Biomedical subjects

L P Samaranayake

Publications and source records attributed to L P Samaranayake.

At least 73 records · Page 4Linked to original sources

PubMed2001

Antifungal effects of lysozyme and lactoferrin against genetically similar, sequential Candida albicans isolates from a human immunodeficiency virus-infected southern Chinese cohort.

A variety of innate defense factors in saliva such as lysozyme and lactoferrin contribute to mucosal protection and modulate Candida populations in the oral cavity. It is also known that in human immunodeficiency virus (HIV)-infected individuals significant variations in the concentrations of lysozyme and lactoferrin in saliva occur during disease progression. Therefore, the aim of this study was to determine the in vitro susceptibility to human lactoferrin and hen egg white lysozyme of genotypically similar oral Candida albicans isolates obtained from six HIV-infected ethnic Chinese during sequential visits over a 12-month period. The similarity of the genotypes (50 in total) was evaluated using a randomly amplified polymorphic DNA assay. A blastospore viability assay was performed to evaluate the sensitivity of the organisms to lysozyme and lactoferrin. Exposure to physiological concentrations of either lysozyme (30 microg/ml) or lactoferrin (20 microg/ml) caused a rapid loss of viability among all isolates to a varying extent. None of the sequential C. albicans isolates demonstrated significant differences in sensitivity to either protein from one visit to the next; similar results were noted when the different genotypes from the same individual were compared. On Spearman correlation analysis of two genotypes that were sequentially isolated from a single patient, a significant negative correlation between lysozyme (r = -0.88; P < 0.02) (but not lactoferrin) resistance and the duration of HIV disease was seen. These results imply that a minority of C. albicans isolates that persist intraorally in individuals with HIV disease develop progressive resistance to innate salivary antifungal defenses such as lysozyme, possibly as an adaptive response. However, the vast majority of the Candida isolates appear to succumb to these nonspecific host immune mediators abundantly present in the oral environment.

AIDS-Related Opportunistic Infections↗

PubMed2001

Adjunctive use of chlorhexidine in oral candidoses: a review.

Oral candidosis is by far the commonest human fungal infection and manifests in a variety of clinical guises. The main reason for its high incidence appears to be the multiplicity of predisposing factors, which facilitate the conversion of oral commensal Candida to a parasitic existence. Despite the availability of a number of effective antimycotics for the treatment of oral candidoses, failure of therapy is not uncommon owing to the unique environment of the oral cavity where the flushing effect of saliva and the cleansing action of the oral musculature tend to reduce the drug concentration to sub-therapeutic levels. For these and other reasons chlorhexidine is widely prescribed in dentistry both as an antiseptic mouthwash and a denture disinfectant in order to supplement other antifungals. Chlorhexidine has a broad spectrum of antimicrobial activity including Candida albicans and other common non-albicans yeast species. In this review we outline the utility of chlorhexidine as an adjunct to conventional antimycotic therapy in the management of oral Candida infections.

Anti-Infective Agents, Local↗

PubMed2001

The impact of chlorhexidine gluconate on the relative cell surface hydrophobicity of oral Candida albicans.

OBJECTIVES: Adherence of Candida albicans has been implicated as the first step in the pathogenesis of oral candidosis, and its relative cell surface hydrophobicity (CSH) a contributory physical force. Chlorhexidine gluconate is by far the commonest antiseptic mouthwash prescribed in dentistry. The intra-oral concentrations of the retained chlorhexidine mouthwash fluctuate considerably due to the dilution effect of saliva and the cleansing action of the oral musculature. Hence the objective of the present study was to investigate the effect of brief exposure to sub-therapeutic concentrations of chlorhexidine gluconate on the relative CSH of C. albicans. DESIGN: The CSH of the isolates was assessed by a biphasic aqueous-hydrocarbon assay. RESULTS: A statistically significant reduction in CSH was observed following the exposure of Candida isolates to 0.005 and 0.0025% chlorhexidine gluconate. CONCLUSIONS: These results elucidate additional mechanisms by which chlorhexidine gluconate suppress candidal pathogenicity despite a brief period of transient exposure within the oral environment.

Adhesiveness↗

PubMed2001

Correlation between the expression of cyclin A protein and p53 activity in oral squamous cell carcinomas.

Cyclins and wild-type p53 protein are prime cell cycle regulators and may be involved in tumorigenesis. Cyclin A is a late S cyclin and its abnormalities have been reported in several cancers, including oral squamous cell carcinomas. To explore whether aberrant G1/S in p53 mutant tumours leads to increased cyclin A protein in oral squamous cell carcinomas (OSCC), a total of 39 samples were evaluated for the expression of cyclin A and p53 protein by an immunohistochemical method using a labelled polymer assay. These samples comprised two hyperkeratotic and three oral premalignant lesions (two moderate and one severe dysplastic lesions), and 27 OSCC, together with seven healthy controls. The results demonstrated that the cyclin A protein was localized and highly expressed in the nuclei of the tumour cells. Although there was no correlation between cyclin A detection and the local lymph node involvement, a positive correlation was noted between the positivity of cyclin A and p53 protein (p <0.05). The results suggested that cyclin A may contribute to the progression of oral cancer and correlated to some degree with that of the p53 gene activity.

Carcinoma, Squamous Cell↗

PubMed2001

Salivary immunoglobulin A levels in rapid and slow plaque formers: a pilot study.

The aim of this study was to investigate the salivary immunoglobulin A concentration in rapid and slow plaque formers. After 3 days of oral hygiene abstinence, 49 healthy volunteers were screened using the plaque index (PI) to assess their plaque formation rates. Five subjects with the highest, and five with the lowest mean PI were selected as rapid and slow plaque formers, respectively. Unstimulated whole saliva was collected from each of these ten subjects and the levels of salivary IgA assessed using a conventional ELISA technique. Reference curves for salivary IgA were established by testing serial dilutions of human IgA with known concentrations. When the differences between the two groups were compared, almost a twofold increase in the mean salivary IgA concentration in the slow (16 microg/ml +/- 4) compared with the rapid (9 microg/ml +/- 3) plaque formers was recorded (p < 0.05). These findings, reported for the first time, imply that salivary IgA may play a crucial role in regulating the pioneer plaque development on enamel surfaces.

Adult↗

PubMed2001

Inhalational and topical steroids, and oral candidosis: a mini review.

Candidosis is by far the commonest oral fungal infection in man and could manifest as an adverse effect of drug therapy such as inhaled or topically applied corticosteroids. Due to the anti-inflammatory and immunosuppressive effect steroids are used in the management of bronchial asthma and oral mucosal diseases. In this mini review we discuss the clinical and laboratory findings on the relationship between steroid inhalers, other topical steroids and oral candidosis, possible mechanisms of pathogenicity following such therapy as well as the precautions that could be taken to minimize this adverse side effect.

Administration, Inhalation↗

PubMed2000

Homozygous deletion of the PTEN tumor-suppressor gene is not a feature in oral squamous cell carcinoma.

A recently identified putative tumor-suppressor gene, PTEN, at 10q23 has been described as mutated or homozygously deleted in many different human tumors. To determine the role of the homozygous deletion of this PTEN gene in oral squamous cell carcinoma (OSCC), we screened two cell lines derived from the latter tissue and 28 tumor samples from patients with OSCC, using a differential display polymerase chain reaction (PCR) system and, direct DNA sequencing methods. All of the nine exons of the PTEN could be successfully amplified using DNA from tumor tissues and the cell lines using this system. DNA sequencing confirmed the accuracy of the PCR procedures. However, none of the samples, either from the cancer tissues or from the cell lines, showed homozygous deletion of PTEN. These data suggest that homozygous deletion of the PTEN gene is unlikely to be a feature of OSCCs.

Aged↗

PubMed2000

In vitro susceptibility of Candida albicans isolates from apical and marginal periodontitis to common antifungal agents.

The susceptibility of a total of 70 Candida albicans strains to five common antifungal agents was determined. Thirty-five of the strains were isolated from persistent cases of apical periodontitis and 35 from cases of marginal periodontitis. The susceptibility of the strains to amphotericin B, 5-fluorocytosine and three azoles: fluconazole, miconazole and clotrimazole, was tested. The antifungal agents and yeast inoculums were prepared according to the NCCLS (National Committee for Clinical Laboratory Standards) recommendations. The yeasts were incubated with ten different concentrations of antifungal agents at 35 degrees C for 48 h. Yeast growth was measured spectrophotometrically. All strains from both isolation sources were susceptible to low concentrations of amphotericin B and 5-fluorocytosine, whereas the susceptibility to the three azoles varied, and three of the strains showed azole cross-resistance. These findings are in agreement with recent reports of increased azole resistance in Candida species in general and suggest the possibility that the oral cavity may act as a reservoir of resistant yeast isolates in systemic infections.

Amphotericin B↗

PubMed2000

Genomic diversity of oral Candida krusei isolates as revealed by DNA fingerprinting and electrophoretic karyotyping.

Candida krusei is receiving increasing attention as an important human pathogen, especially in compromised patients, who frequently manifest with multiepisodes of candidosis. As there is scant information on the genetic diversity of this pathogen the present study was undertaken to establish its genetic profiles using three different typing methods: PFGE (pulsed-field gel electrophoresis), RFLP (restriction fragment length polymorphism), RAPD (randomly amplified polymorphic DNA). When 11 oral isolates of C. krusei were molecular typed by PFGE, 3 to 5 chromosomes with sizes ranging from 1000 kb to 3000 kb per isolate were revealed. All isolates produced a single bright band at approximately 1,100 kb and two to three bands between 2,500 kb and 3,000 kb, demonstrating 5 different karyotypes. RFLP with HinfI yielded 9 different genotypes, while DNA fingerprinting by RAPD with 3 primers (RSD6 (5'GCGATCCCCA3'), RSD7 (5'AGTGAATTCG CGGTGA-GATGCC3') and RSD12 (5'GCATATCAATAAGC GCAGGAAAAG 3')), resulted in 8, 3 and 11 different genotypes, respectively. This study provides evidence hitherto unavailable on the genetic polymorphism of C. krusei isolates colonizing the oral niche under different clinical conditions. Such genotypic polymorphism should help strain delineation in epidemiologic surveillance of either nosocomial or community outbreaks of C. krusei infections.

Base Sequence↗

PubMed2000

An in vivo replica study of microbial colonization in "rapid" and "slow" dental plaque formers.

The aim of the present study was to investigate the morphological features of supragingival plaque development in "rapid" and "slow" plaque formers using the replica technique. Forty-nine healthy volunteers were screened for their plaque formation rate after 3 days of oral hygiene abstinence using the plaque index (PI). Five subjects with the highest mean PI and six with the lowest mean PI were selected as "rapid" and "slow" plaque formers, respectively. After a series of thorough prophylaxis and oral hygiene instruction, all subjects went through a 14-day period of no oral hygiene to allow undisturbed plaque formation. Light body silicone elastomeric impressions were taken for the upper right central incisor of each subject on day-0, 1, 3, 7, and 14. Positive replicas were then poured from the impressions using epoxy resin and observed under a scanning electron microscope. A more complex supragingival plaque structure was seen in the day-1 and day-3 replicas of the "rapid" group compared to the "slow" group. From day-7 to day-14, during the maturation period of supragingival plaque, no discernible differences were noted between the two groups. Quantitatively, the percentage of plaque coverage on the tooth surfaces was higher in the "rapid" group than in the "slow" group in day-1 and day-3 replicas. These observations indicate that the morphological and topographical features of supragingival plaque in "slow" and "rapid" plaque formers differ, especially in the early developmental phase.

Bacteria↗

PubMed2000

Characterization of the genetic diversity in superficial and systemic human isolates of Candida parapsilosis by randomly amplified polymorphic DNA (RAPD).

The application of randomly amplified polymorphic DNA (RAPD) technology for strain delineation of medically important yeasts has proved to be a valuable tool in clinico-epidemiological studies of Candida species. Candida parapsilosis, a form species of the fungi imperfecti, is an emerging pathogen gaining recognition as an opportunistic agent, especially in the immunocompromised. Therefore, 15 clinical isolates of C. parapsilosis obtained from oral, cutaneous and systemic Candida infections were typed by RAPD analysis using four different primers. The primers RSD6 and RSD9 elicited 7 genotypes each, whereas primers RSD7 and RSD12 revealed 6 and 10 genotypes, respectively. When the data were correlated, a higher degree of genomic heterogeneity in systemic isolates was noted compared with the oral and cutaneous isolates, which shared somewhat similar RAPD profiles. However, a single oral isolate (P5) and two systemic isolates (P13 and P15) elicited radically divergent profiles, dissimilar to their counterparts. RAPD study of the latter two isolates with three additional primers (RSD8, RSD10 and RSD11) confirmed the observed genomic disparity. These data substantiate the previous observations on the genomic heterogeneity in C. parapsilosis and point to genetic shifts which may be associated with ecodiversity, as well as the possible existence of distinct genetic groups within this form species.

Candida↗

PubMed2000

Sub-therapeutic exposure to polyene antimycotics elicits a post-antifungal effect (PAFE) and depresses the cell surface hydrophobicity of oral Candida albicans isolates.

Post-antifungal effect (PAFE) is defined as the suppression of growth that persists following limited exposure of fungi to antimycotics and subsequent removal of the drug. The fungal pathogen Candida albicans is the major aetiologic agent of oral candidosis, and the cell surface hydrophobicity (CSH) of this yeast is considered a critical factor contributing to its colonisation potential. As the concentration of topically prescribed antifungals reach sub-therapeutic levels at dosage intervals, the study of the polyene-induced PAFE and its impact on the CSH of oral C. albicans should be of clinical relevance. Hence the aims of this investigation were to measure the PAFE and CSH of 12 isolates of C. albicans following limited exposure (1 h) to nystatin and amphotericin B and also to investigate the ultrastructural features of yeast cells following such antifungal exposure. The yeasts were exposed to sub-lethal concentrations of nystatin (x2 MIC) and amphotericin B (x2 MIC) for a period of 1 h. Following subsequent removal of the drug, the PAFE and the CSH of the isolates were assessed by a turbidometric measurement of growth and a biphasic aqueous-hydrocarbon assay, respectively. The mean duration of PAFE of nystatin and amphotericin B were 5.99 (+/-0.49) h and 8.73 (+/-0.93) h, respectively, while the reduction in CSH following exposure to these drugs were 17.32% (P<0.05 for 83% of the isolates) and 14.26% (P<0.05 for 66% of the isolates), respectively. On scanning electron microscopy the exposed cells were seen to undergo collapse of the internal cell membrane, leaving an intact cell wall, while a proportion of cells were deflated. Some cells showed intense puckering of the cell wall, resulting in a mulberry appearance. Taken together, these data elucidate additional mechanisms by which polyene antimycotics may operate in vivo to suppress candidal pathogenicity.

Amphotericin B↗

PubMed2000

Effect of serum concentration on Candida biofilm formation on acrylic surfaces.

The biofilm formation of the oral fungal pathogen Candida on denture acrylic strips coated with saliva, serum and, saliva-serum pellicle were examined in vitro using Candida albicans (four isolates), Candida glabrata (three isolates) and Candida tropicalis (three isolates). The degree of biofilm activity varied depending upon both the isolate and the pellicle. Significantly increased biofilm activity on the pellicle (particularly serum)-coated strips was observed with three isolates of C. albicans and another of C. glabrata on protein-coated acrylics, with increasing concentration of serum in the pellicle. Similar trends were observed with one isolate of C. albicans and C. glabrata, although the effects of pellicles were not significant. In contrast, with all three isolates of C. tropicalis and a single isolate of C. glabrata, although the biofilm activity on the protein-free control strips was significantly higher than that of saliva-coated strips, the increase in activity of pellicle-admixed biofilm depended upon the serum concentration. Candidal biofilm formation on acrylic surfaces is essentially promoted with increasing concentration of serum in the pellicle. This suggests that inflammation in the oral environment would facilitate fungal colonization on denture acrylic.

Acrylic Resins↗

PubMed2000

Oral yeasts and coliforms in HIV-infected individuals in Hong Kong.

The objective was to determine the oral carriage patterns of yeasts and coliforms and their relationships, if any, with age, risk group, CDC classification, CD4+ count and medications in a predominantly Chinese, HIV-infected cohort in Hong Kong. A prospective longitudinal study was carried out over a 12-month period, of 32 predominantly Chinese male HIV-infected cohort in a hospital setting in Hong Kong. Oral carriage rates were determined by the concentrated rinse culture method and correlated with other clinical parameters using regression analysis. A total of 73 oral rinse samples were collected and the weighted mean carriage rates of oral yeasts and coliforms were 54.8% and 28.8%, respectively. The most common yeast and the Enterobacteriaceae isolated were Candida albicans and Enterobacter cloacae, respectively. An increased carriage rate of yeasts was associated with zidovudine usage and Centres for Disease Control (CDC) stage IV of the HIV infection whereas the opposite was associated with the usage of antiparasitics and multivitamins. Although the oral carriage rate of coliforms was significantly lower in individuals taking antibacterials and multivitamins, it was not significantly influenced by age, CD4+ lymphocyte count and the intake of antivirals, antifungals or folates. These data imply that oral yeast carriage in HIV infection is related to the severity of the disease as opposed to oral coliform carriage which appears to be unusually transient in the study cohort.

Adult↗

PubMed2000

Pathology and clinical correlates in oral candidiasis and its variants: a review.

Although Candida albicans is well recognised as the major agent of oral candidiasis, it is not clear why several variants such as pseudomembranous (PC), erythematous (EC) and hyperplastic candidiasis (HC) manifest in different individuals, sometimes singly and on other occasions, in combination. The present review focuses on recent histopathologic and immunocytochemical studies as well as the pathogenic attributes of the yeast, in an attempt to address the following queries. (1) Do histopathologic studies of the different variants of candidiasis in immunocompetent and immunocompromised individuals help explain these varying manifestations? (2) Under what circumstances does oral candidiasis manifest as a pseudomembranous rather than an erythematous lesion or vice versa? (3) Are there differences in immunoreactivity in closely adjacent mucosae so that the variable presentation of such lesions reflect differences in the local mucosal immune system? Recent studies of PC, EC and HC offer some insights into the pathogenic mechanisms involved. Histopathologic and immunohistochemical finding in cases of PC and EC in HIV-infected patients and controls appear to be comparable, with a marked reduction or even an absence of CD4+ cells. The latter phenomenon is marked in PC compared with the EC, and explicable in terms of a breakdown of the local immune response in the former, and a hypersensitivity reaction against Candida antigens in the latter. Hyperplastic candidiasis on the other hand could be considered a superficial cellular reaction against the pathogen, which cannot entirely be eradicated by the systemic or local host immune response. The virulent attributes of the fungus, such as the production of extracellular proteinases, do significantly differ within and between species and thereby play a contributory role in the genesis of the clinical variants. Although the available data do give a tantalising glimpse of the contributory mechanisms for the aetiopathology of PC, EC and HC, further research is warranted to elucidate response of the host to this ubiquitous fungal pathogen.

AIDS-Related Opportunistic Infections↗

PubMed2000

The effect of brief exposure to sub-therapeutic concentrations of chlorhexidine gluconate on the germ tube formation of oral Candida albicans and its relationship to post-antifungal effect.

OBJECTIVES: Adherence of Candida albicans has been implicated as the first step in the pathogenesis of oral candidosis, and germ tube formation a contributory attribute. Recently, these organisms have also been implicated in persistent apical periodontitis. Chlorhexidine gluconate is by far the commonest antiseptic mouth wash prescribe in dentistry. As the intraoral concentrations of this antiseptic fluctuate considerably due to the dynamics of the oral cavity, the main objective of this study was to investigate the effect of brief exposure to three different sub-therapeutic concentrations of chlorhexidine gluconate (0.005%, 0.0025% and 0.00125%) on the germ tube formation of C. albicans. These findings were then correlated with the chlorhexidine-induced post-antifungal effect (PAFE) values we obtained in a study using the identical organisms and experimental conditions. DESIGN: Ten oral isolates of C. albicans were exposed to three different concentrations of chlorhexidine gluconate for 30 min, the antiseptic removed, and the germ tube formation of these isolates quantified following subsequent incubation in a germ tube inducing medium. The PAFE was evaluated by turbidometric measurement of growth. RESULTS: When compared with the controls, exposure to 0.005%, 0.0025% and 0.00125% chlorhexidine gluconate suppressed the ability to form germ tubes by 81.23% (P < 0.01), 42.74% (P < 0.01) and 9.13% (P > 0.05), respectively, while eliciting a mean PAFE of 9.91 h, 1.65 h and 0.67 h respectively. On regression analysis a significant positive correlation was observed between these two parameters (P < 0.0001; r = 0.7325). CONCLUSIONS: Taken together, these findings imply that short exposure to sub-therapeutic levels of chlorhexidine gluconate may modulate candidal germ tube formation as well as its growth, thereby suppressing its pathogencity in vivo.

Analysis of Variance↗

PubMed2000

Oral colonization, phenotypic, and genotypic profiles of Candida species in irradiated, dentate, xerostomic nasopharyngeal carcinoma survivors.

The aim of this study was to investigate oral yeast colonization and oral yeast strain diversity in irradiated (head and neck), dentate, xerostomic individuals. Subjects were recruited from a nasopharyngeal carcinoma clinic and were segregated into group A (age, <60 years [n = 25; average age +/- standard deviation (SD), 48 +/- 6 years; average postirradiation time +/- SD, 5 +/- 5 years]) and group B (age, >/=60 years [n = 8; average age +/- SD, 67 +/- 4 years; average postirradiation time +/- SD, 2 +/- 2 years]) and were compared with age- and sex-matched healthy individuals in group C (age, <60 years [n = 20; average age +/- SD, 44 +/- 12 years] and group D (age, >/=60 years [n = 10; average age, 70 +/- 3 years]). Selective culture of oral rinse samples was carried out to isolate, quantify, and speciate yeast recovery. All test subjects underwent a 3-month comprehensive oral and preventive care regimen plus topical antifungal therapy, if indicated. A total of 12 subjects from group A and 5 subjects from group B were recalled for reassessment of yeast colonization. Sequential (pre- and posttherapy) Candida isolate pairs from patients were phenotypically (all isolate pairs; biotyping and resistotyping profiles) and genotypically (Candida albicans isolate pairs only; electrophoretic karyotyping by pulsed-field gel electrophoresis, restriction fragment length polymorphism [RFLP], and randomly amplified polymorphic DNA [RAPD] assays) evaluated. All isolates were Candida species. Irradiated individuals were found to have a significantly increased yeast carriage compared with the controls. The isolation rate of Candida posttherapy remained unchanged. A total of 9 of the 12 subjects in group A and 3 of the 5 subjects in group B harbored the same C. albicans or Candida tropicalis phenotype at recall. Varying degrees of congruence in the molecular profiles were observed when these sequential isolate pairs of C. albicans were analyzed by RFLP and RAPD assays. Variations in the genotype were complementary to those in the phenotypic characteristics for some isolates. In conclusion, irradiation-induced xerostomia seems to favor intraoral colonization of Candida species, particularly C. albicans, which appeared to undergo temporal modifications in clonal profiles both phenotypically and genotypically following hygienic and preventive oral care which included topical antifungal therapy, if indicated. We postulate that the observed ability of Candida species to undergo genetic and phenotypic adaptation could strategically enhance its survival in the human oral cavity, particularly when salivary defenses are impaired.

Adult↗

PubMed2000

Oral candidal infections and antimycotics.

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 candidoses. One form of the latter presents classically as a white lesion of "thrush" and is usually easily diagnosed and cured. Nonetheless, a minority of these lesions appears in new guises such as erythematous candidosis, thereby confounding the unwary clinician and complicating its management. Despite the availability of several effective antimycotics for the treatment of oral candidoses, failure of therapy is not uncommon due to the unique environment of the oral cavity, where the flushing effect of saliva and the cleansing action of the oral musculature tend to reduce the drug concentration to sub-therapeutic levels. This problem has been partly circumvented by the introduction of the triazole agents, which initially appeared to be highly effective. However, an alarming increase of organisms resistant to the triazoles has been reported recently. In this review, an overview of clinical manifestations of oral candidoses and recent advances in antimycotic therapy is given, together with newer concepts, such as the post-antifungal effect (PAFE) and its possible therapeutic implications.

AIDS-Related Opportunistic Infections↗