The ability to adhere to biotic and abiotic surfaces represents an essential trait during the early stages of microbial infection. Agglutinin like sequence (Als) cell-wall proteins play a key role in the adhesion of Candida species. In silico analysis led to identification of 5 ALS members in C. parapsilosis genome and 3 ALS members in C. orthopsilosis. The present PhD project was aimed at extending the current knowledge on the opportunistic pathogens C. parapsilosis and C. orthopsilosis, by dissecting the contribution of Als proteins through the generation of mutant strains using conventional gene disruption techniques (SAT1-flipper cassette) and gene editing approaches (episomal CRISPR/Cas9 system). Furthermore, an accurate genome assembly of C. orthopsilosis was generated providing a first insight into the ALS gene family in C. orthopsilosis and the basics for their functional characterization. Analysis of the phenotypic traits of the mutant strains generated in both species revealed an involvement of Als proteins in biofilm formation, adhesion on human buccal epithelial cells (HBECs) and in the pathogenic potential when tested in models of murine candidiasis.