Mini-review: Biofilm responses to oxidative stress

Possibilities of Application of Cold Atmospheric Pressure Plasmas in Dentistry—A Narrative Review

According to the World Human Organization (WHO), dental and periodontal diseases are common among the human population. Traditional dentistry offers a wide range of methods for treating oral diseases and performing esthetic procedures. In contrast, cold atmospheric pressure plasma (CAPP) has been found to be a promising technology in multiple fields, particularly in medical sciences such as dentistry. In this study, CAPP might be a promising adjunct to conventional dental treatments. A substantial number of studies have confirmed the effectiveness of both direct and indirect CAPP applications in dentistry. Because CAPP technology is fast, inexpensive, and noninvasive, we aim to review recent literature focused on the application of this methodology in dentistry.

Nanoscale zero-valent iron alleviated horizontal transfer of antibiotic resistance genes in soil: The important role of extracellular polymeric substances

Extracellular polymeric substances (EPS) are tightly related to the horizontal gene transfer (HGT) of antibiotic resistance genes (ARGs), but often neglected in soil. In this study, nanoscale zero-valent iron (nZVI) was utilized for attenuation of ARGs in contaminated soil, with an emphasis on its effects on EPS secretion and HGT. Results showed during soil microbe cultivation exposed to tetracycline, more EPS was secreted and significant increase of tet was observed due to facilitated HGT. Notably, copies of EPS-tet accounted for 71.39 % of the total tet, implying vital effects of EPS on ARGs proliferation. When co-exposed to nZVI, EPS secretion was decreased by 38.36-71.46 %, for that nZVI could alleviate the microbial oxidative stress exerted by tetracycline resulting in downregulation of genes expression related to the c-di-GMP signaling system. Meanwhile, the abundance of EPS-tet was obviously reduced from 7.04 to 5.12-6.47 log unit, directly causing decrease of total tet from 7.19 to 5.68-6.69 log unit. For the reduced tet, it was mainly due to decreased EPS secretion induced by nZVI resulting in inhibition of HGT especially transformation of the EPS-tet. This work gives an inspiration for attenuation of ARGs dissemination in soil through an EPS regulation strategy.

Cohesive Living Bacterial Films with Tunable Mechanical Properties from Cell Surface Protein Display

Engineered living materials (ELMs) constitute a novel class of functional materials that contain living organisms. The mechanical properties of many such systems are dominated by the polymeric matrices used to encapsulate the cellular components of the material, making it hard to tune the mechanical behavior through genetic manipulation. To address this issue, we have developed living materials in which mechanical properties are controlled by the cell-surface display of engineered proteins. Here, we show that engineered Esherichia coli cells outfitted with surface-displayed elastin-like proteins (ELPs, designated E6) grow into soft, cohesive bacterial films with biaxial moduli around 14 kPa. When subjected to bulge-testing, such films yielded at strains of approximately 10%. Introduction of a single cysteine residue near the exposed N-terminus of the ELP (to afford a protein designated CE6) increases the film modulus 3-fold to 44 kPa and eliminates the yielding behavior. When subjected to oscillatory stress, films prepared from E. coli strains bearing CE6 exhibit modest hysteresis and full strain recovery; in E6 films much more significant hysteresis and substantial plastic deformation are observed. CE6 films heal autonomously after damage, with the biaxial modulus fully restored after a few hours. This work establishes an approach to living materials with genetically programmable mechanical properties and a capacity for self-healing. Such materials may find application in biomanufacturing, biosensing, and bioremediation.

Harnessing microbial biofilms in soil ecosystems: Enhancing nutrient cycling, stress resilience, and sustainable agriculture

Soil ecosystems are complex networks of microorganisms that play pivotal roles in nutrient cycling, stress resilience, and the provision of ecosystem services. Among these microbial communities, soil biofilms, and complex aggregations of microorganisms embedded within extracellular polymeric substances (EPS) exert significant influence on soil health and function. This review delves into the dynamics of soil biofilms, highlighting their structural intricacies and the mechanisms by which they facilitate nutrient cycling, and discusses how biofilms enhance the degradation of pollutants through the action of extracellular enzymes and horizontal gene transfer, contributing to soil detoxification and fertility. Furthermore, the role of soil biofilms in stress resilience is underscored, as they form symbiotic relationships with plants, bolstering their growth and resistance to environmental stressors. The review also explores the ecological functions of biofilms in enhancing soil structure stability by promoting aggregate formation, which is crucial for water retention and aeration. By integrating these insights, we aim to provide a comprehensive understanding of the multifaceted benefits of biofilms in soil ecosystems. This knowledge is essential for developing strategies to manipulate soil biofilms to improve agricultural productivity and ecological sustainability. This review also identifies research gaps and emphasizes the need for practical applications of biofilms in sustainable agriculture.

Rapid Synthesis of Functions-Integrated Hydrogel as a Self-Powered Wound Dressing for Real-Time Drug Release and Health Monitoring

A bio-hydrogel is prepared via a low-cost and time-saving strategy and is studied as a self-powered wound dressing for precision medicine and health monitoring. Promoted by a dual self-catalytic pair composed of Fe3+ and catechol, gelation time is dramatically accelerated to 15 s and the hydrogel can be freely modeled at -18 °C without losing flexibility. As smart wound dressing, the required properties such as self-healing, self-adhesion, antibacterial, and sensing stability, are integrated into one hydrogel. TA@CNC offers abundant hydrogen bond and metal-ligand coordination which facilitate the hydrogel with a self-healing efficiency of 91.6%. Owing to the catechol in TA@CNC, hydrogel can adhere to multiple substrates including skin, and show good antibacterial activity. Inspired by a fruit battery, a self-powered wound dressing is fabricated, which exhibits excellent correlation and efficiency in real-time monitoring of body activity and drug release. In vivo experiments prove that efficient drug release of hydrogel dressing significantly accelerate wound healing. Additionally, the dressing exhibits excellent biocompatibility and has no negative impacts on organs. Herein, a smart wound dressing that is different from the traditional way is proposed. As a self-powered device, it can be integrated with wireless devices and is expected to participate in promising applications.

Curcumin-mediated photodynamic disinfection strategy with specific spectral range for mucoid Pseudomonas Aeruginosa from hospital water

BACKGROUND

Hospital water systems represent critical environments for the transmission of pathogens, including multidrug-resistant strains like mucoid Pseudomonas aeruginosa (M-PA). Conventional disinfection methods often struggle to eradicate these pathogens effectively, highlighting the need for innovative approaches.

OBJECTIVE

This study aimed to develop an enhanced photodynamic disinfection strategy targeting M-PA from hospital water systems, using curcumin-mediated photodynamic inactivation (PDI) with specific spectral range.

METHODS

An M-PA strain isolated from hospital water was subjected to photodynamic treatment using curcumin as the photosensitizer. The efficacy of different wavelengths of light and varying concentrations of curcumin, with and without Tris-EDTA adjuvants, was evaluated through bacterial enumeration, ROS level measurements, transcriptome analysis, and assessment of virulence factors and biofilm formation. In vivo experiments utilizing a DSS-induced colitis mouse model assessed the protective effects of the photodynamic treatment against M-PA infection.

RESULTS

Our findings demonstrated that the combination of curcumin-mediated PDI with specific spectral range effectively reduced M-PA counts in water, particularly when supplemented with Tris-EDTA. Transcriptome analysis revealed significant downregulation of virulence-related genes under sublethal photodynamic conditions. Furthermore, photodynamic treatment inhibited pyocyanin production and biofilm formation in M-PA, highlighting its potential to disrupt pathogenicity mechanisms. In vivo experiments showed that PDI attenuated M-PA-induced colitis in mice, indicating its protective efficacy.

CONCLUSION

This study presents a promising photodynamic disinfection strategy for combating M-PA from hospital water. By optimizing curcumin-mediated PDI with specific spectral range and adjuvants, our approach demonstrates substantial efficacy in reducing bacterial counts, inhibiting virulence factors, and preventing M-PA-associated colitis.

Responses of colonization and development of periphytic biofilms to three typical tire wear particles with or without incubation-aging in migrating aqueous phases

Understanding the behavior of tire wear particles (TWPs) and their impact on aquatic environments after aging is essential. This study explored the characteristics of TWPs generated using different methods (rolling friction, sliding friction, and cryogenic milling) and their transformation after exposure to environmental conditions mimicking runoff and sewage, focusing on their effects on river water and periphytic biofilms. Laboratory experiments indicate that at low exposure levels (0.1 mg/L), TWPs promoted biofilm growth, likely due to zinc release acting as a nutrient and the aggregation of particles serving as biofilm scaffolds. However, at higher concentrations (100 mg/L), TWPs inhibited biofilm development. This inhibition is linked to toxic byproducts like N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone and environmentally persistent free radicals, which reduce biofilm biomass, alter algal diversity, and decrease the production of essential biofilm components such as proteins and polysaccharides, consistent with the inhibitory behavior of TWPs on bis-(3'-5')-cyclic diguanosine monophosphate and quorum sensing signals, including acyl-homoserine lactone and autoinducer-2. Aging processes, particularly after simulated sewage treatment, further affect ecological impacts of TWPs, reducing the benefits observed at low concentrations and intensifying the negative effects at high concentrations. Contribution of here lies in systematically revealing the impact of TWPs on the development of aquatic biofilms, emphasizing the logical relationship between their aging characteristics, environmental behavior, and ecological risks. It assesses not only the release effects of typical additives and conventional size effects but also highlights the emerging photochemical toxicity (persistent free radicals), thus providing valuable insights into the aquatic ecological risk assessment of TWPs.

Nano-sized polystyrene and magnetite collectively promote biofilm stability and resistance due to enhanced oxidative stress response

Despite the growing prevalence of nanoplastics in drinking water distribution systems, the collective influence of nanoplastics and background nanoparticles on biofilm formation and microbial risks remains largely unexplored. Here, we demonstrate that nano-sized polystyrene modified with carboxyl groups (nPS) and background magnetite (nFe3O4) nanoparticles at environmentally relevant concentrations can collectively stimulate biofilm formation and prompt antibiotic resistance. Combined exposure of nPS and nFe3O4 by P. aeruginosa biofilm cells stimulated intracellular reactive oxidative species (ROS) production more significantly compared with individual exposure. The resultant upregulation of quorum sensing (QS) and c-di-GMP signaling pathways enhanced the biosynthesis of polysaccharides by 50 %- 66 % and increased biofilm biomass by 36 %- 40 % relative to unexposed control. Consistently, biofilm mechanical stability (measured as Young's modulus) increased by 7.2-9.1 folds, and chemical stress resistance (measured with chlorine disinfection) increased by 1.4-2.0 folds. For P. aeruginosa, the minimal inhibitory concentration of different antibiotics also increased by 1.1-2.5 folds after combined exposure. Moreover, at a microbial community-wide level, metagenomic analysis revealed that the combined exposure enhanced the multi-species biofilm's resistance to chlorine, enriched the opportunistic pathogenic bacteria, and promoted their virulence and antibiotic resistance. Overall, the enhanced formation of biofilms (that may harbor opportunistic pathogens) by nanoplastics and background nanoparticles is an overlooked phenomenon, which may jeopardize the microbial safety of drinking water distribution systems.

Photosensitive AIEgens sensitize bacteria to oxidative damage and modulate the inflammatory responses of macrophages to salvage the photodynamic therapy against MRSA

The urgent need for antimicrobial agents to combat infections caused by multidrug-resistant bacteria facilitates the exploration of alternative strategies such as photosensitizer (PS)-mediated photoinactivation. However, increasing studies have discovered uncorrelated bactericidal activities among PSs possessing similar photodynamic and pathogen-targeted properties. To optimize the photodynamic therapy (PDT) against infections, we investigated three type-I PSs of D-π-A AIEgens TI, TBI, and TTI. The capacities of reactive oxygen species (ROS) generation of TI, TBI, and TTI did not align with their bactericidal activities. Despite exhibiting the lowest photodynamic efficiency, TI exhibited the highest activities against methicillin-resistant Staphylococcus aureus (MRSA) by impairing the anti-oxidative responses of bacteria. By comparison, TTI, characterized by the strongest ROS production, inactivated intracellular MRSA by potentiating the inflammatory response of macrophages. Unlike TI and TTI, TBI, despite possessing moderate photodynamic activities and inducing ROS accumulation in both MRSA and macrophages, did not exhibit any antibacterial activity. Therefore, relying on the disturbed anti-oxidative metabolism of pathogens or potentiated host immune responses, transient ROS bursts can effectively control bacterial infections. Our study reevaluates the contribution of photodynamic activities of PSs to bacterial elimination and provides new insights into discovering novel antibacterial targets and agents.

Adaptive Evolution for the Efficient Production of High-Quality d-Lactic Acid Using Engineered Klebsiella pneumoniae

d-Lactic acid serves as a pivotal platform chemical in the production of poly d-lactic acid (PDLA) and other value-added products. This compound can be synthesized by certain bacteria, including Klebsiella pneumoniae. However, industrial-scale lactic acid production in Klebsiella pneumoniae faces challenges due to growth inhibition caused by lactic acid stress, which acts as a bottleneck in commercial microbial fermentation processes. To address this, we employed a combination of evolutionary and genetic engineering approaches to create an improved Klebsiella pneumoniae strain with enhanced lactic acid tolerance and production. In flask fermentation experiments, the engineered strain achieved an impressive accumulation of 19.56 g/L d-lactic acid, representing the highest production yield observed in Klebsiella pneumoniae to date. Consequently, this strain holds significant promise for applications in industrial bioprocessing. Notably, our genome sequencing and experimental analyses revealed a novel correlation between UTP-glucose-1-phosphate uridylyltransferase GalU and lactic acid resistance in Klebsiella pneumoniae. Further research is warranted to explore the potential of targeting GalU for enhancing d-lactic acid production.

Efficient nitrate and Cr(VI) removal by denitrifier: The mechanism of S. oneidensis MR-1 promoting electron production, transportation and consumption

When Cr(VI) and nitrate coexist, the efficiency of both bio-denitrification and Cr(VI) bio-reduction is poor because chromate hinders bacterial normal functions (i.e., electron production, transportation and consumption). Moreover, under anaerobic condition, the method about efficient nitrate and Cr(VI) removal remained unclear. In this paper, the addition of Shewanella oneidensis MR-1 to promote the electron production, transportation and consumption of denitrifier and cause an increase in the removal of nitrate and Cr(VI). The efficiency of nitrate and Cr(VI) removal accomplished by P. denitrificans as a used model denitrifier increased respectively from 51.3% to 96.1% and 34.3% to 99.8% after S. oneidensis MR-1 addition. The mechanism investigations revealed that P. denitrificans provided S. oneidensis MR-1 with lactate, which was utilized to secreted riboflavin and phenazine by S. oneidensis MR-1. The riboflavin served as coenzymes of cellular reductants (i.e., thioredoxin and glutathione) in P. denitrificans, which created favorable intracellular microenvironment conditions for electron generation. Meanwhile, phenazine promoted biofilm formation, which increased the adsorption of Cr(VI) on the cell surface and accelerated the Cr(VI) reduction by membrane bound chromate reductases thereby reducing damage to other enzymes respectively. Overall, this strategy reduced the negative effect of chromate, thus improved the generation, transportation, and consumption of electrons. SYNOPSIS: The presence of S. oneidensis MR-1 facilitated nitrate and Cr(VI) removal by P. denitrificans through decreasing the negative effect of chromate due to the metabolites' secretion.

UHPLC-MS/MS and GC-MS Metabolic Profiling of a Medicinal Flourensia Fiebrigii Chemotype

The comparative metabolic profiling and their biological properties of eight extracts obtained from diverse parts (leaves, flowers, roots) of the medicinal plant Flourensia fiebrigii S.F. Blake, a chemotype growing in highland areas (2750 m a.s.l.) of northwest Argentina, were investigated. The extracts were analysed by GC-MS and UHPLC-MS/MS. GC-MS analysis revealed the presence of encecalin (relative content: 24.86 %) in ethereal flower extract (EF) and this benzopyran (5.93 %) together sitosterol (11.35 %) in the bioactive ethereal leaf exudate (ELE). By UHPLC-MS/MS the main compounds identified in both samples were: limocitrin, (22.31 %), (2Z)-4,6-dihydroxy-2-[(4-hydroxy-3,5-dimethoxyphenyl)methylidene]-1-benzofuran-3-one (21.31 %), isobavachin (14.47 %), naringenin (13.50 %), and sternbin, (12.49 %). Phytocomplexes derived from aerial parts exhibited significant activity against biofilm production of Pseudomonas aeruginosa and Staphylococcus aureus, reaching inhibitions of 74.7-99.9 % with ELE (50 μg/mL). Notably, the extracts did not affect nutraceutical and environmental bacteria, suggesting a selective activity. ELE also showed the highest reactive species scavenging ability. This study provides valuable insights into the potential applications of this chemotype.

Biological roles of soil microbial consortium on promoting safe crop production in heavy metal(loid) contaminated soil: A systematic review

Heavy metal(loid) (HM) pollution of agricultural soils is a growing global environmental concern that affects planetary health. Numerous studies have shown that soil microbial consortia can inhibit the accumulation of HMs in crops. However, our current understanding of the effects and mechanisms of inhibition is fragmented. In this review, we summarise extant studies and knowledge to provide a comprehensive view of HM toxicity on crop growth and development at the biological, cellular and the molecular levels. In a meta-analysis, we find that microbial consortia can improve crop resistance and reduce HM uptake, which in turn promotes healthy crop growth, demonstrating that microbial consortia are more effective than single microorganisms. We then review three main mechanisms by which microbial consortia reduce the toxicity of HMs to crops and inhibit HMs accumulation in crops: 1) reducing the bioavailability of HMs in soil (e.g. biosorption, bioaccumulation and biotransformation); 2) improving crop resistance to HMs (e.g. facilitating the absorption of nutrients); and 3) synergistic effects between microorganisms. Finally, we discuss the prospects of microbial consortium applications in simultaneous crop safety production and soil remediation, indicating that they play a key role in sustainable agricultural development, and conclude by identifying research challenges and future directions for the microbial consortium to promote safe crop production.

Green-Synthesized Silver Nanoparticles in the Prevention of Multidrug-Resistant Proteus mirabilis Infection and Incrustation of Urinary Catheters BioAgNPs Against P. mirabilis Infection

This study aimed to assess the activity of AgNPs biosynthesized by Fusarium oxysporum (bio-AgNPs) against multidrug-resistant uropathogenic Proteus mirabilis, and to assess the antibacterial activity of catheters coated with bio-AgNPs. Broth microdilution and time-kill kinetics assays were used to determine the antibacterial activity of bio-AgNPs. Catheters were coated with two (2C) and three (3C) bio-AgNPs layers using polydopamine as crosslinker. Catheters were challenged with urine inoculated with P. mirabilis to assess the anti-incrustation activity. MIC was found to be 62.5 µmol l-1, causing total loss of viability after 4 h and bio-AgNPs inhibited biofilm formation by 76.4%. Catheters 2C and 3C avoided incrustation for 13 and 20 days, respectively, and reduced biofilm formation by more than 98%, while the pristine catheter was encrusted on the first day. These results provide evidence for the use of bio-AgNPs as a potential alternative to combat of multidrug-resistant P. mirabilis infections.

Fungal community dynamics on limestone at the Chichén Itzá archaeological site in Mexico driven by protective treatments

Microorganisms naturally colonize rock-based materials in outdoor environments, thereby contributing to their degradation. Fungi, especially in tropical environments with abundant water and favorable temperatures, play a significant role in biodegradation. However, many aspects of the microorganism-stone interaction, including fungal colonization dynamics and the impact of treatment applications, remain unclear. This study conducted a four-year in-situ evaluation of fungal community dynamics on limestone surfaces in the Temple of the Warriors at the Chichén Itzá archaeological site in Mexico, focusing on cleaning and treatment using nanoparticles (NPs). These NPs included zinc oxide (ZnO) and CaZn2(OH)6·2H2O (CZ)-based NPs synthesized via sol-gel (CZ-SG) and mechanochemical methods (CZ-MC), as well as CZ/Ca(OH)2-based products (CZ:Ca-SG). The microbial colonization cover was assessed using colorimetric measurements, and the surface was sampled for fungal community isolation and identification. The results demonstrated significant impacts of cleaning and nanomaterial applications on cultivable fungal communities (melanized filamentous, hyaline, and microcolonial fungi), altering composition, dynamics, and stone surface coloration. In particular, ZnO NPs caused 50 % decline in fungal species and individuals, whereas CZ:Ca-SG NPs displaced most species, indicating effective inhibition of the cultivable fungal community. Microcolonial fungi (MCF), known for their tolerance to withstand harsh environmental conditions, were the only fungal group found in the CZ:Ca-SG treatment. In contrast, CZ-SG and CZ-MC increased the abundance of melanized species, resulting in darkening and reduced color intensity. This study highlights the importance of microcolonial fungi that are tolerant to cleaning and coating procedures in the preservation of stone cultural heritage. These findings enhance our understanding of fungal colonization dynamics following treatment and provide valuable insights into the challenges associated with preserving stone materials in tropical environments.

Antioxidant N-acetylcysteine removing ROS: an antifouling strategy inspired by mussels

Marine biofouling is a thorny issue that causes serious economic losses and adverse ecological impacts on marine ecosystems. Effective and promising antifouling strategies such as surface hydration, flow shear force, and lubricant injection have been developed to address this challenge. However, for the complex marine environment, they still appear inadequate. Mussels are a common fouling organism with strong surface adhesion ability. However, when hypoxia and the oxidative cross-linking reaction of 3,4-dihydroxy phenyl-L-alanine (DOPA) in the structure of adhesion proteins are disrupted, their adhesion ability will be greatly reduced. Inspired by this, we developed an effective antifouling strategy based on reactive oxygen species (ROS) scavenging using N-acetylcysteine (NAC) and evaluated its performance. As a ROS scavenger interfered with the oxidative cross-linking reaction of DOPA in an aqueous solution, the adhesion of DOPA was also affected on the surface of NAC functionalized polyvinyl chloride (PVC) (PVC-NAC). In addition, the colonization level of mussels and the adhesion rate of marine bacteria and benthic diatoms on PVC-NAC were low. The antifouling strategy proposed in this paper was eco-friendly and broad-spectrum, and may provide a new idea for solving marine biofouling and reducing the environmental and economic impacts of fouling organisms.

Pyrogallol impairs staphylococcal biofilm formation via induction of bacterial oxidative stress

AIMS

To examine the effect of the phenolic compound pyrogallol on staphylococcal biofilm formation.

METHODS AND RESULTS

In crystal violet biofilm assays, pyrogallol-reduced biofilm formation in Staphylococcus epidermidis ATCC 35984, Staph. epidermidis NRRL-B41021, Staphylococcus aureus USA300, and Staph. aureus Newman, without significantly impairing bacterial viability. Pyrogallol-mediated impairment of biofilm formation was likely due to induction of bacterial oxidative stress, as its effect was greater in catalase-deficient versus WT Staph. aureus, and biofilm production was rescued by exogenous catalase. The effect of pyrogallol on staphylococcal biofilm formation mirrored that of the known oxidant hydrogen peroxide, which also reduced biofilm formation in a dose-dependent manner.

CONCLUSIONS

Pyrogallol reduces biofilm formation in S. aureus and Staph. epidermidis in a mechanism involving induction of bacterial oxidative stress.

Antibacterial and immunological properties of piperine evidenced by preclinical studies: a systematic review

Aim: To review in vitro, in vivo, and in silico studies examining the antibacterial and immunomodulatory properties of piperine (PPN). Methods: This systematic review followed PRISMA guidelines, and five databases were searched. Results: A total of 40 articles were included in this study. Six aspects of PPN activity were identified, including antibacterial spectrum, association with antibiotics, efflux pump inhibition, biofilm effects, protein target binding, and modulation of immune functions/virulence factors. Most studies focused on Mycobacterium spp. and Staphylococcus aureus. Cell lineages and in vivo models were employed to study PPN antibacterial effects. Conclusion: We highlight PPN as a potential adjuvant in the treatment of bacterial infections. PPN possesses several antibacterial properties that need further exploration to determine the mechanisms behind its pharmacological activity.

Metabolic and Oxidative Stress Effects on the Spectroelectrochemical Behavior of Single Pseudomonas aeruginosa Cells

Pseudomonas aeruginosa is an opportunistic human pathogen capable of causing a wide range of diseases in immunocompromised patients. In order to better understand P. aeruginosa behavior and virulence and to advance drug therapies to combat infection, it would be beneficial to understand how P. aeruginosa cells survive stressful conditions, especially environmental stressors. Here, we report on a strategy that measures potential-dependent fluorescence of individual P. aeruginosa cells, as a sentinel, for cellular response to starvation, hunger, and oxidative stress. This is accomplished using a micropore electrode array capable of trapping large numbers of isolated, vertically oriented cells at well-defined spatial positions in order to study large arrays of single cells in parallel. We find that conditions promoting either starvation or oxidative stress produce discernible changes in the fluorescence response, demonstrated by an increase in the prevalence of fluorescence transients, one of three canonical spectroelectrochemical behaviors exhibited by single P. aeruginosa cells. In contrast, more modest nutrient limitations have little to no effect on the spectroelectrochemical response when compared to healthy cells in the stationary phase. These findings demonstrate the capabilities of micropore electrode arrays for studying the behavior of single microbial cells under conditions where the intercellular spacing, orientation, and chemical environment of the cells are controlled. Realizing single-cell studies under such well-defined conditions makes it possible to study fundamental stress responses with unprecedented control.

Unlocking the Antibiofilm Potential of Natural Compounds by Targeting the NADH:quinone Oxidoreductase WrbA

Biofilm-dwelling cells endure adverse conditions, including oxidative imbalances. The NADH:quinone oxidoreductase enzyme WrbA has a crucial role in the mechanism of action of antibiofilm molecules such as ellagic and salicylic acids. This study aimed to exploit the potential of the WrbA scaffold as a valuable target for identifying antibiofilm compounds at non-lethal concentrations. A three-dimensional computational model, based on the published WrbA structure, was used to screen natural compounds from a virtual library of 800,000 compounds. Fisetin, morin, purpurogallin, NZ028, and NZ034, along with the reference compound ellagic acid, were selected. The antibiofilm effect of the molecules was tested at non-lethal concentrations evaluating the cell-adhesion of wild-type and WrbA-deprived Escherichia coli strains through fluorochrome-based microplate assays. It was shown that, except for NZ028, all of the selected molecules exhibited notable antibiofilm effects. Purpurogallin and NZ034 showed excellent antibiofilm performances at the lowest concentration of 0.5 μM, in line with ellagic acid. The observed loss of activity and the level of reactive oxygen species in the mutant strain, along with the correlation with terms contributing to the ligand-binding free energy on WrbA, strongly indicates the WrbA-dependency of purpurogallin and NZ034. Overall, the molecular target WrbA was successfully employed to identify active compounds at non-lethal concentrations, thus revealing, for the first time, the antibiofilm efficacy of purpurogallin and NZ034.

Inhibition of Listeria monocytogenes Cocktail Culture Biofilms on Crab and Shrimp Coupons and the Expression of Biofilm-Related Genes

Listeria monocytogenes, a bacterium that is transmitted by tainted food, causes the infection listeriosis. In this study, quercetin was tested for its antibacterial properties and effectiveness as a food additive in preventing the growth of L. monocytogenes cocktail (ATCC19117, ATCC19113, and ATCC15313) biofilms on crabs and shrimps. Quercetin showed the least bactericidal activity and no discernible microbial growth at a minimum inhibitory concentration (MIC) of 250 µg/mL. The biofilm inhibition was performed at sub-MICs (1/2, 1/4, and 1/8 MIC). There was no quercetin added to the control group. Additionally, the present work examines the expression of various genes related to biofilm formation and quorum sensing (flaA, fbp, agrA, hlyA, and prfA). The levels of target genes were all significantly down-regulated. Quercetin (0-125 µg/mL) on the surfaces of the crab and shrimp was studied; its inhibitory effects were measured as log reductions at 0.39-2.31 log CFU/cm² and 0.42-2.36 log CFU/cm², respectively (p < 0.05). Quercetin reduced the formation of biofilms by disrupting cell-to-cell connections and causing cell lysis, which led to the deformation of the cells, evidenced by FE-SEM (field-emission scanning electron microscopy). These findings emphasize the significance of using natural food agents to target bacteria throughout the entire food production process.

Inhibitory effects of vorinostat (SAHA) against food-borne pathogen Salmonella enterica serotype Kentucky mixed culture biofilm with virulence and quorum-sensing relative expression

Salmonella is a food-borne microorganism that is also a zoonotic bacterial hazard in the food sector. This study determined how well a mixed culture of Salmonella Kentucky formed biofilms on plastic (PLA), silicon rubber (SR), rubber gloves (RG), chicken skin and eggshell surfaces. In vitro interactions between the histone deacetylase inhibitor-vorinostat (SAHA)-and S. enterica serotype Kentucky were examined utilizing biofilms. The minimum inhibitory concentration (MIC) of SAHA was 120 µg mL-1. The addition of sub-MIC (60 µg mL-1) of SAHA decreased biofilm formation for 24 h on PLA, SR, RG, Chicken skin, and eggshell by 3.98, 3.84, 4.11, 2.86 and 3.01 log (p < 0.05), respectively. In addition, the initial rate of bacterial biofilm formation was higher on chicken skin than on other surfaces, but the inhibitory effect was reduced. Consistent with this conclusion, virulence genes expression (avrA, rpoS and hilA) and quorum-sensing (QS) gene (luxS) was considerably downregulated at sub-MIC of SAHA. SAHA has potential as an anti-biofilm agent against S. enterica serotype Kentucky biofilm, mostly by inhibiting virulence and quorum-sensing gene expression, proving the histone deacetylase inhibitor could be used to control food-borne biofilms in the food industry.

Promotion effects and mechanisms of molybdenum disulfide on the propagation of antibiotic resistance genes in soil

The rapid development of nanotechnology has aroused considerable attentions toward understanding the effects of engineered nanomaterials (ENMs) on the propagation of antibiotic resistance. Molybdenum disulfide (MoS₂) is an extensively used ENM and poses potential risks associated with environmental exposure; nevertheless, the role of MoS₂ toward antibiotic resistance genes (ARGs) transfer remains largely unknown. Herein, it was discovered that MoS₂ nanosheets accelerated the horizontal transfer of RP4 plasmid across Escherichia coli in a dose-dependent manner (0.5-10 mg/L), with the maximum transfer frequency 2.07-fold higher than that of the control. Integration of physiological, transcriptomics, and metabolomics analyses demonstrated that SOS response in bacteria was activated by MoS₂ due to the elevation of oxidative damage, accompanied by cell membrane permeabilization. MoS₂ promoted bacterial adhesion and intercellular contact via stimulating the secretion of extracellular polysaccharides. The ATP levels were maximally increased by 305.7 % upon exposure to MoS₂, and the expression of plasmid transfer genes was up-regulated, contributing to the accelerated plasmid conjugation and increased ARG abundance in soil. Our findings highlight the roles of emerging ENMs (e.g., MoS₂) in ARGs dissemination, which is significant for the safe applications and risk management of ENMs under the development scenarios of nanotechnology.

UV stabilizers can foster early development of biofilms on freshwater microplastics

Interactions between microbes and microplastics are important as of emerging plastic loads in the global environment. Although diverse plastic additives are used in large amounts, there are very few studies on a quantitative comparison of plastisphere on plastics with different plastic additives. We studied the effects of two widely used UV stabilizers (benzotriazole-type UV-327 and benzophenone-type UV-531 were selected based on their persistence and toxicity) in low-density polyethylene (LDPE) on freshwater microbes. This is the first study on the sole effects of UV stabilizers used as plastic additives on freshwater in situ plastisphere biofilm development. Confocal laser scanning microscopy, assisted with proper differentiating fluorochromes and threshold-based 3D segmentation of data, was used to visualize and quantify biofilm. On the first week of biofilm growth, there was very little biovolume and a negligible amount of phototrophs on pristine LDPE contrasting other substrates. Biovolumes were significantly higher on LDPE with UV stabilizers (up to 159% higher than pristine LDPE), although the biomass was mostly dead due to toxicity (>100% higher dead biovolume than live biovolume in LDPE with UV stabilizers). After the fourth week, marginally higher biovolumes along with a revival of the biomass on LDPE with UV stabilizers were observed. The ability to induce microorganismic intracellular reactive oxygen species by UV stabilizers was detected, which may stimulate biofilm growth during the primary phase of biofilm development. Atomic force microscopy analysis denoted that LDPE with UV stabilizers exhibit considerably stronger adhesion force than pristine LDPE. These observations suggest that UV stabilizers can foster the early attachment of microbes to microplastics while killing the surface contacting layer. An alive upper layer of microbes can get developed on the dead biofilm without much disruption due to the toxicity of UV stabilizers. This occurrence can eventually boost the early development of biofilms on plastics.

Enhanced Cd2+ adsorption and toxicity for microbial biofilms in the presence of TiO2 nanoparticles

Titanium dioxide nanoparticles (TiO₂ NPs) easily combine with other pollutants such as heavy metals because of their excellent physiochemical properties. However, how such an interaction may affect the binding behavior of metals onto biofilms remains largely unclear. This study, examined the effects of TiO₂ NPs on Cd²⁺ accumulation and toxicity for natural periphytic biofilms were examined. The adsorption kinetics showed that adding 0.1 and 1 mg/L TiO₂-NPs increased the Cd²⁺ adsorption of biofilms at equilibrium by 23.5% and 35.8%, respectively. However, adding 10 mg/L TiO₂ NPs increased the Cd²⁺ adsorption of biofilms at equilibrium by only 1.9%. The adsorption isotherms indicate that the presence of TiO₂ NPs considerably increased the Cd²⁺ adsorption capacity of the biofilms; however, this effect became less prominent at high TiO₂ NP concentrations. The optimum pH for Cd²⁺ adsorption increased with increasing Cd²⁺ and TiO₂ NP contents. At low concentrations, the coexistence of Cd²⁺ and TiO₂ NPs may facilitate their respective accumulation by stimulating the secretion of extracellular polymeric substances and enhancing the microbial activity of the biofilm. The presence of TiO₂ NPs increases the surface binding energy between Cd²⁺ and functional groups such as carboxyl groups, enhancing the Cd²⁺ accumulation on the biofilm.

Biofilms: Formation, Research Models, Potential Targets, and Methods for Prevention and Treatment

Due to the continuous rise in biofilm-related infections, biofilms seriously threaten human health. The formation of biofilms makes conventional antibiotics ineffective and dampens immune clearance. Therefore, it is important to understand the mechanisms of biofilm formation and develop novel strategies to treat biofilms more effectively. This review article begins with an introduction to biofilm formation in various clinical scenarios and their corresponding therapy. Established biofilm models used in research are then summarized. The potential targets which may assist in the development of new strategies for combating biofilms are further discussed. The novel technologies developed recently for the prevention and treatment of biofilms including antimicrobial surface coatings, physical removal of biofilms, development of new antimicrobial molecules, and delivery of antimicrobial agents are subsequently presented. Finally, directions for future studies are pointed out.

Antibiofilm Efficacy of Quercetin against Vibrio parahaemolyticus Biofilm on Food-Contact Surfaces in the Food Industry

Vibrio parahaemolyticus, one of the most common foodborne pathogenic bacteria that forms biofilms, is a persistent source of concern for the food industry. The food production chain employs a variety of methods to control biofilms, although none are completely successful. This study aims to evaluate the effectiveness of quercetin as a food additive in reducing V. parahaemolyticus biofilm formation on stainless-steel coupons (SS) and hand gloves (HG) as well as testing its antimicrobial activities. With a minimum inhibitory concentration (MIC) of 220 µg/mL, the tested quercetin exhibited the lowest bactericidal action without visible growth. In contrast, during various experiments in this work, the inhibitory efficacy of quercetin at sub-MICs levels (1/2, 1/4, and 1/8 MIC) against V. parahaemolyticus was examined. Control group was not added with quercetin. With increasing quercetin concentration, swarming and swimming motility, biofilm formation, and expression levels of target genes linked to flagellar motility (flaA, flgL), biofilm formation (vp0952, vp0962), virulence (VopQ, vp0450), and quorum-sensing (aphA, luxS) were all dramatically suppressed. Quercetin (0−110 μg/mL) was investigated on SS and HG surfaces, the inhibitory effect were 0.10−2.17 and 0.26−2.31 log CFU/cm2, respectively (p < 0.05). Field emission scanning electron microscopy (FE-SEM) corroborated the findings because quercetin prevented the development of biofilms by severing cell-to-cell contacts and inducing cell lysis, which resulted in the loss of normal cell shape. Additionally, there was a significant difference between the treated and control groups in terms of motility (swimming and swarming). According to our research, quercetin produced from plants should be employed as an antibiofilm agent in the food sector to prevent the growth of V. parahaemolyticus biofilms. These results indicate that throughout the entire food production chain, bacterial targets are of interest for biofilm reduction with alternative natural food agents in the seafood industry.

Antimicrobial Efficacy of Quercetin against Vibrio parahaemolyticus Biofilm on Food Surfaces and Downregulation of Virulence Genes

For the seafood industry, Vibrio parahaemolyticus, one of the most prevalent food-borne pathogenic bacteria that forms biofilms, is a constant cause of concern. There are numerous techniques used throughout the food supply chain to manage biofilms, but none are entirely effective. Through assessing its antioxidant and antibacterial properties, quercetin will be evaluated for its ability to prevent the growth of V. parahaemolyticus biofilm on shrimp and crab shell surfaces. With a minimum inhibitory concentration (MIC) of 220 µg/mL, the tested quercetin exhibited the lowest bactericidal action without visible growth of bacteria. In contrast, during various experiments in this work, the inhibitory efficacy of quercetin without (control) and with sub-MICs levels (1/2, 1/4, and 1/8 MIC) against V. parahaemolyticus was examined. With increasing quercetin concentration, swarming and swimming motility, biofilm formation, and expression levels of related genes linked to flagella motility (flaA and flgL), biofilm formation (vp0952 and vp0962), and quorum-sensing (luxS and aphA) were all dramatically reduced (p < 0.05). Quercetin (0−110 μg/mL) was investigated on shrimp and crab shell surfaces, the inhibitory effects were 0.68−3.70 and 0.74−3.09 log CFU/cm2, respectively (p < 0.05). The findings were verified using field emission scanning electron microscopy (FE-SEM), which revealed quercetin prevented the development of biofilms by severing cell-to-cell contacts and induced cell lysis, which resulted in the loss of normal cell shape. Furthermore, there was a substantial difference in motility between the treatment and control groups (swimming and swarming). According to our findings, plant-derived quercetin should be used as an antimicrobial agent in the food industry to inhibit the establishment of V. parahaemolyticus biofilms. These findings suggest that bacterial targets are of interest for biofilm reduction with alternative natural food agents in the seafood sector along the entire food production chain.

The Inhibitory Effect of Quercetin on Biofilm Formation of Listeria monocytogenes Mixed Culture and Repression of Virulence

Listeria monocytogenes is the species of foodborne pathogenic bacteria that causes the infection listeriosis. The food production chain employs various methods to control biofilms, although none are completely successful. This study evaluates the effectiveness of quercetin as a food additive in reducing L. monocytogenes mixed cultures (ATCC19113, ATCC19117, and ATCC15313) biofilm formation on stainless steel (SS), silicon rubber (SR), and hand glove (HG) coupons, as well as tests its antimicrobial activities. With a minimum inhibitory concentration (MIC) of 250 µg/mL, the tested quercetin exhibited the lowest bactericidal action with no visible bacterial growth. In contrast, during various experiments in this work, the inhibitory efficacy of quercetin at sub-MICs levels (1/2, 1/4, and 1/8 MIC) against L. monocytogenes was examined. A control group was not added with quercetin. The current study also investigates the effect of quercetin on the expression of different genes engaged in motility (flaA, fbp), QS (agrA), and virulence (hlyA, prfA). Through increasing quercetin concentration, swarming and swimming motility, biofilm formation, and expression levels of target genes linked to flagella motility, virulence, and quorum-sensing were all dramatically reduced. Quercetin (0−125 μg/mL) was investigated on the SS, SR, and HG surfaces; the inhibitory effects were 0.39−2.07, 0.09−1.96 and 0.03−1.69 log CFU/cm2, respectively (p < 0.05). Field-emission scanning electron microscopy (FE-SEM) corroborated the findings because quercetin prevented the development of biofilms by severing cell-to-cell contacts and inducing cell lysis, which resulted in the loss of normal cell shape. Our findings suggest that plant-derived quercetin should be used as an antimicrobial agent in the food industry to control the development of L. monocytogenes biofilms. These outcomes suggest that bacterial targets are of interest for biofilm reduction, with alternative natural food agents in the food sector along the entire food production chain.

Emerging nanozyme-based multimodal synergistic therapies in combating bacterial infections

Pathogenic infections have emerged as major threats to global public health. Multidrug resistance induced by the abuse of antibiotics makes the anti-infection therapies to be a global challenge. Thus, it is urgent to develop novel, efficient and biosafe antibiotic alternatives for future antibacterial therapy. Recently, nanozymes have emerged as promising antibiotic alternatives for combating bacterial infections. More significantly, the multimodal synergistic nanozyme-based antibacterial systems open novel disinfection pathways. In this review, we are mainly focusing on the recent research progress of nanozyme-based multimodal synergistic therapies to eliminate bacterial infections. Their antibacterial mechanism, the synergistic antibacterial systems are systematically summarized and discussed according to the combination of mechanisms and the purpose to improve their antibacterial efficiency, biosafety and specificity. Finanly, the current challenges and prospects of the multimodal synergistic antibacterial systems are proposed.

Antifungal, Antioxidant and Antibiofilm Activities of Essential Oils of Cymbopogon spp

Essential oils (EOs) of Cymbopogon citratus and Cymbopogon proximus are known as sources of monoterpenes and sesquiterpenoids, although their biological activities have not been well investigated. In this study, the compositions of C. citratus and C. proximus EOs of Egyptian origin and their antifungal and antibiofilm properties against Candida spp. and Malassezia furfur were investigated. Antioxidant activities were also evaluated. GC-MS showed the presence of nine and eight constituents in C. citratus and C. proximus EOs, respectively, with geranial and neral as the major compounds of C. citratus EO and piperitone and α-terpinolene as the major compounds of C. proximus EO. Both EOs showed antifungal (MIC values ranging from 1.25 to 20 µL/ mL) and antibiofilm activities (% of reduction ranging from 27.65 ± 11.7 to 96.39 ± 2.8) against all yeast species. The antifungal and antibiofilm activities of C. citratus EO were significantly higher than those observed for C. proximus EO. M. furfur was more susceptible to both EOs than Candida spp. Both EOs exhibited the highest antioxidant activity. This study suggests that C. citratus and C. proximus EOs might be an excellent source of antifungal, antibiofilm and antioxidant drugs and might be useful for preventing Malassezia infections in both medical and veterinary medicine.

Decoding the antifungal resistance mechanisms in biofilms of emerging, ubiquitous and multidrug-resistant species belonging to the Scedosporium/Lomentospora genera

The opportunistic filamentous fungi belonging to the Scedosporium and Lomentospora genera are highly tolerant to all classes of available antifungal drugs. Moreover, the mature biofilm formed by these fungi presents higher antifungal resistance when compared to planktonic cells. Nevertheless, the resistance mechanisms developed by the biofilm lifestyle are not completely elucidated. In the current study, we have investigated the mainly known resistance mechanisms to azoles (voriconazole and fluconazole) and polyenes (amphotericin B - AMB) in S. apiospermum, S. minutisporum, S. aurantiacum, and L. prolificans (formerly S. prolificans) biofilms. Both classes of antifungals can physically bind to the extracellular matrix of mature biofilms, preventing the drugs from reaching their targets on biofilm-forming cells, which precludes their activity and toxicity. In addition, the activity of efflux pumps, measured by Rhodamine 6 G, was increased along the maturation of the biofilm. The efflux pump's inhibition by L-Phe-L-Arg-β-naphthylamide culminated in a 2- to 16-fold increase in azole susceptibility in conidial cells, but not in mature biofilms. Finally, we demonstrated by using specific inhibitors that in conidia, but not in biofilms, AMB induced the production of reactive oxygen species through the activity of the oxidative phosphorylation system (complex I to IV and alternative oxidases). However, the cellular redox imbalance caused by AMB was well coped with the high activity of antioxidative enzymes, such as superoxide dismutase and catalase. Altogether, our results revealed that Scedosporium/Lomentospora biofilm resistance occurs through various mechanisms that operate concomitantly, which could explain the huge challenge in the clinical treatment of scedosporiosis/lomentosporiosis.

Disinfecting Action of Gaseous Ozone on OXA-48-Producing Klebsiella pneumoniae Biofilm In Vitro

Klebsiella pneumoniae is an emerging multidrug-resistant pathogen that can contaminate hospital surfaces in the form of a biofilm which is hard to remove with standard disinfectants. Because of biofilm resistance to conservative disinfectants, the application of new disinfection technologies is becoming more frequent. Ozone gas has antimicrobial activity but there is lack of data on its action against K. pneumoniae biofilm. The aim of this study was to investigate the effects and mechanisms of action of gaseous ozone on the OXA-48-procuding K. pneumoniae biofilm. A 24 h biofilm of K. pneumoniae formed on ceramic tiles was subsequently exposed to different concentrations of ozone during one and two hours to determine the optimal ozone concentration. Afterwards, the total bacteria count, total biomass and oxidative stress levels were monitored. A total of 25 ppm of gaseous ozone was determined to be optimal ozone concentration and caused reduction in total bacteria number in all strains of K. pneumoniae for 2.0 log₁₀ CFU/cm², followed by reduction in total biomass up to 88.15%. Reactive oxygen species levels significantly increased after the ozone treatment at 182% for the representative K. pneumoniae NCTC 13442 strain. Ozone gas in the concentration of 25 ppm caused significant biofilm reduction but did not completely eradicate the K. pneumoniae biofilm formed on ceramics. In conclusion, ozone gas has great potential to be used as an additional hygiene measure in joint combat against biofilm in hospital environments.

UVA as environmental signal for alginate production in Pseudomonas aeruginosa: role of this polysaccharide in the protection of planktonic cells and biofilms against lethal UVA doses

Pseudomonas aeruginosa is an extremely versatile microorganism that survives in a wide variety of niches. It is capable to respond rapidly to changes in the environment by producing secondary metabolites and virulence factors, including alginate. Alginate is an extracellular polysaccharide that protects the bacteria from antibiotics and oxidative agents, and enhances cell adhesion to solid surfaces in the process of biofilm formation. In the present study, we analyzed the role of alginate in the response of P. aeruginosa to lethal doses of ultraviolet-A (UVA) radiation, the major fraction of solar UV radiation reaching the Earth's surface. We also studied the role of alginate in the context of the adaptive responses generated when P. aeruginosa is exposed to sublethal doses of UVA radiation. The survival studies demonstrated that alginate has a key role in the resistance of P. aeruginosa to the oxidative stress generated by lethal UVA doses, both in planktonic cells and in static biofilms. In addition, the presence of alginate proved to be essential in the occurrence of adaptive responses such as induction of biofilm formation and cross-protection against hydrogen peroxide and sodium hypochlorite, both generated by exposure to low UVA doses. Finally, we demonstrated that the increase of biofilm formation is accompanied by an increase in alginate concentration in the biofilm matrix, possibly through the ppGpp-dependent induction of genes related to alginate regulation (algR and algU) and biosynthesis (algD operon). Given the importance of alginate in biofilm formation and its protective roles, better understanding of the mechanisms associated to its functions and synthesis is relevant, given the normal exposure of P. aeruginosa to UVA radiation and other types of oxidative stresses.

Nutrient starvation intensifies chlorine disinfection-stressed biofilm formation

Bacterial surface attachment and subsequent biofilm expansion represent an essential adaptation to environmental signals and stresses, which are of great concern for many natural and engineered ecosystems. Yet the underlying mechanisms and driving forces of biofilm formation in a chlorinated and nutrient-restricted system remain sketchy. In this study, we coupled an experimental investigation and modeling simulation to understand how chlorination and nutrient limitation conspire to form biofilm using Pseudomonas aeruginosa as a model bacterium. Experimental results showed that moderate chlorination at 1.0 mg/L led to biofilm development amplified to 2.6 times of those without chlorine, while additional nutrient limitation (of 1/50-diluted or 0.4 g/L LB broth culture) achieved 4.6 times increment as compared to those of undiluted scenarios (of 20 g/L LB broth culture) with absence of chlorination after 24 h exposure. Meanwhile, intermediate chlorination stimulated instant flagellar motility and subsequently extracellular polymeric substances (EPS) secretion, particularly under limited nutrient condition (of 1/50-diluted or 0.4 g/L LB broth culture) that retarded chlorine consumption and provoked bacterial nutrient-limitation response. From our simulations, chlorine and resource levels along with associated spatio-temporal variations collectively drove bacterial cell movement and EPS excretion. Our results demonstrated that restraining nutrient intensified chlorination-excited cell movement and EPS production that reinforced biological and cell-surface interactions, thereby encouraging bacterial surface attachment and subsequent biofilm development. The findings provide the insights into the linkage of disinfectant and nutrient-regulated bacterial functional responses with consequent micro-habitats and biofilm dynamics.

The Transcription Regulator YgeK Affects Biofilm Formation and Environmental Stress Resistance in Avian Pathogenic Escherichia coli

Simple Summary

Avian pathogenic Escherichia coli (APEC) is the pathogen responsible for colibacillosis in poultry. Transcriptional regulator ygeK has been shown to decrease APEC’s flagellar formation ability, bacterial motility ability, serum sensitivity, and adhesion ability. However, we did not study the effects of ygeK on biofilm formation and environmental stress resistance in APEC. In this study, we investigated ygeK in APEC biofilm formation and bacterial resistance to different environmental stresses. We also analyzed the multi-level regulation of ygeK in APEC and investigated associations between differentially expressed proteins and key ygeK targets. This work provides a basis for further analysis of APEC pathogenesis mechanisms.

Abstract

Avian pathogenic Escherichia coli (APEC) is one of the most common pathogens in poultry and a potential gene source of human extraintestinal pathogenic E. coli (ExPEC), leading to serious economic losses in the poultry industry and public health concerns. Exploring the pathogenic mechanisms underpinning APEC and the identification of new targets for disease prevention and treatment are warranted. YgeK is a transcriptional regulator in APEC and is localized to the type III secretion system 2 of E. coli. In our previous work, the transcription factor ygeK significantly affected APEC flagella formation, bacterial motility, serum sensitivity, adhesion, and virulence. To further explore ygeK functions, we evaluated its influence on APEC biofilm formation and resistance to environmental stress. Our results showed that ygeK inactivation decreased biofilm formation and reduced bacterial resistance to environmental stresses, including acid and oxidative stress. In addition, the multi-level regulation of ygeK in APEC was analyzed using proteomics, and associations between differentially expressed proteins and the key targets of ygeK were investigated. Overall, we identified ygeK’s new function in APEC. These have led us to better understand the transcriptional regulatory ygeK and provide new clues about the pathogenicity of APEC.

E-Cigarette Aerosol Exposure Favors the Growth and Colonization of Oral Streptococcus mutans Compared to Commensal Streptococci

E-cigarettes (e-cigs) have drastically increased in popularity during the last decade, especially among teenagers. While recent studies have started to explore the effect of e-cigs in the oral cavity, little is known about their effects on the oral microbiota and how they could affect oral health and potentially lead to disease, including periodontitis and head and neck cancers. To explore the impact of e-cigs on oral bacteria, we selected members of the genus Streptococcus, which are abundant in the oral cavity. We exposed the commensals Streptococcus sanguinis and Streptococcus gordonii and the opportunistic pathogen Streptococcus mutans, best known for causing dental caries, to e-liquids and e-cig aerosols with and without nicotine and with and without menthol flavoring and measured changes in growth patterns and biofilm formation. Our results demonstrate that e-cig aerosols hindered the growth of S. sanguinis and S. gordonii, while they did not affect the growth of S. mutans. We also show that e-cig aerosols significantly increased biofilm formation by S. mutans but did not affect the biofilm formation of the two commensals. We found that S. mutans exhibits higher hydrophobicity and coaggregation abilities along with higher attachment to OKF6 cells than S. sanguinis and S. gordonii. Therefore, our data suggest that e-cig aerosols have the potential to dysregulate oral bacterial homeostasis by suppressing the growth of commensals while enhancing the biofilm formation of the opportunistic pathogen S. mutans. This study highlights the importance of understanding the consequences of e-cig aerosol exposure on selected commensals and pathogenic species. Future studies modeling more complex communities will provide more insight into how e-cig aerosols and vaping affect the oral microbiota. IMPORTANCE Our study shows that e-cigarette aerosol exposure of selected bacteria known to be residents of the oral cavity hinders the growth of two streptococcal commensals while enhancing biofilm formation, hydrophobicity, and attachment for the pathogen S. mutans. These results indicate that e-cigarette vaping could open a niche for opportunistic bacteria such as S. mutans to colonize the oral cavity and affect oral health.

Physicochemical and Biological Insights Into the Molecular Interactions Between Extracellular DNA and Exopolysaccharides in Myxococcus xanthus Biofilms

Extracellular DNA (eDNA) is a critical component in the extracellular matrix (ECM) of bacterial biofilms, while little is known about the mechanisms underlying how eDNA integrates into the ECM through potential macromolecular interactions. Myxococcus xanthus biofilm was employed as a suitable model for the investigation due to the co-distribution of eDNA and exopolysaccharides (EPS) owing to their direct interactions in the ECM. DNA is able to combine with M. xanthus EPS to form a macromolecular conjugate, which is dominated by the electrostatic forces participating in the polymer-polymer interactions. Without intercalation binding, DNA-EPS interactions exhibit a certain degree of reversibility. Acting as a strong extracellular framework during biofilm formation process, the eDNA-EPS complex not only facilitates the initial cell adhesion and subsequent establishment of ECM architecture, but also renders cells within biofilms stress resistances that are relevant to the survival of M. xanthus in some hostile environments. Furthermore, the EPS protects the conjugated DNA from the degradation by nucleic acid hydrolases, which leads to the continuous and stable existence of eDNA in the native ECM of M. xanthus biofilms. These results will shed light on developing prevention and treatment strategies against biofilm-related risks.

Polyoxometalate-polypeptide nanoassemblies as peroxidase surrogates with antibiofilm properties

Developing artificial metalloenzymes that possess a superior performance to their natural counterparts is an attractive concept. Polyoxometalates (POMs) are a class of anionic molecular metal-oxides with excellent redox properties and bioactivity. We have recently introduced "POMlymers" - covalently conjugated POM-peptide hybrid materials - where the polypeptide chain is obtained through a ring-opening polymerisation (ROP) of α-amino acid N-carboxyanhydrides (NCA) on an inorganic POM scaffold. Attracted by the idea of preparing artificial metalloenzymes, here we report the supramolecular self-assembly of POMlymer hybrids into nanoparticles where an optimal environment for catalysis is created. Our results demonstrate that the self-assembly of covalent POMlymers, enhances the peroxidase-like activity of the parent POM anion whereas, in contrast, the catalytic activity for nanoparticles obtained by ionic self-assembly of the same peptide and POM components practically disappears. Furthermore, POMlymer nanoparticles also present antimicrobial and antibiofilm activity against the skin bacterium Staphylococcus epidermidis; whereas, ionic POM-peptide hybrids significantly increase biofilm production and endogenous production of reactive oxygen species. In summary, we present the self-assembly of POMlymer hybrids into nanoparticles and a combination of peroxidase activity and microbiology assays that show that the POM-peptide covalent bond is essential for the stability of the self-assembled nanoparticles and therefore for their catalytic and biological activity.

Theoretical and Experimental Studies of Phosphonium Ionic Liquids as Potential Antibacterials of MDR Acinetobacter baumannii

A previously developed model to predict antibacterial activity of ionic liquids against a resistant A. baumannii strain was used to assess activity of phosphonium ionic liquids. Their antioxidant potential was additionally evaluated with newly developed models, which were based on public data. The accuracy of the models was rigorously evaluated using cross-validation as well as test set prediction. Six alkyl triphenylphosphonium and alkyl tributylphosphonium bromides with the C₈, C₁₀, and C₁₂ alkyl chain length were synthesized and tested in vitro. Experimental studies confirmed their activity against A. baumannii as well as showed pronounced antioxidant properties. These results suggest that phosphonium ionic liquids could be promising lead structures against A. baumannii.

Impact of Quercetin against Salmonella Typhimurium Biofilm Formation on Food-Contact Surfaces and Molecular Mechanism Pattern

Quercetin is an active nutraceutical element that is found in a variety of foods, vegetables, fruits, and other products. Due to its antioxidant properties, quercetin is a flexible functional food that has broad protective effects against a wide range of infectious and degenerative disorders. As a result, research is required on food-contact surfaces (rubber (R) and hand gloves (HG)) that can lead to cross-contamination. In this investigation, the inhibitory effects of quercetin, an antioxidant and antibacterial molecule, were investigated at sub-MIC (125; 1/2, 62.5; 1/4, and 31.25; 1/8 MIC, μg/mL) against Salmonella Typhimurium on surfaces. When quercetin (0−125 μg/mL) was observed on R and HG surfaces, the inhibitory effects were 0.09−2.49 and 0.20−2.43 log CFU/cm2, respectively (p < 0.05). The results were confirmed by field emission scanning electron microscopy (FE-SEM), because quercetin inhibited the biofilms by disturbing cell-to-cell connections and inducing cell lysis, resulting in the loss of normal cell morphology, and the motility (swimming and swarming) was significantly different at 1/4 and 1/2 MIC compared to the control. Quercetin significantly (p < 0.05) suppressed the expression levels of virulence and stress response (rpoS, avrA, and hilA) and quorum-sensing (luxS) genes. Our findings imply that plant-derived quercetin could be used as an antibiofilm agent in the food industry to prevent S. Typhimurium biofilm formation.

Formation of Biofilm by Tetragenococcus halophilus Benefited Stress Tolerance and Anti-biofilm Activity Against S. aureus and S. Typhimurium

Tetragenococcus halophilus, a halophilic lactic acid bacterium (LAB), plays an important role in the production of high-salt fermented foods. Generally, formation of biofilm benefits the fitness of cells when faced with competitive and increasingly hostile fermented environments. In this work, the biofilm-forming capacity of T. halophilus was investigated. The results showed that the optimal conditions for biofilm formation by T. halophilus were at 3–9% salt content, 0–6% ethanol content, pH 7.0, 30°C, and on the surface of stainless steel. Confocal laser scanning microscopy (CLSM) analysis presented a dense and flat biofilm with a thickness of about 24 μm, and higher amounts of live cells were located near the surface of biofilm and more dead cells located at the bottom. Proteins, polysaccharides, extracellular-DNA (eDNA), and humic-like substances were all proved to take part in biofilm formation. Higher basic surface charge, greater hydrophilicity, and lower intracellular lactate dehydrogenase (LDH) activities were detected in T. halophilus grown in biofilms. Atomic force microscopy (AFM) imaging revealed that biofilm cultures of T. halophilus had stronger surface adhesion forces than planktonic cells. Cells in biofilm exhibited higher cell viability under acid stress, ethanol stress, heat stress, and oxidative stress. In addition, T. halophilus biofilms exhibited aggregation activity and anti-biofilm activity against Staphylococcus aureus and Salmonella Typhimurium. Results presented in the study may contribute to enhancing stress tolerance of T. halophilus and utilize their antagonistic activities against foodborne pathogens during the production of fermented foods.

Basic physiology of Pseudomonas aeruginosa contacted with carbon nanocomposites

Experiments describing properties of nanomaterials on bacteria are frequently limited to the disk diffusion method or other end-point methods indicating viability or survival rate in plate count assay. Such experimental design does not show the dynamic changes in bacterial physiology, mainly when performed on reference microorganisms (Escherichia coli and Staphylococcus aureus). Testing other microorganisms, such as Pseudomonas aeruginosa, could provide novel insights into the microbial response to nanomaterials. Therefore, we aimed to test selected carbon nanomaterials and their components in a series of experiments describing the basic physiology of P. aeruginosa. Concentrations ranging from 15.625 to 1000 µg/mL were tested. The optical density of cultures, pigment production, respiration, growth curve analysis, and biofilming were tested. The results confirmed variability in the response of P. aeruginosa to tested nanostructures, depending on their concentration. The co-incubation with the nanostructures (in concentration 125 µg/mL) could inhibit the population growth (in most cases) or promote it in the case of graphene oxide. Furthermore, a specific concentration of a given nanomaterial could cause contradictory effects leading to stimulation or inhibition of pigmentation, an optical density of the cultures, or biofilm formation. We have found that particularly nanomaterials containing TiO2 could induce pigmentation in P. aeruginosa, which indicates the possibility of increased virulence. On the other hand, nanocomposites containing cobalt nanoparticles had the highest anti-bacterial potential when cobalt was displayed on the surface. Our approach revealed changes in respiration and growth dynamics that can be used to search for nanomaterials’ application in biotechnology.

Antibiotic resistance genes alternation in soils modified with neutral and alkaline salts: interplay of salinity stress and response strategies of microbes

Growing evidence points to the pivotal roles of salt accumulation in mediating antibiotic resistance genes (ARGs) spread in soil, whereas how salt mediates ARGs dissemination remains unknown. Herein, the effects of neutral or alkaline (Ne/Al) salt at low, moderate and high levels (Ne/Al-L, Ne/Al-M, Ne/Al-H) on the dissemination of ten typical ARGs in soils were explored, by simultaneously considering the roles of salinity stress and response strategies of microbes. In the soils amended with Ne/Al-L and Al-M salt, the dissemination of ARGs was negligible and the relative abundances of ARGs and mobile genetic elements (MGEs) were decreased. However, Ne-M and Al-H salt contributed to the dissemination of ARGs in soils, with the significantly increased absolute and relative abundances of ARGs and MGEs. In Ne-H soil, although the absolute abundance of ARGs declined drastically due to serious oxidative damage, their relative abundances were promoted. The facilitated ARGs transfer was potentially related to the excessive generation of intracellular reactive oxygen species and increased activities of DNA repair enzymes involved in SOS system. In addition, the activated intracellular protective response including quorum sensing and energy metabolism largely provided essential factors for ARGs dissemination. The co-occurrence of ARGs and over-expressed salt-tolerant genes in specific halotolerant bacteria further suggested the selection of salt stress on ARGs. Moreover, less disturbance of alkaline salt than neutral salt on ARGs evolution was observed, due to the lower abiotic stress and selective pressure on microbes. This study highlights that soil salinity-sodicity could dose-dependently reshape the dissemination of ARGs and community structure of microbes, which may increase the ecological risks of ARGs in agricultural environment.

Nontypeable Haemophilus influenzae Redox Recycling of Protein Thiols Promotes Resistance to Oxidative Killing and Bacterial Survival in Biofilms in a Smoke-Related Infection Model

Smoke exposure is a risk factor for community-acquired pneumonia, which is typically caused by host-adapted airway opportunists like nontypeable Haemophilus influenzae (NTHi). Genomic analyses of NTHi revealed homologs of enzymes with predicted roles in reduction of protein thiols, which can have key roles in oxidant resistance. Using a clinical NTHi isolate (NTHi 7P49H1), we generated isogenic mutants in which homologs of glutathione reductase (open reading frame NTHI 0251), thioredoxin-dependent thiol peroxidase (NTHI 0361), thiol peroxidase (NTHI 0907), thioredoxin reductase (NTHI 1327), and glutaredoxin/peroxiredoxin (NTHI 0705) were insertionally inactivated. Bacterial protein analyses revealed that protein oxidation after hydrogen peroxide treatment was elevated in all the mutant strains. Similarly, each of these mutants was less resistant to oxidative killing than the parental strain; these phenotypes were reversed by genetic complementation. Analysis of biofilm communities formed by the parental and mutant strains showed reduction in overall biofilm thickness and density and significant sensitization of bacteria within the biofilm structure to oxidative killing. Experimental respiratory infection of smoke-exposed mice with NTHi 7P49H1 showed significantly increased bacterial counts compared to control mice. Immunofluorescent staining of lung tissues showed NTHi communities on lung mucosae, interspersed with neutrophil extracellular traps; these bacteria had transcript profiles consistent with NTHi biofilms. In contrast, infection with the panel of NTHi mutants showed a significant decrease in bacterial load. Comparable results were observed in bactericidal assays with neutrophil extracellular traps in vitro. Thus, we conclude that thiol-mediated redox homeostasis is a determinant of persistence of NTHi within biofilm communities.

IMPORTANCE Chronic bacterial respiratory infections are a significant problem for smoke-exposed individuals, especially those with chronic obstructive pulmonary disease (COPD). These infections often persist despite antibiotic use. Thus, the bacteria remain and contribute to the development of inflammation and other respiratory problems. Respiratory bacteria often form biofilms within the lungs; during growth in a biofilm, their antibiotic and oxidative stress resistance is incredibly heightened. It is well documented that redox homeostasis genes are upregulated during this phase of growth. Many common respiratory pathogens, such as NTHi and Streptococcus pneumoniae, are reliant on scavenging from the host the necessary components they need to maintain these redox systems. This work begins to lay the foundation for exploiting this requirement and thiol redox homeostasis pathways of these bacteria as a therapeutic target for managing chronic respiratory bacterial infections, which are resistant to traditional antibiotic treatments alone.

Phthalate Esters Released from Plastics Promote Biofilm Formation and Chlorine Resistance

Phthalate esters (PAEs) are commonly released from plastic pipes in some water distribution systems. Here, we show that exposure to a low concentration (1-10 μg/L) of three PAEs (dimethyl phthalate (DMP), di-n-hexyl phthalate (DnHP), and di-(2-ethylhexyl) phthalate (DEHP)) promotes Pseudomonas biofilm formation and resistance to free chlorine. At PAE concentrations ranging from 1 to 5 μg/L, genes coding for quorum sensing, extracellular polymeric substances excretion, and oxidative stress resistance were upregulated by 2.7- to 16.8-fold, 2.1- to 18.9-fold, and 1.6- to 9.9-fold, respectively. Accordingly, more biofilm matrix was produced and the polysaccharide and eDNA contents increased by 30.3-82.3 and 10.3-39.3%, respectively, relative to the unexposed controls. Confocal laser scanning microscopy showed that PAE exposure stimulated biofilm densification (volumetric fraction increased from 27.1 to 38.0-50.6%), which would hinder disinfectant diffusion. Biofilm densification was verified by atomic force microscopy, which measured an increase of elastic modulus by 2.0- to 3.2-fold. PAE exposure also stimulated the antioxidative system, with cell-normalized superoxide dismutase, catalase, and glutathione activities increasing by 1.8- to 3.0-fold, 1.0- to 2.0-fold, and 1.2- to 1.6-fold, respectively. This likely protected cells against oxidative damage by chlorine. Overall, we demonstrate that biofilm exposure to environmentally relevant levels of PAEs can upregulate molecular processes and physiologic changes that promote biofilm densification and antioxidative system expression, which enhance biofilm resistance to disinfectants.