Evolutionary studies in vitro offer more controlled and reproducible environments for studying population dynamics during long-term Dasatinib chemical structure exposure to antifungal agents. The genotypes of the starting population, the population size, and the selective pressure during the evolution can be readily controlled, allowing reproducibility of the environmental conditions for each experiment. There are two major types of systems used for in vitro evolution studies: batch serial transfer or continuous cultures. In batch serial transfer experiments, the population is grown either on solid or liquid media, and a small fraction is serially transferred to fresh media containing the antifungal agent periodically

(Cowen et al., 2000). The population undergoes different growth phases during batch cultivation, as the nutrient content of the environment and the physiological state

of the cell both change as a function of time. Continuous culture systems (using chemostats), BGB324 cell line on the other hand, provide a more constant environment, which helps to keep the population in physiological steady state. The effective population sizes in continuous systems are also generally larger than that of batch systems. Both these systems have been used to study the emergence of drug resistance in C. albicans (Cowen et al., 2000; Huang et al., 2011). Molecular studies of isolates from both in vivo and in vitro systems have shown that starting from a single drug-susceptible genotype, multiple resistance mechanisms are involved in the emergence of drug resistance and that the same mechanisms nearly can be found both in experimental

populations and clinical isolates. Thus, while the environmental conditions used in in vitro systems may not exactly mimic those of in vivo systems, the resistance mechanisms of the fungal pathogen have not been found to be different from those of in vivo systems; and they can provide important and useful information by exploring the population dynamics during the emergence of drug resistance. Although C. albicans is a diploid organism with mating type-like loci (Hull & Johnson, 1999) and a parasexual cycle (Bennett & Johnson, 2003), it is still considered to be asexual because of the lack of observed haploid state, spore formation, and many other processes related to sexual reproduction (Olaiya & Sogin, 1979; Riggsby et al., 1982). Therefore, during evolution, C. albicans can be assumed to be evolving asexually. And because there is no evidence that C. albicans can transfer resistance genes horizontally, it is assumed that resistance mechanisms are acquired via mutations. There are currently three major theories describing the population structure during asexual evolution (Fig. 1). The first is the successional-fixation regime (Desai et al., 2007) (Fig.