Molecular characterization of Haemophilus parasuis ferric hydroxamate uptake (fhu) genes and constitutive expression of the FhuA receptor

Abstract

-Bacteria have evolved a set of highly specialized proteins to capture iron in irondepleted environments. The acquisition and uptake of iron present in the extracellular milieu of eukaryotic organisms is indispensable for the growth and survival of microbial pathogens in the course of infection. Haemophilus parasuis is the causative agent of Glässer disease, which is responsible for considerable financial losses in pig-rearing worldwide. To gain insight into the mechanisms involved in siderophore-mediated iron uptake in H. parasuis, genes in the H. parasuis ferric hydroxamate uptake (Fhu) region were amplified in the work being reported here. As has been described in A. pleuropneumoniae, an Fhu genomic region was also present in H. parasuis, being composed of four potential consecutive open reading frames (ORF) designated as fhuC, fhuD, fhuB, and fhuA, respectively. By immunoblotting, using a cross-reactive polyclonal antibody raised against Actinobacillus pleuropneumoniae FhuA protein, it was demonstrated that this protein was constitutively expressed in H. parasuis and its level of expression was not modified under conditions of restricted iron availability. This is the first report describing the presence of the fhu genes in H. parasuis. Our results indicate that FhuA protein expression is not affected under ironrestricted conditions, however, it is one of the targets of the humoral immune response. Haemophilus parasuis / ferric hydroxamate uptake / iron

Comparative proteomic analysis of the membrane proteins of two Haemophilus parasuis strains to identify proteins that may help in habitat adaptation and pathogenesis

“…To our knowledge, this report is the first to identify another tonB-dependent siderophore receptor in H. parasuis , which has low sequence identity (21.2%) with the previously reported ferric hydroxamate uptake protein FhuA [38]. However, H. parasuis does not possess genes that encode proteins associated with siderophore synthesis [39].…”

Identification of a siderophore utilization locus in nontypeable Haemophilus influenzae

“…The gene arrangement seen in both NTHi strain R2846 and A. pleuropneumoniae , has also been reported for a third representative of the family Pasteurellaceae , namely H. parasuis [36]. …”

“…The expression of receptor proteins that recognize siderophores produced by other microorganisms (termed xenosiderophores) is a well established characteristic of many bacterial species. These include members of the Pasteurellaceae , as well as most enteric species, Bordetella species, Pseudomonads and the mycobacteria [24,36-41]. Possession of a system(s) allowing utilization of xenosiderophores may be of benefit to NTHi strains in the complex polymicrobial environment of the human nasopharynx that this organism colonizes.…”

Epidemiologia molecular de Haemophilus parasuis

“…O sorotipo 4 (39%) e os isolados não sorotipáveis (27%) foram os mais prevalentes nos rebanhos norte-americanos (OLIVEIRA et al, 2003) (KIELSTEIN & RAPP-GABRIELSON, 1992;NIELSEN, 1993). Outros estudos têm sido realizados para se comprovar a associação entre a expressão de fatores de patogenicidade e virulência em infecções por H. parasuis (JIN et al, 2008;DEL RÍO et al, 2006a;METCALF & MacINNES, 2007), embora nenhuma associação evidente com virulência pôde ser determinada. O desenvolvimento de ferramentas diagnósticas mais específicas, tais como a detecção de genes específicos para virulência, permitirá a identificação precisa de amostras virulentas.…”