Estudio de la interacción entre los marcadores de virulencia, perfil de resistencia y clones de alto riesgo en los modelos Caenorhabditis elegans y Galleria mellonella. Evaluación del valor predictivo como marcadores pronósticos en la bacteriemia por Pseudomonas aeruginosa

Abstract

Pseudomonas aeruginosa is a pathogen resistant to multiple types of antibiotics. Over the last decades this quality has led to an increase of nosocomial infections caused by MDR/XDR strains, being especially relevant those caused by so-called high-risk clones. These clones are spread worldwide, being ST175, ST111 and ST235 the most widespread nationally. This pathogen also has multiple virulence factors that contribute to the pathogenesis of infections (motility, pigments, toxin secretion systems, etc.). Previous studies have shown that high-risk clones mentioned above have been associated with a decrease of expression of motility, pigments, and fitness. In addition, a relationship between resistance profile, high-risk clones and T3SS genotype has been defined. Specifically, the T3SS exoU gene has been proposed as a relevant factor for mortality from P. aeruginosa bloodstream infections. Furthermore, in a murine model the presence of this gene in the ST235 clone was associated with high pathogenicity. However, mammalian models are not useful for the analysis of large collections. In this context, in recent decades, invertebrate models have proven to be valid for conducting these types of studies, given their experimental simplicity, low cost, and the absence of ethical issues. Accordingly, the first objective of this work was to examine whether this interaction was fulfilled in invertebrate infection models Caenorhabditis elegans and Galleria mellonella, evaluating the virulence of a 140 isolates collection, to subsequently evaluate the predictive value of lethality in C. elegans as a prognostic marker of bacteraemia caused by P. aeruginosa The results obtained allowed us to document in the C. elegans model a clear inverse relation between resistance and virulence of P. aeruginosa, showing the lowest virulence in the XDR profiles. However, virulence varied widely between high-risk clones MDR/XDR, as ST111 and ST235 were virulent, while ST175 were less so. Although, the loss of virulence could not be attributed to any mutation, the presence of a polymorphism in a gene was associated with increased virulence. The high virulence of ST235 could be attributed to the presence of the ExoU toxin in T3SS, related to the increased virulence in this model. Other factors, such as motility and pigment production, were not relevant for virulence in the C. elegans model. As regards the G.mellonella model, an inverse relationship between resistance and virulence was also documented. As in C. elegans model, ST175 showed variable virulence, while ST111 and ST235 clones were virulent; but, the variation in virulence of ST175 could not be attributed to any genetic change. Motility was the only virulence factor associated with the lethality of G. mellonella. While those independently associated with the virulence of P. aeruginosa were the ModR and MultiS profiles, and the epidemic origin of the isolates. As a consequence of the results obtained in C. elegans model, and in order to carry out the second objective which was to evaluate virulence in this model as a prognostic indicator, the study was extended with 593 P. aeruginosa bacteraemia strains. The results indicated that in C. elegans, the virulence phenotype was correlated with the resistance profile, the T3SS genotype and with certain clinical characteristics of the patients, with non-virulent phenotypes being associated with a greater severity of the disease. However, no relation was observed between virulence phenotype and patient’s mortality, indicating that C. elegans is not a good prognostic indicator for this type of infection.