Secretory products of Escherichia coli biofilm modulate Candida biofilm formation and hyphal development

Aim: To investigate the time-and concentration-dependent effects of Escherichia coli biofilm supernatant on Candida biofilm development, and to assess the effect of E. coli supernatant on Candida albicans hypha-specific genes (HSGs) expression. Methods: The effect of E. coli biofilm supernatant on six Candida spp. was assessed by tetrazolium salt (XTT) reduction assay, scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM). The effect of biofilm supernatant on the expression of C. albicans HSGs (ECE1, HWP1, HYR1, RBT1, RBT4, ALS3, and ALS8) and transcription factors (CPH1, CPH2, EFG1, TEC1, RAS1, TUP1, NRG1 and RFG1) was evaluated with real-time polymerase chain reaction (PCR). Results: Escherichia coli biofilm secretory products significantly inhibited C. albicans, C. glabrata, C. tropicalis and C. krusei biofilms at 24 h and all Candida spp. at 48 h (P < 0.05), and SEM and CLSM confirmed these data. HSGs RBT1 and RBT4 were mostly up-regulated and ECE1, HWP1 and HYR1 were mostly down-regulated. ALS3 was totally suppressed. All HSGs were down-regulated at 48 h (P < 0.05). NRG1, RFG1 and EFG1, CPH1 and TEC1, and TUP1 and CPH2 showed similar expression trends and all were downregulated at 48 h (P < 0.05). Conclusions: Escherichia coli secretory elements significantly impair Candida biofilm development possibly by modulating HSGs and its transcriptional regulation.