The Role of Melanin in Aspergillus Tolerance to Biocides and Photosensitisers.
Lett Appl Microbiol. 2020 Dec 09;:
Authors: Pascoe MJ, Maillard JY
Cationic biocides are widely utilised for surface disinfection. Photosensitisers such as toluidine blue O (TBO) produce reactive oxygen species following light excitation and are being investigated as novel biocides for similar applications. Aspergillus brasiliensis conidia contain melanin which protects against environmental stressors. The negative charge and antioxidant properties of melanin may confer resistance to photosensitisers and other biocides. In this study, the yeasticidal and fungicidal activity benzalkonium chloride (BZC), sodium dichloroisocyanurate (NaDCC) and TBO with red light were examined using quantitative suspension tests. All three biocides were highly effective against Candida albicans and >5.0 log10 reductions in viability were attainable within 5 minutes. Wild-type A. brasiliensis conidia were highly tolerant to treatment and 0.4 log10 reductions in viability were observed within the same time frame when treated with TBO or BZC. NaDCC was markedly more effective. Inhibition of melanin biosynthesis by culturing with 100 μg ml-1 kojic acid resulted in a hypopigmented phenotype with significantly increased sensitivity to all three biocides. These observations indicate that melanin is a significant contributor toward A. brasiliensis tolerance of biocides and photosensitisers and demonstrate that cationic biocides are poorly suited to applications where the control of A. brasiliensis is required.
PMID: 33300193 [PubMed – as supplied by publisher]