Abstract
Candida albicans and Candida glabrata are two commonly seen opportunistic fungi in clinical settings and usually co-isolated from the population inflicted with denture stomatitis and oropharyngeal candidiasis. Although C. albicans and C. glabrata mixed biofilm is deemed to possess enhanced virulence compared with their individual counterparts (especially C. albicans single biofilm), the relevant descriptions and experimental evidence on the relationship of Candida virulence with their individual cell number in mixed biofilms are contradictory and insufficient. In this study, two standard C. glabrata isolate and eight C. albicans ones were used to test the cell quantities in their 24- and 48-h single and mixed biofilms. A series of virulence factors including antifungal resistance to caspofungin, secreted aspartic proteinase (SAP) and phospholipase (PL) levels, efflux pump function and β-glucan exposure were evaluated. Through this study, the declines of individual cell counting were observed in the 24- and 48-h Candida mixed biofilms compared with their single counterparts. However, the antifungal resistance to caspofungin, the SAP and phospholipase levels, the rhodamine 6G efflux and the efflux-related gene expressions were increased significantly or kept unchanged accompanying with reduced β-glucan exposure in the mixed biofilms by comparison with the single counterparts. These results reveal that there is a competitive interaction between C. albicans and C. glabrata strains in their co-culture without at the expense of the mixed biofilm virulence. This study presents a deep insight into the interaction between C. albicans and C. glabrata and provides new clues to combat against fungal infections caused by Candida mixed biofilms.
Highlights
Among the pathogenic fungi, Candida species are undoubtedly the major etiological agents that is capable of inducing a variety of uncomfortable or even deadly complications (Arendrup and Patterson, 2017)
When combining C. glabrata ATCC15126 with the eight C. albicans strains, whether at 24 or 48 h, the C. albicans cell populations in the single biofilms were all significantly higher than those in its mixed counterpart (Figure 1), and showed remarkable decrease in most cases compared with the entire cell number in the corresponding mixed biofilms except C. albicans Z2003 (48 h, Figure 1B), Z103 (24 h, Figure 1E), and Z3044 (24 and 48 h, Figure 1H)
These changes included that C. albicans SC5314 and Z3044 cell populations did not show advantages over the total cell number in the corresponding 24h mixed biofilms (Figures 2A,H), and the cell quantities of the 24-h C. albicans Z826 single biofilm and C. glabrata ATCC28226 single biofilm exhibited no significant difference compared with the individual C. albicans cell number and the gross cell counting of the corresponding mixed counterpart (Figure 2F)
Summary
Candida species are undoubtedly the major etiological agents that is capable of inducing a variety of uncomfortable or even deadly complications (Arendrup and Patterson, 2017). Some studies demonstrated that there was a synergism between C. albicans and C. glabrata, and what is more, the pre-colonization of C. albicans facilitated following proliferation of C. glabrata in their mixed biofilms (Pathak et al, 2012; Silva et al, 2013) This mutually beneficial collaboration might be largely due to the “complementary” morphologies as yeast-form C. glabrata can attach to C. albicans hyphae which promotes the fungal cells to penetrate mucosal surfaces of host tissue (Tati et al, 2016)
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