Date of Award

2008

Document Type

Master Thesis

Degree Name

Masters of Science (Research)

Department

Biological Sciences

First Advisor

Dr. John Morrissey

Abstract

Candida causes superficial infections in healthy individuals; however in the immunocompromised host Candida can cause invasive, systemic infections and is a significant cause of morbidity and mortality. This is not due to a more virulent phenotype but to a weakened immune system unable to fight this opportunistic pathogen. The immunocompromised population is ever increasing, due to medical advancements and more aggressive treatments, and hence is the need for epidemiological data of these potentially life threatening infections. The aim of this study was to provide an epidemiological snapshot, of Candida infections from the immunocompromised population in Cork hospitals. Surveillance programmes from the U.S. and globally, have demonstrated a changing epidemiological trend, which suggests an increase in the prevalence of r\on-albicans Candida (NAC), in particular C. glabrata and a decrease in C. albicans infections. This potential epidemiological shift could have strong implications, due to the greater difficulties in the treatment of infections with NAC, particularly those displaying greater resistance patterns. The mortality associated with certain NAC, such as C. krusei, is also greater than that with C. albicans infections. This may put increasing pressure on diagnostic tests for the correct strain identification, which presently are lacking and based on phenotypic rather than molecular applications.

Twenty-five isolates were characterised by strain identification. Each Candida strain was typed by a sugar utilisation method (API Kit), used routinely in hospital laboratories. These results were compared to those generated by a molecular method, which amplifies the domains 1 and 2 (D1/D2) of the large subuit 26S rDNA gene, in which nucleotide variations within this region can be used to differentiate strains. The sensitivity of the API kit could then be determined, by comparison to the sequencing results generated, as the reference for the correct strain identification. The identification results matched in 24/25 cases, indicating the API Kit is a reliable and sensitive (96%) tool. The one discrepancy was identified as C. famata by the API method and C. tropicalis by sequencing, which is the DNA blueprint of the organism, and therefore the definitive result. C albicans accounted for 68% (17/25) of isolates, followed by C. parapsilosis 16% (4/25), and one strain each of C. glabrata, C. lusitaniae, C. tropicalis, and C dubliniensis each representing 4% of the total isolates. This data indicates that C. albicans is the dominant strain, but that there are a variety of NAC

strains also present in Cork hospitals. C. parapsilosis rather than C. glabrata was the second most dominant strain which differs to studies in the U.S. and globally which suggests the emergence of C. glabrata. The presence of C. parapsilosis at 16% is worrying and may suggest hyper alimentation, breaches in catheter control and the need for improvement in infection control practices.

Fluconazole is the most frequently used antifungal agent, administered prophylactically and in the treatment of candidaemia, due to its favourable tolerability and effectiveness. However, it is not effective against C. krusei infection which is intrinsically resistant to fluconazole, C. glabrata which has decreased susceptibility and C. albicans has also developed resistance to this common antifungal agent. In this study, fluconazole susceptibility profiles were assigned to each of the twenty-five strains. All were susceptible to fluconazole with a minimum inhibitory concentration (MIC) of < 8ug/ml. The average MIC of the NAC strains were 6.5 fold more resistant compared to C. albicans isolates. A higher level of resistance among NAC is consistent with similar studies. A tenfold difference in MIC was also noted between some isolates, and the possible role of efflux gene over expression contribution to resistance, remains to be elucidated.

Access Level

info:eu-repo/semantics/openAccess

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