A. N. B. Ellepola

Diabetes mellitus as a contributory factor in oral candidosis

It has been reported that poor glycaemic control predisposes to oral candidal infection in diabetic patients. For instance, the carriage of Candida species and the density of candidal growth in the oral cavity is frequently claimed to be increased in patients with diabetes mellitus. However, the validity of these observations remains controversial. Hence, we review and discuss here the clinical data in the literature on the relationship between diabetes and oral candidal carriage and infection, and possible mechanisms associated with its pathogenicity.

Adhesion of Candida parapsilosis to epithelial and acrylic surfaces correlates with cell surface hydrophobicity

Summary.  We investigated in vitro adherence of 24 isolates of Candida parapsilosis and 12 isolates of Candida albicans with regard to their relative cell‐surface hydrophobicity (CSH), adherence to human buccal epithelial cells (BEC) and acrylic surfaces. There was no significant interspecies difference in the relative adherence of C. parapsilosis and C. albicans isolates to BEC, although the former demonstrated a tendency for increased adherence. However, a significant intra‐species variation in adherence among isolates of C. parapsilosis (P < 0.0001) to BEC, but not of C. albicans was noted. The superficial isolates of C. parapsilosis demonstrated a higher avidity (33%) to BEC than the systemic isolates. On regression analysis a significant positive correlation between C. parapsilosis adherence to BEC and denture acrylic surfaces was noted (r = 0.45, P = 0.02). Similarly, buccal cell adherence correlated strongly with CSH of C. parapsilosis (r = 0.63, P = 0.0008). These results shed further light on the intimate relationship between adherence and CSH in candidal colonization and imply that both C. parapsilosis and C. albicans are equally potent in colonizing mucosal surfaces with respect to the attributes investigated.

Adhesion of oral Candida albicans isolates to denture acrylic following limited exposure to antifungal agents

Candidal adherence to denture acrylic surfaces is implicated as the first step in the pathogenesis of Candida-associated denture stomatitis, the most prevalent form of oral candidosis in the West. This condition is treated by topically administered antifungal agents, mainly belonging to the polyenes and azoles. As the intraoral concentrations of antifungals fluctuate considerably due to the dynamics of the oral environment, the effect of short exposure to sublethal concentrations of antifungals on the adhesion of Candida albicans to denture acrylic surfaces was investigated. Seven oral C. albicans isolates were exposed to four-eight times minimum inhibitory concentrations (MIC) of five antifungal drugs, nystatin, amphotericin B, 5-fluorocytosine, ketoconazole and fluconazole, for 1 h. After removing the drug (by repeated washing) the adhesion of these isolates to acrylic strips was assessed by an in vitro adhesion assay. Exposure to antifungal agents significantly reduced the adherence of all seven C. albicans isolates to denture acrylic. The mean percentage reductions of adhesion after limited exposure to nystatin, amphotericin B, 5-fluorocytosine, ketoconazole and fluconazole were 86.48, 90.85, 66.72, 65.88 and 47.42%, respectively. These findings indicate that subtherapeutic doses of antifungals may modulate oral candidal colonization. Further, these results may have an important bearing on dosage regimens currently employed in treating oral candidosis.

Antimicrobials as a contributory factor in oral candidosis - a brief overview

The advent of the human immunodeficiency virus infection and the increasing prevalence of compromised individuals in the community due to modern therapeutic advances have resulted in a resurgence of opportunistic infections, including oral candidosis, which is by far the most common oral fungal infection in man. Broad-spectrum antibiotics used in the treatment of a wide range of disease conditions have also been attributed as a predisposing factor of oral candidosis. In this mini review we discuss the research findings on the relationship between antibiotics and oral candidosis and possible mechanisms of pathogenicity following such therapy.

Adhesion to denture acrylic surfaces and relative cell-surface hydrophobicity of Candida parapsilosis and Candida albicans

C. parapsilosis is an opportunistic emerging pathogen which together with C. albicans causes diseases in immunocompromised patients. Adhesion of Candida species to various surfaces is an important event in colonization and pathogenesis, and the relative cell‐surface hydrophobicity (CSH) of the organism is a contributory physical force involved. Therefore, in vitro adhesion to acrylic surfaces and relative CSH of 24 isolates of C. parapsilosis and 10 isolates of C. albicans were studied. There was no significant difference in relative adhesion of C. parapsilosis isolates and C. albicans, although the former demonstrated a tendency for increased adhesion. There was significant intra‐species variation in adhesion among isolates of C. parapsilosis (p=0.0001), but not C. albicans. In general, C. parapsilosis isolates demonstrated a two‐fold greater relative CSH than C. albicans (p=0.0003). When the relative CSH of superficial and systemic isolates of C. parapsilosis were compared, the former showed a significantly higher (49.15%) relative CSH than their systemic counterparts (p<0.01). A highly significant positive correlation between adhesion and relative CSH of C. parapsilosis (p=0.74, p<0.0001) was also noted. Taken together, these data suggest that the attributes of adhesion and relative CSH of Candida species may contribute differentially in varying disease states of the human host, such as superficial and systemic Candida infections.

Prevalence of Candida dubliniensis among oral Candida isolates in patients attending the Kuwait University Dental Clinic.

Objectives: The aim of this study was to determine the oral candidal carriage of patients seeking dental treatment at the Kuwait University Dental Clinic and to ascertain the Candida species composition among them. Methods: 370 oral rinse samples were collected from patients. The germ tube test, CHROMagar Candida medium and VITEK 2 yeast identification system were used for species identification. C. dubliniensis isolates were confirmed by the production of rough colonies with hyphal fringes and chlamydospores on simplified sunflower seed agar. Results: Of the 370 samples investigated, 160 (43.24%) showed Candida in culture. The isolation of Candida was significantly higher in individuals who were smokers or were under medication for either diabetics or asthma [99 (62%)] compared to healthy individuals [61 (38%)]. Of the 210 samples which did not yield Candida, 131 (62.38%) were healthy and 79 (37.62%) were associated with smoking or with usage of drugs for aforementioned conditions. Species isolated were C. albicans [102 (63.7%)], C. dubliniensis [23(14.3%)], C. krusei [13 (8.1%)], C. tropicalis [12 (7.5%)] and C. glabrata [10 (6.2%)]. Conclusions:Candida species were more prevalent in patients having predisposing factors implicated in oral candidosis, such as in smokers, diabetic patients and asthmatic patients using inhalation steroids. C. albicans was the most prevalent species isolated, followed by C. dubliniensis.

Cell surface hydrophobicity of oral Candida dubliniensis isolates following limited exposure to sub-therapeutic concentrations of chlorhexidine gluconate

Candidal adhesion has been implicated as the initial step in the pathogenesis of oral candidiasis and cell surface hydrophobicity (CSH) has been implicated in adhesion to mucosal surfaces. Candida dubliniensis is an opportunistic pathogen associated with recurrent oral candidiasis. Chlorhexidine gluconate is by far the commonest antiseptic mouth wash prescribed in dentistry. At dosage intervals the intraoral concentration of this antiseptic fluctuates considerably and reaches sub‐therapeutic levels due to the dynamics of the oral cavity. Hence, the organisms undergo only a limited exposure to the antiseptic during treatment. The impact of this antiseptic following such exposure on CSH of C. dubliniensis isolates has not been investigated. Hence, the main objective of this study was to investigate the effect of brief exposure to sub‐therapeutic concentrations of chlorhexidine gluconate on the CSH of C. dubliniensis isolates. Twelve oral isolates of C. dubliniensis were briefly exposed to three sub‐therapeutic concentrations of 0.005%, 0.0025% and 0.00125% chlorhexidine gluconate for 30 min. Following subsequent removal of the drug, the CSH of the isolates was determined by a biphasic aqueous‐hydrocarbon assay. Compared with the controls, exposure to 0.005% and 0.0025% chlorhexidine gluconate suppressed the relative CSH of the total sample tested by 44.49% (P < 0.001) and 21.82% (P < 0.018), respectively, with all isolates being significantly affected. Although exposure to 0.00125% of chlorhexidine gluconate did not elicit a significant suppression on the total sample tested (7.01%; P > 0.05), four isolates of the group were significantly affected. These findings imply that exposure to sub‐therapeutic concentrations of chlorhexidine gluconate may suppress CSH of C. dublinienis isolates, thereby reducing its pathogenicity and highlights further the pharmacodynamics of chlorhexidine gluconate.

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.

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.

Molecular heterogeneity of fluconazole-resistant and -susceptible oral Candida albicans isolates within a single geographic locale.

The emergence of drug‐resistant Candida albicans in immunocompromised patients is common. A disconcerting aspect of this phenomenon is the rapid emergence of C. albicans strains that are resistant to a widely used azole drug, fluconazole (FLZ). To understand the origin of FLZ‐resistant yeast isolates, we investigated molecular profiles of 20 geographically related oral C. albicans isolates using three genotyping methods: randomly amplified polymorphic DNA‐PCR, with six different primers (OBU1, OBU2, OBU3 RSD6, RSD11 and RSD12); electrophoretic karyotyping by pulsed‐field gel electrophoresis; and HinfI restriction fragment analysis. Of the 20 isolates studied, 10 were FLZ‐ resistant and originated from patients with oral candidosis with a history of FLZ therapy, and the remainder were FLZ susceptible from individuals with oral candidosis, but without a history of FLZ therapy. A composite genotype was generated for each strain by combining molecular types derived from the three independent molecular methods. The composite profiles indicated genetic diversity amongst both the FLZ‐resistant as well as ‐sensitive isolates, and no specific features emerged distinguishing the drug‐resistant and ‐sensitive groups. These observations cast doubt on the theory of a clonal origin of FLZ‐resistant C. albicans isolates.