Isolation Of Candida Albicans Strains From Different Origins And Analysis Their Virulence

The fungus Candida albicans is both a commensal and pathogenic microbe to human and animals. It can cause not only superficial infections, but also life-threatening systemic disease in immunocompromised individuals. With the increase of immunocompromised individuals, organ transplantation and application of broad-spectrum antibiotics and indwelling devices, invasive candidiasis has become a serious health problem. With the use of antifungal agents, the phenomenon that C. albicans resistant to one or more antifungal drug is increasing, the in vitro drug sensitivity test plays an increasingly important role in guiding the rational use of drugs as well as the detection the trends of pathogenic fungi resistant to drugs.Despite the prevalence and consequences of severe candidiasis, its pathogenesis has not yet been elaborated. The objectives of this study were to isolation C. albicans strains from different origins and analysis their virulence and phenotypic characteristics. The isolates screened with significant different virulence can be used to study the pathogenesis of C. albicans. In addition, the chicken model used in this study mimic the host-pathogen interactions better, contributed to understand the co-evolution of C. albicans and host as well as elucidate the pathogenesis of C. albicans. This experiment includes next parts:1. Isolation of C. albicans strains from different origins and in vitro drug sensitivity testIn this study, 100 C. albicans strains were isolated using the Candida chromogenic media and 5.8S-ITS analysis. The results of in vitro drug sensitivity test showed that C. albicans isolates were sensitive to 5-fluorocytosine and fluconazole(sensitivity rate was95.2 % and 100 %, respectively); while the sensitive rate to amphotericin B was only 59.5 %,and the resistant rate to amphotericin B was 19.0 %.2. Analysis the virulence of isolatesThe virulence of isolates were studyed using murine model based on survival and kidney fungal burden. The results showed that virulence varied across the isolates. Among the isolates, the isolate J1(chicken origin) with the strongest virulence while the weakest virulentstrain was isolate G2(dove origin). Considering the different host may influence the consequences of host-pathogen interaction, we used chicken and dove model to re-value the virulence of isolates J1 and G2 and obtained the same results. That is to say, we succeed in screening two isolates(J1 and G2) with significant different virulence.3. Phenotypic and genetic characteristics analysisPhenotypic characteristics, such as response to stress, and expression level of some virulence-associated genes(ALS1, ALS3, HWP1, EFG1, HSP90 and SAP1-6) were evaluated in the isolates J1 and G2. The results showed that most phenotypic characterization were indistinguishable between J1 and G2 other than resistance to cell wall stress induced by Congo Red. The more susceptible to Congo Red suggested the poor integrity of cell wall that make isolate G2 more easier to be cleared by the host immune system, thereby resulting the reduced virulence. In addition, 24 h and/or 48 h post infection, most genes’ expression level of J1 was higher(≥1.5 fold) than those of G2, except for HSP90, SAP1, SAP4 and SAP6. The up-regulation of ALS1, ALS3, HWP1 and EFG1 in vivo could partly account for the observed differences in virulence. The expression level of SAP5 in J1 was obvious higher than G2 both24 h and 48 h p.i., suggesting that Sap5 may contribute to the virulence. In contrast, the SAP1 and SAP4 was down-regulated in G2, suggesting that a certain degree of functional redundancy may exist in SAP family.