Resumen de Study of the cytotoxic activity and immunogenicity of the differentiated morphotypes of the genus mycobacterium, in relation with their cell wall composition
Mycobacterium is a genus of microorganisms that comprise important human pathogens, such as the etiological agent of tuberculosis, Mycobacterium tuberculosis. Many mycobacterial species present two differentiated morphotypes, the rough (R) one characterized by bacillar organization in structures that reassemble cords; and the smooth (S) one without any bacillar aggregation. In pathogenic mycobacteria, R morphotypes are shown to produce more severe illnesses in infected patients than S morphotypes. In fact, this relationship between virulence and cord formation is known since 1947. Studying how bacteria aggregate will help to understand the different virulence associated to the two morphotypes of mycobacteria.
The thesis here presented consists on the study of the cytotoxicity and immunogenicity of these two differentiated morphotypes, the R with a cording phenotype and the S with a non-cording phenotype, in Mycobacterium abscessus and Mycobacterium vaccae. And, in the case of M. abscessus, how these effects in virulence and the cord formation can be related to its cell wall composition.
The two morphotypes of M. abscessus were used to infect human alveolar epithelial cells, and the ones from M. vaccae, in murine macrophages. The results, in both cases, showed that R morphotypes have major effect in suppressing cellular growth and a higher capacity to trigger cytokine production than S morphotypes.
Superficial lipidic extractions were performed in M. abscessus, as the virulence and the cord formation might be related with the expression of determinate external cell wall components. Trehalose polyphleates (TPP) were identified in the superficial extracts from R morphotypes of M. abscessus, but TPP were absent in S morphotype extracts. Although this compound was not cytotoxic for human and murine cells, TPP presented aggregative potential.
When analyzing the superficial expression of TPP in other mycobacterial species, another superficial compound, mycolate ester wax, was detected in Mycobacterium smegmatis, with a similar migration pattern to TPP. In this work, this compound was clearly characterized as pentatriacontatrienyl mycolate, as some uncertainties regarding its structure were previously reported.
In conclusion, R morphotypes from M. abscessus and M. vaccae produced a major cytotoxic effect and major immunogenicity that S morphotypes in cell-based in vitro models. In the case of M. abscessus, this major virulence was accompanied with the superficial expression of TPP, a compound with aggregative properties. These last results point TPP as candidate molecules responsible for the cord formation in R morphotypes of M. abscessus.
