Objective To study the molecular epidemiology of C.albicans isolates in infectious disease patients and to explore biofilm phenotypic characterization responsible for biofilm formation in clinical strains.Methods A total of 104 hospital-acquired C.alibcans clinical isolates collected from sterile sites and mucosal lesions of 92 infectious disease patients ( viral hepatitis, tuberculosis and AIDS) in Shanghai Public Health Clinical Center were analyzed.MLST analysis was performed to identify their phylogenetic status.The capability of biofilm formation was measured by [2,3-bis-(2-methoxy-4-nitro-5-sulphenyl)-2H-tetrazolium-5-carboxanilide] XTT assay.The results were compared using Kruskal-Wallis test.Results MLST analysis identified 63 DSTs with a decentralized phylogeny among 104 C.albicans isolates, of which 41 DSTs (65.1%) had not been reported in the online MLST database.The Single Locus Sequence Query from the C.albicans database identified new alleles.MEGA6 analysis of the MLST data assigned the 104 isolates within 14 of the 18 known clades; among them the clade 1 contained the greatest proportion of isolates (26.9%).Of the 43 novel DSTs isolates, 37 ( 86.0%) clustered within 11 of the 18 known clades.16 high biofilm formers were found from a total of 104 clinical isolates.The biofilm formation capabilities differed in strains isolated from different anatomical sites (H =18.23,P=0.0326).Biofilm formation by blood-originated isolates was lower than that of catheter-originated isolates ( Z=-72.20,P<0.001).Genotypes also affected the biofilm formation capability of the C.albicans isolates (H=10.01,P=0.0185).Conclusions A high level of diversity within C.albicans isolates.Microevlution clearly influences C.albicans genetic alterations upon environmental selection.The site of isolation and genotype associates with the biofilm formation capability.