Evaluation and comparison of commercially available identification techniques of Candida species
Price, Catherine Louise
Cardiff Metropolitan University
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C. albicans is the most predominant species that causes candidiasis; it accounts for over 75% of all cases (Douglas, et al (2000)). C.albicans is found as part of the normal flora of the oral, skin, genital and gastrointestinal tract in approximately 30-50% of the 'normal' population; symbiotically existing with its host. C.albicans is an opportunistic organism, if the host defence system is compromised, or if there is a change in ecological environment e.g. decreases in other commensal organisms due to administration of broad-spectrum antibiotics. The increased immunocompromised population and the widespread use of antimycotics have caused shifts of distribution in candidiasis. (Diekema, et al (2007)) The emergence of other pathogenic candida species as causes of candidiasis include: C. globrota, C. tropicalis, C. parapsilosis, C. Krusei, C. lusitanioe and C. kefyr. (Diekema, et al (2007)) These non-albicons candida species have caused approximately 35-65% of all candidaemias in the general patient population during this time (Barnes, et al (2002)). Although the crude mortality is low for candidaemia, the attributable mortality (which means mortality was associated with candidaemia) is actually higher for non-albicans candida than C.albicons. (Barnes, et al (2002)) C.albicons is susceptible to the majority of the commonly used antimycotics so is usually easily treated. Certain non-albicans candida species however are resistant to the commonly used antimycotics and the incidence of candidiasis caused by these organisms is on the increase, however, since C.albicons is a constituent of the normal skin, oral and gastrointestinal tract flora, there is a high possibility of obtaining mixed cultures of candida species. As detailed above non-albicans will have varying susceptibility to the first line azole antimycotics i.e. treatment and elimination of C.albicans from a mixed population will enable azole resistant organisms to establish a pathogenic hold. There are 3 aims to this project: 1. Comparison and evaluation between the various methods of C.albicons identification: Germ tube production, "spiking", chlamydospore formation. Candida isolates were subjected to germ tube tests using human plasma (gold standard test) horse serum and Mueller-Hinton agar, "spiking" on heated horse blood agar and chlamydospore production on cornmeal/tween 80 agar Horse serum germ tube test gave 100% sensitivity and 100% specificity so is the best alternative to human plasma in comparison to Mueller-Hinton agar which gave 98.5% sensitivity and 100% specificity, Cornmeal/Tween 80 agar which gave 89.9% sensitivity and 100% specificity and "spiking" on heated horse blood agar which gave 85.8% sensitivity and 100% specificity. 2. Determination of the optimum chromogenic agar for identification purposes and use as a primary plate 12 reference strains of candida and 19 wild strains of candida were inoculated onto SABC agar and 4 types of chromogenic agar to determine the optimum agar for use as a primary plate and as an identification media. For identification purposes the optimum agar was Colorex™ Candida agar by E&O laboratories, because it produced all the expected pigmentations, can identify C.albicans directly and has a wide pigmentation range for the presumptive identification of other yeasts. As a primary plate the best plates were SABC agar and ChromID™ Candida agar (CANlD2) by Biomérieux because they were the only plates to give 100% positivity rates. 3. Determination of the optimum agar for detecting mixed cultures The optimum agar for detecting mixed cultures is determined and used to determine the numbers of different pure/mixed condida cultures. The optimum agar was ChromID™ Candida agar (CANlD2) by Biomérieux as this was the only media that was able to detect 100% of the mixed cultures.
BSc (Hons) Biomedical Science (Applied Biomedical Science)
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