Methods: The effect of E. coli ATCC 25922 biofilm supernatant on three different C. albicans strains (ATCC 90028, SC 5314, and a clinical strain) were studied using standard biofilm assay. Candida biofilms were developed on polystyrene surfaces and, filter sterilized 24h E. coli biofilm supernatant was added at 90 min. The effect of supernatant was assessed quantitatively at 24 and 48h by XTT reduction assay (XTT), and qualitatively, by Scanning Electron Microscopy (SEM) and Confocal Laser Scanning Microscopy (CLSM). RNA was extracted from both test and control Candida biofilms at 3h, 24h and 48h. Differential expression of hypha specific genes (HSGs); ECE1, HWP1, HYR1, RBT1, RBT4, ALS3 and ALS8 and the transcription factors; CPH1, CPH2, EFG1, TEC1, RAS1, TUP1, NRG1 and RFG1 were evaluated with Quantitative Real Time PCR (QRTPCR).
Results: XTT data showed that the metabolic activity of all three C. albicans biofilms were significantly inhibited by E. coli supernatant at 24 and 48h (p<0.05). SEM and CLSM further confirmed these data. More than 85% of QRTPCR data demonstrated significant results (p<0.05). HSGs demonstrated similar expression patterns, although RBT1 and RBT4 were mostly up-regulated and ECE1, HWP1 and HYR1 were mostly down-regulated. ALS3 was totally suppressed. However, at 48h, all HSGs were down-regulated. Transcription factors NRG1, RFG1 and EFG1; CPH1 and TEC1; TUP1 and CPH2 showed similar expression trends and all were down regulated in 48h biofilms. Expression of RBT1 and RBT4 correlated well with CPH1 and TEC1, and ECE1, HWP1 and HYR1 with TUP1, and HYR1 with CPH2. Conclusion: Yet to be described elements in E. coli Biofilm supernatants suppress C. albicans biofilm development by modulating HSGs and its transcription regulation pathways.(Supported by CERG#HKU-7624/06M)