Molecular mechanisms of antimicrobial tolerance and resistance in bacterial and fungal biofilms

Global challenges and microbial biofilms: Identification of priority questions in biofilm research, innovation and policy

Priority question exercises are increasingly used to frame and set future research, innovation and development agendas. They can provide an important bridge between the discoveries, data and outputs generated by researchers, and the information required by policy makers and funders. Microbial biofilms present huge scientific, societal and economic opportunities and challenges. In order to identify key priorities that will help to advance the field, here we review questions from a pool submitted by the international biofilm research community and from practitioners working across industry, the environment and medicine. To avoid bias we used computational approaches to group questions and manage a voting and selection process. The outcome of the exercise is a set of 78 unique questions, categorized in six themes: (i) Biofilm control, disruption, prevention, management, treatment (13 questions); (ii) Resistance, persistence, tolerance, role of aggregation, immune interaction, relevance to infection (10 questions); (iii) Model systems, standards, regulatory, policy education, interdisciplinary approaches (15 questions); (iv) Polymicrobial, interactions, ecology, microbiome, phage (13 questions); (v) Clinical focus, chronic infection, detection, diagnostics (13 questions); and (vi) Matrix, lipids, capsule, metabolism, development, physiology, ecology, evolution environment, microbiome, community engineering (14 questions). The questions presented are intended to highlight opportunities, stimulate discussion and provide focus for researchers, funders and policy makers, informing future research, innovation and development strategy for biofilms and microbial communities.

Bioinspired gelated cell sheet-supported lactobacillus biofilm for aerobic vaginitis diagnosis and treatment

Aerobic vaginitis (AV) is a long-standing inflammatory disease that affects female patients. The use of antibiotics is a common means for AV treatment, but it will indiscriminately kill both pathogenic bacteria and beneficial strains, which easily causes vaginal dysbacteriosis and infection recurrence. Herein, we describe a bioinspired strategy for fabricating gelated cell sheet-supported lactobacillus biofilms (GCS-LBs) for AV treatment. Compared with common planktonic probiotic formulations, probiotic biofilms forming on a robust GCS exhibit enhanced stress tolerance and better colonization capacity in the mouse vagina. Moreover, DNA nanodevices are decorated on the GCS and dynamically report the microenvironment change of biofilms for timely evaluating bacterium activity, both in vitro and in vivo. Consequently, GCS-LBs are used for treating AV in an Escherichia coli-infected mouse model, which shows enhanced therapeutic efficacy compared with conventional antibiotic or lactobacillus monotherapy. Overall, the GCS-LB shows promise as a potent multifunctional tool to combat bacterial infection.

Coaxial electrospun nanofiber accelerates infected wound healing via engineered probiotic biofilm

Bacterial infection is the primary cause of delayed wound healing. Infected wounds suffer from a series of harmful factors in the harsh wound microenvironment (WME), greatly damaging their potential for tissue regeneration. Herein, a novel probiotic biofilm-based antibacterial strategy is proposed through experimentation. Firstly, a series of coaxial polycaprolactone (PCL) / silk fibroin (SF) nanofiber films (termed as PSN-n, n = 0.5, 1.0, 1.5, and 2.0, respectively) are prepared by coaxial electrospinning and their physiochemical properties are comprehensively characterized. Afterward, the PSN-1.5 is selected and co-cultured with L. paracasei to allow the formation of probiotic biofilm. The probiotic biofilm-loaded PSN-1.5 nanofiber film (termed as PSNL-1.5) exhibits relatively good broad-spectrum antibacterial activity, biocompatibility, and enhanced pro-regenerative capability by immunoregulation of M2 macrophage. A wound healing assay is performed using an S. aureus-infected skin defect model. The application effect of PSNL-1.5 is significantly better than that of a commercial nano‑silver burn & scald dressing (Anson®), revealing huge potential for clinical translation. This study is of significant novelty in demonstrating the antibacterial and pro-regenerative abilities of probiotic biofilms. The product of this study will be extensively used for treating infected wounds or other wounds.

Biofilm formation of Lactiplantibacillus plantarum food isolates under flow and resistance to disinfectant agents

Bacterial biofilms formed in food processing environments can be resilient against cleaning and disinfection causing recontamination and spoilage of foods. We investigated the biofilm formation of six Lactiplantibacillus plantarum food spoilage isolates (FBR1-FBR6) using WCFS1 as a reference strain, and examined the impact of benzalkonium chloride (BKC) and peracetic acid (PAA) on planktonic and biofilm cells formed under static and dynamic flow conditions. We used a custom-designed setup composed of a 48-well plate with 0.8 ml culture volumes. We quantified biofilm formation under static and dynamic flow conditions with a flow rate of 3.2 ml/h using plate counting, Crystal Violet (CV) staining, and fluorescence staining techniques. Our findings revealed significant differences in biofilm formation and disinfectant resistance among studied strains and cell types. We observed that flow promoted biofilm formation in some strains and increased the number of culturable cells within biofilms in all strains. Furthermore, biofilm cells demonstrated higher resistance to disinfectants in comparison to planktonic cells for certain strains. Interestingly, cells from dispersed under flow biofilms show higher resistance to disinfectants than cells from static biofilms. The results indicate the importance of flow conditions in influencing L. plantarum food isolates biofilm formation and disinfection resistance, which may have implications for product contamination and spoilage risks.

A tale of two old drugs tetracycline and salicylic acid with new perspectives-Coordination chemistry of their Co(II) and Ni(II) complexes, redox activity of Cu(II) complex, and molecular interactions

Extensive use of the broad-spectrum tetracycline antibiotics (TCs) has resulted their wide spread in the environment and drive new microecological balances, including the infamous antibiotic resistance. TCs require metal ions for their antibiotic activity and resistance via interactions with ribosome and tetracycline repressor TetR, respectively, at specific metal-binding sites. Moreover, the Lewis-acidic metal center(s) in metallo-TCs can interact with Lewis-basic moieties of many bioactive secondary metabolites, which in turn may alter their associated chemical equilibria and biological activities. Thus, it is ultimately important to reveal detailed coordination chemistry of metallo-TC complexes. Herein, we report (a) conclusive specific Co2+, Ni2+, and Cu2+-binding of TC revealed by paramagnetic 1H NMR, showing different conformations of the coordination and different metal-binding sites in solution and solid state, (b) significant metal-mediated activity of Cu-TC toward catechol oxidation with different mechanisms by air and H2O2 (i.e., mono- and di-nuclear pathways, respectively), (c) interactions of metallo-TCs with bioactive salicylic acid and its precursor benzoic acid, and (d) noticeable change of TC antibiotic activity by metal and salicylic acid. The results imply that TCs may play broad and versatile roles in maintaining certain equilibria in microecological environments in addition to their well-established antibiotic activity. We hope the results may foster further exploration of previously unknown metal-mediated activities of metallo-TC complexes and other metalloantibiotics.

Choline and geranate ionic liquid for subgingival biofilm control

Periodontitis is a chronic inflammatory disease that causes destruction of the periodontium and eventual tooth loss. The priority in the periodontal treatment is to remove the subgingival biofilm. Chemical removal of biofilms using antimicrobial agents has been applied in clinical practice. However, their clinical effect is still limited because the agents must overcome biofilm's significant drug tolerance, which is primarily caused by the extracellular matrix, a physical barrier that attenuates drug diffusion. This study aimed to study the use of ionic liquids (ILs), a new class of biocompatible materials, for controlling subgingival biofilms because of their excellent permeability. Choline and geranate (CAGE) IL was tested for its highly potent antiseptic behavior and permeability. Antibacterial tests revealed that the significant efficacy of CAGE against periodontopathic microorganisms was derived from their ability to destroy cell membrane, as demonstrated by membrane permeability assay and transmission electron microscopy imaging. Antibiofilm tests using two pathogenic biofilm models revealed that CAGE exerted efficacy against the biofilm-embedded bacteria, conspicuously neutralized the biofilms, and eventually destroyed the biofilm structure. Furthermore, the penetration of CAGE into the biofilm was visually confirmed using confocal laser scanning microscopy. This study highlighted the potential of CAGE as a powerful antibiofilm therapeutic.

Biofilm formation by Listeria monocytogenes from the meat processing industry environment and the use of different combinations of detergents, sanitizers, and UV-A radiation to control this microorganism in planktonic and sessile forms

This study aimed to evaluate the ability of biofilm formation by L. monocytogenes from the meat processing industry environment, as well as the use of different combinations of detergents, sanitizers, and UV-A radiation in the control of this microorganism in the planktonic and sessile forms. Four L. monocytogenes isolates were evaluated and showed moderate ability to form biofilm, as well as carried genes related to biofilm production (agrB, agrD, prfA, actA, cheA, cheY, flaA, sigB), and genes related to tolerance to sanitizers (lde and qacH). The biofilm-forming isolates of L. monocytogenes were susceptible to quaternary ammonium compound (QAC) and peracetic acid (PA) in planktonic form, with minimum inhibitory concentrations of 125 and 75 ppm, respectively, for contact times of 10 and 5 min. These concentrations are lower than those recommended by the manufacturers, which are at least 200 and 300 ppm for QAC and PA, respectively. Biofilms of L. monocytogenes formed from a pool of isolates on stainless steel and polyurethane coupons were subjected to 14 treatments involving acid and enzymatic detergents, QAC and PA sanitizers, and UV-A radiation at varying concentrations and contact times. All treatments reduced L. monocytogenes counts in the biofilm, indicating that the tested detergents, sanitizers, and UV-A radiation exhibited antimicrobial activity against biofilms on both surface types. Notably, the biofilm formed on polyurethane showed greater tolerance to the evaluated compounds than the biofilm on stainless steel, likely due to the material's surface facilitating faster microbial colonization and the development of a more complex structure, as observed by scanning electron microscopy. Listeria monocytogenes isolates from the meat processing industry carry genes associated with biofilm production and can form biofilms on both stainless steel and polyurethane surfaces, which may contribute to their persistence within meat processing lines. Despite carrying sanitizer tolerance genes, QAC and PA effectively controlled these microorganisms in their planktonic form. However, combinations of detergent (AC and ENZ) with sanitizers (QAC and PA) at minimum concentrations of 125 ppm and 300 ppm, respectively, were the most effective.

Mechanism of antibacterial resistance, strategies and next-generation antimicrobials to contain antimicrobial resistance: a review

Antibacterial drug resistance poses a significant challenge to modern healthcare systems, threatening our ability to effectively treat bacterial infections. This review aims to provide a comprehensive overview of the types and mechanisms of antibacterial drug resistance. To achieve this aim, a thorough literature search was conducted to identify key studies and reviews on antibacterial resistance mechanisms, strategies and next-generation antimicrobials to contain antimicrobial resistance. In this review, types of resistance and major mechanisms of antibacterial resistance with examples including target site modifications, decreased influx, increased efflux pumps, and enzymatic inactivation of antibacterials has been discussed. Moreover, biofilm formation, and horizontal gene transfer methods has also been included. Furthermore, measures (interventions) taken to control antimicrobial resistance and next-generation antimicrobials have been discussed in detail. Overall, this review provides valuable insights into the diverse mechanisms employed by bacteria to resist the effects of antibacterial drugs, with the aim of informing future research and guiding antimicrobial stewardship efforts.

Life on a leaf: the epiphyte to pathogen continuum and interplay in the phyllosphere

Epiphytic microbes are those that live for some or all of their life cycle on the surface of plant leaves. Leaf surfaces are a topologically complex, physicochemically heterogeneous habitat that is home to extensive, mixed communities of resident and transient inhabitants from all three domains of life. In this review, we discuss the origins of leaf surface microbes and how different biotic and abiotic factors shape their communities. We discuss the leaf surface as a habitat and microbial adaptations which allow some species to thrive there, with particular emphasis on microbes that occupy the continuum between epiphytic specialists and phytopathogens, groups which have considerable overlap in terms of adapting to the leaf surface and between which a single virulence determinant can move a microbial strain. Finally, we discuss the recent findings that the wheat pathogenic fungus Zymoseptoria tritici spends a considerable amount of time on the leaf surface, and ask what insights other epiphytic organisms might provide into this pathogen, as well as how Z. tritici might serve as a model system for investigating plant-microbe-microbe interactions on the leaf surface.

Emerging trends and future challenges of advanced 2D nanomaterials for combating bacterial resistance

The number of multi-drug-resistant bacteria has increased over the last few decades, which has caused a detrimental impact on public health worldwide. In resolving antibiotic resistance development among different bacterial communities, new antimicrobial agents and nanoparticle-based strategies need to be designed foreseeing the slow discovery of new functioning antibiotics. Advanced research studies have revealed the significant disinfection potential of two-dimensional nanomaterials (2D NMs) to be severed as effective antibacterial agents due to their unique physicochemical properties. This review covers the current research progress of 2D NMs-based antibacterial strategies based on an inclusive explanation of 2D NMs' impact as antibacterial agents, including a detailed introduction to each possible well-known antibacterial mechanism. The impact of the physicochemical properties of 2D NMs on their antibacterial activities has been deliberated while explaining the toxic effects of 2D NMs and discussing their biomedical significance, dysbiosis, and cellular nanotoxicity. Adding to the challenges, we also discussed the major issues regarding the current quality and availability of nanotoxicity data. However, smart advancements are required to fabricate biocompatible 2D antibacterial NMs and exploit their potential to combat bacterial resistance clinically.

Antibacterial and Antibiofilm Activity of Croton urticifolius Lam. Essential Oil Via Membrane Disruption

Antimicrobial resistance is a global health issue, in which microorganisms develop resistance to antimicrobial drugs, making infections more difficult to treat. This threatens the effectiveness of standard medical treatments and necessitates the urgent development of new strategies to combat resistant microbes. Studies have increasingly explored natural sources of new antimicrobial agents that harness the rich diversity of compounds found in plant species. This pursuit holds promise for the discovery of novel treatments for combating antimicrobial resistance. In this context, the chemical composition, antibacterial, and antibiofilm activities of the essential oil from Croton urticifolius Lam. leaves (CuEO) were evaluated. CuEO was extracted via hydrodistillation, and its chemical constituents were identified via gas chromatography-mass spectrometry (GC/MS). The antibacterial activity of CuEO was evaluated in a 96-well plate via the microdilution method, and the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values were determined. The effect of CuEO on biofilm formation was assessed by quantifying the biomass using crystal violet staining and viable cell counting. In addition, alterations in the cellular morphology of biofilms treated with CuEO were examined using scanning electron microscopy (SEM) and laser confocal microscopy. GC/MS analysis identified 26 compounds, with elemicine (39.72%); eucalyptol (19.03%), E-caryophyllene (5.36%), and methyleugenol (4.12%) as the major compounds. In terms of antibacterial activity, CuEO showed bacteriostatic effects against Staphylococcus aureus ATCC 700698, S. aureus ATCC 25923, Staphylococcus epidermidis ATCC 12228, and Escherichia coli ATCC 11303, and bactericidal activity against S. aureus ATCC 700698. In addition, CuEO significantly inhibited bacterial biofilm formation. Microscopic analysis showed that CuEO damaged the bacterial membrane by leaching out the cytoplasmic content. Therefore, the results of this study show that the essential oil of C. urticifolius may be a promising natural alternative for preventing infections caused by bacterial biofilms. This study is the first to report the antibiofilm activity of C. urticifolius essential oil.

Modern Microbiological Methods to Detect Biofilm Formation in Orthopedy and Suggestions for Antibiotic Therapy, with Particular Emphasis on Prosthetic Joint Infection (PJI)

Biofilm formation is a serious problem that relatively often causes complications in orthopedic surgery. Biofilm-forming pathogens invade implanted foreign bodies and surrounding tissues. Such a condition, if not limited at the appropriate time, often requires reoperation. This can be partially prevented by selecting an appropriate prosthesis material that prevents the development of biofilm. There are many modern techniques available to detect the formed biofilm. By applying them we can identify and visualize biofilm-forming microorganisms. The most common etiological factors associated with biofilms in orthopedics are: Staphylococcus aureus, coagulase-negative Staphylococci (CoNS), and Enterococcus spp., whereas Gram-negative bacilli and Candida spp. also deserve attention. It seems crucial, for therapeutic success, to eradicate the microorganisms able to form biofilm after the implantation of endoprostheses. Planning the effective targeted antimicrobial treatment of postoperative infections requires accurate identification of the microorganism responsible for the complications of the procedure. The modern microbiological testing techniques described in this article show the diagnostic options that can be followed to enable the implementation of effective treatment.

Effects of honokiol combined with resveratrol on bacteria responsible for oral malodor and their biofilm

Background

This study aimed to investigate the effect of honokiol combined with resveratrol on bacteria responsible for oral malodor and their biofilm.

Method

This study investigated drug's MIC, FICI and dynamic bactericidal susceptibility activities against Pg and Fn. The effects of drugs on biofilm metabolic activity, biofilm total amount, and biofilm microstructure were determined by CCK-8 experiment, semi-quantitative adhesion experiment and SEM, respectively. The effects of drugs on biofilm genes, extracellular polysaccharides, proteins and DNA content were determined by qRT-PCR, phenol-sulfuric acid method, BCA method and Nano Drop one C, respectively.

Results

The combination had synergistic antibacterial effect on Pg and Fn. 1/2×MIC and 1×MIC combination inhibit the whole process of Pg and Fn growth. The results showed that the combination effectively reduce biofilm metabolic activity and total amount, and destroy biofilm microstructure. The results showed that the combination downregulate the gene expression both Pg and Fn, reduce extracellular polysaccharides and DNA of Pg, and reduce extracellular proteins and DNA of Fn.

Conclusion

This study showed that the combination had a synergistic antibacterial effect on Pg and Fn, reduced the biofilm extracellular matrix, inhibited biofilm formation, and downregulated the expression of genes related to biofilm formation.

Antibiofilm Strategies in Neonatal and Pediatric Infections

Biofilm-related infections pose significant challenges in neonatal and pediatric care, contributing to increased morbidity and mortality rates. These complex microbial communities, comprising bacteria and fungi, exhibit resilience against antibiotics and host immune responses. Bacterial species such as Enterococcus faecalis, Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis commonly form biofilms on medical devices, exacerbating infection risks. Neonates and children, particularly those in intensive care units, are highly susceptible to biofilm-associated infections due to the prolonged use of invasive devices, such as central lines and endotracheal tubes. Enteral feeding tubes, crucial for neonatal nutritional support, also serve as potential sites for biofilm formation, contributing to recurrent microbial contamination. Moreover, Candida species, including Candida pelliculosa, present emerging challenges in neonatal care, with multi-drug resistant strains posing treatment complexities. Current antimicrobial therapies, while important in managing infections, often fall short in eradicating biofilms, necessitating alternative strategies. The aim of this review is to summarize current knowledge regarding antibiofilm strategies in neonates and in children. Novel approaches focusing on biofilm inhibition and dispersal show promise, including surface modifications, matrix-degrading enzymes, and quorum-sensing inhibitors. Prudent use of medical devices and exploration of innovative antibiofilm therapies are imperative in mitigating neonatal and pediatric biofilm infections.

The mechanism of biofilm detachment in porous medium under flow field

Biofilms are communities formed by bacteria adhering to surfaces, widely present in porous medium, and their growth can lead to clogging. Our experiment finds that under certain flow conditions, biofilms detach in pores and form a dynamically changing flow path. We define detachment that occurs far from the boundary of the flow path (with a distance greater than 200 μm) as internal detachment and detachment that occurs at the boundary of the flow path as external detachment. To understand the mechanism of biofilm detachment, we study the detachment behaviors of the Bacillus subtilis biofilm in a porous medium in a microfluidic device, where Bacillus subtilis strain is triple fluorescent labeled, which can represent three main phenotypes during the biofilm formation: motile cells, matrix-producing cells, and spores. We find that slow small-scale internal detachment occurs in regions with very few motile cells and matrix-producing cells, and bacterial movement in these areas is disordered. The increase in the number of matrix-producing cells induces clogging, and after clogging, the rapid detachment of the bulk internal biofilm occurs due to the increased pressure difference at the inlet and outlet. When both internal and external detachments occur simultaneously, the number of matrix-producing cells in the internal detachment area is 2.5 times that in the external detachment area. The results indicate that biofilm detachment occurs in areas with fewer matrix-producing cells, as matrix-producing cells can help resist detachment by secreting extracellular polymeric substances (EPSs).

Persisting cancer cells are different from bacterial persisters

The persistence of drug-sensitive tumors poses a significant challenge in cancer treatment. The concept of bacterial persisters, which are a subpopulation of bacteria that survive lethal antibiotic doses, is frequently used to compare to residual disease in cancer. Here, we explore drug tolerance of cancer cells and bacteria. We highlight the fact that bacteria, in contrast to cancer cells, have been selected for survival at the population level and may therefore possess contingency mechanisms that cancer cells lack. The precise mechanisms of drug-tolerant cancer cells and bacterial persisters are still being investigated. Undoubtedly, by understanding common features as well as differences, we, in the cancer field, can learn from microbiology to find strategies to eradicate persisting cancer cells.

Contemporary strategies and approaches for characterizing composition and enhancing biofilm penetration targeting bacterial extracellular polymeric substances

Extracellular polymeric substances (EPS) constitutes crucial elements within bacterial biofilms, facilitating accelerated antimicrobial resistance and conferring defense against the host's immune cells. Developing precise and effective antibiofilm approaches and strategies, tailored to the specific characteristics of EPS composition, can offer valuable insights for the creation of novel antimicrobial drugs. This, in turn, holds the potential to mitigate the alarming issue of bacterial drug resistance. Current analysis of EPS compositions relies heavily on colorimetric approaches with a significant bias, which is likely due to the selection of a standard compound and the cross-interference of various EPS compounds. Considering the pivotal role of EPS in biofilm functionality, it is imperative for EPS research to delve deeper into the analysis of intricate compositions, moving beyond the current focus on polymeric materials. This necessitates a shift from heavy reliance on colorimetric analytic methods to more comprehensive and nuanced analytical approaches. In this study, we have provided a comprehensive summary of existing analytical methods utilized in the characterization of EPS compositions. Additionally, novel strategies aimed at targeting EPS to enhance biofilm penetration were explored, with a specific focus on highlighting the limitations associated with colorimetric methods. Furthermore, we have outlined the challenges faced in identifying additional components of EPS and propose a prospective research plan to address these challenges. This review has the potential to guide future researchers in the search for novel compounds capable of suppressing EPS, thereby inhibiting biofilm formation. This insight opens up a new avenue for exploration within this research domain.

Research progress on the pharmacological mechanism, in vivo metabolism and structural modification of Erianin

Erianin is an important bibenzyl compound in dendrobium and has a wide spectrum of pharmacological properties. Since Erianin was discovered, abundant results have been achieved in the in vitro synthesis, structural modification, and pharmacological mechanism research. Researchers have developed a series of simple and efficient in vitro synthesis methods to improve the shortcomings of poor water solubility by replacing the chemical structure or coating it in nanomaterials. Erianin has a broad anti-tumor spectrum and significant anti-tumor effects. In addition, Erianin also has pharmacological actions like immune regulation, anti-inflammatory, and anti-angiogenesis. A comprehensive understanding of the synthesis, metabolism, structural modification, and pharmacological action pathways of Erianin is of great value for the utilization of Erianin. Therefore, this review conducts a relatively systematic look back at Erianin from the above four aspects, to give a reference for the evolvement and further appliance of Erianin.

Role of small molecules and nanoparticles in effective inhibition of microbial biofilms: A ray of hope in combating microbial resistance

Microbial biofilms pose a severe threat to global health, as they are associated with deadly chronic infections and antibiotic resistance. To date, very few drugs are in clinical practice that specifically target microbial biofilms. Therefore, there is an urgent need for the development of novel therapeutic options targeting biofilm-related infections. In this review, we discuss nearly seventy-five different molecular scaffolds published over the last decade (2010-2023) which have exhibited their biofilm inhibition potential. For convenience, we have classified these into five different sub-groups based on their origin and design (excluding peptides as they are placed in between small molecules and biologics), namely, heterocycles; inorganic small molecules & metal complexes; small molecules decorated nanoparticles; small molecules derived from natural products (both plant and marine sources); and small molecules designed by in-silico approach. These antibiofilm agents are capable of disrupting microbial biofilms and can offer a promising avenue for future developments in human medicine. A hitherto review of this kind will lay a platform for the researchers to find new molecular entities to curb the serious menace of antimicrobial resistance especially caused by biofilms.

Quenching and quorum sensing in bacterial bio-films

Quorum sensing (QS) is the ability of bacteria to monitor their population density and adjust gene expression accordingly. QS-regulated processes include host-microbe interactions, horizontal gene transfer, and multicellular behaviours (such as the growth and development of biofilm). The creation, transfer, and perception of bacterial chemicals known as autoinducers or QS signals are necessary for QS signalling (e.g. N-acylhomoserine lactones). Quorum quenching (QQ), another name for the disruption of QS signalling, comprises a wide range of events and mechanisms that are described and analysed in this study. In order to better comprehend the targets of the QQ phenomena that organisms have naturally developed and are currently being actively researched from practical perspectives, we first surveyed the diversity of QS-signals and QS-associated responses. Next, the mechanisms, molecular players, and targets related to QS interference are discussed, with a focus on natural QQ enzymes and compounds that function as QS inhibitors. To illustrate the processes and biological functions of QS inhibition in microbe-microbe and host-microbe interactions, a few QQ paradigms are described in detail. Finally, certain QQ techniques are offered as potential instruments in a variety of industries, including agriculture, medical, aquaculture, crop production, and anti-biofouling areas.

Multi-targeting oligopyridiniums: Rational design for biofilm dispersion and bacterial persister eradication

The development of effective antibacterial drugs to combat bacterial infections, particularly the biofilm-related infections, remains a challenge. There are two important features of bacterial biofilms, which are well-known critical factors causing biofilms hard-to-treat in clinical, including the dense and impermeable extracellular polymeric substances (EPS) and the metabolically repressed dormant and persistent bacterial population embedded. These characteristics largely increase the difficulty for regular antibiotic treatment due to insufficient penetration into EPS. In addition, the dormant bacteria are insensitive to the growth-inhibiting mechanism of traditional antibiotics. Herein, we explore the potential of a series of new oligopyridinium-based oligomers bearing a multi-biomacromolecule targeting function as the potent bacterial biofilm eradication agent. These oligomers were rationally designed to be "charge-on-backbone" that can offer a special alternating amphiphilicity. This novel and unique feature endows high affinity to bacterial membrane lipids, DNAs as well as proteins. Such a broad multi-targeting nature of molecules not only enables its penetration into EPS, but also plays vital roles in the bactericidal mechanism of action that is highly effective against dormant and persistent bacteria. Our in vitro, ex vivo, and in vivo studies demonstrated that OPc3, one of the most effective derivatives, was able to offer excellent antibacterial potency against a variety of bacteria and effectively eliminate biofilms in zebrafish models and mouse wound biofilm infection models.

Regulating bacterial biofilms in food and biomedicine: unraveling mechanisms and Innovating strategies

Bacterial biofilm has brought a lot of intractable problems in food and biomedicine areas. Conventional biofilm control mainly focuses on inactivation and removal of biofilm. However, with robust construction and enhanced resistance, the established biofilm is extremely difficult to eradicate. According to the mechanism of biofilm development, biofilm formation can be modulated by intervening in the key factors and regulatory systems. Therefore, regulation of biofilm formation has been proposed as an alternative way for effective biofilm control. This review aims to provide insights into the regulation of biofilm formation in food and biomedicine. The underlying mechanisms for early-stage biofilm establishment are summarized based on the key factors and correlated regulatory networks. Recent developments and applications of novel regulatory strategies such as anti/pro-biofilm agents, nanomaterials, functionalized surface materials and physical strategies are also discussed. The current review indicates that these innovative methods have contributed to effective biofilm control in a smart, safe and eco-friendly way. However, standard methodology for regulating biofilm formation in practical use is still missing. As biofilm formation in real-world systems could be far more complicated, further studies and interdisciplinary collaboration are still needed for simulation and experiments in the industry and other open systems.

Combating antimicrobial resistance: the silent war

Once hailed as miraculous solutions, antibiotics no longer hold that status. The excessive use of antibiotics across human healthcare, agriculture, and animal husbandry has given rise to a broad array of multidrug-resistant (MDR) pathogens, posing formidable treatment challenges. Antimicrobial resistance (AMR) has evolved into a pressing global health crisis, linked to elevated mortality rates in the modern medical era. Additionally, the absence of effective antibiotics introduces substantial risks to medical and surgical procedures. The dwindling interest of pharmaceutical industries in developing new antibiotics against MDR pathogens has aggravated the scarcity issue, resulting in an exceedingly limited pipeline of new antibiotics. Given these circumstances, the imperative to devise novel strategies to combat perilous MDR pathogens has become paramount. Contemporary research has unveiled several promising avenues for addressing this challenge. The article provides a comprehensive overview of these innovative therapeutic approaches, highlighting their mechanisms of action, benefits, and drawbacks.

Tackling strong biofilm and multi-virulent vancomycin-resistant Staphylococcus aureus via natural alkaloid-based porous nanoparticles: perspective towards near future eradication

Introduction

As a growing direction, nano-based therapy has become a successful paradigm used to address the phytogenic delivery-related problems in overcoming multivirulent vancomycin-resistant Staphylococcus aureus (VRSA) infection.

Methods

Hence, our aim was to develop and assess a novel nanocarrier system (mesoporous silica nanoparticles, MPS-NPs) for free berberine (Free-BR) as an antimicrobial alkaloid against strong biofilm-producing and multi-virulent VRSA strains using in vitro and in vivo mouse model.

Results and discussion

Our outcomes demonstrated vancomycin resistance in 13.7% of Staphylococcus aureus (S. aureus) strains categorized as VRSA. Notably, strong biofilm formation was observed in 69.2% of VRSA strains that were all positive for icaA gene. All strong biofilm-producing VRSA strains harbored a minimum of two virulence genes comprising clfA and icaA with 44.4% of them possessing all five virulence genes (icaA, tst, clfA, hla, and pvl), and 88.9% being multi-virulent. The study findings affirmed excellent in vitro antimicrobial and antibiofilm properties of BR-loaded MPS-NPs. Real-time quantitative reverse transcription PCR (qRT-PCR) assay displayed the downregulating role of BR-loaded MPS-NPs on strong biofilm-producing and multi-virulent VRSA strains virulence and agr genes in both in vitro and in vivo mice models. Additionally, BR-loaded MPS-NPs supplementation has a promising role in attenuating the upregulated expression of pro-inflammatory cytokines' genes in VRSA-infected mice with attenuation in pro-apoptotic genes expression resulting in reduced VRSA-induced apoptosis. In essence, the current study recommends the future scope of using BR-loaded MPS-NPs as auspicious alternatives for antimicrobials with tremendous antimicrobial, antibiofilm, anti-quorum sensing (QS), and anti-virulence effectiveness against problematic strong biofilm-producing and multi-virulent VRSA-associated infections.

Strategies to Overcome Antimicrobial Resistance in Nosocomial Infections, A Review and Update

Nosocomial infections, also known as healthcare-associated infections, are a significant global concern due to their strong association with high mortality and morbidity in both developed and developing countries. These infections are caused by a variety of pathogens, particularly the ESKAPE group of bacteria, which includes the six pathogens Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. These bacteria have demonstrated noteworthy resistance to different antibiotics. Antimicrobial resistance mechanisms can manifest in various forms, including restricting drug uptake, modifying drug targets, inactivating drugs, active drug efflux, and biofilm formation. Accordingly, various strategies have been developed to combat antibiotic-resistant bacteria. These strategies encompass the development of new antibiotics, the utilization of bacteriophages that specifically target these bacteria, antimicrobial combination therapy and the use of peptides or enzymes that target the genomes or essential proteins of resistant bacteria. Among promising approaches to overcome antibiotic resistance, the CRISPR/Cas system stands out and offers many advantages. This system enables precise and efficient editing of genetic material at specific locations in the genome. Functioning as a bacterial "adaptive immune system," the CRISPR/Cas system recognizes, degrades, and remembers foreign DNA sequences through the use of spacer DNA segments that are transcribed into CRISPR RNAs (crRNA). This paper has focused on nosocomial infections, specifically the pathogens involved in hospital infections, the mechanisms underlying bacterial resistance, and the strategies currently employed to address this issue. Special emphasis has been placed on the application of CRISPR/Cas technology for overcoming antimicrobial resistance.

Biofilm antimicrobial susceptibility testing: where are we and where could we be going?

Our knowledge about the fundamental aspects of biofilm biology, including the mechanisms behind the reduced antimicrobial susceptibility of biofilms, has increased drastically over the last decades. However, this knowledge has so far not been translated into major changes in clinical practice. While the biofilm concept is increasingly on the radar of clinical microbiologists, physicians, and healthcare professionals in general, the standardized tools to study biofilms in the clinical microbiology laboratory are still lacking; one area in which this is particularly obvious is that of antimicrobial susceptibility testing (AST). It is generally accepted that the biofilm lifestyle has a tremendous impact on antibiotic susceptibility, yet AST is typically still carried out with planktonic cells. On top of that, the microenvironment at the site of infection is an important driver for microbial physiology and hence susceptibility; but this is poorly reflected in current AST methods. The goal of this review is to provide an overview of the state of the art concerning biofilm AST and highlight the knowledge gaps in this area. Subsequently, potential ways to improve biofilm-based AST will be discussed. Finally, bottlenecks currently preventing the use of biofilm AST in clinical practice, as well as the steps needed to get past these bottlenecks, will be discussed.

Association between the Presence of Resistance Genes and Sanitiser Resistance of Listeria monocytogenes Isolates Recovered from Different Food-Processing Facilities

Sanitisers are widely used in cleaning food-processing facilities, but their continued use may cause an increased resistance of pathogenic bacteria. Several genes have been attributed to the increased sanitiser resistance ability of L. monocytogenes. This study determined the presence of sanitiser resistance genes in Irish-sourced L. monocytogenes isolates and explored the association with phenotypic sanitiser resistance. The presence of three genes associated with sanitiser resistance and a three-gene cassette (mdrL, qacH, emrE, bcrABC) were determined in 150 L. monocytogenes isolates collected from Irish food-processing facilities. A total of 23 isolates contained bcrABC, 42 isolates contained qacH, one isolate contained emrE, and all isolates contained mdrL. Additionally, 47 isolates were selected and grouped according to the number and type of resistance genes, and the minimal inhibitory concentration (MIC) of these isolates for benzalkonium chloride (BAC) was determined experimentally using the broth microdilution method. The BAC resistance of the strain carrying the bcrABC gene cassette was significantly higher than that of strains lacking the gene cassette, and the BAC resistance of the strain carrying the qacH gene was significantly higher than that of strains lacking the qacH gene (p < 0.05). Isolates harbouring both the qacH and bcrABC genes did not show higher BAC resistance. With respect to environmental factors, there was no significant difference in MIC values for isolates recovered from different processing facilities. In summary, this investigation highlights the prevalence of specific sanitiser resistance genes in L. monocytogenes isolates from Irish food-processing settings. While certain genes correlated with increased resistance to benzalkonium chloride, the combination of multiple genes did not necessarily amplify this resistance.

Antibiotic persistence and its impact on the environment

From boon molecules to molecules contributing to rising concern has been the sojourn of antibiotics. The problem of antibiotic contamination has gotten worse due to antibiotics' pervasive use in every aspect of the environment. One such consequence of pollution is the increase in infections with antibiotic resistance. All known antimicrobials being used for human benefit lead to their repetitive and routine release into the environment. The misuse of antibiotics has aggravated the situation to a level that we are short of antibiotics to treat infections as organisms have developed resistance against them. Overconsumption is not just limited to human health care, but also occurs in other areas such as aquaculture, livestock, and veterinary applications for the purpose of improving feed and meat products. Due to their harmful effects on non-target species, the trace level of antibiotics in the aquatic ecosystem presents a significant problem. Since the introduction of antibiotics into the environment is more than their removal, they have been given the status of persistent pollutants. The buildup of antibiotics in the environment threatens aquatic life and may lead to bacterial strains developing resistance. As newer organisms are becoming resistant, there exists a shortage of antibiotics to treat infections. This has presented a very critical problem for the health-care community. Another rising concern is that the development of newer drug molecules as antibiotics is minimal. This review article critically explains the cause and nature of the pollution and the effects of this emerging trend. Also, in the latter sections, why we need newer antibiotics is questioned and discussed.

Adding Flying Wings: Butterfly-Shaped NIR-II AIEgens with Multiple Molecular Rotors for Photothermal Combating of Bacterial Biofilms

The ever-increasing threats of multidrug-resistant bacteria and their biofilm-associated infections have bred a desperate demand for alternative remedies to combat them. Near-infrared (NIR)-absorbing photothermal agent (PTAs)-mediated photothermal therapy (PTT) is particularly attractive for biofilm ablation thanks to its superiorities of noninvasive intervention, satisfactory antibacterial efficiency, and less likelihood to develop resistance. Herein, three butterfly-shaped aggregation-induced emission luminogens (AIEgens) with balanced nonradiative decay (for conducting PTT) and radiative decay (for supplying fluorescence in the NIR-II optical window) are rationally designed for imaging-assisted photothermal obliteration of bacterial biofilms. After being encapsulated into cationic liposomes, AIEgens-fabricated nanoparticles can eradicate a wide spectrum of biofilms formed by Gram-positive bacteria (methicillin-resistant Staphylococcus aureus and Enterococcus faecalis) and Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) upon an 808 nm laser irradiation. In vivo experiments firmly demonstrate that the NIR-II AIE liposomes with excellent biocompatibility perform well in both the P. aeruginosa biofilm-induced keratitis mouse model and the MSRA biofilm-induced skin infection mouse model.

Interkingdom interactions between Pseudomonas aeruginosa and Candida albicans affect clinical outcomes and antimicrobial responses

Infections that involve interkingdom microbial communities, such as those between bacteria and yeast pathogens, are difficult to treat, associated with worse patient outcomes, and may be a source of antimicrobial resistance. In this review, we address co-occurrence and co-infections of Candida albicans and Pseudomonas aeruginosa, two pathogens that occupy multiple infection niches in the human body, especially in immunocompromised patients. The interaction between the pathogen species influences microbe-host interactions, the effectiveness of antimicrobials and even infection outcomes, and may thus require adapted treatment strategies. However, the molecular details of bacteria-fungal interactions both inside and outside the infection sites, are insufficiently characterised. We argue that comprehensively understanding the P. aeruginosa-C. albicans interaction network through integrated systems biology approaches will capture the highly dynamic and complex nature of these polymicrobial infections and lead to a more comprehensive understanding of clinical observations such as reshaped immune defences and low antimicrobial treatment efficacy.

Future scope of plant-derived bioactive compounds in the management of methicillin-resistant Staphylococcus aureus: In vitro antimicrobial and antivirulence prospects to combat MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) is a foremost human and animal pathogen with public health and veterinary significance causing hospital and community infections and contagious bovine mastitis. Due to its ability to develop multidrug resistance (MDR) and its pathogenicity, MRSA infection control is becoming a global concern. Natural antibacterial options are needed to combat MDR development and infectious dissemination. This study investigated the antimicrobial resistance and virulence genes profiling of MRSA isolates and explored the antivirulence efficacy of trans-cinnamaldehyde, thymol, and carvacrol essential oils (EOs) against multivirulent and MDR-MRSA isolates. Thirty six S. aureus isolates (25%) were retrieved, of which 34 (94.4%) were MRSA. A high prevalence of MDR (66.7%) was monitored and all 53 molecularly verified isolates possessed icaA and cna virulence genes. Moreover, 94.1% of these isolates were multivirulent with 23.5% of them carrying icaA, cna, eta, tst, and sea virulence genes. Our data proved superior in vitro antimicrobial and antivirulence activities of trans-cinnamaldehyde, thymol, and carvacrol. They inhibited the growth of multi-virulent and MDR-MRSA isolates and downregulated the transcription of examined virulence genes. Our study suggests using EOs as prospective antimicrobials with excellent antivirulence activities against MRSA isolates. We provided data regarding the eventual role of phytogenics in prevention and control of MRSA infection.

Recent Advances in Bacterial Persistence Mechanisms

The recurrence of bacterial infectious diseases is closely associated with bacterial persisters. This subpopulation of bacteria can escape antibiotic treatment by entering a metabolic status of low activity through various mechanisms, for example, biofilm, toxin-antitoxin modules, the stringent response, and the SOS response. Correspondingly, multiple new treatments are being developed. However, due to their spontaneous low abundance in populations and the lack of research on in vivo interactions between persisters and the host's immune system, microfluidics, high-throughput sequencing, and microscopy techniques are combined innovatively to explore the mechanisms of persister formation and maintenance at the single-cell level. Here, we outline the main mechanisms of persister formation, and describe the cutting-edge technology for further research. Despite the significant progress regarding study techniques, some challenges remain to be tackled.

3D-printed wound dressings containing a fosmidomycin-derivative prevent Acinetobacter baumannii biofilm formation

Acinetobacter baumannii causes a wide range of infections, including wound infections. Multidrug-resistant A. baumannii is a major healthcare concern and the development of novel treatments against these infections is needed. Fosmidomycin is a repurposed antimalarial drug targeting the non-mevalonate pathway, and several derivatives show activity toward A. baumannii. We evaluated the antimicrobial activity of CC366, a fosmidomycin prodrug, against a collection of A. baumannii strains, using various in vitro and in vivo models; emphasis was placed on the evaluation of its anti-biofilm activity. We also developed a 3D-printed wound dressing containing CC366, using melt electrowriting technology. Minimal inhibitory concentrations of CC366 ranged from 1 to 64 μg/mL, and CC366 showed good biofilm inhibitory and moderate biofilm eradicating activity in vitro. CC366 successfully eluted from a 3D-printed dressing, the dressings prevented the formation of A. baumannnii wound biofilms in vitro and reduced A. baumannii infection in an in vivo mouse model.

Glutamate-pantothenate pathway promotes antibiotic resistance of Edwardsiella tarda

Although cellular metabolic states have been shown to modulate bacterial susceptibility to antibiotics, the interaction between glutamate (Glu) and chloramphenicol (CAP) resistance remains unclear because of the specificity of antibiotics and bacteria. We found that the level of Glu was upregulated in the CAP-resistant strain of Edwardsiella tarda according to a comparative metabolomics approach based on LC-MS/MS. Furthermore, we verified that exogenous metabolites related to Glu, the tricarboxylic acid (TCA) cycle, and glutathione (GSH) metabolism could promote CAP resistance in survival assays. If GSH metabolism or the TCA cycle is inhibited by L-buthionine sulfoximine or propanedioic acid, the promotion of CAP resistance by Glu in the corresponding pathway disappears. According to metabolomic analysis, exogenous Glu could change pantothenate metabolism, affecting GSH biosynthesis and the TCA cycle. These results showed that the glutamate-pantothenate pathway could promote CAP resistance by being involved in the synthesis of GSH, entering the TCA cycle by direct deamination, or indirectly affecting the metabolism of the two pathways by pantothenate. These results extend our knowledge of the effect of Glu on antibiotic resistance and suggest that the potential effect, which may aggravate antibiotic resistance, should be considered before Glu and GSH administration in the clinic.

Pseudomonas aeruginosa increases the susceptibility of Candida albicans to amphotericin B in dual-species biofilms

BACKGROUND

Biofilms are the leading cause of nosocomial infections and are hard to eradicate due to their inherent antimicrobial resistance. Candida albicans is the leading cause of nosocomial fungal infections and is frequently co-isolated with the bacterium Pseudomonas aeruginosa from biofilms in the cystic fibrosis lung and severe burn wounds. The presence of C. albicans in multispecies biofilms is associated with enhanced antibacterial resistance, which is largely mediated through fungal extracellular carbohydrates sequestering the antibiotics. However, significantly less is known regarding the impact of polymicrobial biofilms on antifungal resistance.

RESULTS

Here we show that, in dual-species biofilms, P. aeruginosa enhances the susceptibility of C. albicans to amphotericin B, an effect that was biofilm specific. Transcriptional analysis combined with gene ontology enrichment analysis identified several C. albicans processes associated with oxidative stress to be differentially regulated in dual-species biofilms, suggesting that P. aeruginosa exerts oxidative stress on C. albicans, likely through the secretion of phenazines. However, the mitochondrial superoxide dismutase SOD2 was significantly down-regulated in the presence of P. aeruginosa. Monospecies biofilms of the sod2Δ mutant were more susceptible to amphotericin B, and the susceptibility of these biofilms was further enhanced by exogenous phenazines.

CONCLUSIONS

We propose that in dual-species biofilms, P. aeruginosa simultaneously induces mitochondrial oxidative stress, while down-regulating key detoxification enzymes, which prevents C. albicans mounting an appropriate oxidative stress response to amphotericin B, leading to fungal cell death. This work highlights the importance of understanding the impact of polymicrobial interactions on antimicrobial susceptibility.

What's in a name? Characteristics of clinical biofilms

In vitro biofilms are communities of microbes with unique features compared to individual cells. Biofilms are commonly characterized by physical traits like size, adhesion, and a matrix made of extracellular substances. They display distinct phenotypic features, such as metabolic activity and antibiotic tolerance. However, the relative importance of these traits depends on the environment and bacterial species. Various mechanisms enable biofilm-associated bacteria to withstand antibiotics, including physical barriers, physiological adaptations, and changes in gene expression. Gene expression profiles in biofilms differ from individual cells but, there is little consensus among studies and so far, a 'biofilm signature transcriptome' has not been recognized. Additionally, the spatial and temporal variability within biofilms varies greatly depending on the system or environment. Despite all these variable conditions, which produce very diverse structures, they are all noted as biofilms. We discuss that clinical biofilms may differ from those grown in laboratories and found in the environment and discuss whether the characteristics that are commonly used to define and characterize biofilms have been shown in infectious biofilms. We emphasize that there is a need for a comprehensive understanding of the specific traits that are used to define bacteria in infections as clinical biofilms.

Antibacterial Carbon Dots: Mechanisms, Design, and Applications

The increase in antibiotic resistance promotes the situation of developing new antibiotics at the forefront, while the development of non-antibiotic pharmaceuticals is equally significant. In the post-antibiotic era, nanomaterials with high antibacterial efficiency and no drug resistance make them attractive candidates for antibacterial materials. Carbon dots (CDs), as a kind of carbon-based zero-dimensional nanomaterial, are attracting much attention for their multifunctional properties. The abundant surface states, tunable photoexcited states, and excellent photo-electron transfer properties make sterilization of CDs feasible and are gradually emerging in the antibacterial field. This review provides comprehensive insights into the recent development of CDs in the antibacterial field. The topics include mechanisms, design, and optimization processes, and their potential practical applications are also highlighted, such as treatment of bacterial infections, against bacterial biofilms, antibacterial surfaces, food preservation, and bacteria imaging and detection. Meanwhile, the challenges and outlook of CDs in the antibacterial field are discussed and proposed.

Polyether Ionophore Antibiotics Target Drug-Resistant Clinical Isolates, Persister Cells, and Biofilms

Polyether ionophores are complex natural products known to transport various cations across biological membranes. While several members of this family are used in agriculture (e.g., as anti-coccidiostats) and have potent antibacterial activity, they are not currently being pursued as antibiotics for human use. Polyether ionophores are typically grouped as having similar functions, despite the fact that they significantly differ in structure; for this reason, how their structure and activity are related remains unclear. To determine whether certain members of the family constitute particularly interesting springboards for in-depth investigations and future synthetic optimization, we conducted a systematic comparative study of eight different polyether ionophores for their potential as antibiotics. This includes clinical isolates from bloodstream infections and studies of the compounds' effects on bacterial biofilms and persister cells. We uncover distinct differences within the compound class and identify the compounds lasalocid, calcimycin, and nanchangmycin as having particularly interesting activity profiles for further development. IMPORTANCE Polyether ionophores are complex natural products used in agriculture as anti-coccidiostats in poultry and as growth promoters in cattle, although their precise mechanism is not understood. They are widely regarded as antimicrobials against Gram-positive bacteria and protozoa, but fear of toxicity has so far prevented their use in humans. We show that ionophores generally have very different effects on Staphylococcus aureus, both in standard assays and in more complex systems such as bacterial biofilms and persister cell populations. This will allow us to focus on the most interesting compounds for future in-depth investigations and synthetic optimizations.

Toxicity of per- and polyfluoroalkyl substances to microorganisms in confined hydrogel structures

Per- and polyfluoroalkyl substances (PFAS) as a group of environmentally persistent synthetic chemicals has been widely used in industrial and consumer products. Bioaccumulation studies have documented the adverse effects of PFAS in various living organisms. Despite the large number of studies, experimental approaches to evaluate the toxicity of PFAS on bacteria in a biofilm-like niche as structured microbial communities are sparse. This study suggests a facile approach to query the toxicity of PFOS and PFOA on bacteria (Escherichia coli K12 MG1655 strain) in a biofilm-like niche provided by hydrogel-based core-shell beads. Our study shows that E. coli MG1655 upon complete confinement in hydrogel beads exhibit altered physiological characteristics of viability, biomass, and protein expression, compared to their susceptible counterpart cultivated under planktonic conditions. We find that soft-hydrogel engineering platforms may provide a protective role for microorganisms from environmental contaminants, depending on the size or thickness of the protective/barrier layer. We expect our study to provide insights on the toxicity of environmental contaminants on organisms under encapsulated conditions that could potentially be useful for toxicity screening and in evaluating ecological risk of soil, plant, and mammalian microbiome.

Nontypeable Haemophilus influenzae released from biofilm residence by monoclonal antibody directed against a biofilm matrix component display a vulnerable phenotype

Bacterial biofilms contribute significantly to pathogenesis, recurrence and/or chronicity of the majority of bacterial diseases due to their notable recalcitrance to clearance. Herein, we examined kinetics of the enhanced sensitivity of nontypeable Haemophilus influenzae (NTHI) newly released (NRel) from biofilm residence by a monoclonal antibody against a bacterial DNABII protein (α-DNABII) to preferential killing by a β-lactam antibiotic. This phenotype was detected within 5 min and lasted for ~ 6 h. Relative expression of genes selected due to their known involvement in sensitivity to a β-lactam showed transient up-regulated expression of penicillin binding proteins by α-DNABII NTHI NRel, whereas there was limited expression of the β-lactamase precursor. Transient down-regulated expression of mediators of oxidative stress supported similarly timed vulnerability to NADPH-oxidase sensitive intracellular killing by activated human PMNs. Further, transient up-regulated expression of the major NTHI porin aligned well with observed increased membrane permeability of α-DNABII NTHI NRel, a characteristic also shown by NRel of three additional pathogens. These data provide mechanistic insights as to the transient, yet highly vulnerable, α-DNABII NRel phenotype. This heightened understanding supports continued validation of this novel therapeutic approach designed to leverage knowledge of the α-DNABII NRel phenotype for more effective eradication of recalcitrant biofilm-related diseases.

Antibacterial Activity of Thesium chinense Turcz Extract Against Bacteria Associated with Upper Respiratory Tract Infections

Purpose

The drug resistance of Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes and Haemophilus influenzae has become more and more serious, and it is urgent to seek new antibacterial drugs. In this study, Thesium chinense Turcz. extracts were tested for its potential antibacterial activities.

Methods

T. chinense powder was extracted with 5 solvents of different polarity (ethyl alcohol, petroleum ether, ethyl acetate, n-butyl alcohol and double distilled water), and their antibacterial activities were tested. The Broth dilution method was used to evaluate the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of highly active plant extracts with a concentration of 1g/mL. The inhibitory activity of this extract on biofilm formation was investigated. Afterwards, we investigated its effect on the transcriptome of S. aureus.

Results

The ethanol extract coded as BRY, only inhibited S. aureus, whereas the ethyl acetate extract coded as BY2 showed inhibitory effect on all the tested bacteria. The MIC of BRY on S. aureus was 128 mg/mL, and the MBC was 512 mg/mL. The MIC of BY2 against S. aureus, S. pneumoniae, S. pyogenes and H. influenzae were 8 mg/mL, 4 mg/mL, 4 mg/mL, and 4 mg/mL, respectively. The MBC of BY2 for these four bacteria ranged from 4 to 256 mg/mL. Mechanism studies have shown that BRY and BY2 have an impact on anti-formation of biofilms at MIC concentrations. Transcriptome sequencing results showed that 531 genes were up-regulated and 340 genes showed down-regulated expression in S. aureus after BY2 treatment.

Conclusion

BY2 has a broader antibacterial spectrum than BRY. Meanwhile, the inhibitory effect of BY2 on S. aureus is better than BRY. The mechanism of BY2 against S. aureus may relate to its inhibition of ribosome synthesis, restriction of key enzymes of citric acid cycle, decrease of pathogenicity and influence on biofilm formation. The results confirmed that BY2 was the main antibacterial part of T. chinense, which can be used as a source of antibacterial agents.

Antibiofilm activity of LAE (ethyl lauroyl arginate) against food-borne fungi and its application in polystyrene surface coating

Several filamentous fungi species as Fusarium oxysporum or Cladosporium sp. can form biofilms by themselves or by participating in polymicrobial biofilms with bacteria. However, despite the high impact of biofilm on the food industry and the high efforts done to control biofilm produced by bacteria in the food area, there has been little study of strategies to control fungal biofilm in this area. In this study, the antibiofilm activity of the safe antimicrobial compound ethyl lauroyl arginate (LAE) was investigated against food spoilage fungi (Cladosporium cladosporioides, Aspergillus ochraceus, Penicillium italicum, Botrytis cynerea and Fusarium oxyspoum). Finally, the efficacy of a varnish-based coating incorporating LAE and coated onto polystyrene microtiter plates has been evaluated as a strategy to reduce fungal biofilm formation. The results of the 2,3-bis-(2-metoxi-4-nitro-5-sulfofenil)-2H-tetrazoilo-5-carboxanilida (XTT) assay, which measure the biofilm metabolic activity of moulds, demonstrated that LAE reduced significantly the formation of fungal biofilm at concentrations from 6 to 25 mg/L. This reduction was confirmed by the micrographs obtained by scanning electronic microscopy (SEM). In addition, LAE also showed antifungal activity against established biofilms. Particularly, it reduced their metabolic activity and viability at concentrations from 6 to 25 mg/L according to results obtained in the XTT assay and observations made by confocal laser scanning microscopy (CLSM). Finally, active coating incorporating from 2% of LAE proved to reduce significantly the biofilm formation in C. cladosporioides, B. cynerea and F. oxyspoum according to the results obtained in the XTT assay. However, the released studies indicated that the retention of LAE in the coating should be improved to prolong their activity.

Overcoming Drug Resistance in a Clinical C. albicans Strain Using Photoactivated Curcumin as an Adjuvant

The limited antifungal drugs available and the rise of multidrug-resistant Candida species have made the efforts to improve antifungal therapies paramount. To this end, our research focused on the effect of a combined treatment between chemical and photodynamic therapy (PDT) towards a fluconazole-resistant clinical Candida albicans strain. The co-treatment of PDT and curcumin in various doses with fluconazole (FLC) had an inhibitory effect on the growth of the FLC-resistant hospital strain of C. albicans in both difusimetric and broth microdilution methods. The proliferation of the cells was inhibited in the presence of curcumin at 3.125 µM and FLC at 41 µM concentrations. The possible involvement of oxidative stress was analyzed by adding menadione and glutathione as a prooxidant and antioxidant, respectively. In addition, we examined the photoactivated curcumin effect on efflux pumps, a mechanism often linked to drug resistance. Nile Red accumulation assays were used to evaluate efflux pumps activity through fluorescence microscopy and spectrofluorometry. The results showed that photoactivated curcumin at 3.125 µM inhibited the transport of the fluorescent substrate that cells usually expel, indicating its potential in combating drug resistance. Overall, the findings suggest that curcumin, particularly when combined with PDT, can effectively inhibit the growth of FLC-resistant C. albicans, addressing the challenge of yeast resistance to azole antifungals through upregulating multidrug transporters.

Antimicrobial Resistance: A Growing Serious Threat for Global Public Health

Antibiotics are among the most important discoveries of the 20th century, having saved millions of lives from infectious diseases. Microbes have developed acquired antimicrobial resistance (AMR) to many drugs due to high selection pressure from increasing use and misuse of antibiotics over the years. The transmission and acquisition of AMR occur primarily via a human-human interface both within and outside of healthcare facilities. A huge number of interdependent factors related to healthcare and agriculture govern the development of AMR through various drug-resistance mechanisms. The emergence and spread of AMR from the unrestricted use of antimicrobials in livestock feed has been a major contributing factor. The prevalence of antimicrobial-resistant bacteria has attained an incongruous level worldwide and threatens global public health as a silent pandemic, necessitating urgent intervention. Therapeutic options of infections caused by antimicrobial-resistant bacteria are limited, resulting in significant morbidity and mortality with high financial impact. The paucity in discovery and supply of new novel antimicrobials to treat life-threatening infections by resistant pathogens stands in sharp contrast to demand. Immediate interventions to contain AMR include surveillance and monitoring, minimizing over-the-counter antibiotics and antibiotics in food animals, access to quality and affordable medicines, vaccines and diagnostics, and enforcement of legislation. An orchestrated collaborative action within and between multiple national and international organizations is required urgently, otherwise, a postantibiotic era can be a more real possibility than an apocalyptic fantasy for the 21st century. This narrative review highlights on this basis, mechanisms and factors in microbial resistance, and key strategies to combat antimicrobial resistance.

Curcumin-stabilized silver nanoparticles encapsulated in biocompatible electrospun nanofibrous scaffold for sustained eradication of drug-resistant bacteria

Due to the misuse of antibiotics, the emerging drug-resistance of pathogenic microbes has aroused considerable concerns for the public health, which demands the continuous search for safe and efficient antimicrobial treatment. In this study, curcumin reduced and stabilized silver nanoparticles (C-Ag NPs) were successfully encapsulated into electrospun nanofiber membranes consisted of polyvinyl alcohol (PVA) cross-linked by citric acids (CA), which exhibited desirable biocompatibility and broad-spectrum antimicrobial activities. The homogeneously distributed and sustained release of C-Ag NPs in the constructed nanofibrous scaffolds yield prominent killing effect against Escherichia coli, Staphylococcus aureus and Methicillin-resistant Staphylococcus aureus (MRSA), which involved the reactive oxygen species (ROS) generation. Outstanding elimination of bacterial biofilms and excellent antifungal activity against Candida albicans was also identified after treated with PVA/CA/C-Ag. Transcriptomic analysis on MRSA treated by PVA/CA/C-Ag revealed the antibacterial process is related to disrupting carbohydrate and energy metabolism, as well as destroying bacterial membranes. Significant down-regulation of the expression of multidrug-resistant efflux pump gene sdrM was observed pointing to the role of PVA/CA/C-Ag to overcome the bacterial resistance. Therefore, the constructed ecofriendly and biocompatible nanofibrous scaffolds provide a robust and versatile nanoplatform of reversal potential to eradicate drug-resistant pathogenic microbe in environmental as well as healthcare applications.

New Strategies to Kill Metabolically-Dormant Cells Directly Bypassing the Need for Active Cellular Processes

Antibiotic therapy failure is often caused by the presence of persister cells, which are metabolically-dormant bacteria capable of surviving exposure to antimicrobials. Under favorable conditions, persisters can resume growth leading to recurrent infections. Moreover, several studies have indicated that persisters may promote the evolution of antimicrobial resistance and facilitate the selection of specific resistant mutants; therefore, in light of the increasing numbers of multidrug-resistant infections worldwide, developing efficient strategies against dormant cells is of paramount importance. In this review, we present and discuss the efficacy of various agents whose antimicrobial activity is independent of the metabolic status of the bacteria as they target cell envelope structures. Since the biofilm-environment is favorable for the formation of dormant subpopulations, anti-persister strategies should also include agents that destroy the biofilm matrix or inhibit biofilm development. This article reviews examples of selected cell wall hydrolases, polysaccharide depolymerases and antimicrobial peptides. Their combination with standard antibiotics seems to be the most promising approach in combating persistent infections.

Responses of Bacillus sp. under Cu(II) stress in relation to extracellular polymeric substances and functional gene expression level

The production and composition of extracellular polymeric substances (EPS), as well as the EPS-related functional resistance genes and metabolic levels of Bacillus sp. under Cu(II) stress, were investigated. EPS production increased by 2.73 ± 0.29 times compared to the control when the strain was treated with 30 mg L^-1 Cu(II). Specifically, the polysaccharide (PS) content in EPS increased by 2.26 ± 0.28 g CDW^-1 and the PN/PS (protein/polysaccharide) ratio value increased by 3.18 ± 0.33 times under 30 mg L^-1 Cu(II) compared to the control. The increased EPS secretion and higher PN/PS ratio in EPS strengthened the cells' ability to resist the toxic effect of Cu(II). Differential expression of functional genes under Cu(II) stress was revealed by Gene Ontology pathway enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis. The enriched genes were most obviously upregulated in the UMP biosynthesis pathway, the pyrimidine metabolism pathway, and the TCS metabolism pathway. This indicates an enhancement of EPS regulation-related metabolic levels and their role as a defense mechanism for cells to adapt to Cu(II) stress. Additionally, seven copper resistance genes were upregulated while three were downregulated. The upregulated genes were related to the heavy metal resistance, while downregulated genes were related to cell differentiation, indicating that the strain had initiated an obvious resistance to Cu(II) despite its severe cell toxicity. These results provided a basis for promoting EPS-regulated associated functional genes and the application of gene-regulated bacteria in heavy metal-containing wastewater treatment.

Perspectives on Usage of Functional Nanomaterials in Antimicrobial Therapy for Antibiotic-Resistant Bacterial Infections

The clinical applications of nanotechnology are emerging as widely popular, particularly as a potential treatment approach for infectious diseases. Diseases associated with multiple drug-resistant organisms (MDROs) are a global concern of morbidity and mortality. The prevalence of infections caused by antibiotic-resistant bacterial strains has increased the urgency associated with researching and developing novel bactericidal medicines or unorthodox methods capable of combating antimicrobial resistance. Nanomaterial-based treatments are promising for treating severe bacterial infections because they bypass antibiotic resistance mechanisms. Nanomaterial-based approaches, especially those that do not rely on small-molecule antimicrobials, display potential since they can bypass drug-resistant bacteria systems. Nanoparticles (NPs) are small enough to pass through the cell membranes of pathogenic bacteria and interfere with essential molecular pathways. They can also target biofilms and eliminate infections that have proven difficult to treat. In this review, we described the antibacterial mechanisms of NPs against bacteria and the parameters involved in targeting established antibiotic resistance and biofilms. Finally, yet importantly, we talked about NPs and the various ways they can be utilized, including as delivery methods, intrinsic antimicrobials, or a mixture.

Selective pressure of PFOA on microbial community: Enrichment of denitrifiers harboring ARGs and the transfer of ferric-electrons

Perfluorooctanoic acid (PFOA), a class of permanent organic pollutants, is frequently detected in surface and ground water, with the latter made up primarily of porous media (such as soils, sediments, and aquifers) that harbor microbial communities. Therefore, we investigated the effects of PFOA on water ecosystems and found that, under stimulation by 2.4 μM PFOA, denitrifiers were significantly enriched due to their hosting antibiotic resistant genes (ARGs), which were 1.45 times more abundant than the control. Furthermore, denitrifying metabolism was enhanced by Fe(II) electron donation. Specifically, 2.4 μM PFOA significantly enhanced the removal of total inorganic nitrogen by 178.6%. The microbial community became predominated by denitrifying bacteria (67.8% abundance). Notably, the nitrate-reduction ferrous-oxidizing (NRFO) bacteria Dechloromonas, Acidovorax, Bradyrhizorium, etc. were significantly enriched. The selective pressures of PFOA driving the enrichment of denitrifiers were twofold. First, the toxic PFOA induced denitrifying bacteria to produce ARGs, mainly including the efflux (occupying 55.4%) and antibiotic inactivation (occupying 41.2%) types, which improved microbial tolerance to PFOA. The risk of horizontal ARGs transmission was elevated as the overall number of horizontally transmissible ARGs increased by 47.1%. Second, Fe(II) electrons were transported via the porin-cytochrome c extracellular electrons transfer system (EET), promoting the expression of nitrate reductases, which in turn further enhanced denitrification. In summary, PFOA regulated the microbial community structure and influenced microbial TN removal functions and increased the contribution of ARGs by the denitrifier hosts, but the PFOA-induced production of ARGs may pose a serious ecological threat that needs to be comprehensively investigated.