Effects of efflux pumps on antifungal activity of chitosan against .

Background: Antifungal resistance is a major problem, commonly caused by drug-efflux pump overexpression. To evaluate if chitosan could be effective in drug-resistant infections, we investigated the effects of efflux pumps on antifungal activity of chitosan.

Materials And Methods: The minimal fungicidal concentration (MFC) of oligomer (7-9 kD) and polymer (900-1,000 kD) chitosan against and were evaluated by broth and agar dilution methods. The MFCs of with single deletion of efflux pump genes, with deletion of seven efflux pumps (), and overexpressing efflux pump genes (, and ) were determined. with homozygous deletions of and of were generated using CRISPR-Cas9 system and tested for chitosan susceptibility.

Results: While deleting any individual efflux pump genes had no effect on chitosan susceptibility, simultaneous deletion of multiple pumps (in ) increased sensitivity to both types of chitosan. Interestingly, the overexpression of , or in barely affected its sensitivity. Moreover, with homozygous deletions of and/or showed similar sensitivity to wildtype.

Conclusion: Thus, susceptibility to chitosan was not affected by drug-efflux pumps. Chitosan may be a promising antifungal agent against pump-overexpressing azole-resistant . .