Date of Award

Fall 2011

Degree Type


Degree Name

Master of Science (MSc)




Dr. Jianping Xu


Dr. Yamamura



Committee Member

Dr. Golding


In Canada the incidence of yeast infections have increased over the past decade, which in turn has resulted in the increased mortality and morbidity rates among the immuno-compromised patients. Yeasts are ubiquitous in nature and constitute a healthy portion of human skin and gut flora. Factors such as the urban settings and food have been previous shown to influence the yeast flora people harbour. This makes us believe that to effectively tackle the rising yeast infections in Canada we need to not only conduct epidemiological yeast studies in clinical settings but should also understand the diversity and distribution of them in the urban environment. This thesis constitutes of an epidemiological fungemia study and an urban environmental yeast profiling study conducted in the city of Hamilton.

In the first chapter of the thesis I discuss the results of the epidemiological candidemia study. We noticed that over the past decade the mean age of the population with candidemia in hospitals within Hamilton has increased by 10 years. DNA fingerprinting analysis suggested that 33% of the blood streamCandida isolates from January 2005 to February 2009 belonged to 18 clusters, some of which were shared between wards and hospitals. we found that for each of the four species, strains isolated closer to each other temporally were overall genetically more similar to each other as well, which suggested that nosocomial sources likely caused repeated candidemia infections. The study is the first of its sort in Canada and the results of this chapter are expected to aid infection control practitioners in the Hamilton hospitals and make the stay of patients in hospitals safer.

In the second chapter, we discuss the diversity and distribution of yeasts prevalent on trees in and around Hamilton. We identified a total of 88 environmental yeasts belonging to 20 species (based on ITS sequence data). The yeast populations were highly heterogeneous in both species and genotype composition. Among the 14 tree species sampled, yeasts were frequently found on cedar, cottonwood and basswood. Interestingly all the Candida parapsilosis strains were found from pine tree only. Some of the potential environmental factors shaping the distribution of yeast populations in Hamilton are discussed.


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