RESUMO
Clostridium septicum is the causative agent of spontaneous gas gangrene or atraumatic myonecrosis, a sudden and frequently fatal infection that is increasingly associated with malignancy of the colon. Little is known about the disease process although the focus of virulence studies has been the alpha-toxin, a pore-forming cytolysin that is encoded by the csa gene and secreted as an inactive protoxin. Until now a lack of techniques for the genetic manipulation of C. septicum has hindered the use of molecular approaches to understand pathogenesis. By introducing plasmids by conjugation from Escherichia coli, we have developed methods for the genetic manipulation of C. septicum and constructed a chromosomal csa mutant by allelic exchange. Virulence testing of an isogenic series of strains consisting of the wild type, the csa mutant, and a csa mutant complemented with the wild-type csa gene revealed that the development of fulminant myonecrosis in mice was dependent on the ability to produce a functional haemolytic alpha-toxin. Furthermore, the inhibition of leukocyte influx into the lesion, which is very typical of clostridial myonecrosis, was also dependent on the ability to produce alpha-toxin. This study represents the first definitive identification of a virulence factor in this organism and opens the way for further studies that will delineate the role of other putative virulence factors in this significant pathogen.
Assuntos
Toxinas Bacterianas/metabolismo , Clostridium/patogenicidade , Músculo Esquelético/microbiologia , Fatores de Virulência/metabolismo , Alelos , Animais , Toxinas Bacterianas/genética , Clostridium/genética , Clostridium/metabolismo , Infecções por Clostridium/microbiologia , Infecções por Clostridium/patologia , Conjugação Genética , DNA Bacteriano/genética , Modelos Animais de Doenças , Escherichia coli/genética , Leucostasia/microbiologia , Camundongos , Músculo Esquelético/patologia , Necrose/microbiologia , Plasmídeos , Virulência , Fatores de Virulência/genéticaRESUMO
A hallmark of gas gangrene (clostridial myonecrosis) pathology is a paucity of leukocytes infiltrating the necrotic tissue. The cause of this paucity most likely relates to the observation of leukocyte aggregates at the border of the area of tissue necrosis, often within the microvasculature itself. Infecting mice with genetically manipulated strains of Clostridium perfringens type A (deficient in either alpha-toxin or theta-toxin production) resulted in significantly reduced leukocyte aggregation when alpha-toxin was absent and complete abrogation of leukocyte aggregation when theta-toxin was absent. Thus, both alpha-toxin and theta-toxin are necessary for the characteristic vascular leukostasis observed in clostridial myonecrosis.