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Biomedical subjects

L P Samaranayake

Publications and source records attributed to L P Samaranayake.

At least 253 records · Page 14Linked to original sources
PubMed1983

Growth and acid production of Candida albicans in carbohydrate supplemented media.

Aerobic and anaerobic growth characteristics and acid production of a clinical and a reference laboratory strain of Candida albicans in 0.1 M, glucose or sucrose-supplemented batch cultures were examined for 72 h, at 37 degrees C. Both strains gave sigmoid growth curves, aerobically, and the pH dropped from 7.0 to 3.5 in 48 h. Candidal growth or acid production was not observed in submerged, anaerobic cultures. The specific growth rate (mu) of the clinical strain of Candida was significantly greater than the reference strain, in both sugar media. The major acidic component initiating and sustaining the pH drop appeared to be acetate, although formate, pyruvate and propionate were detected in varying proportions in glucose or sucrose cultures. These anionic, acidic metabolites of C. albicans, may play a role in the pathogenesis of mucosal candidoses such as chronic atrophic candidosis.

Acetates↗
PubMed1982

Factors affecting the in-vitro adherence of the fungal oral pathogen Candida albicans to epithelial cells of human origin.

An in-vitro technique was used to investigate the effects of oral commensal bacteria, serum, saliva, germ-tube formation and pH on the adherence of two strains of C. albicans to HeLa cells. Streptococcus salivarius and Streptococcus mitior reduced candidal adhesion whereas Streptococcus mutans had no significant effect. A mixed salivary pellicle on HeLa cells significantly enhanced candidal adhesion and a serum layer had no effect. Yeasts pre-incubated in whole saliva for 3 h showed significantly greater adhesion to HeLa and human embryonic kidney epithelial cells than yeasts in phosphate-buffered saline. The adherence of hyphal phase candida was significantly greater than in the blastospore phase. Adhesion varied with the pH of the test medium, maximal adherence was at pH 3 with less under neutral pH conditions. The factors involved in the adhesion of C. albicans to epithelial surfaces are complex and may play a rôle in the aetiopathology of human mucosal candidoses.

Adhesiveness↗
PubMed1982

The effect of dietary carbohydrates on the in-vitro adhesion of Candida albicans to epithelial cells.

The effects of dietary carbohydrates on the adherence of Candida albicans to HeLa epithelial monolayers and buccal epithelial cells were compared by two assay systems. Candida preincubated in 0.5M, glucose, sucrose, galactose, xylitol or maltose medium produced a significant enhancement in adhesion to both types of epithelial cells. Maltose was the most effective sugar and glucose the least effective in promoting adhesion, while lactose had no significant effect. A clinical isolate of C. albicans demonstrated a greater overall enhancement in adhesion from preincubation with glucose, sucrose and maltose, when compared with a reference laboratory strain of Candida. These results imply that exogenous or endogenous carbon sources may affect the oral and vaginal carriage of C. albicans, by modifying their adhesive properties.

Candida albicans↗
PubMed1982

Isotachophoretic analysis of short-chain carboxylic acids produced by Candida albicans.

Short-chain carboxylic acids produced by Candida albicans in glucose supplemented batch cultures and in human denture plaque has been qualitatively and quantitatively analysed using isotachophoresis. This rapid, simple and relatively new technique which has advantages over other conventional methods, such as gas liquid chromatography, could be a valuable tool in the analysis of carboxylic acids produced by other yeasts of clinical and industrial importance.

Acetates↗
PubMed1981

A retrospective study of patients with recurrent chronic atrophic candidosis.

A retrospective study was carried out in thirty-seven patients who had recurrent chronic atrophic candidosis (CAC). The factors commonly believed to predispose to CAC were investigated, including corrected whole blood folate, iron saturation, and vitamin B12. The incidence of CAC based on clinical and microbiologic criteria was assessed before and after antifungal therapy and correction of predisposing factors. No significant difference was found. Hence, the role of additional, less well-known predisposing factors in the etiopathology of CAC should be considered when one is treating patients with recurrent, chronic Candida infections.

Candidiasis, Oral↗
PubMedDate not supplied

Scanning electron microscopy of microbial colonization of 'rapid' and 'slow' dental-plaque formers in vivo.

The aim was to investigate the morphological features of supragingival plaque development in 'rapid' and 'slow' plaque formers using scanning electron microscopy (SEM). Forty-nine healthy volunteers were screened for their plaque-formation rate after 3 days of oral hygiene abstinence using the Plaque Index (PI). Five with the highest and six with the lowest mean PI were selected as 'rapid' and 'slow' plaque formers, respectively. Six enamel blocks measuring 2 x 2 x 1 mm were bonded onto the buccal surfaces of the upper left canine, premolars and first molar of each selected participant after a series of prophylaxes and oral hygiene instruction to ensure clinical gingival health. A 14-day period with no oral hygiene began thereafter. An enamel block was removed at 3 hr, 6 hr, 1 day, 3 days, 7 days and 14 days from each individual, fixed, and processed for SEM. Quantitatively, more bacteria were observed on the 3-hr to 1-day enamel blocks of the 'rapid' plaque formers. The day-1 specimens of the 'rapid' group showed a more complex supragingival plaque structure than those of the 'slow' group. From days 3 to 14, during the maturation period of supragingival plaque, there were no discernible differences between the two groups except that intermicrobial matrix was more prominent in the 'rapid' group. In general, the development of supragingival plaque followed known patterns. These observations indicate that morphological features of supragingival plaque in 'slow' and 'rapid' plaque formers differ, especially in the early developmental phases.

Bacteria↗
PubMedDate not supplied

Relationship between thigmotropism and Candida biofilm formation in vitro.

The biofilm formation of the oral fungal pathogen Candida on denture acrylic strips coated with saliva or serum was examined in relation to the ability to induce hyphae by thigmotropic reaction, using C. albicans (4 isolates), C. glabrata (3 isolates) and C. tropicalis (3 isolates). Both the degree of biofilm formation and the amount of hyphae exhibiting thigmotropism varied depending upon both the species and strains of Candida. Although there was no significant correlation between the amount of hyphae induced by thigmotropic reaction of fungal isolates and biofilm formation on uncoated control specimens (r = 0.577; p < 0.05), the ability of hyphae induced by thigmotropic reaction significantly correlated with the amount of both saliva- and serum-admixed biofilms (r = 0.734; p < 0.05 and r = 0.793; p < 0.01, respectively). Taken together our in vitro data suggested that the hyphal induction by thigmotropic reaction is of importance in candidal biofilm formation on saliva- or serum-coated acrylic surfaces.

Acrylic Resins↗
PubMedDate not supplied

Reverse transcriptase polymerase chain reaction (RT-PCR) detection of HLP gene expression in Candida glabrata and its possible role in in vitro haemolysin production.

Although haemolysins are known to be putative virulence factors contributing to pathogenicity in Candida species, the haemolytic activity of Candida glabrata and its genetic expression is ill understood at present. Thus, we studied a total of 34 Candida glabrata isolates for their in vitro haemolytic activity using a previously described plate assay system. The mRNA expression of HLP, a putative haemolysin gene, of these isolates was also evaluated using a semi-quantitative, non-competitive RT-PCR assay. All 34 C. glabrata isolates exhibited both partial (alpha) and complete (beta) haemolytic activity to varying degrees. In parallel with the haemolytic activity, all isolates were also positive for HLP mRNA expression. The expression levels of HLP mRNA (as relative units) ranged from 1.01 to 1.82, with a mean value of 1.32. On regression analysis of latter values and the haemolytic activity (in terms of the dimension of the haemolytic zone in the plate assay) of the C. glabrata isolates a highly significant positive correlation was noted (r=0.759, p<0.0001). Taken together, our data illustrate not only the phenotypic characteristics of haemolysin(s) and HLP expression of a battery of C. glabrata clinical isolates, but also, for the first time, evidence for a role of HLP in haemolysis.

Base Sequence↗
PubMedDate not supplied

The influence of incubation conditions on the adherence of oral Enterobacteriaceae to HeLa cells.

The adherence of 12 oral isolates and 4 type strains of Enterobacteriaceae (equally representing Enterobacter cloacae, Klebsiella pneumoniae, Escherichia coli and Citrobacter freundii) to HeLa cell monolayers following five different incubation conditions (sucrose, D-mannose, serum, MEM and Candida albicans GDH 1957) was investigated. Incubation with sucrose and D-mannose resulted in the greatest and least adherence, respectively. The presence of preadherent C. albicans GDH 1957 on the HeLa cells tended to enhance the adherence of certain strains of E. cloacae and C. freundii, but had no overall impact on Enterobacteriaceae adherence. While heterogeneity of behaviour existed between strains within species, E. cloacae was the most, and K. pneumoniae the least, adherent species irrespective of incubation conditions. Haemagglutination assays indicated the presence of mannose-resistant type 1 fimbriae associated with all Enterobacteriaceae. In clinical terms, the variations in adherence properties observed in vitro may contribute to an understanding of the different prevalence rates of oral Enterobacteriaceae reported in the literature.

Bacterial Adhesion↗
PubMedDate not supplied

Exposure to subtherapeutic concentrations of polyene antifungals suppresses the adherence of Candida species to denture acrylic.

BACKGROUND: The adherence of Candida species to denture acrylic is the initial event leading to Candida-associated denture stomatitis, with Candida albicans being the main aetiological agent. However, the increased incidence of immunocompromised patients in the community has resulted in the emergence of a number of non-albicans Candida species as causative agents of this disease, which is commonly managed by topically delivered polyene antifungals. Hence, we investigated the effect of the exposure of denture acrylic surfaces to nystatin and amphotericin B on the subsequent adhesion of six different Candida species. METHODS: Acrylic strips were exposed to subtherapeutic concentrations of the two polyenes for 30 min, and the adhesion of 4 isolates each of C. albicans, Candida glabrata, Candida guilliermondii, Candida krusei, Candida parapsilosis and Candida tropicalis was assessed using a previously described in vitro method with slight modifications. RESULTS: Overall, the results indicated a 35.9% (p < 0.01) and 63.1% (p < 0. 01) reduction, respectively, in yeast adhesion to denture acrylic following exposure to nystatin and amphotericin B, although this effect was not uniform for all the tested isolates. Thus, all C. glabrata, 3 C. guilliermondii and a single isolate each of C. krusei, C. parapsilosis and C. tropicalis were not significantly affected by nystatin exposure, and a single isolate each of C. glabrata and C. guilliermondii were not significantly affected by amphotericin B. CONCLUSIONS: The present data, the first on the effect of polyenes on a wide range of Candida species, indicate that the in vitro exposure of denture acrylic to subtherapeutic concentrations of nystatin and amphotericin B suppresses the adherence of pathogenic Candida species in general.

Acrylic Resins↗
PubMedDate not supplied

Evaluation of polyene-azole antagonism in liquid cultures of Candida albicans using an automated turbidometric method.

BACKGROUND: A computerized machine, SPECTRAmax 340, was used to evaluate the recently reported phenomenon of antagonism of the polyene amphotericin B (AMB) in Candida albicans pre-exposed to the triazole fluconazole (FLZ). METHODS: We investigated growth inhibition by varying concentrations of AMB in seven isolates of C. albicans pre-exposed to FLZ (50 microg/ml) for 18 h. All isolates were obtained on sequential visits from human immunodeficiency virus-infected patients not treated with FLZ. RESULTS: Antagonism of AMB activity was observed in 5, 4, 2 and a single isolate for 0.5, 1, 2 and 3 microg/ml of the antifungal, respectively. In the majority of Candida isolates, antagonism was seen within a concentration range of 0.5-1.0 microg/ml AMB; 1 Candida strain (HK1-Sa) was resistant to 3 microg/ml AMB. Higher concentrations of AMB (>3 microg/ml) killed both the controls and FLZ-pre-exposed Candida cells. No significant differences were observed between the periods of antagonism observed for any of the sequential isolates or for any of the AMB concentrations or in the maxima of the growth curves obtained for all Candida isolates. CONCLUSION: We conclude that the SPECTRAmax system is a useful tool to evaluate in vitro pharmacodynamic interactions between antifungal regimens within a fluid culture system, and provides information that cannot be obtained using traditional plate assay systems.

Amphotericin B↗
PubMedDate not supplied

Actinomyces spp. in supragingival plaque of ethnic Chinese preschool children with and without active dental caries.

Very limited molecular epidemiological data are available on the role of Actinomyces spp. in the pathogenesis of caries in the primary dentition. Therefore, we investigated their distribution in supragingival plaque of ethnic Chinese preschool children from Singapore and Hong Kong, either with or without active caries. Plaque samples were taken from intact interproximal enamel areas using dental floss. Bacterial genomic DNA of each sample was extracted and variable regions of 16S ribosomal DNA amplified and labelled with digoxigenin. Oligonucleotide probes specific for Actinomyces bovis, Actinomyces gerencseriae, Actinomyces israelii, Actinomyces meyeri, Actinomyces odontolyticus, catalase-negative Actinomyces naeslundii (genospecies 1 and 2) and catalase-positive Actinomyces naeslundii genospecies 2 (previously Actinomyces viscosus serotype II) were used to detect these species using Southern hybridization with a Minislot and Miniblotter system. A. odontolyticus, A. gerencseriae and A. meyeri were detected with similar frequency in both Singapore and Hong Kong samples or in those with and without active caries. However, the prevalence of A. naeslundii was significantly different in the two locales (p<0.05). A. odontolyticus (88.7%), A. gerencseriae (56.6%) and A. naeslundii (50.9%) were detected in a majority of the samples and the positive hybridization signals of A. gerencseriae in the caries-active group were stronger than from the caries-free group. A. bovis and A. israelii were undetectable in any of the samples. These data imply that A. odontolyticus, A. naeslundii and A. gerencseriae may play an important role in supragingival plaque formation on primary teeth in ethnic Chinese, with others such as A. meyeri contributing.

Actinomyces↗
PubMedDate not supplied

Tuberculous ulcer of the tongue as presenting feature of pulmonary tuberculosis and HIV infection.

Tuberculosis (TB), once a lethal disease, has shown a decrease in incidence with improved public health measures and availability of antituberculous drugs. But with the advent of human immunodeficiency virus (HIV) infection and acquired immunodeficiency syndrome (AIDS), it has re-emerged alarmingly as an opportunistic infection in immunocompromised patients. Lungs are the most commonly affected organs and involvement of the oropharyngeal region in TB is very rare. Two cases of TB manifesting as ulcer of the tongue are reported here. Interestingly, both of these cases were reported within a span of six months and both of the patients were in their early thirties. A primary diagnosis of both pulmonary TB and HIV sero-positivity was made after the diagnosis of the oral TB ulcer.

AIDS-Related Opportunistic Infections↗