Colonization of Candida albicans on cleaned human dental hard tissues

Exploring the biomedical potential of a novel modified glass ionomer cement against the pandrug-resistant oral pathogen Candida albicans SYN-01

Dental caries is an infectious disease that is a major concern for dentists. Streptococci and Lactobacilli were long thought to be the primary etiology responsible for caries. Candida albicans with acidogenic and aciduric characteristics has recently been implicated in the onset and progression of cariogenic lesions. Moreover, due to the increased resistance to common antimicrobials, the discovery of innovative candidates is in high demand. Therefore, our study might be the first report that explores the efficacy of glass ionomer cement (GIC) incorporated with a newly modified carboxylated chitosan derivative (CS-MC) against multidrug-resistant (MDR) and/or pandrug resistant (PDR) C. albicans isolated from the oral cavity. In this work, four CS-MC-GIC groups with different concentrations were formulated. Group four (CS-MC-GIC-4) gave a significant performance as an anticandidal agent against selected PDR Candida strain, with an obvious decrease in its cell viability and high antibiofilm activity. It also, enhanced all the mechanical properties and supports cell viability of Vero cells as a nontoxic compound. Moreover, CS-MC-GIC-4 inhibited neuraminidases completely, which might provide a novel mechanism to prevent dental/oral infections. Thus, findings in this study open up new prospect of the utilization of CS-MC-GIC as a novel dental filling material against oral drug-resistant Candida.

May carriers at nanoscale improve the Endodontic's future?

Nanocarriers (NCs) are dynamic nanovehicles used to transport bioactive derivatives like therapeutical formulations, drugs and/or dyes. The current review assists in understanding the mechanism of action of several recent developed NCs with antimicrobial purposes. Here, nine NCs varieties are portrayed with focus on nineteen approaches that are fulfil described based on outcomes obtained from in vitro antimicrobial assays. All approaches have previously been verified and we underline the biochemical challenges of all NCs, expecting that the present data may encourage the application of NCs in endodontic antimicrobial basic research. Methodological limitations and the evident base gaps made not possible to draw a definite conclusion about the best NCs for achieving efficient antimicrobial outcomes in endodontic studies. Due to the lack of pre-clinical trials and the scarce number of clinical trials in this emergent area, there is still much room for improvement on several fronts.

In Vitro and In Vivo Anti-infective Potential of Thymol Against Early Childhood Caries Causing Dual Species Candida albicans and Streptococcus mutans

Early childhood caries (ECC), a severe form of caries due to cross-kingdom interaction of Candida albicans and Streptococcus mutans, is a serious childhood dental disease that affects majority of the children with poor background. The present study investigated the anti-infective potential of thymol against C. albicans and S. mutans dual species for the management of ECC. Thymol, a plant derivative of the monoterpene group, has been well known for its numerous biological activities. Thymol at 300 μg/ml concentration completely arrested growth and proliferation of dual species of C. albicans and S. mutans. Rapid killing efficacy of pathogens, within a span of 2 min, was observed in the time kill assay. In addition, at sub-inhibitory concentrations, thymol effectively diminished the biofilm formation and virulence of both C. albicans and S. mutans such as yeast-to-hyphal transition, hyphal-to-yeast transition, filamentation, and acidogenicity and acidurity, respectively, in single and dual species state. qPCR analysis was consistent with virulence assays. Also, through the invertebrate model system Galleria mellonella, in vivo toxicity and efficacy of the phytocompound was assessed, and it was found that no significant toxic effect was observed. Moreover, thymol was found to be proficient in diminishing the infection under single and dual state in in vivo condition. Overall, the results from the present study illustrate the anti-infective potential of thymol against the ECC-causing dual species, C. albicans and S. mutans, and the applicability of thymol in medicated dentifrice formulation.

Quantification of the Adhesion Strength of Candida albicans to Tooth Enamel

Caries is one of the most prevalent diseases worldwide, which is caused by the degradation of the tooth enamel surface. In earlier research the opportunistic pathogen Candida albicans has been associated with the formation of caries in children. Colonization of teeth by C. albicans starts with the initial adhesion of individual yeast cells to the tooth enamel surface. In this study, we visualized the initial colonization of C. albicans yeast cells on pellicle-covered enamel by scanning electron microscopy. To quantitatively unravel the initial adhesion strength, we applied fluidic force microscopy-based single-cell force spectroscopy to examine the key adhesion parameters adhesion force, rupture length and de-adhesion work. We analyzed single saliva-treated or untreated yeast cells on tooth enamel specimens with or without salivary pellicle. Under all tested conditions, adhesion forces in the lower nanonewton range were determined. Furthermore, we have found that all adhesion parameters were enhanced on the pellicle-covered compared to the uncovered enamel. Our data suggest that initial adhesion occurs through a strong interaction between yeast cell wall-associated adhesins and the salivary pellicle. Future SCFS studies may show whether specific management of the salivary pellicle reduces the adhesion of C. albicans on teeth and thus contributes to caries prophylaxis.

Fungal species in endodontic infections: A systematic review and meta-analysis

Fungal infections are common on oral mucosae, but their role in other oral sites is ill defined. Over the last few decades, numerous studies have reported the presence of fungi, particularly Candida species in endodontic infections, albeit in relatively small numbers in comparison to its predominant anaerobic bacteriome. Here, we review the fungal biome of primary and secondary endodontic infections, with particular reference to the prevalence and behavior of Candida species. Meta-analysis of the available data from a total of 39 studies fitting the inclusion criteria, indicate the overall weighted mean prevalence (WMP) of fungal species in endodontic infections to be 9.11% (from a cumulative total of 2003 samples), with 9.0% in primary (n = 1341), and 9.3% in secondary infections (n = 662). Nevertheless, WMP for fungi in primary and secondary infections which were 6.3% and 7.5% for culture-based studies, increased to 12.5% and 16.0% in molecular studies, respectively. The most prevalent fungal species was Candida spp. The high heterogeneity in the reported fungal prevalence suggests the need for standardized sampling, and speciation methods. The advent of the new molecular biological analytical platforms, such as the next generation sequencing (NGS), and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF), that enables identification and quantitation of a broad spectrum of hitherto unknown organisms in endodontic infections should radically alter our understanding of the endodontic mycobiome in the future. Candida spp. appear to be co-pathogens with bacteria in approximately one in ten patients with endodontic infections. Hence, clinicians should comprehend the importance and the role of fungi in endodontic infections and be cognizant of the need to eradicate both bacteria and fungi for successful therapy.

Effects of cold atmospheric pressure plasma and disinfecting agents on Candida albicans in root canals of extracted human teeth

Reinfection in endodontically treated teeth is linked to the complexity of the root canal system, which is problematic to reach with conventional disinfection methods. As plasma is expected to have the ability to sanitize narrow areas, the aim of this study was to analyze the effect of cold atmospheric pressure plasma (CAP) on Candida albicans in root canals of extracted human teeth. CAP was applied as mono treatment and in combination with standard endodontic disinfectants (sodium hypochlorite, chlorhexidine and octenidine). Disinfection efficiency was evaluated as reduction of the logarithm of colony forming units per milliliter (log₁₀ CFU/mL) supported by scanning electron microscopy as imaging technique. Plasma alone showed the highest reduction of log₁₀ CFU, suggesting the best disinfection properties of all tested agents.

Effect of Silver Diamine Fluoride on Reducing Candida albicans Adhesion on Dentine

BACKGROUND

Candida albicans is the most frequent pathogenic fungus in oral cavities. It adheres to dental tissues as part of dental plaques and contributes to caries formation.

OBJECTIVES

To evaluate the effect of silver diamine fluoride (SDF) on reducing C. albicans adhesion on dentine surfaces.

METHODS

Flat dentine surfaces were prepared from bovine dental disks, and samples were divided into three groups. The first and second groups were pretreated for 3 min with 299 mM or 2.99 M SDF, respectively, and the third group (control) did not undergo any SDF pretreatment. All samples were washed, inoculated with C. albicans suspension onto their dentine surface, incubated at 30 °C for 6 h, and washed again to remove any nonadherent cells. The abundance of adherent cells was investigated using colorimetric and real-time polymerase chain reaction approaches. Subsequently, the morphological changes in C. albicans by pretreatment with SDF were observed under a scanning electron microscope (SEM).

RESULTS

SDF inhibited candidal growth at concentrations as low as 2.99 µM. Dentine disks pretreated with 299 mM or 2.99 M SDF displayed significantly fewer adhered cells as compared with the control group. Upon pretreatment with SDF, SEM images showed severe morphological changes in the cellular walls, in a dose-dependent manner, suggesting a fungicidal effect of SDF against the yeast.

CONCLUSION

SDF should be considered for clinical applications aimed at inhibiting dental plaque caused by C. albicans, particularly in children and elderly individuals.

Candida biome of severe early childhood caries (S-ECC) and its cariogenic virulence traits

The protected niche of deep-caries lesions is a distinctive ecosystem. We assessed the Candida biome and its cariogenic traits from dentin samples of 50 children with severe-early childhood caries (S-ECC). Asymptomatic, primary molars belonging to International Caries Detection and Assessment-ICDAS caries-code 5 and 6 were analyzed, and C. albicans (10-isolates), C. tropicalis (10), C. krusei (10), and C. glabrata (5) isolated from the lesions were then evaluated for their biofilm formation, acidogenicity, and the production of secreted hydrolases: hemolysins, phospholipase, proteinase and DNase. Candida were isolated from 14/43 ICDAS-5 lesions (32.5%) and 44/57 ICDAS-6 lesions (77.2%). Compared to, ICDAS-5, a significantly higher frequency of multi-species infestation was observed in ICDAS-6 lesions (p=0.001). All four candidal species (above) showed prolific biofilm growth, and an equal potency for tooth demineralization. A significant interspecies difference in the mean phospholipase, as well as proteinase activity was noted (p < 0.05), with C. albicans being the predominant hydrolase producer. Further, a positive correlation between phospholipase and proteinase activity of Candida-isolates was noted (r = 0.818, p < 0.001). Our data suggest that candidal mycobiota with their potent cariogenic traits may significantly contribute to the development and progression of S-ECC.

Candida albicans Increases Dentine Demineralization Provoked by Streptococcus mutans Biofilm

Streptococcus mutans are considered the most cariogenic bacteria, but it has been suggested that Candida albicans could increase their cariogenicity. However, the effect of this dual-species microorganisms' combination on dentine caries has not been experimentally evaluated. Biofilms of C. albicans, S. mutans and C. albicans + S. mutans (n = 12/biofilm) were grown in ultra-filtered tryptone yeast extract broth culture medium for 96 h on root dentine slabs of known surface hardness and exposed 8 times per day for 3 min to 10% sucrose. The medium was changed 2 times per day (after the 8 cariogenic challenges and after the overnight period of famine), and aliquots were analyzed to determinate the pH (indicator of biofilm acidogenicity). After 96 h, the biofilms were collected to determine the wet weight, colony-forming units, and the amounts of extracellular polysaccharides (soluble and insoluble). Dentine demineralization was assessed by surface hardness loss (% SHL). The architecture of the biofilms was analyzed by confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM). Data were analyzed by ANOVA followed by Tukey's test (α = 0.05). The dual-species C. albicans + S. mutans biofilm provoked higher % SHL on dentine (p < 0.05) than the S. mutans and C. albicans biofilm. This was supported by the results of biofilm acidogenicity and the amounts of soluble (6.4 ± 2.14 vs. 4.0 ± 0.94 and 1.9 ± 0.97, respectively) and insoluble extracellular polysaccharides (24.9 ± 9.22 vs. 18.9 ± 5.92 and 0.7 ± 0.48, respectively) (p < 0.05). The C. albicans biofilm alone presented low cariogenicity. The images by CLSM and TEM, respectively, suggest that the C. albicans + S. mutans biofilm is more voluminous than the S. mutans biofilm, and S. mutans cells interact with C. albicans throughout polysaccharides from the biofilm matrix. These findings show that C. albicans enhances the cariogenic potential of the S. mutans biofilm, increasing dentine demineralization.

The Role of Oral Cavity Biofilm on Metallic Biomaterial Surface Destruction-Corrosion and Friction Aspects

Metallic biomaterials in the oral cavity are exposed to many factors such as saliva, bacterial microflora, food, temperature fluctuations, and mechanical forces. Extreme conditions present in the oral cavity affect biomaterial exploitation and significantly reduce its biofunctionality, limiting the time of exploitation stability. We mainly refer to friction, corrosion, and biocorrosion processes. Saliva plays an important role and is responsible for lubrication and biofilm formation as a transporter of nutrients for microorganisms. The presence of metallic elements in the oral cavity may lead to the formation of electro-galvanic cells and, as a result, may induce corrosion. Transitional microorganisms such as sulfate-reducing bacteria may also be present among the metabolic microflora in the oral cavity, which can induce biological corrosion. Microorganisms that form a biofilm locally change the conditions on the surface of biomaterials and contribute to the intensification of the biocorrosion processes. These processes may enhance allergy to metals, inflammation, or cancer development. On the other hand, the presence of saliva and biofilm may significantly reduce friction and wear on enamel as well as on biomaterials. This work summarizes data on the influence of saliva and oral biofilms on the destruction of metallic biomaterials.

Is the oral fungal pathogen Candida albicans a cariogen?

Pathobiology of dental caries is complex. Data from recent molecular microbiologic studies have further redefined the role of the oral microbiome in the etiology of dental caries. This new information challenges the conventional view on the hegemony of classic cariogenic prokaryotes such as Streptococcus mutans in caries etiology, and raises the intriguing possibility of the participation of the eukaryotic oral fungal pathogen Candida in the caries process. The virulence attributes of Candida species such as their acidogenicity and aciduric nature, the ability to develop profuse biofilms, ferment and assimilate dietary sugars, and produce collagenolytic proteinases are all indicative of their latent cariogenic potential. Based on the above, oral candidal counts have been used by some as a caries risk indicator. On the contrary, other studies suggest that Candida is merely a passenger extant in an acidic cariogenic milieu, and not a true pathogen. In this review, we critically examine the varying roles of Candida, and traditionally accepted cariogens such as the mutans group of streptococci in the pathobiology of dental caries. The weight of available data tends to imply that Candida may play a pivotal role as a secondary agent perpetuating the carious process, especially in dentinal caries.

A randomized, double-blind, placebo-controlled clinical trial of fluoride varnish in preventing dental caries of Sjögren's syndrome patients

BACKGROUND

Sjögren's syndrome (SS) patients are prone to caries development due to reduction of salivary flow. Topical fluoride is commonly prescribed for caries prevention.

METHODS

In this 24-month randomized, double-blind, placebo-controlled clinical trial, SS patients were randomly assigned to receive either fluoride varnish or placebo gel quarterly. Development and arrest of caries at the coronal and root surfaces were recorded at 12-month and 24-month and compared to that of the baseline. Effect of fluoride varnish on oral Candida and lactobacilli colonization was explored by comparing baseline oral microbiological assessments to data obtained at 12-month and 24-month.

RESULTS

Seventy-eight SS patients (mean age = 50 years, 2 men) completed this trial. At 24-month, the mean new coronal enamel caries were 1.6 surfaces in both groups, and new dentin caries were 1.4 and 2.7 surfaces in the fluoride and placebo group respectively (p > 0.05). Mean arrested caries were 0.6 and 0.7 surfaces for fluoride and placebo groups respectively and that of root caries were 0.3 and 0.1 surfaces (p > 0.05). The mean oral Candida count was reduced by 30 % in the fluoride group but increased 61 % in the placebo group while no change in oral lactobacilli counts in both groups at 24 months (p > 0.05). SS patients receiving fluoride varnish were significantly less likely to develop dentin caries (p < 0.05). In contrast, those with high baseline DMFS scores (p = 0.05), harbored mixed Candida species (p < 0.05), or unstimulated whole saliva at low pH (p < 0.01) were significantly more likely to develop dentin caries.

CONCLUSIONS

Results of this randomized clinical trial did not provide clear evidence to support or refute that quarterly applications of fluoride varnish can prevent development of dental caries in people with Sjögren's syndrome.

TRIAL REGISTRATION

This study was retrospectively registered at the ISRCTN registry ( ISRCTN85164658 ) on 9 Sept 2016 and was funded by the Research Grant Council of Hong Kong.

β-lactam substituted polycyclic fused pyrrolidine/pyrrolizidine derivatives eradicate C. albicans in an ex vivo human dentinal tubule model by inhibiting sterol 14-α demethylase and cAMP pathway

BACKGROUND

Further quest for new anti-fungal compounds with proven mechanisms of action arises due to resistance and dose limiting toxicity of existing agents. Among the human fungal pathogens C. albicans predominate by infecting several sites in the body and in particular oral cavity and root canals of human tooth.

METHODS

In the present study, we screened a library of β-lactam substituted polycyclic fused pyrrolidine/pyrrolizidine compounds against Candida sp. Detailed molecular studies were carried out with the active compound 3 on C. albicans. Morphological damage and antibiofilm activity of compound 3 on C. albicans was studied using scanning electron microscopy (SEM). Biochemical evidence for membrane damage was studied using flow cytometry. In silico docking studies were carried out to elucidate the mechanism of action of compound 3. Further, the antifungal activity of compound 3 was evaluated in an ex vivo dentinal tubule infection model.

RESULTS

Screening data showed that several new compounds were active against Candida sp. Among them, Compound 3 was most potent and exerted time kill effect at 4h, post antifungal effect up to 6h. When used in combination with fluconazole or nystatin, compound 3 revealed an minimum inhibitory concentration (MIC) decrease by 4 fold for both drugs used. In-depth molecular studies with compound 3 on C. albicans showed that this compound inhibited yeast to hyphae (Y-H) conversion and this involved the cAMP pathway. Further, SEM images of C. albicans showed that compound 3 caused membrane damage and inhibited biofilm formation. Biochemical evidence for membrane damage was confirmed by increased propidium iodide (PI) uptake in flow cytometry. Further, in silico studies revealed that compound 3 docks with the active site of the key enzyme 14-α-demethylase and this might inhibit ergosterol synthesis. In support of this, ergosterol levels were found to be decreased by 32 fold in compound 3 treated samples as analyzed by high performance liquid chromatography (HPLC). Further, the antifungal activity of compound 3 was evaluated in an ex vivo dentinal tubule infection model, which mimics human tooth root canal infection. Confocal laser scanning microscopy studies showed 83% eradication of C. albicans and a 6 log reduction in colony forming unit (CFU) after 24h treatment in the infected tooth samples in this model.

CONCLUSION

Compound 3 was found to be very effective in eradicating C. albicans by inhibiting cAMP pathway and ergosterol biosynthesis.

GENERAL SIGNIFICANCE

The results of this study can pave the way for developing new antifungal agents with well deciphered mechanisms of action and can be a promising antifungal agent or medicament against root canal infection.

Genotypic diversity and cariogenicity of Candida albicans from children with early childhood caries and caries-free children

BACKGROUND

The genotypic diversity and cariogenicity of C. albicans from the dental plaque of children are poorly understood. This study aimed to explore the genotypic diversity and cariogenicity of C. albicans from children with early childhood caries and caries-free children.

METHODS

Dental plaque samples from 238 children with early childhood caries and from 125 caries-free children were collected for C. albicans isolation. A PCR method based on 25S rDNA was used to analyze C. albicans genotypes, and the strains with different genotypes were tested with regard to acidogenicity and aciduricity.

RESULTS

Among 129 C. albicans isolates, 79 (61.2 %) belonged to genotype A. The distribution frequency of genotypes A and C or genotypes B and C showed no significant difference between children with early childhood caries and caries-free children (p = 0.178 and 0.148), whereas genotypes A and B exhibited significantly different distributions (p = 0.010). No significant differences in aciduricity were found among the three genotypes, but the acidogenicity of genotypes B and C differed significantly from that of genotype A at pH 4.0.

CONCLUSIONS

The genotypic distribution of C. albicans is associated with the caries experience of children, and the genotype may be related to its acidogenicity at pH 4.0.

Impact of brief and sequential exposure to nystatin, amphotericin B, ketoconazole, and fluconazole in modulating adhesion traits of oral Candida dubliniensis isolates

AIM

Candida adherence is implicated in the pathogenesis of oral candidosis. Adhesion to buccal epithelial cells (BEC), germ tube (GT) formation, and relative cell surface hydrophobicity (CSH) are colonization attributes of candidal pathogenicity. Candida dubliniensis (C. dubliniensis) is allied with recurrent oral candidosis, which can be treated with nystatin, amphotericin B, ketoconazole, and fluconazole. Due to the diluent effect of saliva and the cleansing effect of the oral musculature in the oral cavity C. dubliniensis isolates undergo brief and sequential exposure to antifungal agents during therapy. Thus, in the present study, we evaluated the adhesion to BEC, GT formation, and the CSH of oral isolates of C. dubliniensis following brief and sequential exposure to nystatin, amphotericin B, ketoconazole, and fluconazole.

METHODS

After determining the minimum inhibitory concentration (MIC) of the aforementioned drugs, 20 oral isolates of C. dubliniensis were briefly (1 h), and sequentially (10 days) exposed to subcidal concentrations of these drugs. Following drug removal, adhesion to BEC, GT formation, and CSH of these isolates were determined.

RESULTS

The percentage reduction of adhesion to BEC, GT formation, and CSH of the isolates following exposure to antifungal agents were as follows: nystatin: 53.55%, 33.98%, and 29.83% (P < 0.001); amphotericin B: 53.84%, 36.23%, and 28.97% (P < 0.001); ketoconazole: 37.43%, 20.51%, and 16.49% (P < 0.001); and fluconazole: 8.93% (P < 0.001), 1.6%, and 0.63% (P > 0.05).

CONCLUSIONS

Brief and sequential exposure of C. dubliniensis to antifungal agents would continue to wield an antifungal effect by altering its adhesion attributes, and elucidate possible pharmacodynamics by which antifungal agents might operate in modulating candidal adherence.

Microorganism penetration in dentinal tubules of instrumented and retreated root canal walls. In vitro SEM study

Objectives

This in vitro study aimed to investigate the ability of Candida albicans (C. albicans) and Enterococcus faecalis (E. faecalis) to penetrate dentinal tubules of instrumented and retreated root canal surface of split human teeth.

Materials and Methods

Sixty intact extracted human single-rooted teeth were divided into 4 groups, negative control, positive control without canal instrumentation, instrumented, and retreated. Root canals in the instrumented group were enlarged with endodontic instruments, while root canals in the retreated group were enlarged, filled, and then removed the canal filling materials. The teeth were split longitudinally after canal preparation in 3 groups except the negative control group. The teeth were inoculated with both microorganisms separately and in combination. Teeth specimens were examined by scanning electron microscopy (SEM), and the depth of penetration into the dentinal tubules was assessed using the SMILE view software (JEOL Ltd).

Results

Penetration of C. albicans and E. faecalis into the dentinal tubules was observed in all 3 groups, although penetration was partially restricted by dentin debris of tubules in the instrumented group and remnants of canal filling materials in the retreated group. In all 3 groups, E. faecalis penetrated deeper into the dentinal tubules by way of cell division than C. albicans which built colonies and penetrated by means of hyphae.

Conclusions

Microorganisms can easily penetrate dentinal tubules of root canals with different appearance based on the microorganism size and status of dentinal tubules.

Determination of Candida species nestled in denture fissures

With the growing number of elderly individuals, Candida is occasionally recognised as a fungal cause of aspiration pneumonia. In addition, there are numerous investigational reports on oral candidiasis. However, there are currently no reports on Candida contamination of denture base materials. This study was conducted to investigate Candida species in the oral cavity, denture parts and oral lesions of older/elderly subjects with oral candidiasis. The Candida strains were isolated and the species identified. Candida was also cultured in a medium with sample of denture resin and observed under an electron microscope. The results demonstrated the presence of several Candida species in the lesions of the oral mucosa and the surface and inner portions of the dentures. The following species of Candida were detected: Candida albicans, Candida glabrata, Candida tropicalis and Candida parapsilosis. Using electron microscopy, the invasion of Candida was observed in the incomplete polymerized resin base material and/or through microcracks (fissures) that have a tendency to form in used dentures. It was concluded that Candida may be present on the surface as well as the deeper portions of dentures. In addition, it appeared necessary to consider denture and oral cavity cleaning and the risks of remaking old dentures.

Impact of brief and sequential exposure to nystatin on the germ tube formation and cell surface hydrophobicity of oral Candida albicans isolates from human immunodeficiency virus-infected patients

OBJECTIVE

To evaluate the impact of brief and sequential exposure to nystatin on the germ tube formation and cell surface hydrophobicity of oral isolates of Candida albicans obtained from patients infected with human immunodeficiency virus (HIV).

MATERIALS AND METHODS

After determining the minimum inhibitory concentration of nystatin, 10 oral isolates of C. albicans from 10 different HIV-infected patients were briefly (1 h) and sequentially (10 days) exposed to subtherapeutic concentrations of nystatin. Following a subsequent drug removal, the germ tube formation and cell surface hydrophobicity of these isolates were determined via a germ tube induction assay and an aqueous hydrocarbon assay, respectively. The data obtained from these assays for the control (unexposed to nystatin) and nystatin-exposed isolates were analyzed using Student's t tests.

RESULTS

The mean percentage reduction in the germ tube formation and cell surface hydrophobicity of the nystatin-exposed isolates compared to the controls was 30.12 ± 1.99 (p < 0.001) and 29.65 ± 2.33 (p < 0.001), respectively.

CONCLUSION

These data elucidate the possible pharmacodynamic mechanisms by which nystatin might operate in vivo in the modulation of candidal virulence.

The postantifungal effect of nystatin and its impact on adhesion attributes of oral Candida dubliniensis isolates

The postantifungal effect (PAFE) has an impact on candidal pathogenicity. However, there is no information on either the PAFE or its impact on adhesion traits of oral Candida dubliniensis isolates. Oral candidosis can be treated topically with nystatin. Adhesion to buccal epithelial cells (BEC), germ tube (GT) formation and relative cell surface hydrophobicity (CSH) are all colonisation attributes of candidal pathogenicity. Hence, the main objective of this study was to investigate the in vitro PAFE on 20 C. dubliniensis isolates following exposure to nystatin. In addition, the impact of nystatin-induced PAFE on adhesion to BEC, GT formation and relative CSH of C. dubliniensis isolates were also evaluated. After determining the minimum inhibitory concentration (MIC) of nystatin, C. dubliniensis isolates were exposed to sublethal concentrations of nystatin for 1 h. Following this exposure, the drug was removed and PAFE, adhesion to BEC, GT formation and relative CSH were determined by a previously described turbidometric method, adhesion assay, germ tube induction assay and biphasic aqueous-hydrocarbon assay respectively. MIC (μg/ml) of C. dubliniensis isolates to nystatin ranged from 0.09 to 0.78. The nystatin-induced mean PAFE (hours) on C. dubliniensis isolates was 2.17. Compared with the controls, exposure to nystatin suppressed the ability of C. dubliniensis isolates to adhere BEC, GT formation and relative CSH by a mean percentage reduction of 74.45% (P < 0.0001), 95.92% (P < 0.0001) and 34.81 (P < 0.05) respectively. Hence, brief exposure of C. dubliniensis isolates to nystatin would continue to wield an antifungal effect by suppressing growth as well as its adhesion attributes.

Differential collagenolytic activity of Candida albicans isolated from oral mucosa and dentinal carious lesions of HIV-infected children

OBJECTIVE

The aim of this study was to compare type I collagen degradation by Candida albicans isolated from oral mucosa (M) and cavitated active dentinal caries (CAD) of HIV-infected children.

STUDY DESIGN

To verify the proteolytic activity, the specimens were cultivated in brain-heart infusion medium and the supernatants were incubated in the presence or absence of type I collagen at 37°C for 12 hours and analyzed using 10% sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Intensity of the bands on the gels was assessed by densitometric analysis using a scanner and images analyzed with software from Kodak Digital Science EDAS 120.

RESULTS

Supernatants of all the C. albicans degraded type I collagen: that from M, on average, by 38.3% (SD 21.67) and that from CAD by 54% (SD 25.94; Wilcoxon test: P < .05). Predisposing factors had no association with the percentage of type I collagen degradation (Mann-Whitney test: P > .05).

CONCLUSIONS

Candida albicans from different sites of the oral cavity of HIV-infected children has proteolytic activity for type I collagen.

The influence of different types of fixed orthodontic appliance on the growth and adherence of microorganisms (in vitro study)

Orthodontic appliances serve as different impact zones and modify microbial adherence and colonization, acting as foreign reserves and possible sources of infection. This study was conducted to investigate the effect of different types of fixed orthodontic appliances on the growth and adherence of microorganisms in oral flora which are Streptococcus mutans (S. mutans) and Candida albicans. Sixty-four of four different fixed orthodontic appliance-samples were used, divided into four groups of sixteen. Type I: Sapphire brackets- Coated wires, type II: Sapphire brackets- Stainless steel wires, type III: Stainless steel brackets- Coated wires and type IV: Stainless steel brackets- Stainless steel wires. Oral strains of S. mutans and Candida albicans were studied in the present study using biochemical test then microbial suspensions were prepared to do the tests of each microorganism including the antimicrobial effects of different appliance-samples on the growth of microorganisms and their adhesion tests. The results showed significant differences between the different appliances in terms of inhibition zone formation (P<0.001). The adhesion test, which is classified into low, medium and high, showed the adhesion of S. mutans, is low with type I and II, medium with type III and high with type IV, whereas the adhesion of Candida albicans is medium with both type I and II and high with both type III and IV with high significant differences (P<0.001). Appliance with high esthetic appearance, sapphire brackets and coated arch wire, showed the least adherence of S. mutans and Candida albicans in comparison to other appliances with less esthetic and more metal components.

Key words:Orthodontic appliance, Adherence, Streptococcus mutans, Candida albicans.

Changes in the cell surface hydrophobicity of oral Candida albicans from smokers, diabetics, asthmatics, and healthy individuals following limited exposure to chlorhexidine gluconate

OBJECTIVE

The objective of this study was to determine the cell surface hydrophobicity of 40 oral Candida albicans isolates obtained from smokers, diabetics, asthmatics using steroid inhalers, and healthy individuals, following brief exposure to subtherapeutic concentrations of chlorhexidine gluconate.

MATERIALS AND METHODS

Forty C. albicans oral isolates (10 isolates each from smokers, diabetics, asthmatics using steroid inhalers, and healthy individuals) were exposed to 3 subtherapeutic concentrations of chlorhexidine gluconate (0.00125, 0.0025, and 0.005%) for 30 min. Thereafter, the antiseptic was removed and the cell surface hydrophobicity was measured by a biphasic aqueous-hydrocarbon assay.

RESULTS

Compared to the unexposed controls, the cell surface hydrophobicity of C. albicans isolates was suppressed by 5.40% (p > 0.05), 21.17% (p < 0.05), and 44.67% (p < 0.05) following exposure to 0.00125, 0.0025, and 0.005% chlorhexidine gluconate, respectively.

CONCLUSIONS

A brief period of transient exposure to subtherapeutic concentrations of chlorhexidine gluconate may modulate the cell surface hydrophobicity of C. albicans isolates and thereby may reduce candidal pathogenicity.

Adherence of Streptococcus mutans and Candida albicans to different bracket materials

Objective:

To quantify the adherence of Streptococcus mutans and Candida albicans on brackets made of stainless steel, plastic, ceramic, titanium, and gold, and to evaluate the various sites of adherence of these microorganisms with scanning electron microscopy (SEM).

Materials and Methods:

Brackets made of stainless steel, plastic, ceramic, titanium, and gold were used. The adherence of S. mutans and C. albicans were studied. The brackets were placed in flat-bottomed vials containing basal medium with 20% sucrose added; the flasks were inoculated with each of the microbial suspensions. The samples were incubated at 37°C for 48 h, after which the brackets were removed. The cells adhering to the glass were counted and the brackets were studied with SEM.

Results:

When evaluated together, the adherence of S. mutans and C. albicans was increased in the ceramic bracket group. When evaluated separately, metallic brackets had increased number of colony-forming units (CFUs) of S. mutans and the use of titanium brackets increased the CFUs of C. albicans. SEM demonstrated that the adherence of S. mutans and C. albicans together varied according to the bracket materials, with ceramic having the greatest and stainless steel having the least adherence.

Conclusions:

Oral hygiene may be of greater concern with esthetic brackets since this study shows that microbial adhesion is greater with these brackets.

Genotypic distribution of Candida albicans in dental biofilm of Chinese children associated with severe early childhood caries

AIM

Candida albicans causes a wide range of infections in the oral mucosa, especially candidiasis. A strong association has been found between C. albicans and dental caries. In this study, we investigated the presence and genotypic distribution of C. albicans in the dental biofilm of Chinese children with severe early childhood caries (S-ECC).

DESIGN

Dental biofilm samples were collected from 41 Chinese children (21 children with S-ECC and 20 children without caries) aged 3-6 years. Samples collected were cultured in CHROMagar Candida (CA) medium. Cellular DNA of typical C. albicans isolates in the CA medium was isolated, and PCR using primers reported to span a transposable intron region in the 25S rRNA gene was performed to determine genotypic subgroups.

RESULTS

C. albicans was detected in 57.1% of individuals with S-ECC. Additionally, three genotypic subgroups of C. albicans (genotypes A, B, and C) were found in children with S-ECC, and genotype A was dominant.

CONCLUSIONS

C. albicans is an important component of dental biofilm associated with S-ECC, and C. albicans genotypic subgroup A is the dominant strain in the dental biofilm of children with S-ECC.

Effects of subtherapeutic concentrations of chlorhexidine gluconate on germ tube formation of oral Candida

OBJECTIVE

The main objective of this study was to investigate the effect of brief exposure to subtherapeutic concentrations of chlorhexidine gluconate on germ tube formation of Candida albicans isolates obtained from smokers, diabetics, asthmatics using steroid inhalers and healthy individuals.

MATERIALS AND METHODS

Forty isolates of C. albicans were used in this study. All these isolates were quantified for germ tube formation without exposure to the drug and were used as the control group for data analysis. Isolates were also exposed to three subtherapeutic concentrations of chlorhexidine gluconate (0.00125, 0.0025 and 0.005%) for 30 min (limited exposure); the antiseptic was then removed and germ tube formation of these isolates was quantified microscopically following incubation in a germ tube-inducing medium.

RESULTS

Compared with the unexposed controls, brief exposure to all concentrations of chlorhexidine gluconate suppressed the ability of the C. albicans isolates to form germ tubes in increasing order by 13.72% (p < 0.001 to p = 0.02), 46.16% (p < 0.001) and 72.46% (p <0.001).

CONCLUSIONS

These findings show that brief exposure to subtherapeutic concentrations of chlorhexidine gluconate may modulate germ tube formation of C. albicans isolates, thereby suppressing their pathogenicity, and further elucidate the pharmacodynamic mechanisms by which chlorhexidine gluconate may operate in vivo.

Experiments on in vivo biofilm formation and in vitro adhesion of Candida species on polysiloxane liners

OBJECTIVES

Microorganisms may colonise polysiloxane soft liners leading to bio-deterioration. The aim of this study was to investigate in vitro adhesion and in vivo biofilm formation of Candida species on polysiloxane surfaces.

METHODS

The materials used in this study were Molloplast B, GC Reline soft, Mollosil Plus, Silagum Comfort and Palapress Vario. The in vitro retention of clinical isolates of Candida albicans to the relining and denture-base materials by microscopic (scanning electron microscopy, SEM), conventional culturing methods and antimicrobial properties of these materials were studied. Candida found on materials and mucosa following long-term use were identified and quantified, and biofilms covering the surfaces were investigated by SEM.

RESULTS

There was a significant decrease in the number of cells attached in vitro to saliva-coated surfaces compared with non-treated surfaces. An oral Candida carriage of 78% was found. Candida albicans, C. glabrata, C. intermedia and C. tropicalis were identified. In vivo biofilm formation on the liners appeared as massive colonisation by microorganisms.

CONCLUSIONS

The results of the in vitro experiments suggest that salivary film influences early colonisation of different C. albicans strains. The film layer also minimises the differences among different strains. The Candida carriage of these patients was similar to denture-wearing patients without soft liners.

Evaluation of antifungal efficacy of erbium, chromium: yttrium-scandium-gallium-garnet laser against Candida albicans

OBJECTIVE

The purpose of this in vitro study was to investigate the ability of Er,Cr:YSGG laser irradiation at different energy settings to eliminate Candida albicans, either with or without 5.25% sodium hypochlorite (NaOCl) treatment.

METHODS

In total, 90 extracted human single-rooted teeth were shaped by using a crown-down technique with HERO Shaper rotary instruments and irrigated with 1 mL of 2.5% NaOCl between each instrument. The specimens were autoclaved and incubated with a suspension of C. albicans (ATCC 90028). Then the specimens were divided into six treatment groups (n = 15 per group): group 1, NaOCl + 1-W laser; group 2, 1-W laser; group 3, NaOCl + 0.75-W laser; group 4, 0.75-W laser, group 5, NaOCl; and group 6, no treatment. Aliquots of the experimental teeth were transferred onto Sabouraud's dextrose agar plates with paper points, and colony-forming units (CFUs) were counted as a measure of antifungal activity. One root from each group, which was not submitted to the sampling procedure, was fixed in glutaraldehyde, split into two halves, and evaluated with scanning electron microscopy (SEM). Statistical analysis was performed by using analysis of variance (ANOVA) and the Dunnett t test. Significance was set at alpha = 0.05.

RESULTS

All the treatment groups resulted in a significant reduction of C. albicans, but no sterilization, and all the groups were significantly different from each other (p < 0.0001). Group 1 (NaOCl and 1-W laser combination) exhibited the greatest reduction, whereas group 5 (NaOCl) resulted in a minimal reduction in CFUs of C. albicans. The SEM observations were in accordance with the microbiologic analysis.

CONCLUSIONS

The 5.25% NaOCl and 1-W laser treatment combination may be a valuable cleaning tool for root canals infected with C. albicans.

Our current understanding of fungal biofilms

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.

Escherichia coli and its lipopolysaccharide modulate in vitro Candida biofilm formation

Demystification of microbial behaviour in mixed biofilms could have a major impact on our understanding of infectious diseases. The objectives of this study were to evaluate in vitro the interactions of six different Candida species and a Gram-negative coliform, Escherichia coli, in dual-species biofilms, and to assess the effect of E. coli LPS on Candida biofilm formation. A single isolate of E. coli ATCC 25922 and six different species of Candida, Candida albicans ATCC 90028, Candida glabrata ATCC 90030, Candida krusei ATCC 6258, Candida tropicalis ATCC 13803, Candida parapsilosis ATCC 22019 and Candida dubliniensis MYA-646, were studied using a standard biofilm assay. Each Candida species was co-cultured with E. coli on a polystyrene surface and biofilm formation was quantified by a c.f.u. assay. The biofilm was then analysed by Live/Dead staining and fluorescence microscopy (confocal laser-scanning microscopy, CLSM), whilst scanning electron microscopy (SEM) was employed to visualize the biofilm architecture. The effect of E. coli LPS on Candida biofilm cell activity at defined time intervals was assessed with an XTT reduction assay. A significant quantitative reduction in c.f.u. counts of C. tropicalis (after 90 min), C. parapsilosis (after 90 min and 24 h), C. krusei (after 24 h) and C. dubliniensis (after 24 and 48 h) was noted on incubation with E. coli in comparison with their monospecies biofilm counterparts (P <0.05). On the other hand, a simultaneous and significant reduction in E. coli cell numbers occurred on co-culture with C. albicans (after 90 min), and an elevation of E. coli cell numbers followed co-culture with C. tropicalis (after 24 h) and C. dubliniensis (after 24 h and 48 h) (P <0.05). All quantitative findings were confirmed by SEM and CLSM analyses. By SEM observation, dual-species biofilms demonstrated scanty architecture with reduced visible cell counts at all stages of biofilm development, despite profuse growth and dense colonization in their single-species counterparts. Significantly elevated metabolic activity, as assessed by XTT readings, was observed in E. coli LPS-treated C. tropicalis and C. parapsilosis biofilms (after 48 h), whilst this had the opposite effect for C. dubliniensis (after 24 h) (P <0.05). These data indicate that E. coli and Candida species in a mixed-species environment mutually modulate biofilm development, both quantitatively and qualitatively, and that E. coli LPS appears to be a key component in mediating these outcomes.

The effect of treatment of radicular dentin on colonization patterns of C. albicans

OBJECTIVE

The aim of this study was to observe the colonization pattern of C. albicans on treated and untreated radicular dentin.

STUDY DESIGN

Root sections of 10 human mandibular premolar teeth were longitudinally separated into halves. The 20 halves were separated into 2 groups and each half served as its own control. In Group 1, only gross pulpal remnants were removed with pliers. Root canal walls in the corresponding 102 halves (Group 2) were instrumented with Gates-Glidden burs and treated with sequential use of 15% EDTA solution for 3 minutes and 2.5% NaOCl solution for 3 minutes. Finally, all teeth were washed with distilled water. Each specimen was placed individually in each well of a 24-well cell culture plate. After the assembly was sterilized with ethylene-oxide, the root canal of each specimen was inoculated with 20 microL of C. albicans (1-1.5 x 10(6) cfu/mL) that was kept in place for 24 hours for initial attachment. Then, 2 mL of SDB was added to each well and the assembly was placed in an incubator at 37 degrees C for 10 days. Following the incubation period, the specimens were washed, fixed, dehydrated, and processed for scanning electron microscopy.

RESULTS

C. albicans was present on the root canal surfaces of all specimens; however, the colonization pattern was different. In the untreated group, the main growth pattern was a dense mass of yeast cells forming biofilm layers while hyphal structures were not common. On the other hand, pseudohyphae invaded all root canal surfaces in Group 2 and yeast cells were occasionally observed.

CONCLUSION

The treatment procedures of root canal dentin have a strong influence on the colonization pattern of C. albicans. This fact should be considered when planning and evaluating in vitro Candida adhesion and/or penetration studies.

One-year follow-up of the effect of fixed orthodontic treatment on colonization by oral Candida

The aim of this study was to assess quantitative and qualitative alterations in the carrier rate of Candida spp. in south-eastern Turkey among adolescents, and to investigate the effect of fixed orthodontic appliances on the Candida count in a 1-year follow-up study. In the first phase of the study, the oral Candida carriage rate of 72 patients was evaluated. Samples were collected from the dorsal surface of the tongue, the mid-palate and saliva. In the second phase of the study, 42 patients who were determined to be carriers of oral Candida were treated with fixed orthodontic appliances, and from these patients a second set of samples were collected from the saliva and the orthodontic brace surfaces of eight teeth adjacent to the enamel surfaces. The saliva samples were collected before and during orthodontic treatment at 1st, 6th and 12th month, and samples from the braces were collected during the 1st, 6th and 12th month of treatment. Forty-two of the 72 patients (58.5%) were oral Candida carriers. The distribution of Candida spp. in these patients was as follows: (i) Candida albicans was identified in 31 patients (73.8%), (ii) C. tropicalis, C. krusei and C. kefyr were found in three patients each (7.14%) and (iii) C. parapsilosis occurred in two patients (4.76%). During orthodontic treatment, the micro-organism count increased both in the saliva and on tooth surfaces. The results indicate that the prevalence of oral Candida spp. is high in young adults in south-eastern Turkey and that the Candida counts increase when braces are involved.

Candida albicans does not invade carious human dentine

AIM

Candida albicans has been proposed to be a caries pathogen, but the evidence for its specific role is lacking. To be considered significant in caries progression, a marked amount of yeasts should be present in a lesion. The aim of the study was to investigate the presence of C. albicans in dentinal caries lesions.

MATERIALS AND METHODS

To demonstrate the extension of caries and to identify the bacteria in a lesion, sections of 10 carious human teeth were stained with Gram and Giemsa stains. C. albicans was detected with periodic acid-Schiff (PAS) staining and by immunohistochemistry using a C. albicans-specific antibody 3H8. Thirty sections were used for each staining (in total 120 sections).

RESULTS

Extensive bacterial invasion and intensive staining by PAS occurred in all samples. However, with the C. albicans-specific antibody, only 30 (3.3%) sections stained weakly positive, with a few stained cells on the lesion surface. However, the positive identification of C. albicans, based on the morphology of the cells, was not possible.

CONCLUSIONS

The results do not support the previous suggestion that C. albicans is important in the dentine caries pathology. In addition, because of its unspecific nature, PAS turned out to be an unsuitable method for detecting yeasts in carious tooth samples.

Influence of Different Orthodontic Brackets on Adherence of Microorganisms In Vitro

OBJECTIVE

To define the capacity of different bracket materials to modify the growth and adherence of microorganisms.

METHODS

Three types of brackets from the right upper central incisor were used: metallic, ceramic, and composite. Streptococcus mutans and Candida albicans were studied. The association of both species was also evaluated. The brackets were placed in flat-bottomed vials containing basal medium with 20% sucrose added; the flasks were inoculated with each of the microbial suspensions. The samples were incubated at 37 degrees C for 48 hours, after which the brackets were removed. The supernatant was removed from the flasks, the cells adhering to the glass were counted, and the brackets were studied with electron microscopy.

RESULTS

The adherence of Streptococcus mutans was not modified by the different brackets. The adherence of Candida albicans was increased by the composite bracket, whereas the use of metallic brackets decreased the number of colony-forming units (CFUs). By electron microscopy we demonstrated that the adherence of Streptococcus mutans plus Candida albicans together varied according to the bracket materials with composite > ceramic > metallic.

CONCLUSIONS

Orthodontic appliances serve as different impact zones and modify microbial adherence and colonization, acting as foreign reserves and possible sources of infection.

Clinical Efficacy of Treatment Procedures in Endodontic Infection Control and One Year Follow-Up of Periapical Healing

The objective was to evaluate the clinical efficacy of chemomechanical preparation of the root canals with sodium hypochlorite and interappointment medication with calcium hydroxide in the control of root canal infection and healing of periapical lesions. Fifty teeth diagnosed with chronic apical periodontitis were randomly allocated to one of three treatments: Single visit (SV group, n = 20), calcium hydroxide for one week (CH group n = 18), or leaving the canal empty but sealed for one week (EC group, n = 12). Microbiological samples were taken to monitor the infection during treatment. Periapical healing was controlled radiographically following the change in the periapical index at 52 wk and analyzed using one-way ANOVA. All cases showed microbiological growth in the beginning of the treatment. After mechanical preparation and irrigation with sodium hypochlorite in the first appointment, 20 to 33% of the cases showed growth. At the second appointment 33% of the cases in the CH group revealed bacteria, whereas the EC group showed remarkably more culture positive cases (67%). Sodium hypochlorite was effective also at the second appointment and only two teeth remained culture positive. Only minor differences in periapical healing were observed between the treatment groups. However, bacterial growth at the second appointment had a significant negative impact on healing of the periapical lesion (p < 0.01). The present study indicates good clinical efficacy of sodium hypochlorite irrigation in the control of root canal infection. Calcium hydroxide dressing between the appointments did not show the expected effect in disinfection the root canal system and treatment outcome, indicating the need to develop more efficient inter-appointment dressings.

The effect of calcium chelating or binding agents on Candida albicans

OBJECTIVE

The aim of this study was to evaluate antifungal effects of calcium-chelating or -binding agents on Candida albicans comparing with conventional antifungal agents.

STUDY DESIGN

Two clinical oral isolates and 1 standard strain of C albicans were included in the study. Test solutions were ethylenediamine-tetraacetic acid (EDTA), ethyleneglycol-tetraacetic acid (EGTA), sodium fluoride (NaF), titanium tetrafluoride (TiF4), nystatin, and ketoconazole. Minimum inhibitory and fungicidal concentrations of the solutions were determined. The results were analyzed statistically using Friedman's nonparametric 2-way ANOVA and Mann-Whitney U tests.

RESULTS

All isolates demonstrated similar susceptibility patterns (P>.05). Except ketoconazole, EDTA had the highest antifungal and fungicidal activity, followed by TiF4. EGTA and NaF were the weakest agents against C albicans among all test solutions.

CONCLUSION

EDTA and TiF4 may be recommended as an alternative irrigating solution particularly in persistent root canal infections and in root canals of patients having a high incidence of oral candidosis.

In vitro cariogenic potential of Candida albicans

The adherence and dissociation of Candida albicans, C. tropicalis, Streptococcus mutans and S. sanguis to six substrates including hydroxylapatite (HAP) which exhibit various hydrophobicity, was examined by the use of a bioluminescent adenosine triphosphate (ATP) assay. Dissolution of HAP by C. albicans or S. mutans was determined spectrophotometrically by the use of o-cresolphthalein complexone. In the adherence of C. tropicalis, S. mutans and S. sanguis, the amount of adherent cells correlated with the hydrophobicity of the substrates. In contrast, the adherence of C. albicans to HAP was extraordinary high, although the adherence of the fungi also correlated with the hydrophobicity of the substrates, except for HAP. The yeasts attached to HAP was effectively removed by high concentration of either phosphate or calcium ions. The amount of calcium-release from HAP caused by C. albicans and S. mutans was 113 microg ml(-1) (final pH = 3.45), and 5.4 microg ml(-1) (final pH 4.81), respectively and the maximum growth of C. albicans and S. mutans was 10(7) cfu ml(-1) and 7.4 x 10(12) cfu ml(-1), respectively. The results, taken together, suggest that C. albicans adhere to HAP specifically through electrostatic interaction, and that, in a much smaller number (1.0/7.4 x 10(5)), C. albicans possesses the ability to dissolve HAP to a greater extent (approximately 20-fold) when compared with S. mutans.

A new method for studying the adhesion of Candida albicans to dentin in the presence or absence of smear layer

OBJECTIVES

The purpose of this study was to develop a reproducible, quantitative model of Candida albicans adhesion to human dentin through the use of a colorimetric method and to evaluate the effect of smear layer on candidal adhesion.

STUDY DESIGN

Dentin disks with or without smear layer were incubated with C albicans (10(8) cells/mL) for 4 hours. After incubation, the disks were exposed to an (2,3)-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)-carbonyl]-2H-tetrazolium hydroxide-coenzyme Q solution for 2 hours. The color of (2,3)-bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)-carbonyl]-2H-tetrazolium hydroxide formazan in the supernatant was determined spectrophotometrically at 492 nm. To relate formazan formation to cell numbers, standard curves were generated with known numbers of yeast cells without dentin. The number of adherent cells per square millimeter was then calculated.

RESULTS

The number of attached C albicans cells was 2.4 x 10(4) per square millimeter in dentin with smear layer and 1.5 x 10(4) in dentin without smear layer (P <.05).

CONCLUSION

(2,3)-Bis(2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)-carbonyl]-2H-tetrazolium hydroxide assay is a potential microbiologic tool for the quantitative determination of Candida adhesion to human dentin.

Yeasts in apical periodontitis

Microbiological reports of apical periodontitis have revealed that yeasts can be isolated from approximately 5-20% of infected root canals. They occur either in pure cultures or together with bacteria. Almost all isolated yeasts belong to the genus Candida, and the predominant species is C. albicans. Pheno- and genotypic profiles of C. albicans isolates show heterogeneity comparable with those of isolates from other oral sites. C. albicans expresses several virulence factors that are capable of infecting the dentin-pulp complex, including dentinal tubules. This causes, consequentially, an inflammatory response around the root apex, which suggests a pathogenic role for this organism in apical periodontitis. Yeasts are particularly associated with persistent root canal infections that do not respond favorably to conservative root canal therapy. This may be due to the resistance of all oral Candida species against a commonly used topical medicament, calcium hydroxide. However, other antimicrobial agents may offer alternative therapeutic approaches and improve the treatment of these persistent cases of apical periodontitis.