Occurrence of filamentous fungi in drinking water: their role on fungal-bacterial biofilm formation

Formation of filamentous fungal biofilms in water and the transformation of resistance to chlor(am)ine disinfection

Biofilms are composed of complex multi-species in nature, potentially threatening drinking water safety. In this work, the formation of single- and multi-species fungal biofilms formed by Aspergillus niger (A. niger) and Aspergillus flavus (A. flavus), and the inactivation of mature biofilms using chlor(am)ine were firstly investigated. Results revealed that the antagonistic interaction occurred between A. niger and A. flavus. Chloramination at 20 mg/L for 30 min achieved 74.74 % and 76.04 % inactivation of A. flavus and multi-species biofilm, which were 1.69- and 1.84-fold higher than that of chlorine at the same condition. However, no significant difference was observed in the inactivation of A. niger biofilm between chlorine and monochloramine disinfection due to the lower amount of extracellular polymeric substance produced by it (p > 0.05). The inactivation of biofilm by monochloramine fitted the Weibull model well. According to the Weibull model, the monochloramine resistance of biofilm were as follows: A. flavus > multi-species > A. niger biofilm. Besides, an increase in reactive oxygen levels, damage of cell membrane, and leakage of intracellular substances in biofilms were observed after chlor(am)ination. More intracellular polysaccharides and proteins were leaked in chloramination inactivation (p < 0.05). This study provides important implications for controlling fungal biofilm.

Effect of Location, Disinfection, and Building Materials on the Presence and Richness of Culturable Mycobiota through Oligotrophic Drinking Water Systems

Safe drinking water is a constant challenge due to global environmental changes and the rise of emerging pathogens-lately, these also include fungi. The fungal presence in water greatly varies between sampling locations. Little is known about fungi from water in combination with a selection of materials used in water distribution systems. Our research was focused on five water plants located in the Pannonian Plain, Slovenia. Sampled water originated from different natural water sources and was subjected to different cleaning methods before distribution. The average numbers of fungi from natural water, water after disinfection, water at the first sampling point in the water network, and water at the last sampling point were 260, 49, 64, and 97 CFU/L, respectively. Chlorination reduced the number of fungi by a factor of 5, but its effect decreased with the length of the water network. The occurrence of different fungi in water and on materials depended on the choice of material. The presence of the genera Aspergillus, Acremonium, Furcasterigmium, Gliomastix, and Sarocladium was mostly observed on cement, while Cadophora, Cladosporium, Cyphellophora, and Exophiala prevailed on metals. Plastic materials were more susceptible to colonization with basidiomycetous fungi. Opportunistically pathogenic fungi were isolated sporadically from materials and water and do not represent a significant health risk for water consumers. In addition to cultivation data, physico-chemical features of water were measured and later processed with machine learning methods, revealing the sampling location and water cleaning processes as the main factors affecting fungal presence and richness in water and materials in contact with water.

Ciprofloxacin-Loaded Mixed Polymeric Micelles as Antibiofilm Agents

In this work, mixed polymeric micelles (MPMs) based on a cationic poly(2-(dimethylamino)ethyl methacrylate)-b-poly(ε-caprolactone)-b-poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA₂₉-b-PCL₇₀-b-PDMAEMA₂₉) and a non-ionic poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO₉₉-b-PPO₆₇-b-PEO₉₉) triblock copolymers, blended at different molar ratios, were developed. The key physicochemical parameters of MPMs, including size, size distribution, and critical micellar concentration (CMC), were evaluated. The resulting MPMs are nanoscopic with a hydrodynamic diameter of around 35 nm, and the ζ-potential and CMC values strongly depend on the MPM's composition. Ciprofloxacin (CF) was solubilized by the micelles via hydrophobic interaction with the micellar core and electrostatic interaction between the polycationic blocks, and the drug localized it, to some extent, in the micellar corona. The effect of a polymer-to-drug mass ratio on the drug-loading content (DLC) and encapsulation efficiency (EE) of MPMs was assessed. MPMs prepared at a polymer-to-drug mass ratio of 10:1 exhibited very high EE and a prolonged release profile. All micellar systems demonstrated their capability to detach pre-formed Gram-positive and Gram-negative bacterial biofilms and significantly reduced their biomass. The metabolic activity of the biofilm was strongly suppressed by the CF-loaded MPMs indicating the successful drug delivery and release. The cytotoxicity of empty and CF-loaded MPMs was evaluated. The test reveals composition-dependent cell viability without cell destruction or morphological signs of cell death.

Occurrence and control of fungi in water: New challenges in biological risk and safety assurance

Recently, the contamination of fungi in water has aroused widespread concern, which will pose a threat to water quality and safety, and raise diseases risk in the immunocompromised individuals. In this review, the characteristics and different physiological state of fungi in water are summarized. A comprehensive evaluation of the control efficiency and mechanism of waterborne fungi by the commonly used disinfection methods is provided as well. During the disinfection processes of chlorine, chlorine dioxide, chloramine and advanced disinfection processes (ADPs) such as O₃-based ADPs and UV-based ADPs, the fungal spores firstly lost their culturability, followed by membrane integrity, and the intracellular reactive oxygen species level increased at the same time, eventually the fungal spores were completely inactivated. The security strategies of drinking water against the contamination of fungi are also discussed in terms of water sources, water treatment plants and pipe network. Finally, future researches need to be explored are proposed: the rapid detection methods, the production laws and control of mycotoxin, and the outbreak conditions of fungi in water. Specifically, exploring efficient, safe and economical technologies, especially ADPs, is still the main direction in the disinfection of fungi in future studies. This review can offer a comprehensive understanding on the occurrence and control of fungi in water to fill the knowledge gap and provide guidance for the future research.

Transboundary intercellular communications between Penicillium and bacterial communities during sludge bulking: Inspirations on quenching fungal dominance

Fungal bulking is caused by the evolution toward a fungi-dominant unbalanced sludge system, which is indeed the phenomenon of fungi competing against bacterial cells. We hypothesized that the cross-kingdom intercellular communication between fungi and bacteria was internal driving force that stimulated fungal bulking. In this study, we identified three signal molecules related to Penicillium fungi bulking under low-pH stress in an activated sludge reactor, which inspired us to propose a sludge bulking prevention strategy using the quorum quenching theory. When pH dropped from 7.0 to 4.5, the abundance of Penicillium increased from 12.5% to 44.8%. However, some functional bacterial genera, such as Nitrosomonas and Sphingopyxis, were washed out from the sludge. The production of quorum-sensing (QS) molecules N-Heptanoyl-L-homoserine lactone (C7-HSL), N-Dodecanoyl-L-homoserine lactone (C12-HSL), and N-Tetradecanoyl-L-homoserine lactone (C14-HSL) was regulated with sludge bulking; especially the response of the latter two was significantly negative to Penicillium blooming (P < 0.05). To test their roles, trace commercial C12-HSL and C14-HSL were added to Penicillium culture, successfully causing 8.3% and 30.2% inhibition of mycelial formation, respectively. They also contributed to the improvement of activated sludge settleability by 6.1% and 39.7%, respectively (represented by sludge volume index). The transcriptome technique further revealed the regulation of the expression of genes in |logFC| >1, involving signal transduction, mycelium synthesis, and metabolic pathways. Our study provided an innovative strategy for controlling fungal bulking from the perspective of microbial transboundary informatics.

Polymeric Coatings and Antimicrobial Peptides as Efficient Systems for Treating Implantable Medical Devices Associated-Infections

Many infections are associated with the use of implantable medical devices. The excessive utilization of antibiotic treatment has resulted in the development of antimicrobial resistance. Consequently, scientists have recently focused on conceiving new ways for treating infections with a longer duration of action and minimum environmental toxicity. One approach in infection control is based on the development of antimicrobial coatings based on polymers and antimicrobial peptides, also termed as “natural antibiotics”.

Synergistic effect of ozone and chlorine on inactivating fungal spores: Influencing factors and mechanisms

Effective control of fungal contamination in water is vital to provide healthy and safe drinking water for human beings. Although ozone was highly effective in inactivating fungi in water, it was limited by a lack of continuous disinfection ability in water supply system. In present study, the inactivation of fungal spores by combining ozone and chlorine was investigated. The synergistic effects of Aspergillus niger and Trichoderma harzianum spores reached 0.47- and 0.55-log within 10 min, respectively. The inactivation efficiency and the synergistic effect would be affected by disinfectant concentration, pH, and temperature. The combined inactivation caused more violent oxidative stimulation and more severe damage to the fungal spores than the individual inactivation based on the flow cytometry analysis and the scanning electron microscopy observation. The synergistic effect during the combined inactivation process was attributed to the generation of hydroxyl radicals by the reaction between ozone and chlorine and the promotion of chlorine penetration by the destruction of cell wall by ozone. The combined inactivation efficiency in natural water samples was reduced by 26.4-43.8% compared with that in PBS. The results of this study provided an efficient and feasible disinfection method for the control of fungi in drinking water.