<i>cyp51A</i> -Based Mechanisms of Aspergillus fumigatus Azole Drug Resistance Present in Clinical Samples from Germany

<jats:title>ABSTRACT</jats:title> <jats:p> Since the mid-1990s, a steady increase in the occurrence of itraconazole-resistant <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Aspergillus fumigatus</jats:named-content> isolates has been observed in clinical contexts, leading to therapeutic failure in the treatment of aspergillosis. This increase has been predominantly linked to a single allele of the <jats:italic>cyp51A</jats:italic> gene, termed TR/L98H, which is thought to have arisen through the use of agricultural azoles. Here, we investigated the current epidemiology of triazole-resistant <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">A. fumigatus</jats:named-content> and underlying <jats:italic>cyp51A</jats:italic> mutations in clinical samples in Germany. From a total of 527 samples, 17 (3.2%) showed elevated MIC <jats:sub>0</jats:sub> values (the lowest concentrations with no visible growth) for at least one of the three substances (itraconazole, voriconazole, and posaconazole) tested. The highest prevalence of resistant isolates was observed in cystic fibrosis patients (5.2%). Among resistant isolates, the TR/L98H mutation in <jats:italic>cyp51A</jats:italic> was the most prevalent, but isolates with the G54W and M220I substitutions and the novel F219C substitution were also found. The isolate with the G54W substitution was highly resistant to both itraconazole and posaconazole, while all others showed high-level resistance only to itraconazole. For the remaining six isolates, no mutations in <jats:italic>cyp51A</jats:italic> were found, indicating the presence of other mechanisms. With the exception of the strains carrying the F219C and M220I substitutions, many itraconazole-resistant strains also showed cross-resistance to voriconazole and posaconazole with moderately increased MIC <jats:sub>0</jats:sub> values. In conclusion, the prevalence of azole-resistant <jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">A. fumigatus</jats:named-content> in our clinical test set is lower than that previously reported for other countries. Although the TR/L98H mutation frequently occurs among triazole-resistant strains in Germany, it is not the only resistance mechanism present. </jats:p>