Differences in the Pathogenic Potential of Candida Species Especially C. albicans

Tobgi, Rajab Salim (1989) Differences in the Pathogenic Potential of Candida Species Especially C. albicans. PhD thesis, University of Glasgow.

Abstract

In 1977, Winner stated that "Candida has turned out to be a key organism in modern medicine, both as an opportunist aggressor and as an indicator of multiple opportunistic infection". During the intervening period, this statement has proved to be true and the prevalence of candidosis has increased dramatically. To date,most of the studies which have been performed on the differences in the pathogenic potential of Candida species have focused on either the virulence attributes of the organism or the host defence parameters. Only a few workers have investigated in depth, in a single comprehensive study, the relationships between different potential pathogenic attributes of a considerable number of Candida species and/or isolates, and putative host defence mechanisms . Most studies have investigated only one factor (e. g. adhesion), with the result that there is very little information about the range of pathogenic factors produced by a single yeast isolate. In the current study, the adhesion of Candida species to buccal epithelial cells (BEC's) and acrylic surfaces; the production of phospholipase and proteinase, and the susceptibility to bron-choalveolar lavage fluid (BLF) and lysozyme of 49 Candida isolates comprising C. albicans (22), C. tropicalis (7), C. krusei (7), C. parapsilosis (5), C guilliermondii (5). and C. glabrata (3), were investigated. The results of this thesis reveal, that variations in adhesion between isolates of the same or different species to either BEC's or acrylic surfaces occur. For example, variations in adhesion, between C. albicans isolates to BEC's ranged from 542 to 1569 yeasts/100 BEC's and 180 to 577 yeast/mm2 acrylic with mean values of 988 and 395 respectively. Moreover, variations in adhesion of C. albicans isolates to BEC's collected from the same donor were also observed. The order of mean adhesion values for the yeast cells to 100 BEC's was as follows: C. albicans (988), C. tropicalis (464) C. parapsilosis (163), C. glabrata (183), C. guil-liermondii (171) and C. krusei (89). However, C. tropica lis (669 yeast/mm2) headed the rank order of adhesion to acrylic strips, followed by: C. albicans (395) C. parapsilosis, (375), C. glabrata (340), C. guilliermondii (222) and C. krusei (131). Only C. albicans isolates produced phospholipase extracellu-larly whereas the other Candida species investigated failed to release this enzyme into the growth medium. The phospholipase activity of C. krusei and C. guilliermondii were investigated for the first time, although they were found to be uniformly negative. The variations in phospholipase activity of the 22 C. albicans isolates tended to follow the adhesion values to BEC's, i. e. , those with high adhesion potential released more phospholipase. Production of phospholipase also appeared to be related to the clinical sources of the isolates; strains isolated from candidosis cases produced more than 30 units of phospholipase activity, whereas those isolated from asymptomatic carriers produced lesser quantities of the enzyme. Proteolytic enzymes were produced in vitro by strains of C. albicans (68.2%), C. tropicalis (71.4%) and C. parapsilosis (100%) but not by the other Candida species studied. No obvious relationships could be demonstrated in the current study, between the proteinase activity of Candida species and either adhesion to BEC's, acrylic surfaces or phospholipase activity. The susceptibility of Candida species to the effect of nonspecific host defences was investigated using lysozyme and BLF. The results of the lysozyme study suggest that due to its anti-candida activity the enzyme which is presented could act as a potent inhibitor of candidal colonization of the oral cavity. Also the lysozyme present in the lysosomes of phagocytes may contribute to the anti-oandida activity of these cells. A significant dose response relationship between lysozyme concentration and fungicidal activity was also found. Overall the results showed variations in the susceptibility of different C. albicans isolates to lysozyme and indeed, however, other Candida species also demonstrated wide variations in their susceptibility to the enzyme. The most susceptible Candida species was C. glabrata followed by C. albicans C. guilliermondii, C. tropicalis, C. parapsilosis and C. krusei. The other non-specific host defence factor studied in this thesis was bronchoalveolar lavage fluid, which was collected from 12 Sprague Dawley rats. The results suggest that BLF may well play an important role in non-specific host defences of the pulmonary tree combating infection with Candida species.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Microbiology, Pathology
• Date of Award: 1989
• Depositing User: Enlighten Team
• Unique ID: glathesis:1989-77995
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 30 Jan 2020 15:44
• Last Modified: 30 Jan 2020 15:44
• URI: https://theses.gla.ac.uk/id/eprint/77995