Variability of biofilm formation in Candida glabrata and Candida parapsilosis and its consequences on the infection process
by Emilia Gómez Molero
Date of Examination:2019-06-14
Date of issue:2019-08-30
Advisor:Dr. Oliver Bader
Referee:Prof. Dr. Uwe Groß
Referee:Prof. Dr. Gerhard Braus
Referee:Prof. Dr. Carsten G. K. Lüder
Referee:PD Dr. Michael Hoppert
Referee:Prof. Dr. Fabian Commichau
Referee:Prof. Dr. Kai Heimel
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Name:EGM-PhD-thesis-Emilia Gómez Molero-SUB-1-290719.pdf
Format:PDFDescription:The incidence of Candida species has increased in the last two decades, becoming the third to fourth most common cause of infections in hospitals. In general, Candida spp. are opportunistic pathogens found as commensals in the Gastrointestinal Tract (GI), the oral cavity, oral mucosa, vagina, or skin, without causing any symptoms or pathology. When the immune system is not stable, a preliminary colonization process of the skin or mucosa leads to life-threatening invasive candidiasis, sepsis, and eventually to death. Therefore, in this PhD thesis, we performed phenotypic and morphological analyses of two C. glabrata and C. parapsilosis clinical strain collections, to decipher how phenotypic and morphological differences will predetermine genome and cell wall proteome as a pathogenic strategy during host infection.
EnglishThe prevalence of Candida species has increased in the last two decades, becoming the third to fourth most common cause of infections in hospitals. In general, Candida spp. are opportunistic pathogens found as commensals in the Gastrointestinal Tract (GI), the oral cavity, oral mucosa, vagina, or skin, without causing any symptoms or pathology. When the immune system is altered (e.g. T-cell deficiencies in immunocompromised patients), a preliminary colonization process of the skin or mucosa (superficial candidiasis) may progress to life-threatening invasive candidiasis, sepsis, and eventually to death. Invasive Candidiasis (IC) has become a serious problem in the last years, affecting young and elderly population. Candida albicans is the most frequent cause of invasive candidiasis globally, but over the last decades non-Candida albicans Candida (NCAC) species have become more medically relevant. Candida spp. are able to exist inside the human host displaying different pathogenicity and antifungal drug resistance strategies. Most microbes, including NCAC species, usually constitute microbial communities encased in an extracellular polymeric substance forming biofilms on abiotic and biotic surfaces. Candida glabrata and Candida parapsilosis are the two most common causes of NCAC infections. Their relevance have been attributed to the ability to form biofilms on abiotic surfaces and the increased multidrug resistance capacity, together leading to different levels of pathogenicity. Both species display superficial, mucosal and systemic infections associated with abiotic devices, presenting clear morphologic and phenotypic differences between them. C. glabrata and C. parapsilosis belong to two different Candida clades, presenting differences at genomic and pathogenic level. The fungal cell wall is the outermost layer involved in host-pathogen recognition, cell structure, permeability, protection and virulence and the phylogenetic distance between both species is reflected by variations in cell wall composition including its proteome. In this study, we performed phenotypic and morphological analyses of two C. glabrata and C. parapsilosis clinical strain collections, to decipher how phenotypic and morphological differences will predetermine genome and cell wall proteome as a pathogenic strategy during host infection. Based on previous studies (de Groot et al., 2008 and Gabaldón et al. 2016), MS/MS analyses and Illumina genome sequence analyses of selected C. glabrata and C. parapsilosis clinical isolates will provide more information regarding cell wall constituents and genomic differences within NCAC clinical isolates. A high variability in phenotypic properties between isolates were found. In this study, we observed that C. glabrata showed a positive correlation between biofilm formation capacity, cell aggregation and cell sedimentation. In case of C. parapsilosis, biofilm formation capacity on abiotic surfaces was influenced by the colony morphotype. C. glabrata and C. parapsilosis proteome is highly variable and it has been divided in a core proteome and a unique variable proteome. Differences in the number of adhesins identified in the cell wall positively correlate with adhesion. Here, we observed that C. glabrata cell wall adhesins enable the co-interaction with C. albicans hyphae facilitating epithelia invasion. Differences in the variable proteome may also elucidate a high immunogenic heterogeneity as a possible host-defense mechanism. In C. parapsilosis, an increased number of adhesins identified in the cell wall correlates with “rough” and high biofilm-forming morphotypes. C. parapsilosis rough morphotypes presented azoles’ and caspofungin reduced-susceptibility, nevertheless, EUCAST-based antifungal susceptibility testing in the collection was not able to predict these variations. Rough morphologies in patient´s culture would be an indicator of biofilm´s presence to start echinocandins therapeutic treatment. Our studies proposed that phenotypic variations in C. glabrata and C. parapsilosis clinical isolates will predetermine differences at genomic and proteomic level. A reduced number of adhesins in the wall correlates with low biofilm-forming (LBF) isolates and high virulence capacity indicating that these morphologies will easily disseminate trough the bloodstream. Genome sequence analyses of selected C. glabrata isolates confirm the presence of deletions and duplications of cell wall adhesin-encoding genes as an important adaptive mechanism moving on from colonization to infection and dissemination.
Keywords: Candida glabrata; Candida parapsilosis; medical devices; biofilm formation; adhesins cell wall proteins; antifungal susceptibility; Mass spectrometry analyses; genome sequencing analyses; clinical isolates