Studies on Candida-Saliva Interactions

Samaranayake, Yuthika Hemamala (1990) Studies on Candida-Saliva Interactions. MSc(R) thesis, University of Glasgow.

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Abstract

Candida species are members of the normal oral flora in 40 to 60% of individuals and are nonpathogenic, but if certain environmental changes occur they can become harmful parasites and cause a variety of oral diseases. Although saliva is a major ecological factor of the oral environment, surprisingly, there is little published information about the interaction of Candida with the constituents of saliva. One salivary factor that has been investigated in this study is the antifungal activity of lysozyme against C. albicans, and three other Candida species. In Chapter 2, the in-vitro antif ungal activity of lysozyme for C. albicans was confirmed and a dose effect between lysozyme concentration and yeast inhibition was shown using a single strain of C. albicans. It is known that Candida can produce a variable layer of extracellular material around their cell wall, the thickness of which depends on the sugar utilized in growth. This layer can protect Candida from the lytic effect of Zymolase-5000, but there is no similar information concerning lysozyme. Since excess carbohydrate appears to be an important factor in Candida growth in saliva, the production of extracellular material in vivo could have an important inhibitory effect on antifungal activity of lysozyme. Therefore in Chapter 2 the antifungal activity of lysozyme on C. albicans GDH 1878 after culture in galactose, sucrose, glucose, maltose, lactose and xylitol was studied. After growth to stationery phase in adefined medium containing 500mM concentrations of each sugar, the inhibitory effect of 20mug/ml of hen egg white lysozyme was measured. The results showed that yeast cells previously cultured in sucrose and galactose were most resistant to the action of lysozyme, while those grown in maltose, xylitol, glucose and lactose were less sensitive to the inhibitory activity of lysozyme (20mug/ml). In order to determine if the protective effect conferred by dietary sugars against lysozyme was concentration dependent, C. albicans, C. tropicalis, C. glabrata, and C. krusei, were cultured in yeast nitrogen base containing three different concentrations of sucrose (0.5M, 0.125M, 0.03M) before exposure to 20mug/ml lysozyme. Generally the results showed that pre-incubation of C. albicans and C. tropicalis in increasing concentrations of sucrose, produced increasing resistance to the antifungal action of lysozyme. The effect of different concentrations of sucrose on the viability of C. glabrata could not be clearly established. However the candidacidal effect of lysozyme on krusei decreased when pre-incubated with increasing concentrations of sucrose. Few studies has been carried out to investigate the growth of Candida in saliva and to identify growth factors involved. In addition, data on growth, pH, acid production and protein degradation is poorly defined. There is some controversy regarding the ability of Candida to degrade salivary proteins and it has been suggested that protein loss may be related to adsorption to the yeast cells as well as to enzyme degradation. Thus it was decided to investigate the ability of albicans GDH 1878, to grow in pooled parotid and pooled mixed saliva. The parameters measured were growth, pH, acid end products (using isotachophoresis) and measurements of salivary protein breakdown by biochemical assay and sodium dodecyl sulphate polyacrylamide gel electrophoresis. When cultured in pooled parotid saliva, C. albicans GDH 1878 demonstrated moderate growth (2.89x10e6 to 6.90x10e7), produced 6 different acid anions and 43% protein degradation while the pH remained alkaline throughout the 72 hours of the experimental period (8.90 to 7.76). This protein breakdown could be due to the alkaline proteases of C. albicans GDH 1878. Since very little is known about the alkaline protease of Candida species no definite conclusions can be drawn from the present finding. However, albicans GDH 1878 cultured in pooled whole saliva demonstrated more profuse growth (5.06x10e6 to 1.39x10e8), produced 6 different acid anions, 83% protein degradation and an average reduction of 4 pH units. Thus pooled whole saliva was judged more suitable for growth experiments than pooled parotid saliva, and was used in subsequent experiments. This study has also demonstrated that the addition of glucose to saliva and the inhibition of the related microflora results in the growth of the four Candida species.

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Keywords: Dentistry, Microbiology
Date of Award: 1990
Depositing User: Enlighten Team
Unique ID: glathesis:1990-78138
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:39
Last Modified: 30 Jan 2020 15:39
URI: http://theses.gla.ac.uk/id/eprint/78138

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