M1-4 | Candida glabrata: A yeast escaping amphotericin B by a change of its sterol cell membrane composition?

摘要

Introduction: Candidaemia is the fourth most common cause of bloodstream infection worldwide. In this context, Candida glabrata plays -as the second leading pathogen- an important role. Furthermore, it has developed various resistance mechanisms to first line therapy including echinocandins and azoles. The polyene amphotericin B is the preferred drug of choice to treat strains which are considered resistant to the aforementioned substances. As it forms extramembranous aggregates which extract ergosterol out of the fungal cell membrane it has a broad susceptibility pattern and little is known about resistance. Objectives: A total number of 115 clinical C. glabrata isolates -which were obtained between 2015 and 2018- were screened for Amphotericin B tolerance. Cell membrane sterol composition of resistant isolates was analysed to identify dysfunctional enzymes involved in ergosterol biosynthesis accompanied by sequencing of the corresponding ERG genes. Materials and Methods: Screening was performed by microdilution according to EUCAST standarts. Sterole analysis was done by GC-MS. ERG genes were amplified by PCRand consequently sequenced. Results: A total of 27 strains were found to be tolerant to amphotericin B (visible growth at 1μg/ml). Some of these strains showed an increase of ergosterol precursor sterols in the fungal cell membrane, indicating defects in the ergosterol biosynthesis. A concordant decrease in ergosterol itself as the major target of polyenes was observed. Loss of enzyme function correlated with mutations in the encrypting ERG genes. Conclusion: Still few polyene tolerant C. glabrata strains are de-scripted. However, our findings indicate that this yeast is able to adapt to the presence of amphotericin B by alterations in the sterol cell wall composition, exchanging the main polyene target ergosterol to its non- toxic precursor sterols.