Sialic acid mediated transcriptional modulation of a highly conserved sialometabolism gene cluster in Haemophilus influenzae and its effect on virulence.
BACKGROUND
Sialic acid has been shown to be a major virulence determinant in the pathogenesis of otitis media caused by the bacterium Haemophilus influenzae. This study aimed to characterise the expression of genes required for the metabolism of sialic acid and to investigate the role of these genes in virulence.


RESULTS
Using qRT-PCR, we observed decreased transcriptional activity of genes within a cluster that are required for uptake and catabolism of 5-acetyl neuraminic acid (Neu5Ac), when bacteria were cultured in the presence of the sugar. We show that these uptake and catabolic genes, including a sialic acid regulatory gene (siaR), are highly conserved in the H. influenzae natural population. Mutant strains were constructed for seven of the nine genes and their influence upon LPS sialylation and resistance of the bacteria to the killing effect of normal human serum were assessed. Mutations in the Neu5Ac uptake (TRAP transporter) genes decreased virulence in the chinchilla model of otitis media, but the attenuation was strain dependent. In contrast, mutations in catabolism genes and genes regulating sialic acid metabolism (siaR and crp) did not attenuate virulence.


CONCLUSIONS
The commensal and pathogenic behaviour of H. influenzae involves LPS sialylation that can be influenced by a complex regulatory interplay of sialometabolism genes.
Molecular Infectious Diseases Group, University of Oxford Department of Paediatrics, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford OX39DS, UK.
Gaynor A
GA
Jenkins
Marisol
M
Figueira
Gaurav A
GA
Kumar
Wendy A
WA
Sweetman
Katherine
K
Makepeace
Stephen I
SI
Pelton
Richard
R
Moxon
Derek W
DW
Hood
D000818:Animals; D002452:Cell Count; D002682:Chinchilla; D015169:Colony Count, Microbial; D017124:Conserved Sequence; D004195:Disease Models, Animal; D006193:Haemophilus influenzae / Q000235:genetics* / Q000472:pathogenicity*; D006801:Humans; D008070:Lipopolysaccharides / Q000737:chemistry / Q000378:metabolism; D053858:Metabolic Networks and Pathways; D005810:Multigene Family; D016296:Mutagenesis; D019158:N-Acetylneuraminic Acid / Q000235:genetics / Q000378:metabolism*; D010033:Otitis Media / Q000382:microbiology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D044967:Serum; D014774:Virulence / Q000235:genetics
D008070:Lipopolysaccharides; D019158:N-Acetylneuraminic Acid