Virgínia M. Siqueira

Filamentous fungi in drinking water, particularly in relation to biofilm formation

The presence of filamentous fungi in drinking water has become an area worthy of investigation with various studies now being published. The problems associated with fungi include blockage of water pipes, organoleptic deterioration, pathogenic fungi and mycotoxins. Fungal biofilm formation is a less developed field of study. This paper updates the topic and introduces novel methods on fungal biofilm analysis, particularly from work based in Brazil. Further recommendations for standard methodology are provided.

Evaluation of antifungal activity of essential oils against potentially mycotoxigenic Aspergillus flavus and Aspergillus parasiticus

The antifungal activity of essential oils of fennel (Foeniculum vulgare Mill., Apiaceae), ginger (Zingiber officinale Roscoe, Zingiberaceae), mint (Mentha piperita L., Lamiaceae) and thyme (Thymus vulgaris L., Lamiaceae) was evaluated against mycotoxin producers Aspergillus flavus and A. parasiticus. High Resolution Gas Chromatography was applied to analyze chemical constituents of essential oils. The effect of different concentrations of essential oils was determined by solid medium diffusion assay. Mycelial growth and sporulation were determined for each essential oil at the concentrations established by solid medium diffusion assay. At the fifth, seventh and ninth days the mycelial diameter (O mm) and spore production were also determined. FUN-1 staining was performed to assess cell viability after broth macrodilution assay. Trans-anethole, zingiberene, menthol and thymol are the major component of essential oils of fennel, ginger, mint and thyme, respectively. The effective concentrations for fennel, ginger, mint and thyme were 50, 80, 50 and 50% (oil/DMSO; v/v), respectively. The four essential oils analysed in this study showed antifungal effect. Additionally, FUN-1 staining showed to be a suitable method to evaluate cell viability of potential mycotoxigenic fungi A. flavus and A. parasiticus after treatment with essential oils.

Surface hydrophobicity of culture and water biofilm of Penicillium spp.

Fungal surface hydrophobicity is involved in several functions in fungal growth and development. Water contact angles measurement has been used as a direct and simple approach for its characterisation in solid cultures. Microsphere adhesion assay is said to be the best method to assess cell hydrophobicity of filamentous fungi. This study aimed to apply these two methods to study hydrophobicity of Penicillium expansum and Penicillium brevicompactum grown as mycelial mats in solid culture, liquid culture and water biofilms. As result, both species in solid cultures were classified as hydrophobic with contact angles ≥90º, but in liquid cultures and water biofilms showed different levels of hydrophobicity when microsphere adhesion assay was applied. In addition, was found that biofilms have specific hydrophobic hyphae which may be involved in fungal ecological functions.

Biofilm formation by filamentous fungi recovered from a water system

Filamentous fungi have been constantly recovered from diverse aquatic environments including drinking water distribution systems. Although most of the works are focused on the study of planktonic form, recent researches have shown that fungi develop biofilm within these systems. In this study, Aspergillus sp. (section Nigri), Aspergillus sp. (section Flavi), Alternaria sp., Botrytis sp., Cladosporium sp., and Penicillium sp. recovered from water biofilms were used to evaluate their capability to grow as biofilms under laboratorial conditions. Morphological and physiological characteristics were analysed using image analysis and biomass and cell activity estimation. All six isolates were able to form biofilm, though different patterns of development were observed. Only Alternaria sp. formed biofilm in water over 24 h of analysis. MEB was shown to be the best culture media for biofilm formation. A direct correlation between biomass and cell activity was not observed, but biomass values and morphological parameters, that is, monolayer and EPS production, were directly correlated. Thus, the results present here highlight the capability of fungi to form biofilms and the emergent necessity to standardize methods for further research in this area.