Abstract

Fungi of the genus Candida belong to the natural microflora of healthy individuals. However, they can also be a cause of opportunistic infections especially among patients with an impaired immune system. The first line therapy of Candida infections is based on triazoles. However, in recent years there an increase of azole resistant Candida spp., in particular C. glabrata and C. krusei, has been observed. For this reason, echinocandin drugs are increasingly being used. Epidemiological studies conducted around the world indicate a low level of Candida resistance to echinocandins. However, echinocandin resistance for C. glabrata is still increasing and in 2015 it was estimated to be over 13%. In the presented PhD dissertation, the echinocandin susceptibility tests was performed for the first time on a microdilution broth of 242 Candida isolates collected from Polish hospitals, and resulted in the finding that 6.6% of isolates are echinocandin resistant. Moreover, the molecular mechanism was investigated by the examination of the mutations occurring in the FKS1 gene encoding the glucan synthase – the molecular target of echinocandin. The FKS1 gene mutation (T4072C) that contributes to echinocandin resistance has been identified in single C. albicans and C. inconspicua isolates. Another part of this research was to investigate the influence of anidulafungin and micafungin exposure to the susceptibility to echinocandin and the expression level of CHS1, CRZ1, CRZ2, UTR2 and HSP90 genes. Anidulafungin exposure cause the overexpression of CHS1 and CRZ2. After the exposure of anidulafungin and then the removal of this compound from the medium the expression level of CHS1, UTR2 and CRZ1 was higher than the initial expression of these genes. The pathogenicity of Candida isolates was also tested using Galleria mellonella larvae as the host organism. The obtained results were compared with the enzymatic activity of different virulence factors. Mortality of G. mellonella larvae infected with different Candida species was distinguished between virulent and non-virulent phenotypes. C. albicans were the most pathogenic species and produced the highest amount of virulence factors, while most C. parapsilosis isolates were avirulent. The pathogenicity of Candida isolates examined in G. mellonella larvae is correlated with protease, haemolysins and esterase activity among Candida clinical isolates.

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