Advances in application of ultraviolet irradiation for biofilm control in water and wastewater infrastructure

Characterization of a novel phage SPX1 and biological control for biofilm of Shewanella in shrimp and food contact surfaces

Shewanella putrefaciens, commonly found in seafood, forms tenacious biofilms on various surfaces, contributing to spoilage and cross-contamination. Bacteriophages, owing to their potent lytic capabilities, have emerged as novel and safe options for preventing and eliminating contaminants across various foods and food processing environments. In this study, a novel phage SPX1 was isolated, characterized by a high burst size (43.81 ± 3.01 PFU/CFU) and a short latent period (10 min). SPX1 belongs to the Caudoviricetes class, exhibits resistance to chloroform, and sensitivity to ultraviolet. It shows stability over a wide range of temperatures (30-50 °C) and pH levels (3-11). The genome of phage SPX1 consists of 53,428 bp with 49.72 % G + C composition, and lacks tRNAs or virulence factors. Genome analysis revealed the presence of two endolysins, confirming its biofilm-removal capacity. Following the treatment of shrimp surface biofilm with the optimal MOI of 0.001 of phage SPX1 for 5 h, the bacterial count decreased by 1.84 ± 0.1 log10 CFU/cm2 (> 98.5 %). Biofilms on the surfaces of the three common materials used in shrimp processing and transportation also showed varying degrees of reduction: glass (1.98 ± 0.01 log10 CFU/cm2), stainless steel (1.93 ± 0.05 log10 CFU/cm2), and polyethylene (1.38 ± 0.1 log10 CFU/cm2). The study will contribute to phage as a novel and potent biocontrol agent for effectively managing S. putrefaciens and its biofilm, ensuring a reduction in spoilage bacteria contamination during the aquaculture, processing, and transportation of seafood products.

Effective management of pre-existing biofilms using UV-LED through inactivation, disintegration and peeling

Managing undesirable biofilms is a persistent challenge in water treatment and distribution systems. Although ultraviolet-light emitting diode (UV-LED) irradiation, an emerging disinfection method with the chemical-free and emission-adjustable merits, has been widely reported effective to inactivate planktonic bacteria, few studies have examined its effects on biofilms. This study aims to fill this gap by exploring the performance and mechanism of UV-LEDs on the prefabricated Escherichia coli (E. coli) biofilms under varying irradiation conditions. The results showed that the wavelength of 275 nm exhibited the best inactivation effect on the biofilm-bound E.coli compared to 268, 312 and 370 nm, achieving 3.2 log inactivation at a fluence of 346.5 mJ/cm2 and an irradiance of 660 μW/cm2. Furthermore, irradiance and irradiation time are proposed for the first time to be a pair of conjugate variables correlated to log inactivation, as a modification of the Bunsen-Roscoe reciprocity law. Additionally, the effect of UV irradiation on extracellular polymeric substances (EPS) in terms of the structure and chemical properties was investigated. The findings support that the oxidative degradation of the polysaccharides and proteins in EPS matrix should be the primary reason for destroying the biofilm framework. Finally, additional hydraulic shear was applied on the irradiated biofilms, suggesting an effective approach for enhancing biofilm removal.

Global transcriptional analysis for molecular responses of Alicyclobacillus acidoterrestris spores in drinking water after low- and medium-pressure ultraviolet irradiation

Ultraviolet (UV) irradiation can effectively disinfect water contaminated with pathogens. However, the biological mechanisms of inactivation by different types of UV irradiation are unknown. The present study investigated the inactivation mechanisms of Alicyclobacillus acidoterrestris spores in water by low-pressure UV (LPUV) and medium-pressure UV (MPUV) using a quasi-collimated beam apparatus. Global transcriptomic data obtained by RNA-seq revealed 291 shared differentially expressed genes (DEGs) that damaged DNA, reduced biofilm formation, and had other reactions. The individual downregulated DEGs (n = 123) mainly related to cell motility, membrane transport, and metabolism were induced by LPUV, and in turn contributed to energy-saving and metabolic activity inhibition, forcing bacteria into a viable but non-culturable (VBNC) state. The individual upregulated DEGs (n = 244) following MPUV treatment were mainly enriched in cell motility, membrane transport, metabolism, DNA replication and repair, and spore germination pathways. This results in high-energy consumption, severe damage to genetic material, and enhanced spore germination accelerated cell death. Additionally, hub genes in the protein-protein interaction network were mainly involved in transcription and translation. These findings contribute to the comprehensive understanding of the inactivation mechanisms of different types of UV irradiation, and will improve applications of UV disinfection in the treatment of water.

Impact of high-speed nanodroplets on various pathogenic bacterial cell walls

Although the development of disinfection technologies with novel mechanisms has stagnated, we demonstrate the bactericidal effects and mechanisms of high-speed nanodroplet generation technology. The first development of this technology in 2017 gushes out a water droplet of 10 nm in size at 50 m/s; however, the target surface does not become completely wet. Nanodroplets were exposed to biofilm models of Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Serratia marcescens. This phenomenon was verified when the nanodroplets collide with the surface of the bacteria at an impact pressure of ~75 MPa. S. aureus was exposed to nanodroplets for 30 seconds at 75 MPa, which exploded the bacterial body and completely sterilized. Eighteen MPa damaged the bacterial surface, causing peptidoglycan leakage. S. aureus was repaired and survives in this state. In contrast, in Gram-negative bacteria, nanodroplets with 18 MPa penetrated some biofilm-forming bacteria but did not hit all of them, and the viable count was not significantly reduced. Although all three bacterial species were completely sterilized at 75 MPa, the disinfectant effect was affected by the biomass of the biofilm formed. In summary, our findings prove that nanodroplets at 18 MPa on the bacterial surface were ineffective in killing bacteria, whereas at 75 MPa, all four bacterial species were completely sterilized. The disinfection mechanism involved a high-velocity collision of nanodroplets with the bacteria, physically destroying them. Our results showed that disinfection using this technology could be an innovative method that is completely different from existing disinfection techniques.

IMPORTANCE

Although existing disinfection techniques demonstrate bactericidal effects through chemical reactions, concerns regarding human toxicity and environmental contamination have been raised. To the best of our knowledge, this study is the first in the world to reveal that the use of this technology, with nanodroplets of less than 100 nm, can destroy and sterilize bacterial cells by colliding with biofilm-forming bacteria at 75 MPa. Furthermore, because this technology uses only water, it can solve the problems of human toxicity and environmental contamination caused by existing disinfection techniques. Because of its minimal water usage, it can be employed for sanitation worldwide without being limited to specific regions. Our report proposes an unprecedented physical disinfection approach that utilizes a high-speed nanodroplet generation technology.

A review of pathogen removal from municipal wastewater using advanced oxidation processes: Agricultural application, regrowth risks, and new perspectives

Pathogen removal in wastewater offers a chance to recover water and nutrients for crop production, reducing environmental contamination and public health risks. However, the risk of pathogens regrowing in treated effluents can endanger public health if reused in agriculture, attracting stringent reuse standards. While advanced oxidation processes (AOPs) promise to reduce pathogens, eliminating regrowth potential in AOP-treated effluents requires further scrutiny. This review aimed to summarize the available evidence on understanding pathogen reduction and regrowth potential in AOP-treated effluents, following best practices for scoping reviews like the preferred reporting items for systematic reviews and meta-analysis (PRISMA). It covers recent pathogen studies under AOPs, current AOP investigations, the impact of AOP dosage and retention time on pathogen control, and challenges in reusing AOP-treated effluents for crop production. Additionally, it identifies areas needing improvement or complementary treatments for pathogen-free effluents with no regrowth potential. The review concludes by summarizing key findings and suggesting research areas for further exploration.

Escaping the ESKAPE pathogens: A review on antibiofilm potential of nanoparticles

ESKAPE pathogens, a notorious consortium comprising Enterococcusfaecium, Staphylococcusaureus, Klebsiellapneumoniae, Acinetobacterbaumannii, Pseudomonasaeruginosa, and Enterobacter species, pose formidable challenges in healthcare settings due to their multidrug-resistant nature. The increasing global cases of antimicrobial-resistant ESKAPE pathogens are closely related to their remarkable ability to form biofilms. Thus, understanding the unique mechanisms of antimicrobial resistance of ESKAPE pathogens and the innate resilience of biofilms against traditional antimicrobial agents is important for developing innovative strategies to establish effective control methods against them. This review offers a thorough analysis of biofilm dynamics, with a focus on the general mechanisms of biofilm formation, the significant contribution of persister cells in the resistance mechanisms, and the recurrence of biofilms in comparison to planktonic cells. Additionally, this review highlights the potential strategies of nanoparticles for managing biofilms in the ESKAPE group of pathogens. Nanoparticles, with their unique physicochemical properties, provide promising opportunities for disrupting biofilm structures and improving antimicrobial effectiveness. The review has explored interactions between nanoparticles and biofilms, covering a range of nanoparticle types such as metal, metal-oxide, surface-modified, and functionalized nanoparticles, along with organic nanoparticles and nanomaterials. The additional focus of this review also encompasses green synthesis techniques of nanoparticles that involve plant extract and supernatants from bacterial and fungal cultures as reducing agents. Furthermore, the use of nanocomposites and nano emulsions in biofilm management of ESKAPE is also discussed. To conclude, the review addresses the current obstacles and future outlooks in nanoparticle-based biofilm management, stressing the necessity for further research and development to fully exploit the potential of nanoparticles in addressing biofilm-related challenges.

Dual polarization for efficient III-nitride-based deep ultraviolet micro-LEDs

The deep ultraviolet (DUV) micro-light emitting diode (μLED) has serious electron leakage and low hole injection efficiency. Meanwhile, with the decrease in the size of the LED chip, the plasma-assisted dry etching process will cause damage to the side wall of the mesa, which will form a carrier leakage channel and produce non-radiative recombination. All of these will reduce the photoelectric performance of μLED. To this end, this study introduces polarized bulk charges into the hole supply layer (p-HSL) and the electron supply layer (n-ESL) respectively (dual-polarized structure) of the DUV μLED at an emission wavelength of 279 nm to enhance the binding of carriers and increase the injection efficiency of carriers. This is because the polarization-induced bulk charge can shield the polarized sheet charge on the interface and reduce the polarization electric field. The reduced polarization electric field in p-HSL can increase the effective barrier height of the conduction band in the p-type region and reduce the effective barrier height of the valence band. The decrease in the polarized electric field of n-HSL can reduce the thermal velocity of electrons, thereby enhancing the electron injection efficiency, reducing the Shockley-Read-Hall (SRH) recombination, and increasing the effective barrier height of the valence band. The study results indicate that the electron concentration and hole concentration of a μLED with dual polarization were increased by 77.93% and 93.6%, respectively. The optical power and maximum external quantum efficiency of μLED reached 31.04 W/cm2 and 2.91% respectively, and the efficiency droop is only 2.06% at 120 A/cm2. These results provide a new approach to solving the problem of insufficient carrier injection and SRH recombination in high-performance DUV μLEDs.

Biofilm formation in food industries: Challenges and control strategies for food safety

Various pathogens have the ability to grow on food matrices and instruments. This grow may reach to form biofilms. Bacterial biofilms are community of microorganisms embedded in extracellular polymeric substances (EPSs) containing lipids, DNA, proteins, and polysaccharides. These EPSs provide a tolerance and favorable living condition for microorganisms. Biofilm formations could not only contribute a risk for food safety but also have negative impacts on healthcare sector. Once biofilms form, they reveal resistances to traditional detergents and disinfectants, leading to cross-contamination. Inhibition of biofilms formation and abolition of mature biofilms is the main target for controlling of biofilm hazards in the food industry. Some novel eco-friendly technologies such as ultrasound, ultraviolet, cold plasma, magnetic nanoparticles, different chemicals additives as vitamins, D-amino acids, enzymes, antimicrobial peptides, and many other inhibitors provide a significant value on biofilm inhibition. These anti-biofilm agents represent promising tools for food industries and researchers to interfere with different phases of biofilms including adherence, quorum sensing molecules, and cell-to-cell communication. This perspective review highlights the biofilm formation mechanisms, issues associated with biofilms, environmental factors influencing bacterial biofilm development, and recent strategies employed to control biofilm-forming bacteria in the food industry. Further studies are still needed to explore the effects of biofilm regulation in food industries and exploit more regulation strategies for improving the quality and decreasing economic losses.

Design of High-Precision Driving Control System for Charge Management

Due to the interaction of accumulated charges on the surface of a test mass with the surrounding electric and magnetic fields, the performance of inertial sensors is affected, necessitating charge management for the test mass. Discharge technology based on Ultraviolet LEDs is internationally recognized as the optimal solution for charge management. Precision driving of Ultraviolet LEDs is considered a key technology in charge management. This paper presents the driving control system used for Ultraviolet LEDs, achieving precision pulse-width-modulation-type current output with controllable pulse width and amplitude. The system generates the pulse-width-controllable pulse voltage signal via analog pulse-width modulation, and subsequently regulates the amplitude of the PWM signal through range switching. To convert the voltage into the pulse-width-modulation-type driving current, the improved Howland current source is employed. The test results demonstrate that the driving control system can output controllable current in the range of 0.01 mA to 10 mA, with a minimum step of 0.01 mA. The accuracy of the current reaches 1%, the stability within 1 h is better than 1%, and the load regulation is better than 2%. The driving control system provides an important reference for the integration of charge management system and the precision drive control method for LEDs.

Liposomal drug delivery strategies to eradicate bacterial biofilms: Challenges, recent advances, and future perspectives

Typical antibiotic treatments are often ineffectual against biofilm-related infections since bacteria residing within biofilms have developed various mechanisms to resist antibiotics. To overcome these limitations, antimicrobial-loaded liposomal nanoparticles are a promising anti-biofilm strategy as they have demonstrated improved antibiotic delivery and eradication of bacteria residing in biofilms. Antibiotic-loaded liposomal nanoparticles revealed remarkably higher antibacterial and anti-biofilm activities than free drugs in experimental settings. Moreover, liposomal nanoparticles can be used efficaciously for the combinational delivery of antibiotics and other antimicrobial compounds/peptide which facilitate, for instance, significant breakdown of the biofilm matrix, increased bacterial elimination from biofilms and depletion of metabolic activity of various pathogens. Drug-loaded liposomes have mitigated recurrent infections and are considered a promising tool to address challenges associated to antibiotic resistance. Furthermore, it has been demonstrated that surface charge and polyethylene glycol modification of liposomes have a notable impact on their antibacterial biofilm activity. Future investigations should tackle the persistent hurdles associated with development of safe and effective liposomes for clinical application and investigate novel antibacterial treatments, including CRISPR-Cas gene editing, natural compounds, phages, and nano-mediated approaches. Herein, we emphasize the significance of liposomes in inhibition and eradication of various bacterial biofilms, their challenges, recent advances, and future perspectives.

Evaluating the Performance of UV Disinfection across the 222-365 nm Spectrum against Aerosolized Bacteria and Viruses

Bioaerosols play a significant role in the transmission of many infectious diseases, especially in enclosed indoor environments. Ultraviolet (UV) disinfection has demonstrated a high efficacy in inactivating microorganisms suspended in the air. To develop more effective and efficient UV disinfection protocols, it is necessary to evaluate and optimize the effectiveness of UV disinfection against aerosolized bacteria and viruses across the entire UV spectrum. In this study, we evaluated the performance of UV disinfection across the UV spectrum, ranging from 222 to 365 nm, against aerosolized bacteria and viruses, including Escherichia coli, Staphylococcus epidermidis, Salmonella enterica, MS2, P22, and Phi6. Six commonly available UV sources, including gas discharge tubes and light-emitting diodes with different emission spectra, were utilized, and their performance in terms of inactivation efficacy, action spectrum, and energy efficiency was determined. Among these UV sources, the krypton chloride excilamp emitting at a peak wavelength of 222 nm was the most efficient in inactivating viral bioaerosols. A low-pressure mercury lamp emitting at 254 nm performed well on both inactivation efficacy and energy efficiency. A UV light-emitting diode emitting at 268 nm demonstrated the highest bacterial inactivation efficacy, but required approximately 10 times more energy to achieve an equivalent inactivation level compared with that of the krypton chloride excilamp and low-pressure mercury lamp. This study provides insights into UV inactivation on bioaerosols, which can guide the development of effective wavelength-targeted UV air disinfection technologies and may significantly help reduce bioaerosol transmission in public areas.

Recent advances on the formation, detection, resistance mechanism, and control technology of Listeria monocytogenes biofilm in food industry

Listeria monocytogenes is an important foodborne pathogen that causes listeriosis, a severe and fatal condition. Biofilms are communities of microorganisms nested within a self-secreted extracellular polymeric substance, and they protect L. monocytogenes from environmental stresses. Biofilms, once formed, can lead to the persistence of L. monocytogenes in processing equipment and are therefore considered to be a major concern for the food industry. This paper briefly introduces the recent advancements on biofilm formation characteristics and detection methods, and focuses on analysis of the mechanism of L. monocytogenes biofilm resistance; Moreover, this paper also summarizes and discusses the existing different techniques of L. monocytogenes biofilm control according to the physical, chemical, biological, and combined strategies, to provide a theoretical reference to aid the choice of effective control technology in the food industry.

Recent progress in mineralization of emerging contaminants by advanced oxidation process: A review

Emerging contaminants are chemicals generated due to the usage of pesticide, endocrine disrupting compounds, pharmaceuticals, and personal care products and are liberated into the environment in trace quantities. The emerging contaminants eventually become a greater menace to living beings owing to their wide range and inhibitory action. To diminish these emerging contaminants from the environment, an Advanced Oxidation Process was considered as an efficient option. The Advanced Oxidation Process is an efficient method for mineralizing fractional or generous contaminants due to the generation of reactive species. The primary aim of this review paper is to provide a thorough knowledge on different Advanced Oxidation Process methods and to assess their mineralization efficacy of emerging contaminants. This study indicates the need for an integrated process for enhancing the treatment efficiency and overcoming the drawbacks of the individual Advanced Oxidation Process. Further, its application concerning technical and economic aspects is reviewed. Until now, most of the studies have been based on lab or pilot scale and do not represent the actual scenario of the emerging contaminant mineralization. Thus, the scaling up of the process was discussed, and the major challenges in large scale implementation were pointed out.

Superoxide dismutase A (SodA) is a c-di-GMP effector protein governing oxidative stress tolerance in Stenotrophomonas maltophilia

C-di-GMP is a bacterial second messenger implicated in the regulation of many key functions including antibiotic tolerance and biofilm formation. Our understanding of how c-di-GMP exerts its action via receptors to modulate different biological functions is still limited. Here we used a c-di-GMP affinity pull-down assay coupled to LC-MS/MS to identify c-di-GMP-binding proteins in the opportunistic pathogen Stenotrophomonas maltophilia. This analysis identified Smlt3238 (SodA), a protein of the superoxide dismutase family, as a c-di-GMP-binding protein. Microscale thermophoresis showed that purified SodA protein bound c-di-GMP with an estimated dissociation constant (Kd) value of 141.5 μM. Using various in vivo and in vitro experiments, we demonstrated that c-di-GMP modulates the enzyme activity of SodA directly. Circular dichroism experiments revealed that SodA protein gradually altered its basic structure with increasing levels of c-di-GMP. Phenotypic experiments conducted in the presence of a range of intracellular c-di-GMP levels showed that SodA function is modulated by c-di-GMP. The findings thus identify a novel c-di-GMP binding protein that governs oxidative stress tolerance in S. maltophilia.

High-efficiency and low-carbon inactivation of UV resistant bacteria in reclaimed water by flow-through electrode system (FES)

With the increasingly serious shortage of water resources globally, it has been paid more attention on how to secure the biosafety of reclaimed water and other non-traditional water sources. However, the 3 most applied disinfection technics, which are chlorine, ultraviolet (UV), and ozone disinfection, all have their disadvantages of selecting undesired bacteria and low energy utilization efficiency. Electrode disinfection is a promising solution, but the current electrode disinfection process still needs to be optimized in terms of the use conditions of the configuration reactivation. In this paper, we built a flow electrode system (FES). To evaluate the disinfection techniques more precisely, we isolated ultraviolet-resistant bacteria (URB) bacteria from the water of the full-scale water plant and tested the disinfection performance of FES and UV. The inactivation rate, reactivation potential, and energy consumption were analyzed. FES could inactivate 99.99 % of the URB and cause irreversible damage to the residual bacteria. FES could make all bacteria strains apoptosis in the subsequent 24 h of storage after alternating pulse current (APC) treatment, 3 V, within 27.7 s. Besides, the energy consumption of FES is about 2 orders lower than that of UV disinfection under the same inactivation rate. In summary, APC-FES is an efficient and low-carbon alternative for future water disinfection, which could achieve the ideal disinfection effect of a high inactivation rate, no reactivation, and low energy consumption.

DBP-FP change of biofilm in drinking water distribution system induced by sequential UV and chlorine disinfection: Effect of UV dose and influencing mechanism

The issue of biofilm-related disinfection byproducts (DBPs) in drinking water distribution system (DWDS) has garnered significant attention. This study sought to examine the changes in biofilm-originated halogenated DBP formation potential (biofilm DBP-FP) in simulated continuous-flow DWDSs subjected to sequential UV and chlorine disinfection (UV-Cl2) treatments with varying UV doses and to propose the underlying mechanism. The formation potential of trihalomethanes (THMs), haloacetic acids (HAAs), and the total organic halogen (TOX, X = Cl and Br) produced by biofilm were measured. Results showed that the biofilm TOCl-FP was at a minimum with a UV dose of 80 mJ/cm2, corresponding to the lowest amounts of protein and polysaccharides in the extracellular polymeric substances (EPS). Sphingobium, Methylobacterium, and Sphingomonas played a crucial role in protein and polysaccharide biosynthesis. Bacterial community composition characterization together with metabolic function analysis indicated that dominant bacteria varied and metabolic function shifted due to UV-Cl2 disinfection, with Alphaproteobacteria increasing in relative abundance and Bacteroidia showing the opposite trend with increasing UV doses. Correlation analysis suggested that the UV-Cl2 disinfection process led to changes in the water matrix, including organics, inorganics, bacteria, and components that provide environmental pressure for the biofilm. These changes ultimately influenced the properties of the biofilm EPS, which had a direct impact on biofilm DBP-FP.

Phenotypic and Transcriptional Responses of Pseudomonas aeruginosa Biofilms to UV-C Irradiation via Side-Emitting Optical Fibers: Implications for Biofouling Control

Biofilms give rise to a range of issues, spanning from harboring pathogens to accelerating microbial-induced corrosion in pressurized water systems. Introducing germicidal UV-C (200-280 nm) irradiation from light-emitting diodes (LEDs) into flexible side-emitting optical fibers (SEOFs) presents a novel light delivery method to inhibit the accumulation of biofilms on surfaces found in small-diameter tubing or other intricate geometries. This work used surfaces fully submerged in flowing water that contained Pseudomonas aeruginosa, an opportunistic pathogen commonly found in water system biofilms. A SEOF delivered a UV-C gradient to the surface for biofilm inhibition. Biofilm growth over time was monitored in situ using optical conference tomography. Biofilm formation was effectively inhibited when the 275 nm UV-C irradiance was ≥8 μW/cm2. Biofilm samples were collected from several regions on the surface, representing low and high UV-C irradiance. RNA sequencing of these samples revealed that high UV-C irradiance inhibited the expression of functional genes related to energy metabolism, DNA repair, quorum sensing, polysaccharide production, and mobility. However, insufficient sublethal UV-C exposure led to upregulation genes for SOS response and quorum sensing as survival strategies against the UV-C stress. These results underscore the need to maintain minimum UV-C exposure on surfaces to effectively inhibit biofilm formation in water systems.

Biofouling in Membrane Bioreactors-Mitigation and Current Status: a Review

Biological fouling as termed biofouling is caused by varied living organisms and is difficult to eliminate from the environment thus becoming a major issue during membrane bioreactors. Biofouling in membrane bioreactors (MBRs) is a crucial problem in increasing liquid pressure due to reduced pore diameter, clogging of the membrane pores, and alteration of the chemical composition of the water which greatly limits the growth of MBRs. Thus, membrane biofouling and/or microbial biofilms is a hot research topic to improve the market competitiveness of the MBR technology. Though several antibiofouling strategies (addition of bioflocculant or sponge into MBRs) came to light, biological approaches are sustainable and more practicable. Among the biological approaches, quorum sensing-based biofouling control (so-called quorum quenching) is an interesting and promising tool in combating biofouling issues in the MBRs. Several review articles have been published in the area of membrane biofouling and mitigation approaches. However, there is no single source of information about biofouling and/or biofilm formation in different environmental settings and respective problems, antibiofilm strategies and current status, quorum quenching, and its futurity. Thus, the objectives of the present review were to provide latest insights on mechanism of membrane biofouling, quorum sensing molecules, biofilm-associated problems in different environmental setting and antibiofilm strategies, special emphasis on quorum quenching, and its futurity in the biofilm/biofouling control. We believe that these insights greatly help in the better understanding of biofouling and aid in the development of sustainable antibiofouling strategies.

Investigation of differences in susceptibility of Campylobacter jejuni strains to UV light-emitting diode (UV-LED) technology

Campylobacter jejuni remains a high priority in public health worldwide. Ultraviolet light emitting-diode technology (UV-LED) is currently being explored to reduce Campylobacter levels in foods. However, challenges such as differences in species and strain susceptibilities, effects of repeated UV-treatments on the bacterial genome and the potential to promote antimicrobial cross-protection or induce biofilm formation have arisen. We investigated the susceptibility of eight C. jejuni clinical and farm isolates to UV-LED exposure. UV light at 280 nm induced different inactivation kinetics among strains, of which three showed reductions greater than 1.62 log CFU/mL, while one strain was particularly resistant to UV light with a maximum reduction of 0.39 log CFU/mL. However, inactivation was reduced by 0.46-1.03 log CFU/mL in these three strains and increased to 1.20 log CFU/mL in the resistant isolate after two repeated-UV cycles. Genomic changes related to UV light exposure were analysed using WGS. C. jejuni strains with altered phenotypic responses following UV exposure were also found to have changes in biofilm formation and susceptibility to ethanol and surface cleaners.

Dry surface biofilms in the food processing industry: An overview on surface characteristics, adhesion and biofilm formation, detection of biofilms, and dry sanitization methods

Bacterial biofilm formation in low moisture food processing (LMF) plants is related to matters of food safety, production efficiency, economic loss, and reduced consumer trust. Dry surfaces may appear dry to the naked eye, however, it is common to find a coverage of thin liquid films and microdroplets, known as microscopic surface wetness (MSW). The MSW may favor dry surface biofilm (DSB) formation. DSB formation is similar in other industries, it occurs through the processes of adhesion, production of extracellular polymeric substances, development of microcolonies and maturation, it is mediated by a quorum sensing (QS) system and is followed by dispersal, leading to disaggregation. Species that survive on dry surfaces develop tolerance to different stresses. DSB are recalcitrant and contribute to higher resistance to sanitation, becoming potential sources of contamination, related to the spoilage of processed products and foodborne disease outbreaks. In LMF industries, sanitization is performed using physical methods without the presence of water. Although alternative dry sanitizing methods can be efficiently used, additional studies are still required to develop and assess the effect of emerging technologies, and to propose possible combinations with traditional methods to enhance their effects on the sanitization process. Overall, more information about the different technologies can help to find the most appropriate method/s, contributing to the development of new sanitization protocols. Thus, this review aimed to identify the main characteristics and challenges of biofilm management in low moisture food industries, and summarizes the mechanisms of action of different dry sanitizing methods (alcohol, hot air, UV-C light, pulsed light, gaseous ozone, and cold plasma) and their effects on microbial metabolism.

Deactivating environmental strains of Escherichia coli, Enterococcus faecalis and Clostridium perfringens from a real wastewater effluent using UV-LEDs

Environmental bacteria strains are known to be more resistant but studies on UV-LEDs are scarce, especially for Clostridium perfringens and Enterococcus faecalis. UV-LEDs of different wavelengths (268 nm, 279 nm and 307 nm) have been used for treating real wastewater from the effluent of the municipal plant in Linares (Spain), with real organic matter content, for E. coli, Enterococcus faecalis and Clostridium perfringens disinfection. Experimental results demonstrate that 268 nm was the most effective wavelength for inactivation of the three different bacteria strains: E. coli showed an inactivation rate of 0.561 at 268 nm vs. 0.245 at 279 nm and 0.0029 for 307 nm; E. faecalis inactivation rate was 0.313 at 268 nm, 0.231 at 279 nm and 0.0023 at 307 nm; and C. perfringens inactivation rate was 0.084 at 268 nm, 0.033 at 279 nm and 6.9e-4 at 307 nm. In general, 307 nm wavelength showed a significantly lower inactivation rate so it would not be recommended for practical applications. C. Perfringens required higher UV doses and longer times to achieve complete inactivation.

Protection and Damage Repair Mechanisms Contributed To the Survival of Chroococcidiopsis sp. Exposed To a Mars-Like Near Space Environment

Chroococcidiopsis spp. can withstand extremely harsh environments, including a Mars-like environment. However, studies are lacking on the molecular mechanisms of Chroococcidiopsis sp. surviving in Mars-like environments. In the HH-21-5 mission, the desert cyanobacterium Chroococcidiopsis sp. was exposed to a Mars-like environment (near space; 35 km altitude) for 4 h, and a single-factor environment of near space was simulated on the ground. We investigated the survival and endurance mechanisms of Chroococcidiopsis sp. ASB-02 after exposing it to near space by studying its physiological and transcriptional properties. After the exposure, Chroococcidiopsis sp. ASB-02 exhibited high cell viability, although photosystem II activity decreased and the levels of reactive oxygen species increased. The single-factor simulation experiments revealed that for the survival of Chroococcidiopsis sp. ASB-02 in near space, UV radiation was the most important limiting factor, and it was followed by temperature. The near space environment triggered multiple metabolic pathway responses in Chroococcidiopsis sp. ASB-02. The upregulation of extracellular polysaccharides as well as carotenoid and scytonemin biosynthesis genes in response to UV radiation attenuated the extent of radiation reaching the cells. At the same time, genes related to protein synthesis were upregulated in response to the low temperature, overcoming the decrease in metabolic activity that was caused by the low temperature. In near space and after rehydration, the genes involved in various DNA and photosystem II repair pathways were upregulated. This reflected the damage to the DNA and photosystem II protein subunits in cells during the flight and suggested that repair mechanisms play an important role in the recovery of Chroococcidiopsis sp. ASB-02. IMPORTANCE This study reported that the protective and repair mechanisms of Chroococcidiopsis sp. ASB-02 contributed to its endurance ability in a Mars-like near space environment. In Chroococcidiopsis sp. ASB-02, a Mars-like near space environment activated the expression of genes involved in extracellular polysaccharides (EPS), carotenoid, scytonemin, and protein syntheses, which provided additional protection. Additionally, the cell damage repair process enhanced the recovery rate of Chroococcidiopsis sp. ASB-02 after the flight. This study will help to enhance the understanding of the tolerance mechanism of Chroococcidiopsis sp. and to provide important guidance as to the survival requirements for microbial life in a Mars-like environment.

Cross-contamination risk and decontamination during changeover after cell-product processing

Introduction

During changeover in cell-product processing, it is essential to minimize cross-contamination risks. These risks differ depending on the patient from whom the cells were derived. Human error during manual cell-product processing increases the contamination risk in biosafety cabinets. Here, we evaluate the risk of cross-contamination during manual cell-processing to develop an evidence-based changeover method for biosafety cabinets.

Methods

Contaminant coverage was analyzed during simulated medium preparation, cell seeding, and waste liquid decanting by seven operators, classified by skill. Environmental bacteria were surveyed at four participating facilities. Finally, we assessed the effect of conventional UV irradiation in biosafety cabinets on bacteria and fungi that pose a cross-contamination risk.

Results

Under simulated conditions, scattered contamination occurred via droplets falling onto the surface from heights of 30 cm, and from bubbles rupturing at this height. Visible traces of contaminants were distributed up to 50 cm from the point of droplet impact, or from the location of the pipette tip when the bubble ruptured. In several facilities, we detected Bacillus subtilis, of which the associated endospores are highly resistant to disinfection. Irradiation at 50 mJ/cm² effectively eliminated Bacillus subtilis vegetative cells and Aspergillus brasiliensis, which is highly resistant to UV. Bacillus subtilis endospores were eliminated at 100 mJ/cm².

Conclusions

Under these simulated optimal conditions, UV irradiation successfully prevents cross-contamination. Therefore, following cell-product processing, monitoring the UV dose in the biosafety cabinet during cell changeover represents a promising method for reducing cross-contamination.

A Review on Membrane Biofouling: Prediction, Characterization, and Mitigation

Water scarcity is an increasing problem on every continent, which instigated the search for novel ways to provide clean water suitable for human use; one such way is desalination. Desalination refers to the process of purifying salts and contaminants to produce water suitable for domestic and industrial applications. Due to the high costs and energy consumption associated with some desalination techniques, membrane-based technologies have emerged as a promising alternative water treatment, due to their high energy efficiency, operational simplicity, and lower cost. However, membrane fouling is a major challenge to membrane-based separation as it has detrimental effects on the membrane's performance and integrity. Based on the type of accumulated foulants, fouling can be classified into particulate, organic, inorganic, and biofouling. Biofouling is considered the most problematic among the four fouling categories. Therefore, proper characterization and prediction of biofouling are essential for creating efficient control and mitigation strategies to minimize the damage associated with biofouling. Moreover, the use of artificial intelligence (AI) in predicting membrane fouling has garnered a great deal of attention due to its adaptive capability and prediction accuracy. This paper presents an overview of the membrane biofouling mechanisms, characterization techniques, and predictive methods with a focus on AI-based techniques, and mitigation strategies.

Effect of UV Light and Sodium Hypochlorite on Formation and Destruction of Pseudomonas fluorescens Biofilm In Vitro

Pseudomonas fluorescens is one of the first colonizers of bacterial biofilm in water systems and a member of opportunistic premise plumbing pathogens (OPPPs). The aim of this study was to examine the effect of UV light and sodium hypochlorite on the formation and destruction of mature P. fluorescens biofilm on ceramic tiles. Planktonic bacteria or bacteria in mature biofilm were exposed to UV light (254 nm) for 5, 20 s. and to 0.4 mg/L sodium hypochlorite for 1 min. Mature biofilm was also exposed to increased concentration of sodium hypochlorite of 2 mg/L for 0.5, 1 and 2 h and combined with UV. Prolonged action of sodium hypochlorite and an increase in its concentration in combination with UV gave the best results in the inhibition of biofilm formation after the pre-treatment and destruction of mature biofilm. The effect of hyperchlorination in combination with UV radiation shows better results after a long exposure time, although even after 120 min there was no completely destroyed biofilm. Furthermore, the mechanism of the effect of combined methods should be explored as well as the importance of mechanical cleaning that is crucial in combating bacterial biofilm in swimming pools.

Engineering efficient artificial nanozyme based on chitosan grafted Fe-doped-carbon dots for bacteria biofilm eradication

Bacterial biofilms have evoked worldwide attention owing to their serious threats to public health, but how to effectively eliminate bacterial biofilms still remains great challenges. Here, we rationally designed a novel and vigorous chitosan grafted Fe-doped-carbon dots (CS@Fe/CDs) as an efficient artificial nanozyme to combat rigid bacterial biofilms through the selective activation of Fenton-like reaction-triggered peroxidase-like catalytic activity and the synergistic antibacterial activity of CS. On the one hand, the peroxidase-like catalytic activity made CS@Fe/CDs catalyze H₂O₂ for producing hydroxyl radicals (•OH), resulting in efficient cleavage of extracellular DNA (eDNA). On the other hand, CS was capable of binding with the negatively charged cell membrane through electrostatic interaction, changing the cell membrane permeability and causing cell death within bacterial biofilms. Based on their synergistic effects, the fragments of bacterial biofilm and exposed bacteria were persistently eradicated. Remarkably, CS@Fe/CDs-based nanozyme not only enabled the effective destroying of gram-positive Staphylococcus aureus (S. aureus) biofilms, but also completely eliminated gram-negative Pseudomonas aeruginosa (P. aeruginosa) biofilms, showing great potential as a promising anti-biofilm agent against bacteria biofilms. This proposed synergistic strategy for bacterial biofilm eradication might offer a powerful modality to manage of bacterial biofilm fouling in food safety and environmental protection.