Similar results have been reported by Perea et al. who detected 13 ERG11 mutations in 20 ITF2357 C. albicans isolates with high level fluconazole resistance of which 11 were linked to resistance
. In contrast, just a single ERG11 mutation profile (comprising the same two mutations) was found in 14 of 15 fluconazole-resistant isolates in another study . To our knowledge the G450V amino acid substitution has not been previously identified among isolates with reduced susceptibility to azoles. Most of the other substitutions described here have previously been seen in azole-resistant isolates [5, 15, 17, 20] In particular, the substitutions G464S, G307S and G448E, known to confer azole resistance [5, 12, 15], were identified in three or more isolates. However, it is notable that the substitutions Y132H, S405F and R467K which appear to be prevalent in the United States and Europe were rare in Australian isolates [5, 12, 13, 15]. Nineteen of the 20 amino acid substitutions, including G450V, present in the test isolates were clustered into the three “”hot-spot”" regions as described previously
. These hot spots include the residues 105–165 near the N-terminus of the protein, region 266–287 and region 405–488 located towards the C terminus of the protein. The exception was the G307S substitution learn more (n = 3 isolates). However, in a computer-generated model of Erg11p, G307S is located close to the heme cofactor binding site. As such, substitutions at this residue might be expected to impact negatively on the binding of the azole . In contrast to the
fluconazole-resistant strains described above, 22% of fluconazole-susceptible isolates contained no ERG11 C1GALT1 mutations and of those that did, substantially fewer (five compared with 20) amino acid substitutions were detected. Also of interest, all Erg11p amino acid substitutions from isolates with reduced azole susceptibility phenotypes were homozygous whereas with one exception (E266D), those in fluconazole-susceptible isolates were present as heterozygous substitutions. While these two observations support the general notion that ERG11 mutations are linked to azole resistance, the presence of ERG11 mutations in susceptible isolates is not readily explained. Development of “”resistance”" requires prolonged exposure to an azole [3, 4]; however previous studies have not attempted to relate mutations in susceptible isolates to fluconazole exposure. Due to the retrospective Wnt drug nature of the present study we were unable to test this association. The limitations of this study are recognised. Given the small numbers of isolates in our collection and that the presence of ERG11 mutations are not necessarily functionally related to resistance, we were unable to determine the clinical relevance of the ERG11 mutations identified.