Adaptation of Fusarium oxysporum and Fusarium dimerum to the specific aquatic environment provided by the water systems of hospitals

Invasive fusariosis

Invasive fusariosis is a serious invasive fungal disease, affecting immunocompetent and, more frequently, immunocompromised patients. Localized disease is the typical clinical form in immunocompetent patients. Immunocompromised hosts at elevated risk of developing invasive fusariosis are patients with acute leukemia receiving chemotherapeutic regimens for remission induction, and those undergoing allogeneic hematopoietic cell transplant. In this setting, the infection is usually disseminated with positive blood cultures, multiple painful metastatic skin lesions, and lung involvement. Currently available antifungal agents have poor in vitro activity against Fusarium species, but a clear-cut correlation between in vitro activity and clinical effectiveness does not exist. The outcome of invasive fusariosis is largely dependent on the resolution of immunosuppression, especially neutrophil recovery in neutropenic patients.

First Report of Hemp Fusarium Wilt Caused by Fusarium oxysporum in Croatia

Wilted hemp (Cannabis sativa L.) plants were observed in August 2019 in commercial fields around Osijek, Croatia. Plants and roots with disease symptoms were collected. The single-spored isolates produced septate cottony white to light pink aerial mycelium and purple undersurface on potato dextrose agar (PDA). Smooth and hyaline hyphae were branched and septate. Macroconidia were fusiform to sickle-shaped with foot-shaped basal cells, elongated apical cells and three to five septa. Sequencing of the internal transcribed spacer and the partial elongation factor 1-α gene identified the species as Fusarium oxysporum. Artificial infection fulfills Koch's postulates, producing plants which show stunted growth and wilt symptoms similar to those observed in the commercial fields. Control seedlings remained symptomless and healthy. To the best of our knowledge, this is the first report of hemp Fusarium wilt causing F. oxysporum in Croatia. Considering that F. oxysporum has been reported in main field crops in Croatia, the presence of this pathogen could cause economically significant hemp production decreases, especially in humid and cold springs and susceptible varieties.

Effect of abiotic factors and culture media on the growth of cheese-associated Nectriaceae species

Nectriaceae species have been described in various natural environments or as plant or human pathogens. Within this family, the Bisifusarium domesticum species is of particular interest for food mycologists as it is used for technological functions in various cheese productions. Moreover, it has only been isolated from the cheese environment so far and, until recently, was the only Nectriaceae species described in this food product. Recently, four novel cheese-associated Nectriaceae species have been described, including two associated to the Bisifusarium genus and two to a new genus, Longinectria gen. nov.. These observations raise questions concerning the potential adaptation of these species to the cheese environment. In this context, this study first focused on determining the impact of abiotic factors on the growth of isolates belonging to the five cheese-associated species (i.e. B. allantoides sp. nov., B. domesticum, B. penicilloides sp. nov., L. lagenoides gen. nov. sp. nov. and L. verticilliforme gen. nov. sp. nov.) but also included phylogenetically close species. To do so, fungal growth kinetics in liquid medium (Potato Dextrose Broth) were determined by laser nephelometry at different temperatures, pH and water activities using NaCl as a depressor. Growth modeling was then performed to estimate cardinal values for each abiotic factor. Secondly, fungal growth was also evaluated on Potato Dextrose Agar (synthetic medium), cheese agar (cheese-mimicking medium) and Raclette de Savoie cheese (actual cheese). Our results clearly highlighted physiological differences in growth characteristics between the studied cheese-associated Nectriaceae spp. and the "non-cheese" species which could suggest, for the former, an adaptation to this food matrix. Indeed, regarding the impact of the tested abiotic factors, statistical analyses confirmed this dichotomy, with for example the lowest optimal temperatures estimated for the cheese-associated species (T_opt 19.1-23.1 °C) while the other Bisifusarium species exhibited the highest optimal temperatures (T_opt 26.1-36.2 °C). As for the impact of growth media, radial growth measurements highlighted that B. domesticum was the least affected species for growth on Raclette de Savoie and even grew faster on cheese agar than on synthetic medium confirming its strong adaptation to the cheese environment.

Water distribution systems in Sardinian hospitals host invasive clonal lineages of the Fusarium oxysporum and Fusarium solani species complexes

Several Fusarium species cause disease on human hosts, including commonly fatal infections in immunocompromised individuals. Recently, cases of hospitalized patients affected by fusaria were reported in the Tyrrhenian Island of Sardinia, Italy. To precisely characterize the Fusarium species and haplotypes present in hospitals of the region, a multilocus DNA sequence typing (MLST) approach was applied. Water distribution systems in four departments belonging to four Sardinian hospitals were sampled. Fusarium species and sequence types (STs) were identified using MLST based on sequences of the elongation factor 1-alpha (EF-1α) gene, the nuclear ribosomal DNA intergenic spacer region (IGS rDNA), and/or a portion of the second-largest subunit of RNA polymerase (RPB2) gene. The majority of isolates obtained from Sardinian hospitals (90.7%) were identified as representatives of the Fusarium oxysporum species complex (FOSC), followed by those of the F. solani species complex (FSSC) (8.2%), and F. dimerum (1.1% of all isolates). Ten STs were found among the FOSC and FSSC, with more than 60% of the isolates identified as either FOSC ST 33 or FSSC 1 (F. petroliphilum). More than half of the FOSC isolates obtained from the water systems in all four hospitals belonged to the worldwide distributed clonal lineage ST 33. This haplotype is the most prevalent among the FOSC in different countries, being responsible for the vast majority of cases of human fusariosis.

Disinfectants in a Hemodialysis Setting: Antifungal Activity Against Aspergillus and Fusarium Planktonic and Biofilm Cells and the Effect of Commercial Peracetic Acid Residual in Mice

Aspergillus and Fusarium cause a broad spectrum of infections in humans, mainly in immunocompromised patients. Among these, patients undergoing hemodialysis are highly susceptible to infections, requiring a constant and adequate environmental disinfection program. Nevertheless, monitoring the residual disinfectants can contribute to the morbidity and mortality reduction in these patients. Here, we evaluated the susceptibility of Aspergillus spp. (n=19) and Fusarium spp. (n=13) environmental isolates against disinfectants (acetic acid, citric acid, peracetic acid, sodium hypochlorite, and sodium metabisulphite) at different concentrations and time exposures. Also, we investigated the in vivo toxicity of the peracetic acid residual concentration in mice. Fusarium isolates were identified by F. equiseti, F. oxysporum and F. solani while Aspergillus presented clinically relevant species (A. fumigatus, A. niger and A. terreus) and environmental ones. Against planktonic cells, only two disinfectants (acetic acid and sodium hypochlorite) showed a fungicidal effect on Fusarium spp., while only one (sodium hypochlorite) was effective against Aspergillus spp. Both fungi formed robust in vitro biofilms with large amounts of the extracellular matrix, as evidenced by electron micrographs. Exposure of fungal biofilms to disinfectants showed sensitivity to three (acetic, citric, and peracetic acids), although the concentrations and times of exposure varied according to the fungal genus. Mice exposure to the residual dose of peracetic acid during 60 weeks showed anatomopathological, hematological, and biochemical changes. The implementation of news control measures and those that already exist can help reduce infections, the second cause of death and morbidity in these patients, besides providing safety and well-being to them, a priority of any quality health program.

Critical Review: Propensity of Premise Plumbing Pipe Materials to Enhance or Diminish Growth of Legionella and Other Opportunistic Pathogens

Growth of Legionella pneumophila and other opportunistic pathogens (OPs) in drinking water premise plumbing poses an increasing public health concern. Premise plumbing is constructed of a variety of materials, creating complex environments that vary chemically, microbiologically, spatially, and temporally in a manner likely to influence survival and growth of OPs. Here we systematically review the literature to critically examine the varied effects of common metallic (copper, iron) and plastic (PVC, cross-linked polyethylene (PEX)) pipe materials on factors influencing OP growth in drinking water, including nutrient availability, disinfectant levels, and the composition of the broader microbiome. Plastic pipes can leach organic carbon, but demonstrate a lower disinfectant demand and fewer water chemistry interactions. Iron pipes may provide OPs with nutrients directly or indirectly, exhibiting a high disinfectant demand and potential to form scales with high surface areas suitable for biofilm colonization. While copper pipes are known for their antimicrobial properties, evidence of their efficacy for OP control is inconsistent. Under some circumstances, copper's interactions with premise plumbing water chemistry and resident microbes can encourage growth of OPs. Plumbing design, configuration, and operation can be manipulated to control such interactions and health outcomes. Influences of pipe materials on OP physiology should also be considered, including the possibility of influencing virulence and antibiotic resistance. In conclusion, all known pipe materials have a potential to either stimulate or inhibit OP growth, depending on the circumstances. This review delineates some of these circumstances and informs future research and guidance towards effective deployment of pipe materials for control of OPs.

The effect of temperature on airborne filamentous fungi in the indoor and outdoor space of a hospital

Fungi are one of the bioaerosols in indoor air of hospitals. They have adverse effects on staff and patients. The aim of this study was to investigate the effects of three incubation temperature on the density and composition of airborne fungi in an indoor and outdoor space of hospital. Sabouraud dextrose agar was used for culture the fungi. For improvement of aseptic properties, chloramphenicol was added to this medium. The density of airborne fungi was less than 282 CFU/m³. The highest density was detected in emergency room and the lowest of them was in neonatal intensive care unit (NICU) and operation room (OR). Results showed that fungi levels at 25 °C were higher than 37 and 15 °C (p = 0.006). In addition, ten different genera of fungi were identified in all departments. The predominant fungi were Fusarium spp., Penicillium spp., Paecilomyces spp., and Aspergillus niger. Moreover, the density and trend of distribution of Fusaruim spp. in the indoor space was directivity to outdoor space by ventilation system. The present study has provided that incubation temperature had effect on airborne fungi remarkably. We are suggested that more studies would be conducted on incubation temperature and other ambient factors on airborne fungi.

Epitypification of Fusarium oxysporum - clearing the taxonomic chaos

Fusarium oxysporum is the most economically important and commonly encountered species of Fusarium. This soil-borne fungus is known to harbour both pathogenic (plant, animal and human) and non-pathogenic strains. However, in its current concept F. oxysporum is a species complex consisting of numerous cryptic species. Identification and naming these cryptic species is complicated by multiple subspecific classification systems and the lack of living ex-type material to serve as basic reference point for phylogenetic inference. Therefore, to advance and stabilise the taxonomic position of F. oxysporum as a species and allow naming of the multiple cryptic species recognised in this species complex, an epitype is designated for F. oxysporum. Using multi-locus phylogenetic inference and subtle morphological differences with the newly established epitype of F. oxysporum as reference point, 15 cryptic taxa are resolved in this study and described as species.

In vitro and in vivo antifungal efficacy of plant based lawsone against Fusarium oxysporum species complex

Fusarium oxysporum is an ascomycete facultative fungus which generally affects to plants. However, it is recently known as a serious emerging opportunistic pathogen of human and other animals. F. oxysporum shows broad resistance to commonly used antifungal agents and therefore development of alternative therapeutic agents is required. In this study, we investigated the antifungal efficacy of plant based natural lawsone against pathogenic F. oxysporum. Antifungal susceptibility test determined the concentration dependent growth inhibition of lawsone against F. oxysporum with minimum inhibitory concentration (MIC) at 100μg/mL. Ultra-structural analysis indicates the prominent damage on cell wall of the mycelium after lawsone treatment, and suggests that it could increase the membrane permeability and disintegration of cells leading to cellular death. Propidium iodide (PI) uptake assay results showed the higher level of cell death in lawsone treated F. oxysporum which further confirms the loss of plasma membrane integrity. Also, detection of reactive oxygen species (ROS) using DCFH-DA has clearly indicated that lawsone (100μg/mL) can induce the ROS level in the filaments of F. oxysporum. MTT assay results showed the loss of viability and germination capacity of F. oxysporum spores by lawsone in concentration dependent manner. Moreover, lawsone treatment induced the mRNA expression of two autophagy related genes (ATG1 and ATG8) indicating that lawsone may activate the autophagy related pathways in F. oxysporum due to the oxidative stress generated by ROS. F. oxysporum infected zebrafish has recovered after lawsone therapy as a topical treatment suggesting that lawsone is a potential natural antifusariosis agent.

First report of Fusarium oxysporum species complex infection in zebrafish culturing system

Fusarium oxysporum species complex (FOSC) is a highly diverse fungus. Recently, F. oxysporum infection was identified from zebrafish (Danio rerio) culturing system in Korea. Initially, a rapid whitish smudge was appeared in the water with the fungal blooming on walls of fish tanks. Microscopic studies were conducted on fungal hyphae, colony pigmentation and chlamydospore formation and the presence of macro- and microspores confirmed that the isolated fungus as F. oxysporum. Furthermore, isolated F. oxysporum was confirmed by internal transcribed spacer sequencing which matched (100%) to nine F. oxysporum sequences available in GenBank. Experimental hypodermic injection of F. oxysporum into adult zebrafish showed the development of fungal mycelium and pathogenicity similar to signs observed. Histopathologic results revealed a presence of F. oxysporum hyphae in zebrafish muscle. Fusarium oxysporum growth was increased with sea salt in a concentration-dependent manner. Antifungal susceptibility results revealed that F. oxysporum is resistant to copper sulphate (up to 200 μg mL^-1 ) and sensitive to nystatin (up to 40 μg mL^-1 ). This is the first report of FOSC from zebrafish culture system, suggesting it appears as an emerging pathogen, thus posing a significant risk on zebrafish facilities in the world.

A Clonal Lineage of Fusarium oxysporum Circulates in the Tap Water of Different French Hospitals

Fusarium oxysporum is typically a soilborne fungus but can also be found in aquatic environments. In hospitals, water distribution systems may be reservoirs for the fungi responsible for nosocomial infections. F. oxysporum was previously detected in the water distribution systems of five French hospitals. Sixty-eight isolates from water representative of all hospital units that were previously sampled and characterized by translation elongation factor 1α sequence typing were subjected to microsatellite analysis and full-length ribosomal intergenic spacer (IGS) sequence typing. All but three isolates shared common microsatellite loci and a common two-locus sequence type (ST). This ST has an international geographical distribution in both the water networks of hospitals and among clinical isolates. The ST dominant in water was not detected among 300 isolates of F. oxysporum that originated from surrounding soils. Further characterization of 15 isolates by vegetative compatibility testing allowed us to conclude that a clonal lineage of F. oxysporum circulates in the tap water of the different hospitals.

IMPORTANCE

We demonstrated that a clonal lineage of Fusarium oxysporum inhabits the water distribution systems of several French hospitals. This clonal lineage, which appears to be particularly adapted to water networks, represents a potential risk for human infection and raises questions about its worldwide distribution.

Genus-Specific Primers for Study of Fusarium Communities in Field Samples

Fusarium is a large and diverse genus of fungi of great agricultural and economic importance, containing many plant pathogens and mycotoxin producers. To date, high-throughput sequencing of Fusarium communities has been limited by the lack of genus-specific primers targeting regions with high discriminatory power at the species level. In the present study, we evaluated two Fusarium-specific primer pairs targeting translation elongation factor 1 (TEF1). We also present the new primer pair Fa+7/Ra+6. Mock Fusarium communities reflecting phylogenetic diversity were used to evaluate the accuracy of the primers in reflecting the relative abundance of the species. TEF1 amplicons were subjected to 454 high-throughput sequencing to characterize Fusarium communities. Field samples from soil and wheat kernels were included to test the method on more-complex material. For kernel samples, a single PCR was sufficient, while for soil samples, nested PCR was necessary. The newly developed primer pairs Fa+7/Ra+6 and Fa/Ra accurately reflected Fusarium species composition in mock DNA communities. In field samples, 47 Fusarium operational taxonomic units were identified, with the highest Fusarium diversity in soil. The Fusarium community in soil was dominated by members of the Fusarium incarnatum-Fusarium equiseti species complex, contradicting findings in previous studies. The method was successfully applied to analyze Fusarium communities in soil and plant material and can facilitate further studies of Fusarium ecology.