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L P Samaranayake

Publications and source records attributed to L P Samaranayake.

At least 109 records · Page 6Linked to original sources

Guidelines for the use of antimicrobial agents to minimise development of resistance.

There is currently worldwide concern about the problems of antimicrobial resistance. A number of important bodies such as the World Health Organisation and the British House of Lords have identified the reasons for the emergence of resistance to antimicrobial agents and the preventive measures which need to be urgently implemented to curb the spread of resistant organisms. The reasons for the emergence of resistant organisms are not difficult to find. During the past half-century, since the discovery of penicillin by Fleming, people in both the developing and the developed world have accepted antimicrobial agents as a fundamental right, not only to demand at the first sign of a trivial infection but also to self prescribe with readily available, cheap antimicrobial agents. Such unbridled abuse of antimicrobial agents not only in man but also in animals could lead down a slippery slope to an era where the microbe may rule supreme once again. Indeed some authorities are forecasting a 'post-antibiotic era' (as opposed to the pre-antibiotic era before the discovery of penicillin) in the foreseeable future when many infectious diseases will once again be almost impossible to treat.

Animals↗

Caries removal techniques and instrumentation: a review.

The invention of rotary instruments not only improved the speed of caries removal but also the destruction of sound tooth substance. Hence, as early as the 1950s, there were attempts to develop a less invasive technique, such as the air-abrasive and ultrasonic technique, for the purpose of caries removal. The proposed use of air-polishing was published in the early 1980s. Subsequent better understanding of the carious process saw the introduction of the enzyme technique in the late 1980s. Other techniques, such as chemomechanical caries removal and laser systems, have also been attempted and researched during the last four decades to minimise the unnecessary removal of sound tooth substance, although these and other techniques reviewed in this article have not yet superseded the use of rotary instruments. Furthermore, the concept of micro-cavity preparation developed in recent years and the introduction of acid-etch techniques, resin bonding and the use of glass-ionomer cements have also revolutionised the principles of cavity preparation in conservative dentistry. This article reviews the development of these various caries removal techniques and instrumentation and the evolutionary philosophies of cavity preparation promulgated over the last century or so.

Dental Caries↗

The effect of limited exposure to antimycotics on the relative cell-surface hydrophobicity and the adhesion of oral Candida albicans to buccal epithelial cells.

Candida albicans is the major aetiological agent of oral candidosis. Adhesion to oral mucosal surfaces is considered a prerequisite for its successful colonization and subsequent infection, and its relative cell-surface hydrophobicity (CSH) is a contributory physical force. Thus, the main aim here was to determine the CSH of 10 isolates of oral C. albicans after a short exposure to sublethal concentrations of four antifungal agents and to correlate these findings with their adhesion to human buccal epithelial cells (BEC). The yeasts were exposed to sublethal concentrations of nystatin [x 6 minimal inhibitory concentration (MIC)], 5-fluorocytosine (x 8 MIC), ketoconazole (x 4 MIC) and fluconazole (x 4 MIC) for 1 h. The drug was then removed, and the CSH and BEC adhesion assessed by a biphasic aqueous-hydrocarbon assay and a microscopic method, respectively. The mean percentage reductions of CSH after exposure to nystatin, 5-fluorocytosine, ketoconazole and fluconazole were 27.14% (p = 0.01), 9.46% (p = 0.43), 19.47% (p = 0.04) and 6.16% (p = 0.59). Similarly, exposure to all the drugs except 5-fluorocytosine resulted in a significant inhibition of yeast adhesion to BEC, with nystatin eliciting the highest and fluconazole the least inhibition. Further, on regression analysis a strong positive correlation was observed between CSH and adhesion to BEC after limited exposure to 5-fluorocytosine (r = 0.48, p < 0.0001), ketoconazole (r = 0.48, p < 0.0001), fluconazole (r = 0.55, p < 0.0001) as well as in the unexposed controls (r = 0.41, p = 0.001), although nystatin was an exception (r = 0.09, p = 0.44). Taken together, these data elucidate further mechanisms by which antimycotics may operate in vivo to suppress candidal pathogenicity.

Adult↗

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.

Adhesiveness↗

The relationship between the cell length, adhesion to acrylic and relative cell surface hydrophobicity of Candida parapsilosis.

Candida parapsilosis is an emerging opportunistic pathogen which causes systemic and superficial infections in immunocompromised hosts. Successful colonization and subsequent infection of the host by a microorganism depends upon its ability to adhere to host surfaces, and its relative cell surface hydrophobicity (CSH) is a contributory physical force involved in the process. During a comprehensive study of a battery of C. parapsilosis isolates, we noted wide variations in their cell size. Hence we examined the relationship between the cell length, in vitro adhesion to acrylic surfaces and relative CSH of 24 isolates of C. parapsilosis from superficial and systemic sources. A strong positive correlation was observed between the cell length and adhesion of Candida to acrylic surfaces (r=0.56; P=0.004) as well as the cell length and the relative CSH, as measured by a hydrocarbon assay method (r=0.72, P=0.0001). Further, the cell length of both the superficial and systemic isolates correlated well with their CSH (r=0.63, P=0.01; r=0.63, P=0.03 for superficial and systemic isolates, respectively). These data provide a tantalizing glimpse of the structural and functional dynamics of the candidal cell surface.

Acrylic Resins↗

The relative pathogenicity of Candida krusei and C. albicans in the rat oral mucosa.

The relative pathogenicity of Candida krusei and C. albicans was investigated by assessing their colonisation and infectivity of the Sprague-Dawley rat oral mucosa. During an initial 21-week period with intermittent oral inoculation, both Candida spp. demonstrated variable surface colonisation of the oral mucosa. After 3 days of oral inoculation, both yeast species were recovered from all animals. During the 21-week period the mean oral load of C. albicans in the control group of rats varied between (26-274) x 10(1) cfu/ml whereas the two test groups of rats carrying C. krusei CK9 and CK13 had a mean load of (2-10) x 10(1) cfu/ml. Although oral colonisation by C. albicans was greater than that of C. krusei, neither species induced candidal infection during this period. Subsequent immunosuppression of the rats by intramuscular cyclophosphamide (40 mg/kg body weight) initiated C. albicans infection of the dorsal tongue (around the conical papillae area) after 4 weeks, in all of three animals while similar lesions due to C. krusei were seen--albeit after 5-7 weeks--in three of eight animals. Characteristic histological changes of mucosal candidosis were discernible on the lingual mucosa of rats infected with both Candida spp. including parakeratosis, absence of a stratum granulosum, thickened rete ridges, micro-abscess formation and polymorph infiltration of the lingual epithelium. Although both species produced fungal hyphae that penetrated the epithelium up to the prickle cell layer, C. albicans hyphae tended to be relatively more profuse. Taken together these results substantiate, for the first time in an animal model, the clinical evidence that C. krusei, once considered an innocuous commensal, is capable of transforming into an invasive pathogen under conditions of immunosuppression.

Animals↗

Antimicrobial susceptibility of oral isolates of Enterobacter cloacae and Klebsiella pneumoniae from a southern Chinese population.

The antibiotic susceptibilities of 59 Enterobacter cloacae and 39 Klebsiella pneumoniae human oral isolates collected from a southern Chinese population in Hong Kong were investigated for their susceptibility to eight antibiotics: ampicillin, cephalothin, cefuroxime, ceftazidime, ciprofloxacin, gentamicin, tetracycline and trimethoprim/sulfamethoxazole using the E-Test method for direct quantification of minimum inhibitory concentrations. Most strains were sensitive to all antibiotics except ampicillin and cephalothin. Ampicillin resistance was exhibited by 82% of K. pneumoniae and 69% of E. cloacae isolates. Eighty-eight percent of E. cloacae isolates were resistant to cephalothin. Several strains fell within the intermediate category of sensitivity for ampicillin (E. cloacae and K. pneumoniae), cefuroxime (E. cloacae) and tetracycline (K. pneumoniae). Comparison with other Hong Kong data suggests that resistance rates to cefuroxime, ceftazidime, ciprofloxacin, gentamicin, tetracycline and trimethoprim/sulfamethoxazole exhibited by the oral isolates are generally lower than in enterobacters and Klebsiella spp. isolated from urine, skin and soft tissues in Hong Kong populations.

Adult↗

Subgingival microbiota of shallow periodontal pockets in individuals after head and neck irradiation.

This study aimed at investigating the subgingival plaque microorganisms of shallow pockets (< or = 5 mm) in subjects who previously received irradiation in the head and neck region for treatment of nasopharyngeal carcinoma. Direct microscopy and anaerobic culture were used. Subgingival paper point samples were taken from 6 tooth-sites (one/sextant) per subject for direct microscopy (n = 108). Another set of paper points was taken from the deepest of the previously selected sites (one per subject) with: group A) no bleeding on probing to the sulcus depth (n = 9) and group B) bleeding on probing to the sulcus depth (n = 6) for microscopic and anaerobic culture study. Under the microscope, the microflora was found to be a complex mixture comprising gram-positive and gram-negative cocci, rods and filaments, fusiforms, curved rods and spirochetes. Low level of fungi were observed and mycelia were occasionally detected. There was no significant variation in the plaque bacterial morphotypes observable according to sites of isolation and no significant difference between group A and group B in morphotypes of the different microflora. The predominant cultivable microflora comprised several species of facultative and obligate anaerobic bacteria: Gemella, Peptostreptococcus, Staphylococcus, Stomatococcus, Streptococcus, Actinomyces, Eubacterium, Lactobacillus, Propionibacterium, Neisseria, Veillonella, Bacteroides, Campylobacter, Capnocytophaga, Fusobacterium, Kingella, Porphyromonas and Prevotella species. There was no difference between the two groups except the significantly higher proportion of Kingella dentrificans isolated from group B sites. However, colonization of the gingival sulcus in these individuals by microbes that are normal flora of: skin (Peptostreptococcus prevotii and Propionibacterium granulosum) and gut (Eubacterium aerofaciens, Fusobacterium mortiferum and Fusobacterium varium) was detected. These findings appear to suggest that the major components of the subgingival microflora of shallow sites in previously head- and neck-irradiated individuals are similar to that of gingivitis sites in the normal population although they may contain bacterial or fungal species uncommon in normal subjects.

Adult↗

The effect of limited exposure to antifungal agents on the germ tube formation of oral Candida albicans.

Candidal adherence has been implicated as the first step in the pathogenesis of oral candidosis, and germ tube formation by Candida albicans has been attributed as a co-factor that promotes adherence. Oral candidosis is treated with polyenes and the azole group of antifungal agents. As the intraoral concentrations of antifungals fluctuate considerably due to the dynamics of the oral cavity, we investigated the effect of short exposure to sub-lethal concentrations of antifungals on the germ tube formation of Candida albicans. After determining the minimum inhibitory concentration (MIC) of the antifungal agents, ten oral isolates of Candida albicans were exposed to sub-lethal concentrations of nystatin (6xMIC), amphotericin B (8xMIC), 5-fluorocytosine (8xMIC), ketoconazole (4xMIC) and fluconazole (4xMIC), for 1 h. Following removal of the antifungal agent and subsequent incubation in a germ tube-inducing medium, the germ tube formation of these isolates was quantified. When compared with the controls, exposure to nystatin and amphotericin B almost completely inhibited germ tube formation of all the isolates (mean percentage reduction of 97.68 and 97.52%, respectively; P<0.0001), while ketoconazole suppressed this activity to a lesser degree (30.84%; P=0.0174). However, 5-fluorocytosine- and fluconazole-mediated germ tube suppression was minimal (12.63 and 15.93%, respectively; P=0.3255 and P=0.3791). In clinical terms, these findings indicate that short exposure to sub-therapeutic levels of commonly prescribed antifungals may modulate candidal germ tube formation, and thereby the clearance of the organisms from the oral cavity.

AIDS-Related Opportunistic Infections↗

Adhesion of oral C. albicans to human buccal epithelial cells following limited exposure to antifungal agents.

The major aetiologic agent of oral candidosis is C. albicans, and adhesion to oral mucosal surfaces is considered a vital prerequisite for successful colonisation and subsequent infection by this agent. Although many antimycotics are available for the treatment of oral candidosis, the diluent effect of saliva and the cleansing action of the oral musculature often tend to reduce the availability of the agents below that of the effective therapeutic concentration. Therefore, the yeasts undergo only a limited exposure to the antifungals during therapy. Hence, the main aim of the present study was to determine the in vitro adhesion of ten isolates of oral C. albicans to buccal epithelial cells (BEC) following a short exposure to sublethal concentrations of four antifungal agents. The yeasts were exposed to sublethal concentrations of nystatin (x6 MIC), 5-fluorocytosine (x8 MIC), ketoconazole (x4 MIC) and fluconazole (x4 MIC) for a period of 1 h. Following subsequent removal of the drug, the adhesion of these isolates to BEC was assessed by a previously described adhesion assay. The mean percentage reductions of candidal adhesion to BEC following exposure to sublethal concentrations of nystatin, 5-fluorocytosine, ketoconazole and fluconazole were 72.88%, 16.52%, 40.16% and 24.36%, respectively. Ultrastructural studies revealed that short exposure to nystatin and the azoles (but not 5-fluorocytosine) resulted in aberrant cellular features. These findings indicate that subtherapeutic levels of antifungals may modulate candidal colonisation of the oral mucosa and thereby suppress the invasive potential of the pathogen.

Antifungal Agents↗

The postantifungal effect (PAFE) of antimycotics on oral C. albicans isolates and its impact on candidal adhesion.

OBJECTIVE: Postantifungal effect (PAFE) is defined as the suppression of growth that persists following limited exposure of yeasts to antimycotics and subsequent removal of the drug. As there are no data on the PAFE of oral C. albicans isolates the main aim of this investigation was to measure the PAFE of 10 oral isolates of C. albicans following limited exposure (1 h) to five antifungal drugs, including nystatin which has not been previously used in PAFE assays. A secondary aim of the study was to evaluate the biological significance of PAFE, using a nystatin pre-exposed isolate of C. albicans and observing its adherence to denture acrylic surfaces, during the PAFE period. DESIGN: A total of 10 oral isolates of C. albicans were examined for the presence of the PAFE after 1 h exposure to five antifungal drugs, nystatin, amphotericin B, 5-fluorocytosine, ketoconazole and fluconazole. PAFE was automatically assessed with the help of a Spectramax machine which utilizes the principle of periodic turbidometric assessment of growth rates at a given temperature over a given period. The data thus collected are automatically processed in a graphic format as a computer printout. The PAFE was determined as the difference in time (h) required for growth of the drug-free control and the drug-exposed test cultures to increase to 0.05 absorbance level following removal of the antifungal agent (by repeated washing). The adhesion of the single isolate to denture acrylic following limited exposure to nystatin was assessed by a previously described in vitro adhesion assay. RESULTS: Significant PAFE were observed for nystatin, amphotericin-B and 5-fluorocytosine. A marginal PAFE was observed for ketoconazole and little or none for fluconazole. The mean duration of the PAFE of nystatin, amphotericin-B, 5-fluorocytosine, ketoconazole and fluconazole were 2.89 (+/- 0.27) h, 2.83 (+/- 0.23) h, 3.18 (+/- 0.31) h, 0.65 (+/- 0.11) h and 0.16 (+/- 0.06) h, respectively. The mean percentage reduction of adhesion of oral C. albicans BU47204 to denture acrylic during the PAFE period following exposure to nystatin for 10, 30, 50, 70 and 90 min was 9.12%, 61.73%, 65.99%, 82.16% and 83.14%, respectively. CONCLUSIONS: These in vitro findings imply that even a short period of exposure to antifungals may result in modulation of the growth and the virulent attributes of C. albicans, which however is largely dictated by the antimycotic agent in question. Whether such mechanisms operate in vivo needs to be clarified by further studies.

Acrylic Resins↗

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.

Acrylic Resins↗

Chromosome length polymorphism in clinical isolates of Candida parapsilosis.

Chromosome length polymorphism among 24 clinical isolates of Candida parapsilosis obtained from several human sources was analysed using pulsed-field gel electrophoresis. The isolates, from both superficial and deep infections, comprised a miscellaneous collection from the oral cavity, blood cultures, ear infections, wound secrete, a venous catheter and peritoneal dialysis fluid. Contour-clamped homogenous field electrophoresis using a hexagonal electrode was used for pulsed field gel electrophoresis. The chromosome numbers varied from seven to nine and their sizes ranged from 0.75 to 2.6 Mb. According to the electrophoretic karyotype patterns the 24 isolates could be divided into 9 profiles. However, the majority (18 isolates) fell into 3 groups comprising 7, 8 and 9 chromosomes, containing 5, 11, and 2 isolates, respectively. The remaining six isolates, all of which were from either an oral or another superficial site of isolation, could be categorized into a further six groups. These data confirm previous observations on the genomic heterogeneity of clinical isolates of C. parapsilosis, and illustrate the possible commonality in strains from related clinical habitats.

Candida↗

Miconazole lacquer in the treatment of denture stomatitis: clinical and microbiological findings in Chinese patients.

OBJECTIVE: To investigate the efficacy of a miconazole lacquer in producing mycological and clinical cure of Candida-associated denture stomatitis in a Chinese cohort and to study the microbiology of the conditions. DESIGN: A cross-sectional study of the clinical and microbiological features of the condition and its response to treatment with the lacquer. SUBJECTS AND METHOD: Twenty-one Chinese adults with palatal erythema; 15 denture wearers matched for age and sex as controls for microbiology. Clinical examination, impression for culture, photograph of palate to monitor response to treatment, and lacquer application on upper denture base on days 0, 7 and 14. Impression and photograph repeated on day 21; impression cultures quantified by image analysis. Palatal impression in controls; dummy impression as control for impression culture procedures. MAIN OUTCOME MEASURES: Severity of lesion, incidence and type of microorganism at presentation and during treatment; qualitative and quantitative assessment of yeast growth; the latter by statistical analysis of pixel units of yeast colonies; correlation of clinical and mycological cure. RESULTS: Out of the 21 lesions (16 Newton's stage I and 5 stage II), 57% had yeasts at presentation, 10% coliforms and 33% no significant growth. Clinical cure in 3 weeks in 71%, mycological cure in 75% in 7 days; clinical and mycological cure coincided only in 43%. Polymicrobial growth of yeasts and coliforms throughout the course in some. CONCLUSIONS: Miconazole lacquer was a viable treatment option for Candida-associated denture stomatitis in this adult, Chinese cohort; microbiology comprised yeasts, mainly C. albicans and coliforms, especially Klebsiella and Enterobacter species; the pathogenic role of the latter is questionable.

Adult↗

A microbiological study of pre- and postoperative apicoectomy sites.

There is little information on the microbiology of periapical lesions, and no data on the residual microbial flora in the periapex, if any, after apicoectomy procedures. Hence, 64 patients treated by apicoectomy procedures were prospectively studied to assess the bacterial flora in the periapex and to evaluate the residual bacteria in postoperative apicoectomy sites. Of the 64 lesions studied, 14 (22%) were sterile and 50 (78%) yielded bacteria preoperatively. Bacteria could be recovered from 28 (56%) of the latter lesions after apicoectomy and curettage. A total of 105 bacterial strains was isolated from 50 lesions, yielding a range of 1-4 (mean 2.1) species per sample. The isolates comprised 84 (80%) facultative anaerobes and 21 (20%) strict anaerobes. A polymicrobial growth was obtained from 39 lesions whilst 11 lesions yielded pure cultures. On detailed microbiological analyses of 29 lesions, 40% of the isolates were identified as alpha-haemolytic streptococci, half of which were Streptococcus sanguis; anaerobic streptococci were the predominant anaerobes. None of the organisms or group(s) of organisms emerged as recalcitrant colonisers which were difficult to dislodge after surgical debridement. These data indicate that the majority of periapical lesions harbour a variety of flora which cannot be eradicated despite thorough apicoectomy procedures.

Actinomyces↗

Effects of dietary sugars and, saliva and serum on Candida bioflim formation on acrylic surfaces.

The effect of two dietary sugars, glucose and galactose, on biofilm formation of the oral fungal pathogen Candida on denture acrylic strips coated with saliva and serum pellicles was examined in vitro using Candida albicans (3 isolates), C. glabrata (2 isolates) and C. tropicalis (2 isolates). The degree of biofilm activity was affected by both the dietary sugar and the nature of the pellicle (ANOVA, p < 0.01). With most isolates the glucose grown yeasts demonstrated significantly more bioflim activity than the galactose grown fungi, in the presence of pellicles (ANOVA, p < 0.01 or P < 0.01). In contrast, one isolate of galactose-grown yeast elicited significantly higher biofilm activity than glucose-grown yeasts on the control strips (ANOVA, p < 0.01). Taken together, these results imply that a saliva or a serum pellicle, and the carbon source in the environment, act a complex manner modulating Candida bioflim formation.

Acrylic Resins↗