Free living amoebae could enhance Fusarium oxysporum growth

The Survival and Treatment of Fusarium oxysporum f. sp. cubense in Water

Fusarium oxysporum f. sp cubense (Foc), the causal agent of Fusarium wilt, is one of the most devastating constraints to banana production worldwide. The spread of Foc in water is particularly concerning, as infested water can rapidly contaminate disease-free areas. The objectives of this study were to investigate the survival of Foc in water and to test the effectiveness of water treatment with chlorine, ozone, UV, and peracetic acid. The study indicated that Foc spores can survive in water for more than 120 days, but that viability was reduced in stagnant water, probably due to anaerobic conditions when spores settled at the bottom. It is therefore recommended that surface water be extracted and treated before it is used for irrigation. The efficacy of all water treatments was reduced in the presence of soil, implying that water needs to be soil-free before treatment. The use of peracetic acid is recommended to treat Foc-contaminated water, as it is safe for use and does not require installation costs although it is effective at treating Foc-contaminated water, ozone would require significant input costs and chlorine can produce harmful disinfection by-products. UV would be impractical for field application because of the high doses required to eliminate Foc.

Free-living amoebae promote Candida auris survival and proliferation in water

Candida auris is an emerging species responsible for life-threatening infections. Its ability to be resistant to most systemic antifungal classes and its capacity to persist in a hospital environment have led to health concerns. Currently, data about environmental reservoirs are limited but remain essential in control of C. auris spread. The aim of our study was to explore the interactions between C. auris and two free-living amoeba (FLA) species, Vermamoeba vermiformis and Acanthamoeba castellanii, potentially found in the same water environment. Candida auris was incubated with FLA trophozoites or their culture supernatants. The number of FLA and yeasts was determined at different times and transmission electron microscopy (TEM) was performed. Supernatants of FLAs promoted yeast survival and proliferation. Internalization of viable C. auris within both FLA species was also evidenced by TEM. A water environmental reservoir of C. auris can therefore be considered through FLAs and contamination of the hospital water networks would consequently be possible.

Polymicrobial interactions involving fungi and their importance for the environment and in human disease

Understanding polymicrobial interactions involving fungi in the environment and the human mycobiome is necessary to address environmental and medically related problems such as drought or antimicrobial resistance. The diversity of these interactions highlights the complexity of fungi, considering how some interactions can be antagonistic, while others synergistic. Over the years, an increase in studies on the mycobiome have revealed similarities between the human and environmental hosts. More recently, studies have focused on microbial commensal relationships and identifying causative agents of human disease. The overlap of some of these interactions is impossible to ignore, indicating that there are areas for medical exploitation that need to be further investigated. This review provides the latest advances in polymicrobial interactions involving fungi and discusses the importance of the fungal lifestyle in the environment and in human disease.

The 'Amoeboid Predator-Fungal Animal Virulence' Hypothesis

The observation that some aspects of amoeba-fungal interactions resemble animal phagocytic cell-fungal interactions, together with the finding that amoeba passage can enhance the virulence of some pathogenic fungi, has stimulated interest in the amoeba as a model system for the study of fungal virulence. Amoeba provide a relatively easy and cheap model system where multiple variables can be controlled for the study of fungi-protozoal (amoeba) interactions. Consequently, there have been significant efforts to study fungal⁻amoeba interactions in the laboratory, which have already provided new insights into the origin of fungal virulence as well as suggested new avenues for experimentation. In this essay we review the available literature, which highlights the varied nature of amoeba-fungal interactions and suggests some unsolved questions that are potential areas for future investigation. Overall, results from multiple independent groups support the 'amoeboid predator⁻fungal animal virulence hypothesis', which posits that fungal cell predation by amoeba can select for traits that also function during animal infection to promote their survival and thus contribute to virulence.

Vermamoeba vermiformis: a Free-Living Amoeba of Interest

Free-living amoebae are protists that are widely distributed in the environment including water, soil, and air. Although the amoebae of the genus Acanthamoeba are still the most studied, other species, such as Vermamoeba vermiformis (formerly Hartmannella vermiformis), are the subject of increased interest. Found in natural or man-made aquatic environments, V. vermiformis can support the multiplication of other microorganisms and is able to harbor and potentially protect pathogenic bacteria or viruses. This feature is to be noted because of the presence of this thermotolerant amoeba in hospital water networks. As a consequence, this protist could be implicated in health concerns and be indirectly responsible for healthcare-related infections. This review highlights, among others, the consequences of V. vermiformis relationships with other microorganisms and shows that this free-living amoeba species is therefore of interest for public health.

Exploring Virulence Determinants of Filamentous Fungal Pathogens through Interactions with Soil Amoebae

Infections with filamentous fungi are common to all animals, but attention is rising especially due to the increasing incidence and high mortality rates observed in immunocompromised human individuals. Here, Aspergillus fumigatus and other members of its genus are the leading causative agents. Attributes like their saprophytic life-style in various ecological niches coupled with nutritional flexibility and a broad host range have fostered the hypothesis that environmental predators could have been the actual target for some of their virulence determinants. In this mini review, we have merged the recent findings focused on the potential dual-use of fungal defense strategies against innate immune cells and soil amoebae as natural phagocytes. Well-established virulence attributes like the melanized surface of fungal conidia or their capacity to produce toxic secondary metabolites have also been found to be protective against the model amoeba Dictyostelium discoideum. Some of the recent advances during interaction studies with human cells have further promoted the adaptation of other amoeba infection models, including the wide-spread generalist Acanthamoeba castellanii, or less prominent representatives like Vermamoeba vermiformis. We further highlight prospects and limits of these natural phagocyte models with regard to the infection biology of filamentous fungi and in comparison to the phagocytes of the innate immune system.

Vermamoeba vermiformis-Aspergillus fumigatus relationships and comparison with other phagocytic cells

Free living amoebae (FLA) are protists ubiquitously present in the environment. Aspergillus fumigatus is a mould responsible for severe deep-seated infections, and that can be recovered in the same habitats as the FLA. By conducting coculture experiments and fungal incubation with amoebal supernatants, we report herein that Vermamoeba vermiformis, a FLA present in hospital water systems, promotes filamentation and growth of A. fumigatus. This finding is of particular importance to institutions whose water systems might harbor FLA and could potentially be used by immunocompromised patients. Also, the relationships between V. vermiformis and A. fumigatus were compared to those between this fungus and two other phagocytic cells: Acanthamoeba castellanii, another FLA, and macrophage-like THP-1 cells. After 4 h of coincubation, the percentages of the three phagocytic cell types with adhered conidia were similar, even though the types of receptors between FLA and macrophagic cell seemed different. However, the percentage of THP-1 with internalized conidia was considerably lower (40 %) in comparison with the two other cell types (100 %). Thus, this study revealed that interactions between A. fumigatus and these three phagocytic cell types show similarities, even though it is premature to extrapolate these results to interpret relationships between A. fumigatus and macrophages.