Role of Force-Sensitive Amyloid-Like Interactions in Fungal Catch Bonding and Biofilms

The Candida albicans Als adhesin Als5p has an amyloid-forming sequence that is required for aggregation and formation of model biofilms on polystyrene. Because amyloid formation can be triggered by force, we investigated whether laminar flow could activate amyloid formation and increase binding to surfaces. Shearing Saccharomyces cerevisiae cells expressing Als5p or C. albicans at 0.8 dyne/cm² increased the quantity and strength of cell-to-surface and cell-to-cell binding compared to that at 0.02 dyne/cm². Thioflavin T fluorescence showed that the laminar flow also induced adhesin aggregation into surface amyloid nanodomains in Als5p-expressing cells. Inhibitory concentrations of the amyloid dyes thioflavin S and Congo red or a sequence-specific anti-amyloid peptide decreased binding and biofilm formation under flow. Shear-induced binding also led to formation of robust biofilms. There was less shear-activated increase in adhesion, thioflavin fluorescence, and biofilm formation in cells expressing the amyloid-impaired V326N-substituted Als5p. Similarly, S. cerevisiae cells expressing Flo1p or Flo11p flocculins also showed shear-dependent binding, amyloid formation, biofilm formation, and inhibition by anti-amyloid compounds. Together, these results show that laminar flow activated amyloid formation and led to enhanced adhesion of yeast cells to surfaces and to biofilm formation.     

Quantitative Analyses of Force-Induced Amyloid Formation in Candida albicans Als5p: Activation by Standard Laboratory Procedures

Candida albicans adhesins have amyloid-forming sequences. In Als5p, these amyloid sequences cluster cell surface adhesins to create high avidity surface adhesion nanodomains. Such nanodomains form after force is applied to the cell surface by atomic force microscopy or laminar flow. Here we report centrifuging and resuspending S. cerevisiae cells expressing Als5p led to 1.7-fold increase in initial rate of adhesion to ligand coated beads. Furthermore, mechanical stress from vortex-mixing of Als5p cells or C. albicans cells also induced additional formation of amyloid nanodomains and consequent activation of adhesion. Vortex-mixing for 60 seconds increased the initial rate of adhesion 1.6-fold. The effects of vortex-mixing were replicated in heat-killed cells as well. Activation was accompanied by increases in thioflavin T cell surface fluorescence measured by flow cytometry or by confocal microscopy. There was no adhesion activation in cells expressing amyloid-impaired Als5p^V326N or in cells incubated with inhibitory concentrations of anti-amyloid dyes. Together these results demonstrated the activation of cell surface amyloid nanodomains in yeast expressing Als adhesins, and further delineate the forces that can activate adhesion in vivo. Consequently there is quantitative support for the hypothesis that amyloid forming adhesins act as both force sensors and effectors.     

Candida albicans Als adhesins have conserved amyloid-forming sequences

The cell wall-bound Als adhesins of Candida albicans mediate both yeast-to-host tissue adherence and yeast aggregation. This aggregation is amyloid-like, with self-propagating secondary-structure changes, amyloid-characteristic dye binding, and induced birefringence (J. M. Rauceo, N. K. Gaur, K. G. Lee, J. E. Edwards, S. A. Klotz, and P. N. Lipke, Infect. Immun. 72:4948-4955, 2004). Therefore, we determined whether Als proteins could form amyloid fibers with properties like those in cellular aggregation. The beta-aggregation predictor TANGO identified a heptapeptide sequence present in a highly conserved sequence with amyloid-forming potential in Als1p, Als3p, and Als5p. A tridecapeptide containing this sequence formed fibers that bound Congo red and thioflavin T and had characteristic amyloid morphology. Als5p(20-431) and Als5p(20-664), large fragments of Als5p containing the amyloid sequence, also formed amyloid-like fibers and bound Congo red under native conditions. K(a)/K(s) analysis showed that the amyloid-forming sequences are highly conserved in Als proteins and evolve more slowly than other regions of the proteins. Therefore, amyloid-forming ability itself is conserved in these proteins.     

Peptide Detection of Fungal Functional Amyloids in Infected Tissue

Many fungal cell adhesion proteins form functional amyloid patches on the surface of adhering cells. The Candida albicans Agglutinin-like sequence (Als) adhesins are exemplars for this phenomenon, and have amyloid forming sequences that are conserved between family members. The Als5p amyloid sequence mediates amyloid fibril formation and is critical for cell adhesion and biofilm formation, and is also present in the related adhesins Als1p and Als3p. We have developed a fluorescent peptide probe containing the conserved Als amyloid-forming sequence. This peptide bound specifically to yeast expressing Als5p, but not to cells lacking the adhesin. The probe bound to both yeast and hyphal forms of C. albicans. Δals1/Δals3 single and double deletion strains exhibited reduced fluorescence, indicating that probe binding required expression of these proteins. Additionally, the Als peptide specifically stained fungal cells in abscesses in autopsy sections. Counterstaining with calcofluor white showed colocalization with the amyloid peptide. In addition, fungi in autopsy sections derived from the gastrointestinal tract showed colocalization of the amyloid-specific dye thioflavin T and the fluorescent peptide. Collectively, our data demonstrate that we can exploit amyloid sequence specificity for detection of functional amyloids in situ.     

Threonine-rich repeats increase fibronectin binding in the Candida albicans adhesin Als5p

Commensal and pathogenic states of Candida albicans depend on cell surface-expressed adhesins, including those of the Als family. Mature Als proteins consist of a 300-residue N-terminal region predicted to have an immunoglobulin (Ig)-like fold, a 104-residue conserved Thr-rich region (T), a central domain of a variable number of tandem repeats (TR) of a 36-residue Thr-rich sequence, and a heavily glycosylated C-terminal Ser/Thr-rich stalk region, also of variable length (N. K. Gaur and S. A. Klotz, Infect. Immun. 65: 5289-5294, 1997). Domain deletions in ALS5 were expressed in Saccharomyces cerevisiae to excrete soluble protein and for surface display. Far UV circular dichroism indicated that soluble Ig-T showed a single negative peak at 212 nm, consistent with previous data indicating that this region has high beta-sheet content with very little alpha-helix. A truncation of Als5p with six tandem repeats (Ig-T-TR(6)) gave spectra with additional negative ellipticity at 200 nm and, at 227 to 240 nm, spectra characteristic of a structure with a similar fraction of beta-sheet but with additional structural elements as well. Soluble Als5p Ig-T and Ig-T-TR(6) fragments bound to fibronectin in vitro, but the inclusion of the TR region substantially increased affinity. Cellular adhesion assays with S. cerevisiae showed that the Ig-T domain mediated adherence to fibronectin and that TR repeats greatly increased cell-to-cell aggregation. Thus, the TR region of Als5p modulated the structure of the Ig-T region, augmented cell adhesion activity through increased binding to mammalian ligands, and simultaneously promoted fungal cell-cell interactions.     

Separate Molecular Determinants in Amyloidogenic and Antimicrobial Peptides

Several amyloid-forming and antimicrobial peptides (AMYs and AMPs) have the ability to bind to and damage cell membranes. In addition, some AMYs possess antimicrobial activity and some AMPs form amyloid-like fibrils, relating the two peptide types and their properties. However, a comparison of their sequence characteristics reveals important differences. The high β-strand and aggregation propensities typical of AMYs are largely absent in α-helix-forming AMPs, which are instead marked by a strong amphipathic moment not generally found in AMYs. Although a few peptides, for example, islet amyloid polypeptide and dermaseptin S9, combine some determinants of both groups, the structural distinctions suggest that antimicrobial activity and amyloid formation are separate features not generally associated.     

Role of aromatic interactions in amyloid formation by peptides derived from human Amylin

Numerous polypeptides and proteins form amyloid deposits in vivo or in vitro. The mechanism of amyloid formation is not well-understood particularly in the case where unstructured polypeptides assemble to form amyloid. Aromatic-aromatic interactions are known to be important in globular proteins, and the possibility that they might play a key role in amyloid formation has been raised. The results of Ala-scanning experiments on short polypeptides derived from Amylin have suggested that aromatic interactions could be particularly important for this system. Here, we examine a set of Amylin-derived polypeptides in which the single aromatic residue has been substituted with a Leu and Ala. A peptide corresponding to residues 21-29 with a Phe-23 to Leu substitution, a free N terminus, and amidated C terminus readily forms amyloid. Shorter peptides derived from the putative minimal amyloid-forming segment of Amylin, residues 22-27, also form amyloid when Phe-23 is replaced by Leu. Amyloid formation is more facile when the N terminus is deprotonated and the peptide is uncharged. Substitution of the Phe with Ala results in a peptide that is noticeably less prone to form amyloid. A peptide corresponding to residues 10-19 of human Amylin with blocked termini and the sole aromatic residue, Phe-15, substituted by Leu readily forms amyloid. A Phe-15 to Ala substitution reduces significantly the ability to form amyloid. These results indicate that an aromatic residue is not required for amyloid formation in these systems and indicates that other factors such as size, beta-sheet propensity, and hydrophobicity of the side chain in question are also important.     

Enrichment of amyloidogenesis at an air-water interface

The aggregation of proteins or peptides into amyloid fibrils is a hallmark of protein misfolding diseases (e.g., Alzheimer's disease) and is under intense investigation. Many of the experiments performed are in vitro in nature and the samples under study are ordinarily exposed to diverse interfaces, e.g., the container wall and air. This naturally raises the question of how important interfacial effects are to amyloidogenesis. Indeed, it has already been recognized that many amyloid-forming peptides are surface-active. Moreover, it has recently been demonstrated that the presence of a hydrophobic interface can promote amyloid fibrillization, although the underlying mechanism is still unclear. Here, we combine theory, surface property measurements, and amyloid fibrillogenesis assays on islet amyloid polypeptide and amyloid-β peptide to demonstrate why, at experimentally relevant concentrations, the surface activity of the amyloid-forming peptides leads to enriched fibrillization at an air-water interface. Our findings indicate that the key that links these two seemingly different phenomena is the surface-active nature of the amyloid-forming species, which renders the surface concentration much higher than the corresponding critical fibrillar concentration. This subsequently leads to a substantial increase in fibrillization.     

Characterizing the role of cell-wall β-1,3-exoglucanase Xog1p in Candida albicans adhesion by the human antimicrobial peptide LL-37

Candida albicans is the major fungal pathogen of humans. Its adhesion to host-cell surfaces is the first critical step during mucosal infection. Antimicrobial peptides play important roles in the first line of mucosal immunity against C. albicans infection. LL-37 is the only member of the human cathelicidin antimicrobial peptide family and is commonly expressed in various tissues, including epithelium. We previously showed that LL-37 significantly reduced C. albicans adhesion to plastic, oral epidermoid OECM-1 cells, and urinary bladders of female BALB/c mice. The inhibitory effect of LL-37 on cell adhesion occurred via the binding of LL-37 to cell-wall carbohydrates. Here we showed that formation of LL-37-cell-wall protein complexes potentially inhibits C. albicans adhesion to polystyrene. Using phage display and ELISA, we identified 10 peptide sequences that could bind LL-37. A BLAST search revealed that four sequences in the major C. albicans cell-wall β-1,3-exoglucanase, Xog1p, were highly similar to the consensus sequence derived from the 10 biopanned peptides. One Xog1p-derived peptide, Xog1p(90-115), and recombinant Xog1p associated with LL-37, thereby reversing the inhibitory effect of LL-37 on C. albicans adhesion. LL-37 reduced Xog1p activity and thus interrupted cell-wall remodeling. Moreover, deletion of XOG1 or another β-1,3-exoglucanase-encoding gene EXG2 showed that only when XOG1 was deleted did cellular exoglucanase activity, cell adhesion and LL-37 binding decrease. Antibodies against Xog1p also decreased cell adhesion. These data reveal that Xog1p, originally identified from LL-37 binding, has a role in C. albicans adhesion to polystyrene and, by inference, attach to host cells via direct or indirect manners. Compounds that target Xog1p might find use as drugs that prevent C. albicans infection. Additionally, LL-37 could potentially be used to screen for other cell-wall components involved in fungal cell adhesion.     

Yeast Cell Adhesion Molecules Have Functional Amyloid-Forming Sequences

The occurrence of highly conserved amyloid-forming sequences in Candida albicans Als proteins (H. N. Otoo et al., Eukaryot. Cell 7:776–782, 2008) led us to search for similar sequences in other adhesins from C. albicans and Saccharomyces cerevisiae. The β-aggregation predictor TANGO found highly β-aggregation-prone sequences in almost all yeast adhesins. These sequences had an unusual amino acid composition: 77% of their residues were β-branched aliphatic amino acids Ile, Thr, and Val, which is more than 4-fold greater than their prevalence in the S. cerevisiae proteome. High β-aggregation potential peptides from S. cerevisiae Flo1p and C. albicans Eap1p rapidly formed insoluble amyloids, as determined by Congo red absorbance, thioflavin T fluorescence, and fiber morphology. As examples of the amyloid-forming ability of the native proteins, soluble glycosylphosphatidylinositol (GPI)-less fragments of C. albicans Als5p and S. cerevisiae Muc1p also formed amyloids within a few days under native conditions at nM concentrations. There was also evidence of amyloid formation in vivo: the surfaces of cells expressing wall-bound Als1p, Als5p, Muc1p, or Flo1p were birefringent and bound the fluorescent amyloid-reporting dye thioflavin T. Both of these properties increased upon aggregation of the cells. In addition, amyloid binding dyes strongly inhibited aggregation and flocculation. The results imply that amyloid formation is an intrinsic property of yeast cell adhesion proteins from many gene families and that amyloid formation is an important component of cellular aggregation mediated by these proteins.Protein amyloids are characteristic of pathological conditions, including neurodegenerative diseases (4, 11, 17, 38). These protein aggregates can also occur naturally in adhesive bacterial curli (3), melanosomes (14), condensed peptide hormone arrays (24), as regulatory prions in yeast (2, 5), and fungal hydrophobins, which are nonantigenic coats to some fungi (1, 33, 39). Nevertheless, such natural occurrences are relatively few, considering the negative free energy for amyloid formation (28).We have recently discovered that there are amyloid-forming sequences in the cell surface Als adhesins of Candida albicans. Cells that express these adhesins aggregate readily, and the aggregation has amyloid-like properties, including protein conformational shifting, surface birefringence, and ability to bind the amyloid-active dyes Congo red and amino-naphthalene sulfonic acid (ANS) (29). A five- to seven-residue sequence in Als1p, Als3p, and Als5p has extremely high potential for formation of β-aggregates, according to the protein state prediction program TANGO (13, 27, 31). Such β-aggregates include amyloids, which are ordered structures with paracrystalline regions of stacked parallel β-strands that are perpendicular to the long axis of micrometer-long fibrils. The strands are stabilized by interaction of identical sequences from many protein molecules (31, 32). Where TANGO analyses have shown that specific sequences have β-aggregate potentials greater than 20%, an insoluble β-aggregate state is likely to form. These β-aggregates nucleate formation of amyloids if the proteins can associate to form fibers (13, 27, 31). Sequences in the conserved 127-residue T region of Als1p, Als3p, and Als5p have β-aggregation potentials of >90% (27). An oligopeptide with this sequence, as well as 412- and 645-residue fragments of Als5p formed authentic amyloids, as determined by characteristic dye binding and fiber morphology. The amyloid-forming sequences were rich in the β-branched amino acids Thr, Val, and Ile. This amino acid composition is unusual among proteins in general, but is common in the Thr-rich mid-piece domains of yeast adhesins.Yeasts display many cell-wall-bound adhesins that mediate colonial and biofilm interactions as well as host-pathogen binding (9, 21, 41). Such adhesins have a common mosaic structure. In general, the adhesins have N-terminal globular binding domains (often immunoglobulin-like or lectin-like), Thr-rich mid-piece sequences including tandem repeats, and 300- to 800-residue heavily glycosylated Ser and Thr-rich “stalk” domains near the C-terminal domain that extend the active regions from the surface of the wall. The adhesins are covalently cross-linked to wall polysaccharides through modified glycosylphosphatidylinositol (GPI) anchors and/or glycosyl esters of glutamic acid (9, 18).Because the yeast adhesins share this common modular domain structure, we searched among known and putative yeast adhesins for sequences with high β-aggregation potential. We have found that many of these proteins share amyloid-forming sequences and amyloid-like behavior on activation.     

The broad-spectrum antibiofilm activity of amyloid-forming hexapeptides

Evidence suggests that short amyloid-forming peptides derived from bacterial proteomes have functional roles; however, the reported activities are diverse and the underlying mechanisms remain unclear. In this study, we simulated short amyloid-forming peptides from the amyloid-forming truncated protein C123 of Streptococcus mutans (S. mutans), studied their biological functions in microbial proliferation and biofilm formation, and further investigated the underlying mechanism. Fourteen hexapeptides were simulated, 13 of which were successfully synthesized. We found that the amyloid-forming hexapeptides (AFhPs) displayed efficient broad-spectrum antibiofilm activity against the Gram-positive bacteria S. mutans, Streptococcus sanguis and Staphylococcus aureus, Gram-negative bacteria Escherichia coli and fungus Candida albicans, by aggregating into rigid amyloid fibres agglutinating microbes, whereas the non-amyloid-forming hexapeptides (non-AFhPs) did not. The AFhPs did not kill microbes and showed little or no cytotoxicity. Furthermore, a set of AFhPs displayed broad-spectrum antibiofilm activity, regardless of its source. The microbial cell wall carbohydrates, peptidoglycan (PGN), lipoteichoic acid (LTA), glucan and zymosan A, mediated AFhP binding and triggered significant AFhP fibrillation. Although amyloid fibres agglutinated lipid membrane model – large unilamellar vesicles (LUVs) – and LUVs facilitated AFhP fibrillation, the roles of lipid membranes in AFhP antibiofilm activities remain to be elucidated. We highlight the potential use of AFhPs as novel antibiofilm agents.     

Candida albicans and Saccharomyces cerevisiae expressing ALA1/ALS5 adhere to accessible threonine,serine, or alanine patches

Saccharomyces cerevisiae transformed with Candida albicans ALA1/ALS5 exhibits adherence properties similar to C. albicans. Adherence of the fungi to immobilized proteins involves hydrogen bonds, is stable to shear forces, and is resistant to competition from various biological molecules. The specificity determinants of target recognition in Ala1/Als5p-mediated adherence are not known. To determine features of target recognition, proteins and small peptides were covalently coupled at the N-terminus to the surface of carboxylate-modified magnetic beads. C. albicans yeast cells, germ tubes and pseudohyphae and S. cerevisiae expressing the adhesin, Ala1/Als5p, adhered to beads coated with fibronectin, laminin, type IV collagen, bovine serum albumin, and casein. No adherence to beads was observed if a single amino acid was coupled to the beads. However, 10-mer homopolymers of threonine, serine, and alanine served as ligands for adherence. The presence of a minimum of four contiguous threonine residues in a peptide was required for maximal adherence. Coupling of 10-mer peptides from fibronectin and Ala1/Als5p each possessing 5-7 threonine or serine residues also initiated adherence. On the other hand, a collagen and a fibronectin 10-mer peptide with few threonine and serine residues and lysine at the C-terminus did not serve as adherence ligands. Both of them are converted to adherence ligands by adding threonine or serine residues at the C-terminus or removing the lysine residue and adding threonine residues anywhere in the peptide. The presence of lysine at the C-terminus may have resulted in coupling of the peptides at both the N- and C-termini, thus making the threonine residues inaccessible for adherence. Thus, Ala1/Als5p recognizes patches of certain amino acids, which must be accessible before adherence will occur.     

Molecular Dynamics Simulations to Investigate the Structural Stability and Aggregation Behavior of the GGVVIA Oligomers Derived from Amyloid β Peptide

Abstract

Several neurodegenerative diseases, such as Alzheimer's, Parkinson's, and Huntington's dis-eases, are associated with amyloid fibrils formed by different polypeptides. Recently, the atomic structure of the amyloid-forming peptide GGVVIA from the C-terminal hydrophobic segment of amyloid-β (Aβ) peptide has been determined and revealed a dry, tightly self-com-plementing structure between two β-sheets, termed as “steric zipper”. In this study, several all-atom molecular dynamics simulations with explicit water were conducted to investigate the structural stability and aggregation behavior of the GGVVIA oligomers with various sizes. The results of our single-layer models suggested that the structural stability of the GGVVIA oligomers increases remarkably with increasing the numbers of β-strands. We fur-ther identified that SH2-ST2 may act as a stable seed in prompting amyloid fibril formations. Our results also demonstrated that hydrophobic interaction is the principle driving force to stabilize and associate the GGVVIA oligomers between β-strands; while the hydrophobic steric zipper formed via the side chains of V3, V4, and I5 plays a critical role in holding the two neighboring β-sheets together. Single glycine substitution at V3, V4, and I5 directly disrupted the hydrophobic steric zipper between these two β-sheets, resulting in the destabili-zation of the oligomers. Our simulation results provided detailed insights into understanding the aggregation behavior of the GGVVIA oligomers in the atomic level. It may also be help-ful for designing new inhibitors able to prevent the fibril formation of Aβ peptide.     

Complementary adhesin function in C. albicans biofilm formation

BACKGROUND: Biofilms are surface-associated microbial communities with significant environmental and medical impact. Here, we focus on an adherence mechanism that permits biofilm formation by Candida albicans, the major invasive fungal pathogen of humans. RESULTS: The Als surface-protein family has been implicated in biofilm formation, and we show that Als1 and Als3 have critical but redundant roles. Overexpression of several other Als proteins permits biofilm formation in a biofilm-defective als1/als1 als3/als3 strain, thus arguing that the function of Als proteins in this process is governed by their respective expression levels. The surface protein Hwp1 is also required for biofilm formation, and we find that a mixture of biofilm-defective hwp1/hwp1 and als1/als1 als3/als3 strains can form a hybrid biofilm both in vitro and in vivo in a catheter infection model. Complementary function of Hwp1 and Als1 and 3 seems to reflect their interaction because expression of Hwp1 in the heterologous host S. cerevisiae permits adherence to wild-type C. albicans, but not to an als1/als1 als3/als3 strain. CONCLUSIONS: The complementary roles of Hwp1 and Als1 and Als3 in biofilm formation are analogous to the roles of sexual agglutinins in mating reactions. This analogy suggests that biofilm-adhesin complementarity may promote formation of monospecies biofilms.     

Characterizations of distinct amyloidogenic conformations of the Abeta (1-40) and (1-42) peptides

Major constituents of the amyloid plaques found in the brain of Alzheimer's patients are the 39-43 residue beta-amyloid (Abeta) peptides. Extensive in vitro as well as in vivo biochemical studies have shown that the 40- and 42-residue Abeta peptides play major roles in the neurodegenerative pathology of Alzheimer's disease. Although the two Abeta peptides share common aggregation properties, the 42-residue peptide is more amyloidogenic and more strongly associated with amyloid pathology. Thus, characterizations of the two Abeta peptides are of critical importance in understanding the molecular mechanism of Abeta amyloid formation. In this report, we present combined CD and NMR studies of the monomeric states of the two peptides under both non-amyloidogenic (<5 degrees C) and amyloid-forming conditions (>5 degrees C) at physiological pH. Our CD studies of the Abeta peptides showed that initially unfolded Abeta peptides at low temperature (<5 degrees C) gradually underwent conformational changes to more beta-sheet-like monomeric intermediate states at stronger amyloidogenic conditions (higher temperatures). Detailed residue-specific information on the structural transition was obtained by using NMR spectroscopy. Residues in the N-terminal (3-12) and 20-22 regions underwent conformational changes to more extended structures at the stronger amyloidogenic conditions. Almost identical structural transitions of those residues were observed in the two Abeta peptides, suggesting a similar amyloidogenic intermediate for the two peptides. The 42-residue Abeta (1-42) peptide was, however, more significantly structured at the C-terminal region (39-42), which may lead to the different aggregation propensity of the two peptides.     

Adherence and biofilm formation of non-Candida albicans Candida species

Most cases of candidosis have been attributed to Candida albicans, but recently non-C. albicans Candida species have been identified as frequent human pathogens. Candida pathogenicity has been attributed to several factors, including adhesion to medical devices and/or host cells, biofilm formation, and secretion of hydrolytic enzymes (proteases, phospholipases and haemolysins). Although 'new'Candida species are emerging, there is still a lack of information about their pathogenicity. This review discusses recent advances in our knowledge of Candida glabrata, Candida parapsilosis and Candida tropicalis virulence factors, specifically those of adhesion and biofilm formation, which are key components in Candida pathogenicity.     

肉桂醛对根管内白色念珠菌生物膜作用的体外研究

目的研究肉桂醛对体外白色念珠菌生物膜的影响。方法采用琼脂扩散法进行肉桂醛和洗必泰对白色念珠菌敏感性的比较;MTT法评价肉桂醛对白色念珠菌生物膜及细胞黏附的影响。结果 2 048μg/mL肉桂醛与2%洗必泰抑菌环直径比较差异无统计学意义(P>0.05);4 096μg/mL肉桂醛对白色念珠菌生物膜的抑菌率达93.02%;不同浓度肉桂醛对60、90和120 min的白色念珠菌细胞粘附都具有抑制作用。结论肉桂醛对体外白色念珠菌生物膜有较明显的抑制作用。     

Variation of cell surface hydrophobicity and biofilm formation among genotypes of Candida albicans and Candida dubliniensis under antifungal treatment

Candida infections are frequently associated with formation of biofilms on artificial medical devices. This work studied variation of cell surface hydrophobicity (CSH) and formation of biofilm in relation to Candida albicans and Candida dubliniensis genotypes and an effect of some conventional antifungal agents on both CSH and biofilm. The 50 isolates of C. albicans and C. dubliniensis were classified into genotypes A, B, C, and D, genotype D being exclusively represented by C. dubliniensis. No significant differences between CSH of genotypes A and B and B and C were observed with respect to cultivation temperature 25 or 37 degrees C. Candida dubliniensis showed increased CSH in comparison with other C. albicans genotypes (p < 0.001) regardless of temperature used. Using XTT reduction assay and dry masses, genotypes B and C showed reduced ability to form biofilm in comparison with genotype A (p < 0.05) and C. dubliniensis (p < 0.001). Fluconazole reduced biofilm in C. albicans genotypes A, B, and C (p < 0.05) but not CSH. The opposite effect was observed in C. dubliniensis. Voriconazole effectively reduced both biofilm formation and CSH in all tested genotypes of C. albicans and C. dubliniensis (p < 0.05).