RTX toxins in Pasteurellaceae

Abstract

RTX toxins (repeats in the structural toxin) are pore-forming protein toxins produced by a broad range of pathogenic Gram-negative bacteria. In vitro, RTX toxins mostly exhibit a cytotoxic and often also a hemolytic activity. They are particularly widespread in species of the family Pasteurellaceae which cause infectious diseases, most frequently in animals but also in humans. Most RTX toxins are proteins with a molecular mass of 100 ± 200 kDa and are post-translationally activated by acylation via a specific activator protein. The repeated structure of RTX toxins, which gave them their name, is composed of iterative glycine-rich nonapeptides binding Ca 2 on the C-terminal half of the protein. Genetic analysis of RTX toxins of various species of Pasteurellaceae and of a few other Gram-negative bacteria gave evidence of horizontal transfer of genes encoding RTX toxins and led to speculations that RTX toxins might have originated from Pasteurellaceae. The toxic activities of RTX toxins in host cells may lead to necrosis and apoptosis and the underlying detailed mechanisms are currently under investigation. The impact of RTX toxins in pathogenicity and the immune responses of the host were described for several species of Pasteurellaceae. Neutralizing antibodies were shown to significantly reduce the cytotoxic activity of RTX toxins. They constitute a valuable strategy in the development of immuno-prophylactics against several animal diseases caused by pathogenic species of Pasteurellaceae. Although many RTX toxins possess cytotoxic and hemolytic activities toward a broad range of cells and erythrocytes, respectively, a few RTX toxins were shown to have cytotoxic activity only against cells of specific hosts and/or show cell-type specificity. Further evidence exists that RTX toxins play a potential role in host specificity of certain pathogens.

Development and Use of a Multiplex Polymerase Chain Reaction Assay Based on Apx Toxin Genes for Genotyping of Actinobacillus Pleuropneumoniae Isolates

“…Group 3 comprised serotype 10 isolates. 4,5 The goal of this study was to develop a multiplex PCR using sets of primers that would amplify all the Apx toxins-secreting genes in the different serotypes of A. pleuropneumoniae in a single reaction. Serological techniques currently used for serotyping A. pleuropneumoniae have some cross-reactivity problems.…”

Phylogenetic relationship of equine Actinobacillus species and distribution of RTX toxin genes among clusters

“…Many representatives of RTX toxins are found in Pasteurellaceae [7]. The aims of the present investigation were to examine the phylogenetic relationship of a collection of strains of A. equuli and assess the distribution of the RTX toxin genes aqx and apxIA, apxIIA, apxIIIA and apxIV in phylogenetic clusters established.…”

Fatal Pulmonary Hemorrhage Associated with RTX Toxin-Producing Actinobacillus Equuli Subspecies Haemolyticus Infection in an Adult Horse

“…8 Aqx protein, a new member of the RTX family, has recently been shown by genetic and phenotypic assays to be present only in hemolytic A. equuli isolates from horses. 2,10 These hemolytic strains have been reclassified as A. equuli subsp.…”