51
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Khodavandi A, Harmal NS, Alizadeh F, Scully OJ, Sidik SM, Othman F, Sekawi Z, Ng KP, Chong PP. Comparison between allicin and fluconazole in Candida albicans biofilm inhibition and in suppression of HWP1 gene expression. PHYTOMEDICINE : INTERNATIONAL JOURNAL OF PHYTOTHERAPY AND PHYTOPHARMACOLOGY 2011; 19:56-63. [PMID: 21924600 DOI: 10.1016/j.phymed.2011.08.060] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2011] [Revised: 06/29/2011] [Accepted: 08/08/2011] [Indexed: 05/31/2023]
Abstract
Candida albicans is an opportunistic human pathogen with the ability to differentiate and grow in filamentous forms and exist as biofilms. The biofilms are a barrier to treatment as they are often resistant to the antifungal drugs. In this study, we investigated the antifungal activity of allicin, an active compound of garlic on various isolates of C. albicans. The effect of allicin on biofilm production in C. albicans as compared to fluconazole, an antifungal drug, was investigated using the tetrazolium (XTT) reduction-dependent growth and crystal violet assays as well as scanning electron microscopy (SEM). Allicin-treated cells exhibited significant reduction in biofilm growth (p<0.05) compared to fluconazole-treated and also growth control cells. Moreover, observation by SEM of allicin and fluconazole-treated cells confirmed a dose-dependent membrane disruption and decreased production of organisms. Finally, the expression of selected genes involved in biofilm formation such as HWP1 was evaluated by semi-quantitative RT-PCR and relative real time RT-PCR. Allicin was shown to down-regulate the expression of HWP1.
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Affiliation(s)
- Alireza Khodavandi
- Department of Paramedical Sciences, Gachsaran Branch, Islamic Azad University, Gachsaran, Iran
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52
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Bisbibenzyls, a new type of antifungal agent, inhibit morphogenesis switch and biofilm formation through upregulation of DPP3 in Candida albicans. PLoS One 2011; 6:e28953. [PMID: 22174935 PMCID: PMC3236236 DOI: 10.1371/journal.pone.0028953] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2011] [Accepted: 11/17/2011] [Indexed: 11/19/2022] Open
Abstract
The yeast-to-hypha transition plays a crucial role in the pathogenesis of C. albicans. Farnesol, a quorum sensing molecule (QSM) secreted by the fungal itself, could prevent the formation of hyphae and subsequently lead to the defect of biofilm formation. The DPP3, encoding phosphatase, is a key gene in regulating farnesol synthesis. In this study, we screened 24 bisbibenzyls and 2 bibenzyls that were isolated from bryophytes or chemically synthesized by using CLSI method for antifungal effect. Seven bisbibenzyls were found to have antifungal effects with IC80 less than 32 µg/ml, and among them, plagiochin F, isoriccardin C and BS-34 were found to inhibit the hyphae and biofilm formation of C. albicans in a dose-dependent manner. To uncover the underlying relationship between morphogenesis switch and QSM formation, we measured the farnesol production by HPLC-MS and quantified Dpp3 expression by detecting the fluorescent intensity of green fluorescent protein tagged strain using Confocal Laser Scanning microscopy and Multifunction Microplate Reader. The DPP3 transcripts were determined by real-time PCR. The data indicated that the bisbibenzyls exerted antifungal effects through stimulating the synthesis of farnesol via upregulation of Dpp3, suggesting a potential antifungal application of bisbibenzyls. In addition, our assay provides a novel, visual and convenient method to measure active compounds against morphogenesis switch.
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53
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Ramage G, Rajendran R, Gutierrez-Correa M, Jones B, Williams C. Aspergillus biofilms: clinical and industrial significance. FEMS Microbiol Lett 2011; 324:89-97. [PMID: 22092808 DOI: 10.1111/j.1574-6968.2011.02381.x] [Citation(s) in RCA: 87] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2011] [Revised: 08/09/2011] [Accepted: 08/09/2011] [Indexed: 11/30/2022] Open
Abstract
The biofilm phenotype is an increasingly important concept in mycological research. Recently, there has been a developing interest in whether Aspergillus species are truly able to form biofilms or not. Industrial mycologists have long been aware of biofilms and their benefit in fermentation processes, whereas clinically their role is uncertain. This review provides an update on the impact that Aspergillus biofilms have medically and industrially, and will discuss biofilm development, and our current understanding of its molecular basis. The role of exopolymeric substance and how this substance relates to antimicrobial recalcitrance will also be discussed.
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Affiliation(s)
- Gordon Ramage
- School of Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, UK.
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54
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Cairns S, Thomas JG, Hooper SJ, Wise MP, Frost PJ, Wilson MJ, Lewis MAO, Williams DW. Molecular analysis of microbial communities in endotracheal tube biofilms. PLoS One 2011; 6:e14759. [PMID: 21423727 PMCID: PMC3056660 DOI: 10.1371/journal.pone.0014759] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Accepted: 10/30/2010] [Indexed: 11/22/2022] Open
Abstract
Background Ventilator-associated pneumonia is the most prevalent acquired infection of patients on intensive care units and is associated with considerable morbidity and mortality. Evidence suggests that an improved understanding of the composition of the biofilm communities that form on endotracheal tubes may result in the development of improved preventative strategies for ventilator-associated pneumonia. Methodology/Principal Findings The aim of this study was to characterise microbial biofilms on the inner luminal surface of extubated endotracheal tubes from ICU patients using PCR and molecular profiling. Twenty-four endotracheal tubes were obtained from twenty mechanically ventilated patients. Denaturing gradient gel electrophoresis (DGGE) profiling of 16S rRNA gene amplicons was used to assess the diversity of the bacterial population, together with species specific PCR of key marker oral microorganisms and a quantitative assessment of culturable aerobic bacteria. Analysis of culturable aerobic bacteria revealed a range of colonisation from no growth to 2.1×108 colony forming units (cfu)/cm2 of endotracheal tube (mean 1.4×107 cfu/cm2). PCR targeting of specific bacterial species detected the oral bacteria Streptococcus mutans (n = 5) and Porphyromonas gingivalis (n = 5). DGGE profiling of the endotracheal biofilms revealed complex banding patterns containing between 3 and 22 (mean 6) bands per tube, thus demonstrating the marked complexity of the constituent biofilms. Significant inter-patient diversity was evident. The number of DGGE bands detected was not related to total viable microbial counts or the duration of intubation. Conclusions/Significance Molecular profiling using DGGE demonstrated considerable biofilm compositional complexity and inter-patient diversity and provides a rapid method for the further study of biofilm composition in longitudinal and interventional studies. The presence of oral microorganisms in endotracheal tube biofilms suggests that these may be important in biofilm development and may provide a therapeutic target for the prevention of ventilator-associated pneumonia.
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Affiliation(s)
- Scott Cairns
- University Hospital of Wales, Cardiff, United Kingdom
| | - John Gilbert Thomas
- West Virginia University, Morgantown, West Virginia, United States of America
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55
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LaFleur MD, Lucumi E, Napper AD, Diamond SL, Lewis K. Novel high-throughput screen against Candida albicans identifies antifungal potentiators and agents effective against biofilms. J Antimicrob Chemother 2011; 66:820-6. [PMID: 21393183 DOI: 10.1093/jac/dkq530] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
OBJECTIVES Microbial adhesion and biofilms have important implications for human health and disease. Candida albicans is an opportunistic pathogen which forms drug-resistant biofilms that contribute to the recalcitrance of disease. We have developed a high-throughput screen for potentiators of clotrimazole, a common therapy for Candida infections, including vaginitis and thrush. The screen was performed against C. albicans biofilms grown in microtitre plates in order to target the most resilient forms of the pathogen. METHODS Biofilm growth, in individual wells of 384-well plates, was measured using the metabolic indicator alamarBlue® and found to be very consistent and reproducible. This assay was used to test the effect of more than 120 000 small molecule compounds from the NIH Molecular Libraries Small Molecule Repository, and compounds that enhanced the activity of clotrimazole or acted on the biofilms alone were identified as hits. RESULTS Nineteen compounds (0.016% hit rate) were identified and found to cause more than 30% metabolic inhibition of biofilms compared with clotrimazole alone, which had a modest effect on biofilm viability at the concentration tested. Hits were confirmed for activity against biofilms with dose-response measurements. Several compounds had increased activity in combination with clotrimazole, including a 1,3-benzothiazole scaffold that exhibited a >100-fold improvement against biofilms of three separate C. albicans isolates. Cytotoxicity experiments using human fibroblasts confirmed the presence of lead molecules with favourable antifungal activity relative to cytotoxicity. CONCLUSIONS We have validated a novel approach to identify antifungal potentiators and completed a high-throughput screen to identify small molecules with activity against C. albicans biofilms. These small molecules may specifically target the biofilm and make currently available antifungals more effective.
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Affiliation(s)
- Michael D LaFleur
- Antimicrobial Discovery Center and Department of Biology, Northeastern University, 360 Huntington Avenue, Boston, MA 02118, USA.
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56
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Martinez LR, Fries BC. Fungal Biofilms: Relevance in the Setting of Human Disease. CURRENT FUNGAL INFECTION REPORTS 2010; 4:266-275. [PMID: 21660222 DOI: 10.1007/s12281-010-0035-5] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The use of indwelling medical devices is rapidly growing and is often complicated by infections with biofilm-forming microbes that are resistant to antimicrobial agents and host defense mechanisms. Fungal biofilms have emerged as a clinical problem associated with these medical device infections, causing significant morbidity and mortality. This review discusses the recent advances in the understanding of fungal biofilms, including the role of fungal surface components in adherence, gene expression, and quorum sensing in biofilm formation. We propose novel strategies for the prevention or eradication of microbial colonization of medical prosthetic devices.
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Affiliation(s)
- Luis R Martinez
- Albert Einstein College of Medicine, 1300 Morris Park Avenue Bronx, Morris Park, NY 10461, USA
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57
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The transcriptional regulator Nrg1p controls Candida albicans biofilm formation and dispersion. EUKARYOTIC CELL 2010; 9:1531-7. [PMID: 20709787 DOI: 10.1128/ec.00111-10] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The ability of Candida albicans to reversibly switch morphologies is important for biofilm formation and dispersion. In this pathogen, Nrg1p functions as a key negative regulator of the yeast-to-hypha morphogenetic transition. We have previously described a genetically engineered C. albicans tet-NRG1 strain in which NRG1 expression levels can be manipulated by the presence or absence of doxycycline (DOX). Here, we have used this strain to ascertain the role of Nrg1p in regulating the different stages of the C. albicans biofilm developmental cycle. In an in vitro model of biofilm formation, the C. albicans tet-NRG1 strain was able to form mature biofilms only when DOX was present in the medium, but not in the absence of DOX, when high levels of NRG1 expression blocked the yeast-to-hypha transition. However, in a biofilm cell retention assay in which biofilms were developed with mixtures of C. albicans tet-NRG1 and SC5314 strains, tet-NRG1 yeast cells were still incorporated into the mixed biofilms, in which an intricate network of hyphae of the wild-type strain provided for biofilm structural integrity and adhesive interactions. Also, utilizing an in vitro biofilm model under conditions of flow, we demonstrated that C. albicans Nrg1p exerts an exquisite control of the dispersal process, as overexpression of NRG1 leads to increases in dispersion of yeast cells from the biofilms. Our results demonstrate that manipulation of NRG1 gene expression has a profound influence on biofilm formation and biofilm dispersal, thus identifying Nrg1p as a key regulator of the C. albicans biofilm life cycle.
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Use of a new gelling agent (Eladium©) as an alternative to agar-agar and its adaptation to screen biofilm-forming yeasts. Appl Microbiol Biotechnol 2010; 88:1095-102. [PMID: 20703874 DOI: 10.1007/s00253-010-2800-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2010] [Revised: 07/19/2010] [Accepted: 07/26/2010] [Indexed: 10/19/2022]
Abstract
The incidence of yeast-induced infections has increased in the last decade, mainly because of the increasing number of immunodeficient patients. Since biofilm production is believed to be responsible for fungal virulence, we propose screening yeasts of various genera in order to determine their ability to form biofilms. This is an important issue because yeast cells that form biofilms are particularly resistant to anti-fungal agents used in human patients. For screening, we used Eladium©, a new polysaccharide produced by a Rhizobium sp., as an alternative gelling agent to agar. We also established the conditions necessary to detect biofilm formation. The adapted medium provides the missing link between liquid and solid media. Its advantages include enhancement of growth of microorganisms and facilitation of quick and easy monitoring of biofilm formation.
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59
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Zhou L, Tong Z, Wu G, Feng Z, Bai S, Dong Y, Ni L, Zhao Y. Parylene coating hinders Candida albicans adhesion to silicone elastomers and denture bases resin. Arch Oral Biol 2010; 55:401-9. [DOI: 10.1016/j.archoralbio.2010.03.013] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2010] [Revised: 03/02/2010] [Accepted: 03/15/2010] [Indexed: 11/29/2022]
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60
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Seneviratne CJ, Wang Y, Jin L, Abiko Y, Samaranayake LP. Proteomics of drug resistance in Candida glabrata
biofilms. Proteomics 2010; 10:1444-54. [DOI: 10.1002/pmic.200900611] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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61
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Ramage G, Mowat E, Jones B, Williams C, Lopez-Ribot J. Our current understanding of fungal biofilms. Crit Rev Microbiol 2010; 35:340-55. [PMID: 19863383 DOI: 10.3109/10408410903241436] [Citation(s) in RCA: 326] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Fungal biofilms are an escalating clinical problem associated with significant rates of mortality. Candida albicans is the most notorious of all fungal biofilm formers. However, non-Candida species, yeasts such as Cryptococcus neoformans, and filamentous moulds such as Aspergillus fumigatus, have been shown to be implicated in biofilm-associated infections. Fungal biofilms have distinct developmental phases, including adhesion, colonisation, maturation and dispersal, which are governed by complex molecular events. Recalcitrance to antifungal therapy remains the greatest threat to patients with fungal biofilms. This review discusses our current understanding of the basic biology and clinical implications associated with fungal biofilms.
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Affiliation(s)
- Gordon Ramage
- Section of Infection and Immunity, Glasgow Dental School and Hospital, Faculty of Medicine, University of Glasgow, UK.
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62
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Nakamura M, Fujibayashi T, Tominaga A, Satoh N, Kawarai T, Shinozuka O, Watanabe H, Yamazaki T, Senpuku H. Hinokitiol Inhibits Candida albicans Adherence to Oral Epithelial Cells. J Oral Biosci 2010. [DOI: 10.1016/s1349-0079(10)80007-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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63
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De Sordi L, Mühlschlegel FA. Quorum sensing and fungal-bacterial interactions in Candida albicans: a communicative network regulating microbial coexistence and virulence. FEMS Yeast Res 2009; 9:990-9. [PMID: 19845041 DOI: 10.1111/j.1567-1364.2009.00573.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Microorganisms have evolved a complex signature of communication termed quorum sensing (QS), which is based on the exchange and sensing of low molecular- weight signal compounds. The ability to communicate within the microbial population gives the advantage to coordinate a groups behaviour leading to a higher fitness in the environment. The polymorphic fungus Candida albicans is an opportunistic human pathogen able to regulate virulence traits through the production of at least two QS signal molecules: farnesol and tyrosol. The ability to adopt multiple morphotypes and form biofilms on infected surfaces are the most important pathogenic characteristics regulated by QS and are of clinical relevance. In fact, traditional antimicrobial approaches are often ineffective towards these characteristics. Moreover, the intimate association between C. albicans and other pathogens, such as Pseudomonas aeruginosa, increases the complexity of the infection system. This review outlines the current knowledge on fungal QS and fungal-bacterial interactions emphasizing on C. albicans. Further investigations need to concentrate on the molecular mechanisms and the genetic regulation of these phenomena in order to identify putative novel therapeutic options.
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Affiliation(s)
- Luisa De Sordi
- Department of Biosciences, University of Kent, Canterbury, UK
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64
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Paulitsch AH, Willinger B, Zsalatz B, Stabentheiner E, Marth E, Buzina W. In-vivoCandida biofilms in scanning electron microscopy. Med Mycol 2009; 47:690-6. [DOI: 10.3109/13693780802635237] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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65
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Seneviratne CJ, Silva WJ, Jin LJ, Samaranayake YH, Samaranayake LP. Architectural analysis, viability assessment and growth kinetics of Candida albicans and Candida glabrata biofilms. Arch Oral Biol 2009; 54:1052-60. [PMID: 19712926 DOI: 10.1016/j.archoralbio.2009.08.002] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2008] [Revised: 02/18/2009] [Accepted: 08/01/2009] [Indexed: 11/25/2022]
Abstract
The human fungal pathogen Candida is able to form biofilms in almost all the medical devices in current use. Indeed, biofilm formation is a major virulence attribute of microorganisms and account for a majority of human infections. Therefore, understanding processes appertaining to biofilm development is an important prerequisite for devising new strategies to prevent or eradicate biofilm-related infections. In the present study we used an array of both conventional and novel analytical tools to obtain a comprehensive view of Candida biofilm development. Enumeration of colony forming units, colorimetric (XTT) assay, Scanning Electron Microscopy (SEM) and novel Confocal Laser Scanning Microscopy (CLSM) coupled with COMSTAT software analyses were utilised to evaluate growth kinetics; architecture and viability of biofilms of a reference (ATCC) and a clinical strain each of two Candida species, C. albicans and C. glabrata. Biofilm growth kinetics on a polystyrene substrate was evaluated from the initial adhesion step (1.5 h) up to 72 h. These analyses revealed substantial inter- and intra-species differences in temporal organisation of Candida biofilm architecture, spatiality and cellular viability, while reaching maturity within a period of 48 h, on a polystyrene substrate. There were substantial differences in the growth kinetics upon methodology, although general trend seemed to be the same. Detailed architectural analysis provided by COMSTAT software corroborated the SEM and CSLM views. These analyses may provide a strong foundation for down stream molecular work of fungal biofilms.
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Affiliation(s)
- C J Seneviratne
- Oral Bio-Sciences, Faculty of Dentistry, The University of Hong Kong, Hong Kong.
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66
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Hasan F, Xess I, Wang X, Jain N, Fries BC. Biofilm formation in clinical Candida isolates and its association with virulence. Microbes Infect 2009; 11:753-61. [PMID: 19409507 DOI: 10.1016/j.micinf.2009.04.018] [Citation(s) in RCA: 152] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2009] [Revised: 04/06/2009] [Accepted: 04/08/2009] [Indexed: 01/07/2023]
Abstract
Biofilm formation, an important virulence trait of Candida species was measured in 107 Candida isolates from 32 candidemic patients by XTT [2,3-bis (2-methoxy-4nitro-5-sulfo-phenyl)-2H-tetra-zolium-5-carboxanilide] activity and compared to biofilm formation of Candida isolates from oropharyngeal lesions of 19 AIDS patients. Biofilm formation by XTT varied among species and C. albicans; C. lusitaniae and C. krusei produced more biofilm than the other Candida species. C. tropicalis was the most dominant species isolated from blood followed by C. albicans, and other non-albicans species whereas only C. albicans was recovered from oral lesions. Importantly, though Biofilm formation was variable within a species it was stable in sequential isolates during chronic infection. Sequential isolates exhibited identical Karyotype pattern or RAPD patterns unless patients were co-infected with more than one strain. High biofilm formation was associated with slow growth rate but not with adherence. Murine infection studies demonstrated that, degree of in-vitro biofilm formation was associated with virulence in mice, as mice infected both with no and low biofilm formers survived longer than mice infected with high biofilm former C. albicans (p< or =0.001). We conclude that biofilm formation is a stable but strain specific characteristic that can greatly vary among C. albicans and non-albicans strains, and plays an important role in persistence of infection.
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Affiliation(s)
- Fahmi Hasan
- Department of Microbiology, All India Institute of Medical Sciences, New Delhi, India
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67
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Quindós G, Villar-Vidal M, Eraso E. Actividad de la micafungina contra las biopelículas de Candida. Rev Iberoam Micol 2009; 26:49-55. [DOI: 10.1016/s1130-1406(09)70008-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2009] [Accepted: 02/12/2009] [Indexed: 01/10/2023] Open
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68
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Abstract
The Candida albicans cell wall maintains the structural integrity of the organism in addition to providing a physical contact interface with the environment. The major components of the cell wall are fibrillar polysaccharides and proteins. The proteins of the cell wall are the focus of this review. Three classes of proteins are present in the candidal cell wall. One group of proteins attach to the cell wall via a glycophosphatidylinositol remnant or by an alkali-labile linkage. A second group of proteins with N-terminal signal sequences but no covalent attachment sequences are secreted by the classical secretory pathway. These proteins may end up in the cell wall or in the extracellular space. The third group of proteins lack a secretory signal, and the pathway(s) by which they become associated with the surface is unknown. Potential constituents of the first two classes have been predicted from analysis of genome sequences. Experimental analyses have identified members of all three classes. Some members of each class selected for consideration of confirmed or proposed function, phenotypic analysis of a mutant, and regulation by growth conditions and transcription factors are discussed in more detail.
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69
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Espinel-Ingroff A. Mechanisms of resistance to antifungal agents: yeasts and filamentous fungi. Rev Iberoam Micol 2008; 25:101-6. [PMID: 18473504 DOI: 10.1016/s1130-1406(08)70027-5] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Failure to respond to antifungal therapy could be due to in vitro resistance (intrinsic or developed during therapy) or clinical resistance; the latter is associated with numerous factors related to the host, the antifungal agent, or the infecting isolate. Recently, a susceptible MIC breakpoint ( < or =2 microg/ml) was designed for Candida spp. to all three available echinocandins, anidulafungin (Pfizer), caspofungin (Merck) and micafungin (Astellas) and treatment failures have been associated with MICs > 2 microg/ml. In some of these cases, clinical failure was associated with the genetic mutations described below. Azole and flucytosine breakpoints, and the echinocandin susceptible breakpoint, are useful when isolates are tested by CLSI standardized methods; breakpoints are also available by the EUCAST method. More recently, in vitro resistant MIC breakpoints have been assigned for filamentous fungi (moulds) vs. five antifungal agents, but these categories are not based on correlations of in vitro with in vivo response to therapy. However, itraconazole (Janssen), amphotericin B (Bristol-Myers) and voriconazole (Pfizer) clinical failures in aspergillosis have been correlated with MICs > 2 microg/ml. This article provides a review of reported resistance molecular mechanisms to antifungal agents since 2005; previous related reviews are also listed.
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Affiliation(s)
- Ana Espinel-Ingroff
- VCU Medical Center, Department of Medicine, Division of Infectious Diseases, Richmond, VA 23298-0049, USA.
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70
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Abstract
Pneumocystis spp. can cause a lethal pneumonia in hosts with debilitated immune systems. The manner in which these fungal infections spread throughout the lung, the life cycles of the organisms, and their strategies used for survival within the mammalian host are largely unknown, due in part to the lack of a continuous cultivation method. Biofilm formation is one strategy used by microbes for protection against environmental assaults, for communication and differentiation, and as foci for dissemination. We posited that the attachment and growth of Pneumocystis within the lung alveoli is akin to biofilm formation. An in vitro system comprised of insert wells suspended in multiwell plates containing supplemented RPMI 1640 medium supported biofilm formation by P. carinii (from rat) and P. murina (from mouse). Dramatic morphological changes accompanied the transition to a biofilm. Cyst and trophic forms became highly refractile and produced branching formations that anastomosed into large macroscopic clusters that spread across the insert. Confocal microscopy revealed stacking of viable organisms enmeshed in concanavalin A-staining extracellular matrix. Biofilms matured over a 3-week time period and could be passaged. These passaged organisms were able to cause infection in immunosuppressed rodents. Biofilm formation was inhibited by farnesol, a quorum-sensing molecule in Candida spp., suggesting that a similar communication system may be operational in the Pneumocystis biofilms. Intense staining with a monoclonal antibody to the major surface glycoproteins and an increase in (1,3)-beta-D-glucan content suggest that these components contributed to the refractile properties. Identification of this biofilm process provides a tractable in vitro system that should fundamentally advance the study of Pneumocystis.
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71
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Monitoring ALS1 and ALS3 Gene Expression During In Vitro Candida albicans Biofilm Formation Under Continuous Flow Conditions. Mycopathologia 2008; 167:9-17. [DOI: 10.1007/s11046-008-9148-6] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2008] [Accepted: 07/15/2008] [Indexed: 10/21/2022]
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72
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Li F, Palecek SP. Distinct domains of the Candida albicans adhesin Eap1p mediate cell–cell and cell–substrate interactions. Microbiology (Reading) 2008; 154:1193-1203. [DOI: 10.1099/mic.0.2007/013789-0] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Affiliation(s)
- Fang Li
- Department of Chemical and Biological Engineering, University of Wisconsin – Madison, Madison, WI 53706, USA
| | - Sean P. Palecek
- Department of Chemical and Biological Engineering, University of Wisconsin – Madison, Madison, WI 53706, USA
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Fichtner L, Schulze F, Braus GH. Differential Flo8p-dependent regulation of FLO1 and FLO11 for cell-cell and cell-substrate adherence of S. cerevisiae S288c. Mol Microbiol 2008; 66:1276-89. [PMID: 18001350 PMCID: PMC2780560 DOI: 10.1111/j.1365-2958.2007.06014.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Cell–cell and cell–surface adherence represents initial steps in forming multicellular aggregates or in establishing cell–surface interactions. The commonly used Saccharomyces cerevisiae laboratory strain S288c carries a flo8 mutation, and is only able to express the flocculin-encoding genes FLO1 and FLO11, when FLO8 is restored. We show here that the two flocculin genes exhibit differences in regulation to execute distinct functions under various environmental conditions. In contrast to the laboratory strain Σ1278b, haploids of the S288c genetic background require FLO1 for cell–cell and cell–substrate adhesion, whereas FLO11 is required for pseudohyphae formation of diploids. In contrast to FLO11, FLO1 repression requires the Sin4p mediator tail component, but is independent of the repressor Sfl1p. FLO1 regulation also differs from FLO11, because it requires neither the KSS1 MAP kinase cascade nor the pathways which lead to the transcription factors Gcn4p or Msn1p. The protein kinase A pathway and the transcription factors Flo8p and Mss11p are the major regulators for FLO1 expression. Therefore, S. cerevisiae is prepared to simultaneously express two genes of its otherwise silenced FLO reservoir resulting in an appropriate cellular surface for different environments.
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Affiliation(s)
- Lars Fichtner
- Institut für Mikrobiologie und Genetik, DFG Research Center for Molecular Physiology of the Brain (CMPB), Georg-August Universität Göttingen, Grisebachstr. 8, D-37077 Göttingen, Germany
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74
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Agarwal V, Lal P, Pruthi V. Prevention of Candida albicans biofilm by plant oils. Mycopathologia 2008; 165:13-9. [PMID: 17968673 DOI: 10.1007/s11046-007-9077-9] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2007] [Accepted: 10/15/2007] [Indexed: 11/25/2022]
Abstract
The inhibitory effect of 30 plant oils was evaluated against biofilm forming Candida albicans strain (CA I) isolated from clinical samples, which was sensitive to 4 microg/ml of fluconazole, used as a positive control. The standard strain (MTCC 227, CA II) used in this study was found to be highly resistant to fluconazole, 3,000 microg/ml of which was required to inhibit the growth of this strain partially, and complete inhibition could not be achieved. Eighteen among the 30 plant oils tested were found to show anti-Candida activity by disc diffusion assay. Effective plant oils were assessed using XTT (2, 3-bis [2-Methoxy-4-nitro-5-sulphophenyl]-2H-tetrazolium-5-carboxanilide) reduction assay for biofilm quantification. Four oils eucalyptus, peppermint, ginger grass and clove showed 80.87%, 74.16%, 40.46% and 28.57% biofilm reduction respectively. Minimum inhibitory concentration (MIC) values were calculated using agar dilution assay. Scanning electron microscopic (SEM) analysis further revealed reduction in C. albicans biofilm in response to effective oils. The substantial antifungal activity shown by these plant oils suggests their potential against infections caused by C. albicans.
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Affiliation(s)
- Vishnu Agarwal
- Molecular Microbiology Laboratory, Department of Biotechnology, Indian Institute of Technology, Roorkee, Uttarakhand 247667, India.
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75
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Braga PC, Alfieri M, Culici M, Dal Sasso M. Inhibitory activity of thymol against the formation and viability of Candida albicans hyphae. Mycoses 2007; 50:502-6. [PMID: 17944714 DOI: 10.1111/j.1439-0507.2007.01412.x] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
As the capacity of Candida albicans to produce hyphae is considered an important virulence factor in the pathogenesis of candiasis, the aim of this study was to investigate whether thymol, the major component of thyme oil, can interfere with the filamentous forms of Candida albicans and their viability. The morphological transition from yeasts to filamentous forms was investigated by analysing the morphological index (MI), which classifies the differentiated forms and blastoconidia; viability was investigated by means of fluorescence microscopy using a new SYTO-9 and propidium iodide method previously used to stain only blastoconidia. Without thymol, there was an average of 94.00 +/- 3.06% hyphal forms. After 6 h of incubation with 1x MIC (125 microg ml(-1)), 1/2x MIC and 1/4x MIC of thymol, filamentation was, respectively, 14.33 +/- 8.25%, 28.33 +/- 7.17% and 45.67 +/- 8.09% in comparison with control (all statistically significant). In the absence of thymol, viable cells accounted for an average of 93.00 +/- 4.00% whereas, after 6 h of incubation with 1x MIC, 1/2x MIC and 1/4x MIC of thymol, the presence of 54.33 +/- 1.86%, 29.00 +/- 3.61% and 23.00 +/- 2.52% of yellow-orange coloured forms indicated damaged membranes and reduced viability. Our findings show that thymol interferes with the formation and viability of hyphae. This can be attributed to the characteristics of thymol disturbing Candida cell membranes and metabolism, probably by affecting fungal cell-wall synthesising enzymes.
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Affiliation(s)
- P C Braga
- Department of Pharmacology, School of Medicine, University of Milan, Milan, Italy.
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76
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Ramage G, Wickes BL, López-Ribot JL. Inhibition on Candida albicans biofilm formation using divalent cation chelators (EDTA). Mycopathologia 2007; 164:301-6. [PMID: 17909983 DOI: 10.1007/s11046-007-9068-x] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2007] [Accepted: 09/19/2007] [Indexed: 11/29/2022]
Abstract
Candida albicans can readily form biofilms on both inanimate and biological surfaces. In this study we investigated a means of inhibiting biofilm formation using EDTA (Ethylenediaminetetra-acetic acid), a divalent cation chelating agent, which has been shown to affect C. albicans filamentation. Candida albicans biofilms were formed in 96-well microtitre plates. Cells were allowed to adhere for 1, 2, and 4 h at 37 degrees C, washed in PBS, and then treated with different concentrations of EDTA (0, 2.5, 25, and 250 mM). EDTA was also added to the standardized suspension prior to adding to the microtiter plate and to a preformed 24 h biofilm. All plates were then incubated at 37 degrees C for an additional 24 h to allow for biofilm formation. The extent and characteristics of biofilm formation were then microscopically assessed and with a semi-quantitative colorimetric technique based on the use of an XTT-reduction assay. Northern blot analysis of the hyphal wall protein (HWP1) expression was also monitored in planktonic and biofilm cells treated with EDTA. Microscopic analysis and colorimetric readings revealed that filamentation and biofilm formation were inhibited by EDTA in a concentration dependent manner. However, preformed biofilms were minimally affected by EDTA (maximum of 31% reduction at 250 mM). The HWP1 gene expression was reduced in EDTA-treated planktonic and biofilm samples. These results indicate that EDTA inhibits C. albicans biofilm formation are most likely through its inhibitory effect on filamentation and indicates the potential therapeutic effects of EDTA. This compound may serve a non-toxic means of preventing biofilm formation on infections with a C. albicans biofilm etiology.
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Affiliation(s)
- Gordon Ramage
- Section of Infection and Immunity, Glasgow Dental School and Hospital, The University of Glasgow, Glasgow, UK
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77
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Perumal P, Mekala S, Chaffin WL. Role for cell density in antifungal drug resistance in Candida albicans biofilms. Antimicrob Agents Chemother 2007; 51:2454-63. [PMID: 17502416 PMCID: PMC1913227 DOI: 10.1128/aac.01237-06] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Biofilms of Candida albicans are less susceptible to many antifungal drugs than are planktonic yeast cells. We investigated the contribution of cell density to biofilm phenotypic resistance. Planktonic yeast cells in RPMI 1640 were susceptible to azole-class drugs, amphotericin B, and caspofungin at 1 x 10(3) cells/ml (standard conditions) using the XTT [2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide sodium salt] assay. As reported by others, as the cell concentration increased to 1 x 10(8) cells/ml, resistance was observed with 10- to 20-fold-greater MICs. Biofilms that formed in microtiter plate wells, like high-density planktonic organisms, were resistant to drugs. When biofilms were resuspended before testing, phenotypic resistance remained, but organisms, when diluted to 1 x 10(3) cells/ml, were susceptible. Drug-containing medium recovered from high-cell-density tests inhibited low-cell-density organisms. A fluconazole-resistant strain showed greater resistance at high planktonic cell density, in biofilm, and in resuspended biofilm than did low-density planktonic or biofilm organisms. A strain lacking drug efflux pumps CDR1, CDR2, and MDR1, while susceptible at a low azole concentration, was resistant at high cell density and in biofilm. A strain lacking CHK1 that fails to respond to the quorum-sensing molecule farnesol had the same response as did the wild type. FK506, reported to abrogate tolerance to azole drugs at low cell density, had no effect on tolerance at high cell density and in biofilm. These observations suggested that cell density has a role in the phenotypic resistance of biofilm, that neither the drug efflux pumps tested nor quorum sensing through Chk1p contributes to resistance, and that azole drug tolerance at high cell density differs mechanistically from tolerance at low cell density.
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Affiliation(s)
- Palani Perumal
- Department of Microbiology and Immunology, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
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78
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Li F, Svarovsky MJ, Karlsson AJ, Wagner JP, Marchillo K, Oshel P, Andes D, Palecek SP. Eap1p, an adhesin that mediates Candida albicans biofilm formation in vitro and in vivo. EUKARYOTIC CELL 2007; 6:931-9. [PMID: 17416898 PMCID: PMC1951519 DOI: 10.1128/ec.00049-07] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Candida albicans is the leading cause of systemic fungal infections in immunocompromised humans. The ability to form biofilms on surfaces in the host or on implanted medical devices enhances C. albicans virulence, leading to antimicrobial resistance and providing a reservoir for infection. Biofilm formation is a complex multicellular process consisting of cell adhesion, cell growth, morphogenic switching between yeast form and filamentous states, and quorum sensing. Here we describe the role of the C. albicans EAP1 gene, which encodes a glycosylphosphatidylinositol-anchored, glucan-cross-linked cell wall protein, in adhesion and biofilm formation in vitro and in vivo. Deleting EAP1 reduced cell adhesion to polystyrene and epithelial cells in a gene dosage-dependent manner. Furthermore, EAP1 expression was required for C. albicans biofilm formation in an in vitro parallel plate flow chamber model and in an in vivo rat central venous catheter model. EAP1 expression was upregulated in biofilm-associated cells in vitro and in vivo. Our results illustrate an association between Eap1p-mediated adhesion and biofilm formation in vitro and in vivo.
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Affiliation(s)
- Fang Li
- Department of Chemical & Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, WI 53706, USA
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79
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He M, Du M, Fan M, Bian Z. In vitro activity of eugenol against Candida albicans biofilms. Mycopathologia 2007; 163:137-43. [PMID: 17356790 DOI: 10.1007/s11046-007-0097-2] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2006] [Accepted: 02/01/2007] [Indexed: 10/23/2022]
Abstract
Most manifestations of candidiasis are associated with biofilm formation occurring on the surfaces of host tissues and medical devices. Candida albicans is the most frequently isolated causative pathogen of candidiasis, and the biofilms display significantly increased levels of resistance to the conventional antifungal agents. Eugenol, the major phenolic component of clove essential oil, possesses potent antifungal activity. The aim of this study was to investigate the effects of eugenol on preformed biofilms, adherent cells, subsequent biofilm formation and cell morphogenesis of C. albicans. Eugenol displayed in vitro activity against C. albicans cells within biofilms, when MIC(50) for sessile cells was 500 mg/L. C. albicans adherent cell populations (after 0, 1, 2 and 4 h of adherence) were treated with various concentrations of eugenol (0, 20, 200 and 2,000 mg/L). The extent of subsequent biofilm formation were then assessed with the tetrazolium salt reduction assay. Effect of eugenol on morphogenesis of C. albicans cells was observed by scanning electron microscopy (SEM). The results indicated that the effect of eugenol on adherent cells and subsequent biofilm formation was dependent on the initial adherence time and the concentration of this compound, and that eugenol can inhibit filamentous growth of C. albicans cells. In addition, using human erythrocytes, eugenol showed low hemolytic activity. These results indicated that eugenol displayed potent activity against C. albicans biofilms in vitro with low cytotoxicity and therefore has potential therapeutic implication for biofilm-associated candidal infections.
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Affiliation(s)
- Miao He
- Key Laboratory for Oral Biomedical Engineering of Ministry of Education, School and Hospital of Stomatology, Wuhan University, Luoyu Road 65, Wuhan, 430079, Hubei, China
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80
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Bruzual I, Riggle P, Hadley S, Kumamoto CA. Biofilm formation by fluconazole-resistant Candida albicans strains is inhibited by fluconazole. J Antimicrob Chemother 2007; 59:441-50. [PMID: 17261564 DOI: 10.1093/jac/dkl521] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
OBJECTIVES The fungal pathogen Candida albicans forms biofilms on implanted medical devices, resulting in infections with high mortality. Fully developed biofilms, which are adherent communities of microorganisms, characteristically exhibit high resistance to antimicrobial drugs, making treatment of device-associated infection problematic. The aim of this study was to determine the effect of the addition of the azole antifungal fluconazole on the initiation of biofilm formation by both drug-susceptible and drug-resistant C. albicans strains. RESULTS Our data reported here show that biofilm formation by both fluconazole-susceptible and fluconazole-resistant C. albicans strains was inhibited when fluconazole was present. For the fluconazole-susceptible strains, inhibition of growth due to the presence of the antifungal drug probably prevented the acquisition of high-level fluconazole resistance. However, for fluconazole-resistant strains, the inhibition of biofilm development was unexpected. CONCLUSIONS Unexpectedly, fluconazole inhibited biofilm formation by a variety of laboratory isolated and clinically isolated fluconazole-resistant strains.
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Affiliation(s)
- Igor Bruzual
- Department of Molecular Biology and Microbiology, Tufts University, 136 Harrison Ave., Boston, MA 02111, USA
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81
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Cannizzo FT, Eraso E, Ezkurra PA, Villar-Vidal M, Bollo E, Castellá G, Cabañes FJ, Vidotto V, Quindós G. Biofilm development by clinical isolates ofMalassezia pachydermatis. Med Mycol 2007; 45:357-61. [PMID: 17510859 DOI: 10.1080/13693780701225767] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
Malassezia pachydermatis fungemia has been reported in patients receiving parenteral nutrition. Biofilm formation on catheters may be related to the pathogenesis of this mycosis. We investigated the biofilm-forming ability of 12 M. pachydermatis strains using a metabolic activity plate-based model and electronic microscopic evaluation of catheter surfaces. All M. pachydermatis strains developed biofilms but biofilm formation showed variability among the different strains unrelated to their clinical origin. This study demonstrates the ability of M. pachydermatis to adhere to and form biofilms on the surfaces of different materials, such as polystyrene and polyurethane.
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Affiliation(s)
- Francesca T Cannizzo
- Laboratorio de Micología Médica, Departamento de Inmunología, Microbiología y Parasitología, Facultad de Medicina y Odontología, Universidad del País Vasco-Euskal Herriko Unibertsitatea, Bilbao, Spain
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82
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Affiliation(s)
- Deborah A Hogan
- Department of Microbiology and Immunology, HB7550, Dartmouth Medical School, Hanover NH 03755, USA.
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83
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Zhao X, Daniels KJ, Oh SH, Green CB, Yeater KM, Soll DR, Hoyer LL. Candida albicans Als3p is required for wild-type biofilm formation on silicone elastomer surfaces. MICROBIOLOGY-SGM 2006; 152:2287-2299. [PMID: 16849795 PMCID: PMC2583121 DOI: 10.1099/mic.0.28959-0] [Citation(s) in RCA: 141] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Candida albicans ALS3 encodes a large cell-surface glycoprotein that has adhesive properties. Immunostaining of cultured C. albicans germ tubes showed that Als3p is distributed diffusely across the germ tube surface. Two-photon laser scanning microscopy of model catheter biofilms grown using a PALS3-green fluorescent protein (GFP) reporter strain showed GFP production in hyphae throughout the biofilm structure while biofilms grown using a PTPI1-GFP reporter strain showed GFP in both hyphae and yeast-form cells. Model catheter biofilms formed by an als3 Delta/als3 Delta strain were weakened structurally and had approximately half the biomass of a wild-type biofilm. Reintegration of a wild-type ALS3 allele restored biofilm mass and wild-type biofilm structure. Production of an Als3p-Ag alpha 1p fusion protein under control of the ALS3 promoter in the als3 Delta/als3 Delta strain restored some of the wild-type biofilm structural features, but not the wild-type biofilm mass. Despite its inability to restore wild-type biofilm mass, the Als3p-Ag alpha 1p fusion protein mediated adhesion of the als3 Delta/als3 Delta C. albicans strain to human buccal epithelial cells (BECs). The adhesive role of the Als3p N-terminal domain was further demonstrated by blocking adhesion of C. albicans to BECs with immunoglobulin reactive against the Als3p N-terminal sequences. Together, these data suggest that portions of Als3p that are important for biofilm formation may be different from those that are important in BEC adhesion, and that Als3p may have multiple functions in biofilm formation. Overexpression of ALS3 in an efg1 Delta/efg1 Delta strain that was deficient for filamentous growth and biofilm formation resulted in growth of elongated C. albicans cells, even under culture conditions that do not favour filamentation. In the catheter biofilm model, the ALS3 overexpression strain formed biofilm with a mass similar to that of a wild-type control. However, C. albicans cells in the biofilm had yeast-like morphology. This result uncouples the effect of cellular morphology from biofilm formation and underscores the importance of Als3p in biofilm development on silicone elastomer surfaces.
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Affiliation(s)
- Xiaomin Zhao
- Department of Pathobiology, 2522 VMBSB, 2001 S. Lincoln Avenue, University of Illinois, Urbana, IL 61802, USA
| | - Karla J. Daniels
- Department of Biological Sciences, University of Iowa, Iowa City, IA 52242, USA
| | - Soon-Hwan Oh
- Department of Pathobiology, 2522 VMBSB, 2001 S. Lincoln Avenue, University of Illinois, Urbana, IL 61802, USA
| | - Clayton B. Green
- Department of Pathobiology, 2522 VMBSB, 2001 S. Lincoln Avenue, University of Illinois, Urbana, IL 61802, USA
| | - Kathleen M. Yeater
- Department of Pathobiology, 2522 VMBSB, 2001 S. Lincoln Avenue, University of Illinois, Urbana, IL 61802, USA
| | - David R. Soll
- Department of Biological Sciences, University of Iowa, Iowa City, IA 52242, USA
| | - Lois L. Hoyer
- Department of Pathobiology, 2522 VMBSB, 2001 S. Lincoln Avenue, University of Illinois, Urbana, IL 61802, USA
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LaFleur MD, Kumamoto CA, Lewis K. Candida albicans biofilms produce antifungal-tolerant persister cells. Antimicrob Agents Chemother 2006; 50:3839-46. [PMID: 16923951 PMCID: PMC1635216 DOI: 10.1128/aac.00684-06] [Citation(s) in RCA: 336] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Fungal pathogens form biofilms that are highly recalcitrant to antimicrobial therapy. The expression of multidrug resistance pumps in young biofilms has been linked to increased resistance to azoles, but this mechanism does not seem to underlie the resistance of mature biofilms that is a model of in vivo infection. The mechanism of drug resistance of mature biofilms remains largely unknown. We report that biofilms formed by the major human pathogen Candida albicans exhibited a strikingly biphasic killing pattern in response to two microbicidal agents, amphotericin B, a polyene antifungal, and chlorhexidine, an antiseptic, indicating that a subpopulation of highly tolerant cells, termed persisters, existed. The extent of killing with a combination of amphotericin B and chlorhexidine was similar to that observed with individually added antimicrobials. Thus, surviving persisters form a multidrug-tolerant subpopulation. Interestingly, surviving C. albicans persisters were detected only in biofilms and not in exponentially growing or stationary-phase planktonic populations. Reinoculation of cells that survived killing of the biofilm by amphotericin B produced a new biofilm with a new subpopulation of persisters. This suggests that C. albicans persisters are not mutants but phenotypic variants of the wild type. Using a stain for dead cells, rare dark cells were visible in a biofilm after amphotericin B treatment, and a bright and a dim population were physically sorted from this biofilm. Only the dim cells produced colonies, showing that this method allows the isolation of yeast persisters. Given that persisters formed only in biofilms, mutants defective in biofilm formation were examined for tolerance of amphotericin B. All of the known mutants affected in biofilm formation were able to produce normal levels of persisters. This finding indicates that attachment rather than formation of a complex biofilm architecture initiates persister formation. Bacteria produce multidrug-tolerant persister cells in both planktonic and biofilm populations, and it appears that yeasts and bacteria have evolved analogous strategies that assign the function of survival to a small part of the population. In bacteria, persisters are dormant cells. It remains to be seen whether attachment initiates dormancy that leads to the formation of fungal persisters. This study suggests that persisters may be largely responsible for the multidrug tolerance of fungal biofilms.
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Affiliation(s)
- Michael D LaFleur
- Department of Biology, Northeastern University, 360 Huntington Ave., 134 Mugar Hall, Boston, MA 02115, USA
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