Production of farnesol in Candida albicans biofilms of resistant and standard strains in different media

Objective To compare the production of farnesol between Candida albicans (C. albicans) biofilms formed by resistant and standard strains in different media, and to investigate the changing trend of farnesol production in different phases of biofilm formation and the features of farnesol production by resistant C. albicans. Methods Fluconazole-resistant C. albicans strains were induced in vitro. Standard strains and fluconazole-resistant strains of C. albicans were separately inoculated onto different media, including RPMI 1640 medium, yeast extract peptone dextrose (YPD) medium, yeast nitrogen base (YNB) + 0.5% glucose medium, RPMI 1640 + 10% fetal calf serum (FCS) , so as to form C. albicans biofilms. Morphological changes of C. albicans biofilms at 24 hours were observed under an inverted microscope, and gas chromatography-mass spectrometry (GC/MS) was performed to detect the level of farnesol at 1.5, 3, 6, 12, 24, 36 and 48 hours. Results There were no obvious differences in the morphology of C. albicans biofilms between the resistant and standard strains when they were cultured in the same medium, while the morphology of C. albicans biofilms markedly differed between the 2 kinds of strains in the different media. Three-factor analysis of variance showed that the production of farnesol in the C. albicans biofilms changed over time (F= 70.628, P < 0.001) . Concretely speaking, during the formation of resistant and standard C. albicans biofilms, the production of farnesol gradually increased in the RPMI 1640, YPD and YNB+ 0.5% glucose media until the biofilms matured, then showed a decreasing trend. However, the time to peak levels of farnesol was different between the 2 kinds of strains in these media. Moreover, the levels of farnesol in the 2 kinds of strains both slowly increased in the RPMI 1640+ 10% FCS medium within 12-48 hours. Culture media also significantly affected the production of farnesol (F= 176.665, P < 0.001) , and the levels of farnesol in the resistant and standard C. albicans biofilms were both higher in the YNB+ 0.5% glucose medium. When resistant and standard strains were separately cultured in the RPMI 1640 media and the YPD media, the level of farnesol was significantly higher in the resistant strains than in the standard stains (RPMI 1640 media at 36 hours: 1.157 ± 0.064 vs. 0.250 ± 0.075, P < 0.05; YPD media at 6 hours: 0.262 ± 0.036 vs. 0.055 ± 0.062, P < 0.05; YPD media at 12 hours: 0.730 ± 0.030 vs. 0.482 ± 0.024, P < 0.05) . However, when they were separately cultured in the YNB+ 0.5% glucose media, the farnesol level was significantly higher in the standard stains than in the resistant strains (36 hours: 2.950 ± 0.677 vs. 0.523 ± 0.266, P= 0.020) . Conclusion The media markedly affect the production of farnesol in the C. albicans biofilms, and there is a certain difference in the production of farnesol between resistant and standard C. albicans strains. Key words: Candida albicans; Biofilms; Drug resistance, fungal; Farnesol; Culture media; Gas chromatography-mass spectrometry