Toxina Shiga-like e hemolisina TlyA em cepas de Corynebacterium diphtheriae: identificação, caracterização funcional e influência no potencial de virulência

Abstract

The clinical features observed in cases of classic diphtheria caused by Corynebacterium diphtheriae are associated with diphtheria toxin production (DT), its main virulence factor. However, non-DT-producing strains have been isolated from invasive infections. Recent studies have demonstrated the involvement of a multifactorial virulence mechanism expressed by C. diphtheriae strains. The analysis of the pangenome of this species identified the presence of 57 genomic islands, indicating that horizontal gene transfer is a strategy frequently used by corynebacteria to establish differences in pathogen-host interactions. Several studies indicate that the genes encoding Shiga toxin are transferable between species. In Corynebacterium ulcerans, the Rbp protein, similar to the A chain of Escherichia coli Shiga toxin (SLT-1), whose function is to inhibit the synthesis of ribosomes causing cell death, was previously identified. Additionally, genes encoding hemolysins, another important virulence factor, may cause cell damage through pore formation. The alpha-hemolysin (HlyA) genes from E. coli and other bacterial species are also capable of horizontal transfer. Some C. diphtheriae strains possibly produce specific hemolysins, as they are classified according to hemolytic activity. Genomic sequencing of C. diphtheriae biotype gravis NCTC 13129 strain identified the sequence of a hypothetical hemolysin-like protein (TlyA) from Mycobacterium tuberculosis. Therefore, the presence and expression of genes similar to Shiga-like toxins and hemolysin were demonstrated in different Corynebacterium species. Additionally, the following experiments for the investigation of phenotypic expression were performed: i) construction of mutant strains for the target genes: ii) gene expression by real-time PCR; iii) Vero cell cytotoxicity assays; iv) influence of environmental conditions on the expressions of these genes; v) arthritogenic potential using an animal model (murine). Data obtained through bioinformatics analysis showed that different Corynebacterium species presented genes that encode proteins with expressive homology to the toxins Rbp (Shiga-like toxin) and TlyA (hemolysin) toxins. Phenotypic assays verified the cytotoxic effects of these proteins on different C. diphtheriae strains. In conclusion, C. diphtheriae strains isolated from cases of diphtheria and/or invasive infections may also utilize the production of TlyA hemolysin and Shiga-like toxin in the strain-dependent mechanisms of pathogenicity. Additional studies related to these virulence factors remain ongoing for both C. diphtheriae and other clinically relevant corynebacteria