructose: [→4)-3-O-Ac-β-D-GlcpNAc-(1→3)-[β-D-Fruf-(2→2)]-α-D-Galp-(1→PO(4)(-)→]. In addition, the serotype O:2 lipopolysaccharide was shown to express a sialylated O-chain [→3)-β-D-Galp-(1→4)-[Neu5Ac-(2→3)-α-D-Galp-(1→6)]-β-D-Glcp-(1→6)-β-D-GlcpNAc-(1→]. As (1→6)-β-D-glucan is ubiquitous in the environment, low levels of antibodies in the animals are predicted to prevent disease by K:1/O:1 strains. The greater potential associated with K:2/O:2 and K:2/O:1 strains is most likely due to the absence of (1→6)-β-D-glucan as the K antigen and, in the case of K:2/O:2, the presence of sialic acid in the lipopolysaccharide, a nonulosonic acid known to promote evasion of host recognition.

Topics: Acetylation; Actinobacillus Infections; Actinobacillus suis; Animals; Antigens, Bacterial; Antigens, Surface; Bacterial Capsules; beta-Glucans; Carbohydrate Sequence; Lipopolysaccharides; Magnetic Resonance Spectroscopy; Molecular Sequence Data; N-Acetylneuraminic Acid; O Antigens; Polysaccharides, Bacterial; Serotyping; Sus scrofa; Swine; Swine Diseases; Virulence Factors