Enzymatic and toxigenic ability of opportunistic fungi contaminating intensive care units and operation rooms at Assiut University Hospitals, Egypt

Urease of Aspergillus fumigatus Is Required for Survival in Macrophages and Virulence

The number of patients suffering from fungal diseases has constantly increased during the last decade. Among the fungal pathogens, the airborne filamentous fungus Aspergillus fumigatus can cause chronic and fatal invasive mold infections. So far, only three major classes of drugs (polyenes, azoles, and echinocandins) are available for the treatment of life-threatening fungal infections, and all present pharmacological drawbacks (e.g., low solubility or toxicity). Meanwhile, clinical antifungal-resistant isolates are continuously emerging. Therefore, there is a high demand for novel antifungal drugs, preferentially those that act on new targets. We studied urease and the accessory proteins in A. fumigatus to determine their biochemical roles and their influence on virulence. Urease is crucial for the growth on urea as the sole nitrogen source, and the transcript and protein levels are elevated on urea media. The urease deficient mutant displays attenuated virulence, and its spores are more susceptible to macrophage-mediated killing. We demonstrated that this observation is associated with an inability to prevent the acidification of the phagosome. Furthermore, we could show that a nickel-chelator inhibits growth on urea. The nickel chelator is also able to reverse the effects of urease on macrophage killing and phagosome acidification, thereby reducing virulence in systemic and trachea infection models. IMPORTANCE The development of antifungal drugs is an urgent task, but it has proven to be difficult due to many similarities between fungal and animal cells. Here, we characterized the urease system in A. fumigatus, which depends on nickel for activity. Notably, nickel is not a crucial element for humans. Therefore, we went further to explore the role of nickel-dependent urease in host-pathogen interactions. We were able to show that urease is important in preventing the acidification of the phagosome and therefore reduces the killing of conidia by macrophages. Furthermore, the deletion of urease shows reduced virulence in murine infection models. Taken together, we identified urease as an essential virulence factor of A. fumigatus. We were able to show that the application of the nickel-chelator dimethylglyoxime is effective in both in vitro and in vivo infection models. This suggests that nickel chelators or urease inhibitors are potential candidates for the development of novel antifungal drugs.

Antifungal activity and mechanism of action of natural product derivates as potential environmental disinfectants

There have been a considerable number of antifungal studies that evaluated natural products (NPs), such as medicinal plants and their secondary metabolites, (phenolic compounds, alkaloids), essential oils, and propolis extracts. These studies have investigated natural antifungal substances for use as food preservatives, medicinal agents, or in agriculture as green pesticides because they represent an option of safe, low-impact, and environmentally friendly antifungal compounds; however, few have studied these NPs as an alternative to disinfection/sanitation for indoor air or environmental surfaces. This review summarizes recent studies on NPs as potential fungal disinfectants in different environments and provides information on the mechanisms of inactivation of these products by fungi. The explored mechanisms show that these NPs can interfere with ATP synthesis and Ca++ and K+ ion flow, mainly damaging the cell membrane and cell wall of fungi, respectively. Another mechanism is the reactive oxygen species effect that damages mitochondria and membranes. Inhibition of the overexpression of the efflux pump is another mechanism that involves damage to fungal proteins. Many NPs appear to have potential as indoor environmental disinfectants.

ONE-SENTENCE SUMMARY

This review shows the latest advances in natural antifungals applied to different indoor environments. Fungi have generated increased tolerance to the mechanisms of traditional antifungals, so this review also explores the various mechanisms of action of various natural products to facilitate the implementation of technology.

The role of fungi in fungal keratitis

Fungal keratitis (FK) accounts for approximately half of the microbial keratitis encountered in low middle income countries (LMICs) and predominantly affect the working rural-poor. FK causes significant morbidity with the majority of patients left with moderate or worse visual impairment and approximately 25% requiring expensive and often unsuccessful surgical interventions. The severity of FK and the resultant corneal damage or resolution can be attributed to i) the virulence and bioburden of the fungal pathogen, ii) the host defense mechanism and immune response and iii) sub-optimal diagnostics and anti-fungal treatment strategies. This review provides a comprehensive overview of the multifaceted components that drive FK progression and resolution, highlighting where knowledge gaps exist and areas that warrant further research.

Identification of fungi in Tunisian olive orchards: characterization and biological control potential

Background

Olive production is the main agricultural activity in Tunisia. The diversity of fungi was explored in two different olive groves located in two distant geographical zones in Sfax (Tunisia) with different management practices.

Results

Fungal isolation was made from soil and the major olive tree pests, namely the Olive fly, Bactrocera oleae Gmelin (Diptera: Tephritidae), and the Olive psyllid, Euphyllura olivina Costa (Homoptera: Psyllidae). A total of 34 fungal isolates were identified according to their phenotypic, genotypic, biochemical and biological activities. Twenty fungal species were identified belonging to six different genera (Alternaria, Aspergillus, Cladosporium, Fusarium, Lecanicillium and Penicillium) by the analysis of their ITS1–5.8S–ITS2 ribosomal DNA region. Different bioassays performed in this work revealed that 25/34 (73.5%) of the identified fungal isolates showed an entomopathogenic and/or antagonistic activity, 9/34 (26.5%) of them displayed phytopathogenic features.

Conclusions

Fungal species that showed entomopathogenic and/or antagonistic potentialities and that are non-phytopathogenic, (17/34; 50%) of our fungal isolates, could be explored for olive protection against fungal diseases and pests, and might have a future application as biocontrol agents.