Influence of culture media on biofilm formation by Candida species and response of sessile cells to antifungals and oxidative stress

Biofilm production by the multidrug-resistant fungus Candida haemulonii is affected by aspartic peptidase inhibitor

Candida haemulonii is an emerging, opportunistic, and multidrug-resistant fungal pathogen. Recently, our group reported the ability of C. haemulonii to form biofilm and secrete aspartic-type peptidases (Saps). Herein, we investigated the correlation between Saps production and biofilm formation along C. haemulonii growth in yeast carbon base medium supplemented with albumin (a Sap-inducing condition) and in the presence of the classical Sap inhibitor pepstatin A. Under these conditions, the biofilm biomass increased on a polystyrene surface, reaching its maximum at 96 h, while maximum biofilm viability was detected at 48 h. The release of Saps during biofilm formation showed an inverse trend, with the highest enzymatic activity measured after 24 h. In the presence of pepstatin A, a significant reduction in biofilm parameters (biomass and viability), as well as in albumin consumption by biofilm-forming cells was detected. These findings underscore the importance of Saps during the biofilm development in C. haemulonii.

The arrangement of dual-species biofilms of Candida albicans and Issatchenkia orientalis can be modified by the medium: effect of Voriconazole

Both Candida albicans and Issatchenkia orientalis have been isolated from different types of infections over the years. They have the ability to form communities of microorganisms known as biofilms. It has been demonstrated that the medium employed in studies may affect the biofilm development. The aim of this study was to investigate the arrangement of dual-species biofilms of C. albicans and I. orientalis cultivated on either RPMI-1640 or Sabouraud Dextrose Broth (SDB), as well as the inhibitory effect of Voriconazole (VRC). For the experiments performed, ATCC strains were used, and yeast-mixed suspensions were inoculated in 96-well plates with either RPMI-1640 or SDB, in the presence or absence of VRC. The results were observed by counting the number of CFU obtained from scraping off the biofilms produced and plating the content on CHROMagar Candida medium. It was observed that for all conditions tested the medium chosen affected the arrangement of dual-species biofilms: when RPMI-1640 was used, there was a prevalence of C. albicans, while the opposite was noted when SDB was used. It could be suggested that the medium and environment could regulate interactions between both yeast species, including the response to different antifungal drugs.

Miconazole induces aneuploidy-mediated tolerance in Candida albicans that is dependent on Hsp90 and calcineurin

Antifungal resistance and antifungal tolerance are two distinct terms that describe different cellular responses to drugs. Antifungal resistance describes the ability of a fungus to grow above the minimal inhibitory concentration (MIC) of a drug. Antifungal tolerance describes the ability of drug susceptible strains to grow slowly at inhibitory drug concentrations. Recent studies indicate antifungal resistance and tolerance have distinct evolutionary trajectories. Superficial candidiasis bothers millions of people yearly. Miconazole has been used for topical treatment of yeast infections for over 40 years. Yet, fungal resistance to miconazole remains relatively low. Here we found different clinical isolates of Candida albicans had different profile of tolerance to miconazole, and the tolerance was modulated by physiological factors including temperature and medium composition. Exposure of non-tolerant strains with different genetic backgrounds to miconazole mainly induced development of tolerance, not resistance, and the tolerance was mainly due to whole chromosomal or segmental amplification of chromosome R. The efflux gene CDR1 was required for maintenance of tolerance in wild type strains but not required for gain of aneuploidy-mediated tolerance. Heat shock protein Hsp90 and calcineurin were essential for maintenance as well as gain of tolerance. Our study indicates development of aneuploidy-mediated tolerance, not resistance, is the predominant mechanism of rapid adaptation to miconazole in C. albicans, and the clinical relevance of tolerance deserves further investigations.

Estimating the expression levels of genes controlling biofilm formation and evaluating the effects of different conditions on biofilm formation and secreted aspartic proteinase activity in Candida albicans and Saccharomyces cerevisiae: a comparative study

Background

Characterization of yeast virulence genes is an important tool for identifying the molecular pathways involved in switching yeast virulence. Biofilm formation (BF) and secreted aspartic proteinase (SAP) activity are essential virulence factors that contribute to yeast pathogenicity.

Results

Four Candida albicans and two Saccharomyces cerevisiae strains were tested for BF and SAP activity under optimum conditions, and the expression levels of several genes controlling BF were quantified under the optimal conditions. Biofilm formation was assessed by the microplate method at different pH values, incubation times and culture media. Similarly, SAP activity was assessed at different pH values and incubation periods. The expression levels of nine genes were determined via qRT-PCR technique. All tests were carried out in triplicate, and the values presented as the means ± standard deviations and were analysed with the SPSS programme. Only C. albicans (1), C. albicans (2) and S. cerevisiae 43 formed biofilms. The optimal BF was obtained after culture in sabouraud dextrose broth with 8% glucose at pH 7.5, 4 and 6, respectively, for 48h. Candida albicans biofilm production was more significant than that of S. cerevisiae 43. Moreover, the SAP activity was estimated under the optimum conditions. All yeasts showed optimal SAP activity at pH 4, but astonishingly the SAP activity of S. cerevisiae 44 was higher than that of C. albicans. The expression levels of EFG1 and ZAP1 (transcription factors); ALS3, HWP1and YWP1 (adhesion genes); SAP1 and SAP4 (aspartic proteinase) in C. albicans (1); and FLO11 (adhesion gene) and YPS3 (aspartic proteinase) in S. cerevisiae 43 were quantified during biofilm development at different time intervals. The expression levels of EFG1, ALS3, YWP1, SAP1, SAP4, FLO11 and YPS3 were upregulated at 8 h, while that of ZAP1 was upregulated at 48 h. Only HWP1 was downregulated.

Conclusions

The findings of the present study may provide information for overcoming yeast BF and pathogenicity by regulating specific genes at specific times. Additionally, this study revealed the virulence of the commensal S. cerevisiae, which may take the pathogenicity direction as C. albicans.

Synergistic Interactions between Pseudomonas aeruginosa and Candida albicans, Candida glabrata, Candida krusei, Candida parapsilosis as well as Candida tropicalis in the Formation of Polymicrobial Biofilms

The interactions between pathogens during infection and the impact of these interactions on drug effectiveness are poorly understood, making polymicrobial infections challenging to treat. During an infection, cross-interactions between bacteria and fungi can strengthen virulence mechanisms and affect how the disease develops. The purpose of this study is to determine how Pseudomonas aeruginosa interacts with Candida glabrata, Candida albicans, Candida krusei, Candida parapsilosis, and Candida tropicalis in the development of polymicrobial biofilms. Pseudomonas aeruginosa, Candida albicans, Candida krusei, Candida parapsilosis, Candida glabrata, and Candida tropicalis isolates were used in this experimental investigation. After preparing a 0.5 Mc Farland suspension of each isolate, the gold standard for measuring biofilm was applied: the Tissue Plate Culture (TCP) method. After that, an ELISA reader with a wavelength of 595 nm was used to measure the optical density (OD) of the biofilm. SPSS 26.0 was then used for statistical analysis to compare the OD values between Pseudomonas aeruginosa that had not been exposed to Candida and those that had. Pseudomonas aeruginosa and Candida are found to interact synergistically if there is an increase in OD, and antagonistic interaction is discovered if there is a decrease in OD. In comparison to the group that was not exposed to Candida, Pseudomonas aeruginosa exposed to Candida albicans, Candida krusei, Candida parapsilosis, Candida glabrata, and Candida tropicalis showed an increase in the OD value of biofilm. Pseudomonas aeruginosa and Candida albicans, Candida glabrata, Candida krusei, Candida parapsilosis, and Candida tropicalis interact synergistically.

Exploring the Complexity of the Interaction between T. rubrum and S. aureus/S. epidermidis in the Formation of Polymicrobial Biofilms

Dermatophytes associated with bacteria can lead to severe, difficult-to-treat infections and contribute to chronic infections. Trichophyton rubrum, Staphylococcus aureus, and Staphylococcus epidermidis can form biofilms influenced by nutrient availability. This study investigated biofilm formation by these species by utilizing diverse culture media and different time points. These biofilms were studied through scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), biomass, metabolic activity, and colony-forming units (CFUs). The results revealed that mixed biofilms exhibited high biomass and metabolic activity when cultivated in the brain heart infusion (BHI) medium. Both bacterial species formed mature biofilms with T. rubrum within 72 h, irrespective of media. The timing of bacterial inoculation was pivotal in influencing biomass and metabolic activity. T. rubrum's development within mixed biofilms depended on bacterial addition timing, while pre-adhesion influenced fungal growth. Bacterial communities prevailed initially, while fungi dominated later in the mixed biofilms. CLSM revealed 363 μm thick T. rubrum biofilms with septate, well-developed hyphae; S. aureus (177 μm) and S. epidermidis (178 μm) biofilms showed primarily cocci. Mixed biofilms matched T. rubrum's thickness when associated with S. epidermidis (369 μm), with few hyphae initially. Understanding T. rubrum and Staphylococcal interactions in biofilms advances antimicrobial resistance and disease progression knowledge.

Real-time monitoring of biofilm growth identifies andrographolide as a potent antifungal compound eradicating Candida biofilms

Candida species cause life-threatening infections with high morbidity and mortality rates and their resistance to conventional therapy is closely linked to biofilm formation. Thus, the development of new approaches to study Candida biofilms and the identification of novel therapeutic strategies could yield improved clinical outcomes. In the current study, we have set up an impedance-based in vitro system to study Candida spp. biofilms in real-time and to evaluate their sensitivity to two conventional antifungal groups used in clinical practice - azoles and echinocandins. Both fluconazole and voriconazole were unable to inhibit biofilm formation in most strains tested, while echinocandins showed biofilm inhibitory capacity at relatively low concentrations (starting from 0.625 mg/L). However, assays performed on 24 h Candida albicans and C. glabrata biofilms revealed that micafungin and caspofungin failed to eradicate mature biofilms at all tested concentrations, evidencing that once formed, Candida spp. biofilms are extremely difficult to eliminate using currently available antifungals. We then evaluated the antifungal and anti-biofilm effect of andrographolide, a natural compound isolated from the plant Andrographis paniculata with known antibiofilm activity on Gram-positive and Gram-negative bacteria. Optical density measures, impedance evaluation, CFU counts, and electron microscopy data showed that andrographolide strongly inhibits planktonic Candida spp. growth and halts Candida spp. biofilm formation in a dose-dependent manner in all tested strains. Moreover, andrographolide was capable of eliminating mature biofilms and viable cell numbers by up to 99.9% in the C. albicans and C. glabrata strains tested, suggesting its potential as a new approach to treat multi-resistant Candida spp. biofilm-related infections.

The inhibitory effect of photodynamic therapy on dual-species biofilms of Candida albicans and Candida krusei can be determined by Candida albicans/Candida krusei ratio

Candida krusei and Candida albicans present the ability to form communities of microorganisms called biofilms. Biofilms can be composed of a single species or more and are an important virulence factor. The inhibition of C. albicans and C. krusei as well as of their dual-species biofilms by antimicrobial Photodynamic Therapy (aPDT) has been demonstrated. This study aimed to investigate the effect of aPDT, with TBO, on dual-species biofilms of C. albicans and C. krusei using different culture mediums, RPMI-1640 and Sabouraud-dextrose broth (SDB) to produce biofilms presenting different C. albicans/C. krusei ratio. Biofilms formed using RPMI-1640 presented a higher C. albicans/C. krusei ratio, however, biofilms formed using SDB presented a predominance of C. krusei. The metabolic activity of biofilms produced using RPMI-1640 was inhibited by aP (∼40%), while biofilms produced using SDB were not affected by aPDT. In addition, biofilm biomass was reduced in biofilms produced using RPMI-1640 and treated with aPDT (∼20%). The results demonstrated that aPDT reduces C. albicans development in dual-species biofilms with C. krusei. However, no effect could be observed on C. krusei, demonstrating that C. krusei, when present in the structure of dual-species biofilms can be resistant to aPDT.

Dental Plaque Removal with Two Special Needs Toothbrushes in Patients with Down Syndrome: A Parallel-Group Randomised Clinical Trial of Efficacy

PURPOSE

To compare the effectiveness of two varieties of special needs toothbrushes in terms of dental plaque removal and bacterial contamination vs a conventional toothbrush in patients with Down syndrome.

MATERIALS AND METHODS

This single-blinded, two-group, randomised clinical trial included 16 patients diagnosed with Down syndrome (age 6-15 years) from various special needs centers located in the Jazan Province of Saudi Arabia. The patients were randomly allocated to two groups based on the type of special needs toothbrush provided (Collis Curve or superfine nano). The plaque and bleeding indices of the patients in both groups were measured at baseline (T0) and both groups were initially given a conventional toothbrush to use for four weeks. After this period, the plaque and bleeding indices were re-evaluated (T1). The patients were instructed to use the special needs toothbrush for 4 weeks, after which the periodontal indices were re-evaluated (T2). Microbial contamination on the bristles of the special needs brushes was evaluated at T2.

RESULTS

No notable changes in the mean plaque and bleeding indices were observed between the two groups at each visit; however, statistically significant reductions were noted between visits in both groups (p < 0.05). The CFU scores in cultures from the Collis Curve toothbrush bristles (1411.5 ± 541.1) were higher than those obtained from the superfine nano-toothbrush bristles (1118.3 ± 423.9), but without statistically significant differences.

CONCLUSION

The findings indicate that the use of special needs toothbrushes can statistically significantly improve the gingival health status in individuals with Down syndrome in terms of both resolution of periodontal inflammation and reduction of plaque accumulation.

2D nanomaterial sensing array using machine learning for differential profiling of pathogenic microbial taxonomic identification

An integrated custom cross-response sensing array has been developed combining the algorithm module’s visible machine learning approach for rapid and accurate pathogenic microbial taxonomic identification. The diversified cross-response sensing array consists of two-dimensional nanomaterial (2D-n) with fluorescently labeled single-stranded DNA (ssDNA) as sensing elements to extract a set of differential response profiles for each pathogenic microorganism. By altering the 2D-n and different ssDNA with different sequences, we can form multiple sensing elements. While interacting with microorganisms, the competition between ssDNA and 2D-n leads to the release of ssDNA from 2D-n. The signals are generated from binding force driven by the exfoliation of either ssDNA or 2D-n from the microorganisms. Thus, the signal is distinguished from different ssDNA and 2D-n combinations, differentiating the extracted information and visualizing the recognition process. Fluorescent signals collected from each sensing element at the wavelength around 520 nm are applied to generate a fingerprint. As a proof of concept, we demonstrate that a six-sensing array enables rapid and accurate pathogenic microbial taxonomic identification, including the drug-resistant microorganisms, under a data size of n = 288. We precisely identify microbial with an overall accuracy of 97.9%, which overcomes the big data dependence for identifying recurrent patterns in conventional methods. For each microorganism, the detection concentration is 10⁵ ~ 10⁸ CFU/mL for Escherichia coli, 10² ~ 10⁷ CFU/mL for E. coli-β, 10³ ~ 10⁸ CFU/mL for Staphylococcus aureus, 10³ ~ 10⁷ CFU/mL for MRSA, 10² ~ 10⁸ CFU/mL for Pseudomonas aeruginosa, 10³ ~ 10⁸ CFU/mL for Enterococcus faecalis, 10² ~ 10⁸ CFU/mL for Klebsiella pneumoniae, and 10³ ~ 10⁸ CFU/mL for Candida albicans. Combining the visible machine learning approach, this sensing array provides strategies for precision pathogenic microbial taxonomic identification.

Identification of Secondary Metabolites from Mexican Plants with Antifungal Activity against Pathogenic Candida Species

In the last three decades, invasive fungal infections caused by Candida species have become an important public health problem, because they are associated with high rates of morbidity and mortality in immunocompromised and hospitalized patients. The diagnosis and treatment of candidiasis are difficult and usually inefficient. Accordingly, a diversity of available drugs, currently employed to attack candidiasis, frequently induce resistance in patients promoting toxicity due to long-term treatments. Therefore, development of accurate diagnoses and novel antifungals is of high priority to improve life’s quality and expectancy of individuals infected with this pathogen. Plants are invaluable sources of new biologically active compounds. Among the plants used in Mexico in traditional herbolary medicine which have empirically been demonstrated to have antifungal activity are Pedilanthus tithymaloides, Thymus vulgaris, and Ocimum basilicum. In the present study, we analyzed whether these plants contain metabolites with antifungal activity against five Candida species. The extracts from the different plant organs were obtained by macerating them in ethyl alcohol or hexane and filtering. The obtained extracts were preserved in amber flasks at 4°C until used. The minimum inhibitory concentrations (MICs) of the active compound were determined by a microdilution assay. In addition, the following secondary metabolites were identified: linalool (3,7-dimethylocta-1,6-dien-3-ol), eugenol (4-allyl-2-methoxyphenol), limonene (1-methyl-4-(1-methylethenyl)-cyclohexene), and borneol ([(2R)-1,7,7-trimethyl-2-bicyclo[2.2.1]heptanyl] formate). All these compounds were found in the three plants, traditionally used in everyday life, and proved to be effective against Candida species and therefore a viable alternative to conventional antifungals.

Multi-Strain and -Species Investigation of Volatile Metabolites Emitted from Planktonic and Biofilm Candida Cultures

Candida parapsiliosis is a prevalent neonatal pathogen that attains its virulence through its strain-specific ability to form biofilms. The use of volatilomics, the profiling of volatile metabolites from microbes is a non-invasive, simple way to identify and classify microbes; it has shown great potential for pathogen identification. Although C. parapsiliosis is one of the most common clinical fungal pathogens, its volatilome has never been characterised. In this study, planktonic volatilomes of ten clinical strains of C. parapsilosis were analysed, along with a single strain of Candida albicans. Headspace-solid-phase microextraction coupled with gas chromatography-mass spectrometry were employed to analyse the samples. Species-, strain-, and media- influences on the fungal volatilomes were investigated. Twenty-four unique metabolites from the examined Candida spp. (22 from C. albicans; 18 from C. parapsilosis) were included in this study. Chemical classes detected across the samples included alcohols, fatty acid esters, acetates, thiols, sesquiterpenes, and nitrogen-containing compounds. C. albicans volatilomes were most clearly discriminated from C. parapsilosis based on the detection of unique sesquiterpene compounds. The effect of biofilm formation on the C. parapsilosis volatilomes was investigated for the first time by comparing volatilomes of a biofilm-positive strain and a biofilm-negative strain over time (0–48 h) using a novel sampling approach. Volatilomic shifts in the profiles of alcohols, ketones, acids, and acetates were observed specifically in the biofilm-forming samples and attributed to biofilm maturation. This study highlights species-specificity of Candida volatilomes, and also marks the clinical potential for volatilomics for non-invasively detecting fungal pathogens. Additionally, the range of biofilm-specificity across microbial volatilomes is potentially far-reaching, and therefore characterising these volatilomic changes in pathogenic fungal and bacterial biofilms could lead to novel opportunities for detecting severe infections early.

Effect of Voriconazole on Biofilm of Filamentous Species Isolated from Keratitis

Background: Biofilm formation is a vital feature of the pathogenesis in filamentous fungi. Objectives: Herein, we investigated in vitro antifungal pattern of biofilm of filamentous species keratitis isolates, and the effect of different concentrations of voriconazole on biofilm morphology changes using scanning electron microscopy. Methods: Here 25 ocular fungal isolates were included (Fusarium solani; (n = 15) and Aspergillus flavus; (n = 10). We determined the biofilm formation of isolates in terms of their susceptibilities to different antifungals on sessile cells. This procedure was performed according to CLSI-M38-3rd. Biofilm morphology changes revealed with scanning electron microscopy (SEM). Results: Twelve F. solani strains displayed the capacity to form biofilms from patients wearing contact lenses, while 8 A. flavus strains were recovered from cornea scrapings of trauma. Itraconazole, posaconazole and natamycin had the maximum activity against biofilms of all tested filamentous strains (MIC ranging from 0.031 - 0.25 µg/mL, 0.031 - 0.25 µg/mL and 2 - 4 µg/mL), respectively. Three F. solani and one A. flavus strains showed the high MIC values against voriconazole (MIC ≥ 1 µg/mL). Posaconazole revealed the lowest MIC values against biofilms of two strains (MIC ranging from 0.031 - 0.25 µg/mL); however, no significant difference was observed for itraconazole (P > 0.05). The efficacy of 16 µg/mL and 4 µg/mL of voriconazole was confirmed for biofilm of F. solani and A. flavus, respectively. The considerable changes in the morphologies of improved biofilms were seen by SEM. Conclusions: For the successful treatment of fungal biofilm infections, it was necessary to have knowledge of the mechanism of action, penetration rates, and therapeutic concentrations of drugs.

Candida albicans Biofilm Formation and Growth Optimization for Functional Studies Using Response Surface Methodology

AIM

Optimization of Candida growth and biofilm formation is essential for understanding the recalcitrance of this pathogen to advance functional analysis on hospital tools and material surfaces. Optimization and quantification of biofilm have always been a challenge using the conventional One Variable at a Time (OVAT) method. The present study uses Central Composite Design-based Response Surface Methodology for optimization of conditions to induce growth and biofilm formation in Candida albicans on polystyrene microtitre plates.

METHODS & RESULTS

The variables considered in the design matrix were pH, temperature, incubation period, shaker speed, and inoculum size. A four-pronged quantification approach with XTT assay (cell viability), crystal violet assay (biofilm), calcofluor white assay, and wet/dry weight measurements (cell mass) were used to understand different aspects of biofilm. Heterogeneity in growth conditions for local strains of C. albicans clinical isolates were observed. Cell viability and cell mass were inversely related; however, biofilm was independent of these two factors. The study also highlighted the fact that Foetal Bovine Serum does not significantly contribute to cell adhesion and biofilm formation in vitro.

CONCLUSIONS

A high throughput optimization of C. albicans growth and biofilm formation on polystyrene microplate has been developed & validated.

SIGNIFICANCE AND IMPACT OF STUDY

The microtiter plate-based approach can be used for future screening of therapeutics for the control of C. albicans.

Multifactorial Mechanisms of Tolerance to Ketoconazole in Candida albicans

Candida albicans is a prevalent opportunistic human fungal pathogen for which treatment is limited to only four main classes of antifungal drugs, with the azole and echinocandin classes being used most frequently. Drug tolerance, the ability of some cells to grow slowly in supra-MIC drug concentrations, decreases the number of available treatment options. Here, we investigated factors affecting tolerance and resistance to ketoconazole in C. albicans. We found both temperature and the composition of growth medium significantly affected tolerance with little effect on resistance. In deletion analysis of known efflux pump genes, CDR1 was partially required for azole tolerance, while CDR2 and MDR1 were dispensable. Tolerance also required Hsp90 and calcineurin components; CRZ1, which encodes a transcription factor downstream of calcineurin, was required only partially. Deletion of VMA11, which encodes a vacuolar ATPase subunit, and concanamycin A, a V-ATPase inhibitor, abolished tolerance, indicating the importance of vacuolar energy transactions in tolerance. Thus, tolerance to ketoconazole is regulated by multiple factors, including physiological and genetic mechanisms. IMPORTANCE Due to the ever-expanding range of invasive medical procedures and treatments, invasive fungal infections now pose a serious global threat to many people living in an immunocompromised status. Like humans, fungi are eukaryotic, which significantly limits the number of unique antifungal targets; the current arsenal of antifungal agents is limited to just three frontline drug classes. Additional treatment complexities result from the development of drug tolerance and resistance, which further narrows therapeutic options; however, the difference between tolerance and resistance remains largely unknown. This study demonstrates that tolerance and resistance are regulated by multiple genetic and physiological factors. It is prudent to note that some factors affect tolerance only, while other factors affect both tolerance and resistance. The complex underlying mechanisms of these drug responses are highlighted by the fact that there are both shared and distinct mechanisms that regulate tolerance and resistance.

The Impact of Cultivation Media on the In Vitro Biofilm Biomass Production of Candida spp

The yeasts of the genus Candida are among the most clinically significant fungal pathogenic agents. One of the unique features of the Candida species' pathogenicity is their ability to form biofilms. Generally, infections caused by biofilm-forming microorganisms tend to have chronic course and are difficult to treat. This fact highlights the need to search for drugs with anti-biofilm activities. At present, there are variety of protocols for performing antifungal anti-biofilm activity testing in which fundamental differences, especially in the choice of cultivation media for biofilm formation, can be noted. In our study, we focused on the effect of four different culture media on biofilm biomass formation in ten Candida spp. strains. With emphasis placed on clinical significance, strains of the C. albicans species were predominantly included in this study. Based on our results, we can conclude that the availability of other components in the culture media, such as amino acids or proteins, and not just the commonly mentioned glucose availability, helps promote the transition of Candida yeasts into a sessile form and leads to in vitro robust biofilm formation. We revealed that biofilm formation in C. albicans strains was enhanced, especially in media supplemented with fetal bovine serum (FBS). The nutritionally balanced cultivation medium with 10 g/L glucose and 10% (v/v) FBS evidently showed the most significant benefit for in vitro biofilm production in C. albicans strains.

Biofilm Formation by Histoplasma capsulatum in Different Culture Media and Oxygen Atmospheres

Histoplasma capsulatum is a dimorphic fungus that causes an important systemic mycosis called histoplasmosis. It is an infectious disease with high prevalence and morbidity that affects the general population. Recently, the ability of these fungi to form biofilms, a phenotype that can induce resistance and enhance virulence, has been described. Despite some efforts, data regarding the impact of nutrients and culture media that affect the H. capsulatum biofilm development in vitro are not yet available. This work aimed to study H. capsulatum biofilms, by checking the influence of different culture media and oxygen atmospheres in the development of these communities. The biofilm formation by two strains (EH-315 and G186A) was characterized under different culture media: [Brain and Heart Infusion (BHI), Roswell Park Memorial Institute (RPMI) with 2% glucose, Dulbecco’s Modified Eagle’s Medium (DMEM) supplemented with 10% fetal bovine serum and nutrient medium HAM-F12 (HAM-F12) supplemented with glucose (18.2 g/L), glutamic acid (1 g/L), HEPES (6 g/L) and L-cysteine (8.4 mg/L)] and oxygen atmospheres (aerobiosis and microaerophilia), using the XTT reduction assay to quantify metabolic activities, crystal violet staining for biomass, safranin staining for the quantification of polysaccharide material and scanning electron microscopy (SEM) for the observation of topographies. Results indicated that although all culture mediums have stimulated the maturation of the communities, HAM-F12 provided the best development of biomass and polysaccharide material when compared to others. Regarding the oxygen atmospheres, both stimulated an excellent development of the communities, however in low oxygen conditions an exuberant amount of extracellular matrix was observed when compared to biofilms formed in aerobiosis, mainly in the HAM-F12 media. SEM images showed yeasts embedded by an extracellular matrix in several points, corroborating the colorimetric assays. However, biofilms formed in BHI, RPMI, and DMEM significantly induced yeast to hyphae reversal, requiring further investigation. The results obtained so far contribute to in vitro study of biofilms formed by these fungi and show that nutrition promoted by different media modifies the development of these communities. These data represent advances in the field of biofilms and contribute to future studies that can prove the role of these communities in the fungi-host interaction.

Electric toothbrush for biofilm control in individuals with Down syndrome: a crossover randomized clinical trial

Poor oral hygiene seems to be the norm in children and teenagers with Down Syndrome (DS). Advances in design and types of toothbrushes may improve biofilm control. This randomized, single-blind, crossover clinical trial evaluated the effectiveness of electric toothbrushes regarding mechanical control of biofilm in children and teenagers with DS and their cooperation. Twenty-nine participants with DS, aged 6 to 14 years, used both types of toothbrushes: electric (ET) and manual (MT). The order of use of the different types of toothbrushes was randomly defined, including a 7-day period with each type with 7-day washout period in between. The Turesky-Quigley-Hein biofilm index was used before and after brushing to assess the effectiveness of the technique. Frankl's behavioral scale was used during toothbrushing to assess the participants' cooperation. Paired T-test, Mann Whitney, Chi-square, and Fisher's Exact tests were applied, with a significance level of 5%. The quantity of dental biofilm was significantly reduced after both brushing techniques (p < 0.001). However, no significant difference was found in total biofilm (ET: 0.73 ± 0.36; MT: 0.73 ± 0.34; p = 0.985) or % biofilm reduction (ET: 72.22%; MT: 70.96%; p = 0.762) after brushing between techniques or in % biofilm reduction between toothbrushes of age groups (6 -9 years, p = 0.919; 10-14 years, p = 0.671). Participants showed similar cooperation level with the two types of toothbrush (p = 1.000). The use of electric or manual toothbrush had no effect on the quantity of dental biofilm removed in children and teenagers with DS, nor did it influence their cooperation during the procedure.

Effect of phenotypic switching on biofilm traits in Candida tropicalis

Candida tropicalis can undergo multiple forms of phenotypic switching. We have reported a switching system in C. tropicalis that is associated with changes in virulence attributes. We aimed to assess biofilm formation by distinct switch states of C. tropicalis and evaluate whether their sessile cells exhibit altered virulence traits. C. tropicalis strains included the parental phenotype (a clinical isolate) and four switch phenotypes (crepe, rough, revertant of crepe and revertant of rough). Biofilm formation and adhesion capability of sessile cells on polystyrene were assessed through quantification of total biomass. Filamentous forms were characterized by direct counting of sessile cells. A virulence assay was conducted using the Galleria mellonella infection model. Switch variants (crepe and rough) and their revertant counterparts produced higher biofilm biomass (P < 0.05) than the parental strain. Additionally, filamentous forms were enriched among sessile cells of switched strains compared to those observed for sessile cells of the parental strain, with the exception of the revertant of rough. Sessile cells of switched strains showed higher adhesion to polystyrene compared to the parental strain. Sessile cells of the crepe variant and its revertant strain (RC) exhibited higher virulence against G. mellonella larvae than sessile cells of the parental strain. Our findings indicate that switching events in C. tropicalis affect biofilm development and that sessile cells of distinct switch states may exhibit increased adhesion ability and enhanced virulence towards G. mellonella larvae.

Simple Carbohydrate Derivatives Diminish the Formation of Biofilm of the Pathogenic Yeast Candida albicans

The opportunistic human fungal pathogen Candida albicans relies on cell morphological transitions to develop biofilm and invade the host. In the current study, we developed new regulatory molecules, which inhibit the morphological transition of C. albicans from yeast-form cells to cells forming hyphae. These compounds, benzyl α-l-fucopyranoside and benzyl β-d-xylopyranoside, inhibit the hyphae formation and adhesion of C. albicans to a polystyrene surface, resulting in a reduced biofilm formation. The addition of cAMP to cells treated with α-l-fucopyranoside restored the yeast-hyphae switch and the biofilm level to that of the untreated control. In the β-d-xylopyranoside treated cells, the biofilm level was only partially restored by the addition of cAMP, and these cells remained mainly as yeast-form cells.

Role of major facilitator superfamily transporter Qdr2p in biofilm formation by Candida glabrata

Candida glabrata represents the second-most frequent cause of candidiasis infections of the mucosa, bloodstream and genito-urinary tract in immunocompromised individuals. The incidence of C glabrata infection has increased significantly in the last two decades, mainly due to this species' abilities to resist various antifungal drugs and to form biofilms. We focused on the relationship between biofilm formation and the product of QDR2, a C glabrata member of the major facilitator superfamily (MFS) gene family, given that fungal biofilm formation limits drug penetration and is associated with persistent infection. The fungal cells in biofilms were compared between a C glabrata ∆qdr2 mutant and its wild-type strain. Cells were analysed for metabolism activity and drug susceptibility (using tetrazolium assay), adhesion activity, growth assay and intracellular pH (using flow cytometry). Compared to the wild type, the C glabrata ∆qdr2 showed lower adhesion activity and higher fluconazole susceptibility when assessed as a biofilm. The mutant also showed decreased metabolic activity during biofilm formation. Furthermore, the mutant grew more slowly under neutral-basic pH conditions. The qdr2 deletion in C glabrata resulted in an impaired ability to maintain pH homeostasis, which led in turn to a reduction of cell growth and of adherence to an artificial matrix. These results suggested that the Qdr2p function is needed for proper biofilm formation and biofilm maintenance in C glabrata as well as biofilm drug resistance towards fluconazole. Qdr2p may play an important role in C glabrata's ability to form biofilms on implanted medical devices in human bodies.

Thermosensitive hydrogels as a controlled release system for alkannin to improve localized treatment of Candida vaginitis after external beam radiotherapy in vitro and in vivo

External beam radiotherapy increases the risk of Candida vaginitis in cervical cancer patients, which brings a lot of insufferable influence to their life. Here, we explored the efficacy of alkannin in the treatment of Candida vaginitis after external beam radiotherapy. We exploit thermosensitive hydrogel-mediated alkannin as the topical formulation in a rat model established in our work. Periodic acid-Schiff of vaginas indicated little Candida albicans adhered to the vaginal tissue in treatment group. Additionally, hematoxylin and eosin stain revealed that inflammatory response of high dose alkannin was reduced. Above all, the animal model was first established in our work for the clinical desire. Our results suggested the promising application of alkannin for the disease with satisfying fungicidal activity and anti-inflammatory activity.

Candida spp. and phagocytosis: multiple evasion mechanisms

Invasive fungal infections are a global health problem, mainly in hospitals, where year by year hundreds of patients die because of these infections. Commensal yeasts may become pathogenic to human beings, affecting mainly immunocompromised patients. During infectious processes, the immune system uses phagocytes to eliminate invader microorganisms. In order to prevent or neutralize phagocyte attacks, pathogenic yeasts can use virulence factors to survive, as well as to colonize and infect the host. In this review, we describe how Candida spp., mainly Candida albicans, interact with phagocytes and use several factors that contribute to immune evasion. Polymorphism, biofilm formation, gene expression and enzyme production mediate distinct functions such as adhesion, invasion, oxidative stress response, proteolysis and escape from phagocytes. Fungal and human cells have similar structures and mechanisms that decrease the number of potential targets for antifungal drugs. Therefore, research on host-pathogen interaction may aid in the discovery of new targets and in the development of new drugs or treatments for these diseases and thus to save lives.

The clinical Biofilm Ring Test: a promising tool for the clinical assessment of biofilm-producing Candida species

Candida species are opportunistic pathogens responsible for a variety of diseases, ranging from skin and mucosal lesions to severe systemic, life-threatening infections. Candida albicans accounts for more than 70% of all Candida infections, however, the clinical relevance of other species such as Candida parapsilosis and Candida krusei are being increasingly recognized. Biofilm-producing yeasts cells acquire an increased resistance to antifungal agents, often leading to therapeutic failure and chronic infection. Conventional methods such as crystal violet (CV) and tetrazolium (XTT) reduction assay, developed to evaluate biofilm formation in Candida species are usually time-consuming, present a high intra- and inter-assay variability of the results and are therefore hardly applicable to routine diagnostics. This study describes an in-vitro assay developed for the measurement of biofilm formation in Candida species based on the clinical Biofilm Ring Test® (cBRT). We found a significant concordance between the cBRT and both CV (k = 0.74) and XTT (k = 0.62), respectively. Nevertheless, the cBRT resulted more reliable and reproducible than CV and XTT, requiring a minimal sample manipulation and allowing a high throughput assessment, directly on viable cells. The results indicate that the cBRT may provide a suitable, cost-effective technique for routine biofilm testing in clinical microbiology.

The use of polyhydroxylated carboxylic acids and lactones to diminish biofilm formation of the pathogenic yeastCandida albicans

The vaginal microbiome of healthy women is a diverse and dynamic system of various microorganisms. Any sudden change in microbe composition can increase the vaginal pH and thus lead to vaginal infections, conditions that affect a large percentage of women each year. The most common fungal strains involved in infections belong to the yeast species Candida albicans. The main virulence factor of C. albicans is the ability to transform from planktonic yeast-form cells into a filamentous form (hyphae or pseudohyphae), with the subsequent formation of biofilm. The hyphal form, constituted by filamentous cells, has the ability to invade tissue and induce inflammation. Our hypothesis is that certain polyhydroxylated carboxylic acids, that may serve as an alternative carbohydrate source and at the same time lower the pH, function as an indicator of a nutrient-rich environment for C. albicans, which favors planktonic cells over hyphae, and thus diminish the formation of biofilm. We have shown that the biofilm formation in C. albicans and other Candida species can be significantly reduced by the addition of glucono-δ-lactone (GDL).

Treatment of Candida albicans with glucono δ-lactone results in less formation of hyphae and diminish biofilm formation.

Tetrasodium EDTA Is Effective at Eradicating Biofilms Formed by Clinically Relevant Microorganisms from Patients' Central Venous Catheters

The colonization of catheters by microorganisms often precludes their long-term use, which can be a problem for human patients that have few body sites available for new catheters. The colonizing organisms often form biofilms, and increasingly these organisms are resistant to multiple antibiotics, making them difficult to treat. In this article, we have taken microorganisms that are associated with biofilm formation in catheters from two Canadian hospitals and tested them with tetrasodium EDTA, a new antimicrobial catheter lock solution. Tetrasodium EDTA was effective at eliminating Gram-positive, Gram-negative, and fungal species and represents a promising alternative to antibiotic treatment with less chance of the organisms developing resistance. We expect that our results will be of interest to researchers and clinicians and will lead to improved patient care.

Central venous access devices (CVADs) are an essential component of modern health care. However, their prolonged use commonly results in microbial colonization, which carries the potential risk of hospital-acquired bloodstream infections. These infections complicate the treatment of already sick individuals and cost the existing health care systems around the world millions of dollars. The microbes that colonize CVADs typically form multicellular biofilms that are difficult to dislodge and are resistant to antimicrobial treatments. Clinicians are searching for better ways to extend the working life span of implanted CVADs, by preventing colonization and reducing the risk of bloodstream infections. In this study, we analyzed 210 bacterial and fungal isolates from colonized CVADs or human bloodstream infections from two hospitals geographically separated in the east and west of Canada and screened the isolates for biofilm formation in vitro. Twenty isolates, representing 12 common, biofilm-forming species, were exposed to 4% tetrasodium EDTA, an antimicrobial lock solution that was recently approved in Canada for use as a medical device. The EDTA solution was effective at eradicating surface-attached biofilms from each microbial species, indicating that it could likely be used to prevent biofilm growth within CVADs and to eliminate established biofilms. This new lock solution fits with antibiotic stewardship programs worldwide by sparing the use of important antibiotic agents, targeting prevention rather than the expensive treatment of hospital-acquired infections.

IMPORTANCE The colonization of catheters by microorganisms often precludes their long-term use, which can be a problem for human patients that have few body sites available for new catheters. The colonizing organisms often form biofilms, and increasingly these organisms are resistant to multiple antibiotics, making them difficult to treat. In this article, we have taken microorganisms that are associated with biofilm formation in catheters from two Canadian hospitals and tested them with tetrasodium EDTA, a new antimicrobial catheter lock solution. Tetrasodium EDTA was effective at eliminating Gram-positive, Gram-negative, and fungal species and represents a promising alternative to antibiotic treatment with less chance of the organisms developing resistance. We expect that our results will be of interest to researchers and clinicians and will lead to improved patient care.

A study on biofilm production and antifungal drug resistance among Candida species from vulvovaginal and bloodstream infections

Introduction

Candida species, one among the opportunistic fungi, has become a common pathogen causing vaginal thrush and nosocomial bloodstream infections (BSIs). This study aims to evaluate the prevalence and antifungal susceptibility of various Candida species and slime production by Candida species in BSIs and vulvovaginal candidiasis (VVC).

Materials and methods

A total of 176 samples were collected for a period of 1 year. Anti-fungal susceptibility testing and biofilm production testing were performed by the Kirby-Bauer method and crystal violet assay, respectively.

Results

Out of 176 samples, 74 (42%) were from BSIs and 102 (58%) were from VVC. The biofilm production was comparatively high in blood isolates, 55 (74%), than cervical isolates, 45 (44%). Increase in the trends of non-albicans Candida (NAC) species was seen in our setup. Good susceptibility rates were seen among Candida species, 82.38% to voriconazole and an increasing resistance pattern of 26.13% to fluconazole.

Conclusion

Speciation of Candida becomes important as the prevalence of NAC is increasing. Antifungal susceptibility testing by the disk diffusion method is cost effective and should be adopted in routine testing as there is an increasing azole resistance, especially in invasive NAC infections. In this study, there was no correlation of antifungal drugs with the biofilm production.

Isolation and characterization of culturable bacteria present in the spent nuclear fuel pool water

A spent nuclear fuel (SNF) pool is a key facility for safe management of nuclear waste, where spent nuclear fuel rods are stored in a water pool. The spent fuel rods carry a significant amount of radioactivity; they are either recycled or stored for further processing. Pool water acts as a heat sink as well as a shield against the radiation present in spent/burned fuel rods. The water used in these pools is filtered by an ultra-filtration process which makes certain the purity of water. As the life span of these pools is approximately 20 to 40 years, the maintenance of pure water is a big challenge. A number of researchers have shown the presence of bacterial communities in this ultrapure water. The bacterial types present in SNF pool water is of increasing interest for their potential bioremediation applications for radioactive waste. The present study showed the isolation of six bacterial species in the SNF pool water samples, which had significant radio-tolerance (D₁₀ value 248 Gy to 2 kGy) and also biofilm-forming capabilities. These strains were also investigated for their heavy metal removal capacity. Maximum biofilm-mediated heavy metal (Co and Ni) removal (up to 3.8 μg/mg of biomass) was observed by three isolates (FPB1, FPB4, and FPB6). The ability of these bacterial isolates to survive in radioactive environments can be of great interest for remediation of radioactive contaminants.

Candida species isolated from different body sites and their antifungal susceptibility pattern: Cross-analysis of Candida albicans and Candida glabrata biofilms

Candida species are regular commensal in humans, but-especially in immunocompromised patients-they represent opportunistic pathogens giving rise to systemic infection. The aim of the present work was to isolate and characterize for their antifungal profile Candida species from different body sites and to analyze the biofilms produced by C. albicans and C. glabrata isolates. Eighty-one strains of Candida species from 77 patients were identified. Epidemiological study showed that the most isolated species were C. albicans (44), C. glabrata (13) and C. parapsilosis (13) mainly from Hematology, Infectious Diseases, Medicine, Neonatology and Oncology Divisions, the majority of the biological samples were swabs (44) and blood cultures (16). The analysis of the biofilm formation was performed at 24 and 48-hours comparing resistant and susceptible strains of C. albicans to resistant and susceptible strains of C. glabrata. Candida albicans has a greater ability to form biofilm compared to C. glabrata, both in the susceptible and resistant strains reaching maturity after 24 hours with a complex structure composed of blastospores, pseudohyphae, and hyphae embedded in a matrix. On the contrary, C. glabrata biofilm was composed exclusively of blastospores that in the resistant strain, after 24 hours, were organized in a compact multilayer different to the discontinuous structure observed in the susceptible analyzed strains. In conclusion, the increasing of the incidence of Candida species infection together with their emerging drug resistance also related to the biofilm forming capability underline the need to monitor their distribution and susceptibility patterns for improving the surveillance and for a correct management of the infection.

The optimal ethanol lock therapy regimen for treatment of biofilm-associated catheter infections: an in-vitro study

BACKGROUND

Ethanol-based lock therapy (LT) solutions are used as an alternative to antibiotics for the conservative management of catheter-related bloodstream infection. However, no clear consensus on regimen or dose has been reached.

AIM

To find the ethanol-based lock solution containing a sufficiently low concentration of ethanol for reduction of the metabolic activity of bacterial and fungal biofilms.

METHODS

Using an in-vitro model, three concentrations of ethanol (25%, 40%, 70%) were tested, with and without 60 IU of heparin, at six different time-points and against 24 h preformed biofilms of Staphylococcus aureus ATCC29213, Staphylococcus epidermidis (clinical isolate), Enterococcus faecalis ATCC33186, Candida albicans ATCC14058, and Escherichia coli ATCC25922. The reduction in the metabolic activity of the biofilm was measured using the tetrazolium salt assay and LT was considered to be successful when metabolic activity fell by >90%. Regrowth inhibition was then tested within 24 h and seven days after each LT regimen only at the ethanol concentration of the most successful LT regimen.

FINDINGS

The most successful LT was achieved with 40% ethanol + 60 IU of heparin only at 24, 72, and 24 h for seven-day regimens (P < 0.05). However, none of the regimens reached 45% RI within seven days of therapy.

CONCLUSION

According to our in-vitro data, an ethanol-based lock solution with 40% ethanol + 60 IU heparin administered daily for 72 h is sufficient to almost eradicate the metabolic activity of bacterial and fungal biofilms. Future studies are needed to study cell regrowth after LT.

In vitro assessment of the anti-biofilm activity of ethanol alone and in combination with enoxaparin 60IU

INTRODUCTION

Catheter-related bloodstream infection (C-RBSI) can sometimes be managed without catheter removal by combining systemic therapy with catheter lock therapy. Most antiseptic lock solutions are made up of ethanol combined with an anticoagulant. However, data regarding the anti-biofilm activity of ethanol combined with enoxaparin are scarce. We aimed to assess the efficacy of ethanol at different concentrations combined with enoxaparin 60IU as a lock solution for eradication of the biofilm of different microorganisms.

METHODS

Using a static 96-well plate in vitro model, we tested 30%, 35%, and 40% ethanol alone and combined with 60IU of enoxaparin against 24-h-old biofilm from the following microorganisms: Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Escherichia coli, and Candida albicans. Time of exposure was assessed during a 2-h and 24-h regimen. We analysed the percentage reduction in metabolic activity using the XTT assay. We considered therapy to be successful when metabolic activity was reduced by >90%.

RESULTS

In the 2-h regimen, the therapy was successful against all microorganisms at 35% and 40% ethanol without enoxaparin (p<0.001). In the 24-h regimen, the therapy was successful against all microorganisms at all ethanol solutions without enoxaparin (p<0.001). When ethanol was combined with enoxaparin, the therapy was only successful in the 24-h regimen in biofilms of S. epidermidis, C. albicans and E. coli at all concentrations of ethanol assessed.

CONCLUSIONS

Our in vitro model demonstrated that when ethanol is combined with enoxaparin in a lock solution, it negatively affects ethanol anti-biofilm activity after both short and long exposures.

The Effect of Nutritive and Non-Nutritive Sweeteners on the Growth, Adhesion, and Biofilm Formation of Candida albicans and Candida tropicalis

OBJECTIVE

To determine the effect of glucose, sucrose, and saccharin on growth, adhesion, and biofilm formation of Candida albicans and Candida tropicalis.

MATERIALS AND METHODS

The growth rates of mono-cultures of planktonic C. albicans and C. tropicalis and 1:1 mixed co-cultures were determined in yeast nitrogen broth supplemented with 5% (30 mM) and 10% (60 mM) glucose, sucrose, and saccharin, using optical density measurements at 2-h intervals over a 14-h period. Adhesion and biofilm growth were performed and the growth quantified using a standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The biofilm architecture was visualized using scanning electron microscopy. One- and two-way analysis of variance (ANOVA) was performed to analyse the differences among multiple means.

RESULTS

The highest planktonic growth was noted in 5% glucose after 14 h (p < 0.05). No significant planktonic growth was observed in either concentration of saccharin. Both the concentrations of glucose and sucrose elicited significantly increased adhesion from MTT activity of 0.017 to >0.019 in mono- as well as co-cultures (p < 0.05), whilst the lower concentration of saccharin significantly dampened the adhesion. Maximal biofilm growth was observed in both species with the lower concentration of sucrose (5%), although a similar concentration of saccharin abrogated biofilm development: the highest MTT value (>0.35) was obtained for glucose and the lowest (>0.15) for saccharin.

CONCLUSION

In this study, glucose and sucrose accelerated the growth, adhesion, and biofilm formation of Candida species. However, the non-nutritive sweetener saccharin appeared to dampen, and in some instances suppress, these virulent attributes of Candida.

Inhibition of secreted aspartyl proteinase activity in biofilms of Candida species by mycogenic silver nanoparticles

Candida species are pleomorphic, commensal fungi associated with candidiasis. The extracellular hydrolytic-secreted aspartyl proteinases are recognized as chief agents for pathogenesis of Candida species, involved in the degradation of proteins and adhesion during biofilm formation. This study aimed at exploring inhibitory effect of mycogenic silver nanoparticles (Ag NPs) against C. albicans and non-albicans' biofilm growth and aspartyl proteinase enzyme activity in-vitro. Biofilm forming, drug-resistant clinical isolates of C. albicans (n = 25) and non-albicans (n= 20) were assessed for their ability to reduce the metabolic and aspartyl proteinase activities using XTT assay and spectrophotometric analysis at different concentrations of mycogenic Ag NPs. After 24 h of incubation, significant reduction (>50%) in metabolic activity was observed with 100 ppm mycogenic Ag NPs. Incubation time has greater inhibitory effect against Candida spp. biofilms secreted aspartyl proteinase after treatment with 100 ppm mycogenic Ag NPs. Inhibition of secreted aspartyl proteinase by mycogenic Ag NPs provides an insight towards the mechanism for the treatment of Candida-associated infections involving biofilms-related infections.

Assessment of herbal drugs for promising anti-Candida activity

BACKGROUND

Microbial infections are diverse and cause serious human diseases. Candida albicans infections are serious healthcare-related infections that are complicated by its morphological switching from yeast to hyphae, resistant biofilm formation and mixed infections with bacteria. Due to the increase in drug resistance to currently used antimicrobial agents and the presence of undesirable side effects, the need for safe and effective novel therapies is important. Compounds derived from plants are known for their medicinal properties including antimicrobial activities. The purpose of the study was to compare and evaluate the anti-Candida activities of several medicinal plants in order for the selection of a herbal drug for human use as effective antimicrobial. The selection was taking into considerations two important parameters; parameters related to the selected drug including activity, stability, solubility and toxicity and parameters related to the pathogen including its different dynamic growth and its accompanied secondary bacterial infections.

METHODS

Seven different plants including Avicennia marina (Qurm), Fagonia indica (Shoka'a), Lawsania inermis (Henna), Portulaca oleracea (Baq'lah), Salvadora persica (Souwak), Ziziphus spina- Christi (Sidr) and Asphodelus tenuifolius (Kufer) were ground and extracted with ethanol. The ethanol extracts were evaporated and the residual extract dissolved in water prior to testing against Candida albicans in its different morphologies. The antibacterial and cytotoxic effects of the plants extracts were also tested.

RESULTS

Out of the seven tested plants, L. inermis and P. oleracea showed significant anti-Candida activity with MIC ~10 μg/mL. Furthermore, both plant extracts were able to inhibit C. albicans growth at its dynamic growth phases including biofilm formation and age resistance. Accompanied secondary bacterial infections can complicate Candida pathogenesis. L. inermis and P. oleracea extracts showed effective antibacterial activities against S. aureus, P. aeruginosa, E. coli, and the multidrug resistant (MDR) A. baumannii and Klebsiella pneumoniae. Both extracts showed no toxicity when measured at their MIC on human erythrocytes.

CONCLUSION

The results from this study suggested that L. inermis and P. oleracea extracts and/or their chemicals are likely to be promising drugs for human use against C. albicans and MDR bacteria.

Identification of proteins involved in the adhesionof Candida species to different medical devices

Adhesion is the first step for Candida species to form biofilms on medical devices implanted in the human host. Both the physicochemical nature of the biomaterial and cell wall proteins (CWP) of the pathogen play a determinant role in the process. While it is true that some CWP have been identified in vitro, little is known about the CWP of pathogenic species of Candida involved in adhesion. On this background, we considered it important to investigate the potential role of CWP of C. albicans, C. glabrata, C. krusei and C. parapsilosis in adhesion to different medical devices. Our results indicate that the four species strongly adher to polyvinyl chloride (PVC) devices, followed by polyurethane and finally by silicone. It was interesting to identify fructose-bisphosphate aldolase (Fba1) and enolase 1 (Eno1) as the CWP involved in adhesion of C. albicans, C. glabrata and C. krusei to PVC devices whereas phosphoglycerate kinase (Pgk) and Eno1 allow C. parapsilosis to adher to silicone-made implants. Results presented here suggest that these CWP participate in the initial event of adhesion and are probably followed by other proteins that covalently bind to the biomaterial thus providing conditions for biofilm formation and eventually the onset of infection.

Biosynthesis of micro- and nanocrystals of Pb (II), Hg (II) and Cd (II) sulfides in four Candida species: a comparative study of in vivo and in vitro approaches

Nature produces biominerals (biogenic minerals) that are synthesized as complex structures, in terms of their physicochemical properties. These biominerals are composed of minerals and biological macromolecules. They are produced by living organisms and are usually formed through a combination of chemical, biochemical and biophysical processes. Microorganisms like Candida in the presence of heavy metals can biomineralize those metals to form microcrystals (MCs) and nanocrystals (NCs). In this work, MCs and NCs of PbS, HgS or HgCl₂ as well as CdS are synthesized both in vitro (gels) and in vivo by four Candida species. Our in vivo results show that, in the presence of Pb²⁺, Candida cells are able to replicate and form extracellular PbS MCs, whereas in the presence of Hg²⁺ and Cd²⁺, they did synthesize intercellular MCs from HgS or HgCl₂ and CdS NCs respectively. The MCs and NCs biologically obtained in Candida were compared with those PbS, HgS and CdS crystals synthetically obtained in vitro through the gel method (grown either in agarose or in sodium metasilicate hydrogels). This is, to our knowledge, the first time that the biosynthesis of the various MCs and NCs (presented in several species of Candida) has been reported. This biosynthesis is differentially regulated in each of these pathogens, which allows them to adapt and survive in different physiological and environmental habitats.

Culture media profoundly affect Candida albicans and Candida tropicalis growth, adhesion and biofilm development

As there are sparse data on the impact of growth media on the phenomenon of biofilm development for Candida we evaluated the efficacy of three culture media on growth, adhesion and biofilm formation of two pathogenic yeasts, Candida albicans and Candida tropicalis. The planktonic phase yeast growth, either as monocultures or mixed cultures, in sabouraud dextrose broth (SDB), yeast nitrogen base (YNB), and RPMI 1640 was compared, and adhesion as well as biofilm formation were monitored using MTT and crystal violet (CV) assays and scanning electron microscopy. Planktonic cells of C. albicans, C. tropicalis and their 1:1 co-culture showed maximal growth in SDB. C. albicans/C. tropicalis adhesion was significantly facilitated in RPMI 1640 although the YNB elicited the maximum growth for C. tropicalis. Similarly, the biofilm growth was uniformly higher for both species in RPMI 1640, and C. tropicalis was the slower biofilm former in all three media. Scanning electron microscopy images tended to confirm the results of MTT and CV assay. Taken together, our data indicate that researchers should pay heed to the choice of laboratory culture media when comparing relative planktonic/biofilm growth of Candida. There is also a need for standardisation of biofilm development media so as to facilitate cross comparisons between laboratories.

Management of Candida biofilms: state of knowledge and new options for prevention and eradication

Biofilms formed by Candida species (spp.) on medical devices represent a potential health risk. The focus of current research is searching for new options for the treatment and prevention of biofilm-associated infections using different approaches including modern nanotechnology. This review summarizes current information concerning the most relevant resistance/tolerance mechanisms to conventional drugs and a role of additional factors contributing to these phenomena in Candida spp. (mostly Candida albicans). Additionally, it provides an information update in prevention and eradication of a Candida biofilm including experiences with 'lock' therapy, potential utilization of small molecules in biomedical applications, and perspectives of using photodynamic inactivation in the control of a Candida biofilm.

Moonlight-like proteins of the cell wall protect sessile cells of Candida from oxidative stress

Biofilms of Candida species are associated with high morbidity and hospital mortality. Candida forms biofilms by adhering to human host epithelium through cell wall proteins (CWP) and simultaneously neutralizing the reactive oxygen species (ROS) produced during the respiratory burst by phagocytic cells. The purpose of this paper is to identify the CWP of Candida albicans, Candida glabrata, Candida krusei and Candida parapsilosis expressed after exposure to different concentrations of H2O2 using a proteomic approach. CWP obtained from sessile cells, both treated and untreated with the oxidizing agent, were resolved by one and two-dimensional (2D-PAGE) gels and identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Some of these proteins were identified and found to correspond to moonlighting CWP such as: (i) glycolytic enzymes, (ii) heat shock, (iii) OSR proteins, (iv) general metabolic enzymes and (v) highly conserved proteins, which are up- or down-regulated in the presence or absence of ROS. We also found that the expression of these CWP is different for each Candida species. Moreover, RT-PCR assays allowed us to demonstrate that transcription of the gene coding for Eno1, one of the moonlight-like CWP identified in response to the oxidant agent, is differentially regulated. To our knowledge this is the first demonstration that, in response to oxidative stress, each species of Candida, differentially regulates the expression of moonlighting CWP, which may protect the organism from the ROS generated during phagocytosis. Presumptively, these proteins allow the pathogen to adhere and form a biofilm, and eventually cause invasive candidiasis in the human host. We propose that, in addition to the antioxidant mechanisms present in Candida, the moonlighting CWP also confer protection to these pathogens from oxidative stress.