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Chapter 7 : Detection and Clinical Significance of Variability among Candida Isolates
Category: Fungi and Fungal Pathogenesis; Clinical Microbiology
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Strain variability is a central topic in the discussion of Candida biology. Most of the Candida isolates that are studied are derived from clinical specimens. Therefore, a discussion of variability among Candida isolates within a particular species starts with decisions that are made in the diagnostic microbiology laboratory. Studies of Candida genetic variability may also be conducted from the perspective of assessing genomic rearrangements. The nature of genomic rearrangements in the diploid Candida albicans was understood more clearly from construction of a physical map of its eight pairs of chromosomes. DNA fingerprinting probe sequences useful in phylogenetic and epidemiological studies are derived from the major repeat sequence (MRS). The MRS is also present in the closely related Candida dubliniensis. Events such as mutation and mitotic recombination also can contribute to variability among C. albicans strains. One study examined whether the local wildlife population was responsible for maintaining a reservoir of C. albicans isolates specific to a defined geographic area in the midwestern United States. The work was expanded to include collection of C. albicans isolates from domestic animals. Results showed that there is a significant difference in the clade distribution of isolates from humans and wildlife, demonstrating population isolation between the groups. The work demonstrates the impressive display of genetic variability that C. albicans can develop when challenged with exposure to antifungal drugs. A given isolate of C. albicans can undergo an impressive range of genetic changes at the level of point mutation to alterations in whole chromosomes.
Dendrogram constructed using the unweighted-pair group method with arithmetic mean for 1,391 C. albicans isolates typed by MLST ( 46 ). The scale at the bottom shows P distances, with the vertical dashed line at the P value of 0.04 used to designate clades. Clade numbers are shown on the right, with vertical bars to indicate their relative sizes. C. africana isolates are placed into clade 13, which is the cluster that is least similar to the others ( 32 , 46 ). Reprinted from Eukaryotic Cell ( 46 ) with permission of the publisher. doi:10.1128/9781555817176.ch7.f1