Optimization of staining with SYTO 9/propidium iodide: interplay, kinetics and impact on Brevibacillus brevis

Fabrication of a ZnO/Polydopamine/ε-Polylysine Coating with Good Corrosion Resistance and a Joint Antibacterial Pathway on the Surface of Medical Stainless Steel

Medical stainless steel (SS) is a widely used alloy in orthopedic and dental implant applications. However, SS can cause local corrosion in the body, which may affect cell proliferation and differentiation, and is prone to related bacterial infection. Therefore, surface modification is required to improve the corrosion resistance and antibacterial performance of SS to extend its service life. To achieve this goal, a new type of composite coating was established on the surface of SS. First, zinc oxide (ZnO) nanoparticles were deposited on the surface of SS by electrochemical deposition. Then, polydopamine (PDA) was formed through the self-polymerization of dopamine. Finally, the Michael addition reaction between ε-polylysine (ε-PL) and PDA was used to chemically graft a cationic antimicrobial peptide (AMP), namely, ε-PL, constructing a corrosion-resistant and antibacterial ZnO/PDA/ε-PL coating on the surface of the SS (SZP/ε-PL). The results indicated that the obtained composite coating could significantly improve the corrosion resistance of SS because of the introduction of ZnO. After being irradiated with near-infrared (NIR) light (wavelength: 1064 nm, power: 1 W/cm2) for 8 min, the temperature of SZP/ε-PL increased from 22.4 to 57.8 °C. Moreover, there was no significant temperature decay after four cycles, which indicated the good photothermal performance and stability of SZP/ε-PL owing to the function of PDA. Combining photothermal sterilization and AMP contact sterilization, the antibacterial rates of SZP/ε-PL against Escherichia coli and Staphylococcus aureus both reached nearly 100%. In addition, SZP/ε-PL has excellent blood compatibility. With the above advantages, SZP/ε-PL was expected to become a safe and efficient implant material.

Investigating the effects of microwave plasma on bacterial cell structures, viability, and membrane integrity

Plasma-mediated bacterial inactivation holds great promise but presents several challenges. This study investigates the antibacterial effect of 2.45 GHz non-thermal microwave (MW) plasma on Staphylococcus aureus (S. aureus) and Salmonella abony (S. abony) suspended in phosphate-buffered saline (PBS). A 6-log reduction in both bacterial strains was achieved within 300 s of plasma exposure. The enhanced inactivation is attributed to elevated levels of reactive oxygen species (ROS), particularly ·OH (30.30% in S. aureus, 40.13% in S. abony) and H2O2 (173.27% in S. aureus, and 391.84% in S. abony), which caused oxidative stress and membrane depolarization, detected via fluorescence spectrofluorometry. Morphological changes were confirmed through field emission scanning electron microscopy (FE-SEM). Membrane impairment led to leakage of intracellular contents such as proteins, lipids, and nucleic acids. DNA damage was evident from hyperchromic effects observed at 260 nm. Confocal microscopy revealed a qualitative increase in red fluorescent (dead) cells with longer exposure. Flow cytometry further quantified the dead cells at 88% in S. aureus and 95% in S. abony. These findings provide comprehensive insight into the bacterial inactivation mechanism and demonstrate the strong potential of non-thermal MW plasma for applications in sterilization, infection control, and food safety.

A Self-Circulated Microenvironment-Adaptive Nanozyme for Wound Healing Acceleration

Nanozyme-mediated reactive oxygen species (ROS) homeostasis regulation in vivo is a promising strategy for accelerating the healing of pathogen-infected wounds. It is detrimental in nanozyme preparation to strike a balance between ROS production and scavenging, being adaptive to the wound microenvironment, especially to overcome the irreversible and inevitable inactivation caused by the enzymatic active center loss. Herein, with adjusting ligands and metal charge transfer, we prepared a nanozyme with a regenerated Fe(II) active center, which endowed cyclic and continuous oxidoreductase reactions of peroxidase, superoxide dismutase, catalase, and oxidase under the same neutral pH environment. The versatile enzymatic activity could be easily triggered with oxygen/ROS and cascaded into controllable and reversible ROS generation and scavenging, as well as oxygen release for acceleration of sterilization during infected wound recovery. Under ultralow dosage of Fe-DHB, remarkable effectiveness against 1.0 × 106 drug-resistant bacteria and a wound-healing rate of around 6.3 mm2 per day were realized. Our work presents a key breakthrough in nanozyme-based wound healing strategy design.

Metabolic characterization of alkane monooxygenases and the growth phenotypes of Pseudomonas aeruginosa ATCC 33988 on hydrocarbons

There is a demand and widespread interest in evaluating microbial community structures and metabolic processes in hydrocarbon environments. The current work aims to detect microbial subgroups (phenotypic subsets) and their metabolic processes, such as substrate specificity and expression of niche-associated genes. In this study, we were able to discriminate different cell types in real time from a complex sample matrix to allow the detection of live, dead, and injured cell populations in jet fuels. We found that the expression of alkB1 and alkB2 genes is induced in a growth-dependent manner and alkB2 induction started before alkB1. This indicates that as an early response of Pseudomonas aeruginosa cells' exposure to alkanes, cells activate alkB2 gene induction. Deletion of alkB1 and alkB2 genes completely inhibited P. aeruginosa ATCC 33988 growth in jet fuel, suggesting that two alkane monooxygenases are responsible for the degradation of alkanes and jet fuel. Interestingly, the AlkB2 has a broader (n-C8-n-C16) substrate range compared to AlkB1 (n-C12-n-C16). The data indicate that two alkane utilization pathways can coexist in P. aeruginosa ATCC 33988, and they are differentially expressed in response to n-C6-n-C16 alkanes found in jet fuel. This study provided additional information on the heterogeneity and phenotypic diversity within the same species after exposure to hydrocarbons. This work advances our understanding of microbial community structures and provides new insight into the alkane metabolism of P. aeruginosa.IMPORTANCEAlkane degradation allows for the natural breakdown of hydrocarbons found in crude oil, which can significantly contribute to environmental remediation. The metabolic process of microbes to hydrocarbons and the expression of niche-associated genes are not well understood. Pseudomonas aeruginosa ATCC 33988, originally isolated from a jet fuel tank, degrades hydrocarbons effectively and outcompetes the type strain Pseudomonas aeruginosa PAO1. In this study, we found differential expression of alkB1 and alkB2 alkane monooxygenase genes and the relative importance of these genes in alkane degradation. We found different phenotypic subsets within the same genotype, which are influenced by hydrocarbon stress. Overall, the research conducted in this study significantly contributes to our knowledge about microbial processes and community structure in hydrocarbon environments.

Microfluidic chip systems for color-based antimicrobial susceptibility test a review

Clinical bacteria pose a significant public health threat, underscoring the need for reliable and rapid diagnostic methods for early disease detection, which can facilitate patient recovery. Current diagnostic methods for rapid pathogen detection often take hours to days and require numerous reagents and lengthy protocols. Microfluidic chip system offers a promising solution for clinical microbiology detection by reducing detection time with minimal setup and providing a point-of-care solution for patients. These systems are also easier to handle and, with advancements in technology, offer more conclusive observations. This review focuses on recent developments in microfluidic chip-based systems that use colored fluorescent and non-fluorescent dyes for phenotypic tests in clinical pathogen detection. Recent advancements in non-conventional observation methods, such as smartphones and software combined with microscopy, are paving the way for microfluidic systems to revolutionize point-of-care devices. Significant challenges for these systems include antimicrobial susceptibility testing protocols, which depend on color formation, observation methods, and reducing detection time. In the future, working with live cultures remains a major hurdle in developing efficient and accurate microfluidic diagnostic systems for antimicrobial susceptibility testing.

Dual-Functional Antimicrobial and Low-Fouling Cellulose Coatings

Surfaces contaminated with pathogens raise significant concerns due to their potential role in increasing the risk of disease transmission and subsequent infection. Existing surface coatings face several challenges that undermine their effectiveness and their broader applicability. These include the impact of surface topography on pathogen adhesion, which leads to biofouling, high production costs, scalability issues, as well as environmental concerns stemming from the utilization of toxic antifoulants and biocides. Here, we report dual-functional surface coatings with intrinsic antimicrobial and low fouling properties that are synergistic. The coatings are a porous reactive cellulose fibers network with dialdehyde functionality that demonstrates high antibacterial and antiviral performance against Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, Escherichia coli, and influenza A/H1N1 virus. Furthermore, we showed that the wettability of the coating significantly reduces the adhesion and colony formation of bacteria and their dead debris after inactivation by dialdehyde groups. The reactive cellulose fibers did not demonstrate any acute toxicity on L929 cells, which can meet the safe use of coating on the contact surfaces. The cellulose fibers coating derived from agricultural waste is cost-effective, eco-friendly, and highly scalable and is promising for use in packaging, household products, public facilities, and medical settings surfaces.

NIR-activated catechol-functionalized nanodiamond nanofibers for accelerating on-demand MRSA and E. coli biofilm eradication

The rise of antibiotic resistance has made bacterial infections a persistent global health issue. In particular, extracellular polymeric substances (EPS) secreted by bacteria limit the effectiveness of conventional antibiotics, making biofilm removal challenging. To address this, we created ND@PDA nanoparticles by coating the surface of nanodiamonds (ND) with polydopamine (PDA). These nanoparticles were then integrated into polyvinyl alcohol to fabricate PVA/ND@PDA nanofiber scaffolds, resulting in an innovative platform with enhanced photothermal, antibacterial and antibiofilm properties. Upon exposure to near-infrared (NIR) light, the scaffolds exhibited a significant photothermal activity, oxidative stress and effectively damaging key bacterial components, such as biofilm, bacterial membranes, and proteins. Additionally, the catechol groups in PDA provided strong cell adhesion and high biocompatibility on the nanofiber surface. Our research proposes a platform that not only effectively addresses antibiotic-resistant infections but also contributes to advancements in wound healing therapies by enabling controlled antibacterial action with minimal toxicity.

Discovery of membrane-targeting amphiphilic honokiol derivatives containing an oxazolethione moiety to combat methicillin-resistant Staphylococcus aureus (MRSA) infections

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a major pathogen causing infections in hospitals and the community, and there is an urgent need for the development of novel antibacterials to combat MRSA infections. Herein, a series of amphiphilic honokiol derivatives containing an oxazolethione moiety were prepared and evaluated for their in vitro antibacterial and hemolytic activities. The screened optimal derivative, I3, exhibited potent in vitro antibacterial activity against S. aureus and clinical MRSA isolates with MIC values of 2-4 μg/mL, which was superior to vancomycin in terms of its rapid bactericidal properties and was less susceptible to the development of resistance. The SARs analysis indicated that amphiphilic honokiol derivatives with fluorine substituents had better antibacterial activity than those with chlorine and bromine substituents. In vitro and in vivo toxicity studies revealed that I3 has relatively low toxicity. In a MRSA-infected mouse skin abscess model, I3 (5 mg/kg) effectively killed MRSA at the infected site and attenuated the inflammation effects, comparable to vancomycin. In a MRSA-infected mouse sepsis model, I3 (12 mg/kg) was found to significantly reduce the bacterial load in infected mice and increase survival of infected mice. Mechanistic studies indicated that I3 has membrane targeting properties and can interact with phosphatidylglycerol (PG) and cardiolipin (CL) of MRSA cell membranes, thereby disrupting MRSA cell membranes, further inducing the increase of reactive oxygen species (ROS), protein and DNA leakage to achieve rapid bactericidal effects. Finally, we hope that I3 is a potential candidate molecule for the development of antibiotics to conquer superbacteria-related infections.

Antibacterial and Antiallergic Effects of Three Tea Extracts on Histamine-Induced Dermatitis

Atopic dermatitis (AD) is a persistent and recurrent inflammatory skin condition with a genetic basis. However, the fundamental reasons and mechanisms behind this phenomenon remain incompletely understood. While tea extracts are known to reduce histamine-induced skin allergies and inflammation, the specific mechanisms by which various types of Chinese tea provide their protective effects are still not fully elucidated. In this study, a model of skin itching induced by histamine is used to explore the functions and mechanisms of three types of tea extract (Keemun black tea (HC), Hangzhou green tea (LC), and Fujian white tea (BC)) in alleviating histamine-induced dermatitis. The components of three tea extracts are identified by UPLC-Q-TOF-MS, and we found that their main components are alkaloids, fatty acyls, flavonoids, organic acids, and phenols. The inhibitory effects of three types of tea extract on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) in skin injury are investigated by MIC and flow cytometry. The three types of tea extract have an inhibitory effect on the growth of bacterial flora, with HC showing the best inhibitory activity. The effect of the three types of tea extract on histamine-induced dermatitis is also evaluated. Furthermore, itchy skin experiments, HE staining, toluidine blue staining, and immunohistochemical staining of mouse skin tissues were performed to determine the variations of scratching, epidermal thickness, mast cell number, IL-1β, and NGF content after the administration of the tea extracts. The three types of tea extracts all alleviate and inhibit skin itching, epidermal hyperplasia, and allergic dermatitis. BC effectively alleviates epidermal hyperplasia caused by skin allergies, and LC significantly downregulates NGF. HC reduces histamine-induced mast cell infiltration and downregulates IL-1β to alleviate skin itching. Consequently, tea emerges a potent natural product that can inhibit the growth of skin wound bacterial flora and exhibit skin repair effects on histamine-induced allergic dermatitis.

Novel treatment of infectious keratitis in canine corneas using ultraviolet C (UV-C) light

OBJECTIVE

To investigate the therapeutic effect of 275 nm wavelength ultraviolet C (UV-C) light for treatment of bacterial keratitis in canine corneas using an affordable, broadly available modified handheld device.

METHODS

UV-C therapy (UVCT) was evaluated in two experiments: in vitro using triplicates of three bacterial genera (Staphylococcus, Streptococcus, Pseudomonas spp., and a mix of all species) where the UVCT was performed at a distance of 10, 15, and 20 mm with 1 or 2 doses (4 h apart) for 5, 15, or 30 s; ex vivo model where healthy canine corneal buttons were inoculated superficially and deep (330 μm) with the same bacterial isolates and treated at a 10 mm distance for 15 s with one dose of 22.5 mJ/cm2. Fluorescent marker (STYO9-PI) was used to label (green = live bacteria, red = dead bacteria), and confocal microscopy was used to image the bacteria.

RESULTS

In vitro results showed all plates treated with UVCT had 100% bactericidal effect for all isolates with single dose of 15 s at 10 mm distance or two doses, 4 h apart at 15 mm and was ineffective with single dose at 15-20 mm. The ex vivo results confirmed a significant decrease in bacterial load for all isolates on samples inoculated superficially but were inconclusive for intrastromal ones.

CONCLUSIONS

UVCT confirmed the therapeutic potential for all tested isolates, for both in vitro and ex vivo experiments using a single exposure of 15 s. While safety studies are underway, clinical trials are warranted.

PACAP sequence modifications modulate the peptide antimicrobial activity against bacterial pathogens affecting aquaculture

The global aquaculture industry has significant losses each year due to disease outbreaks. Antibiotics are one of the common methods to treat fish infections, but prolonged use can lead to the emergence of resistant strains. Aeromonas spp. Infections are a common and problematic disease in fish, and members of this genera can produce antibiotic resistant strains. Antimicrobial peptides (AMPs) have emerged as an alternative method to treat and prevent infections and pituitary adenylate cyclase activating polypeptide (PACAP) is a prominent member of this family. The objective of this research was to study PACAP's direct antimicrobial activity and its toxicity in fish cells. Four synthetic variants of the natural PACAP from Clarias gariepinus were tested in addition to the natural variant. The experimental results show a different antimicrobial activity against A. salmonicida and A. hydrophila of each PACAP variant, and for the first time show dependence on the culture broth used. Furthermore, the results suggest that the underlying mechanism of PACAP antimicrobial activity includes a bacterial membrane permeabilizing effect, classifying PACAP as a membrane disruptive AMP. This study also demonstrated that the five PACAP variants evaluated showed low toxicity in vitro, at concentrations relevant for in vivo applications. Therefore, PACAP could be a promising alternative to antibiotics in the aquaculture sector.

Simulated aging of draught beer line tubing increases biofilm contamination

Craft brewing is continually gaining popularity in the United States. Craft brewers are committed to producing a wide variety of products and have a vested interest in product quality. Therefore, these brewers have the expectation that the beer poured at the tap will match the quality product that left the brewery. The presence of biofilm in draught lines is hypothesized as a contributing factor when this expectation is not achieved. Clean in place strategies based on the Sinner's Circle of Cleaning are used to remediate organic and inorganic accumulation in beer draught lines, including controlling biofilm accumulation. A study was conducted to determine if repeated exposure to chemical cleaning of vinyl beer tubing impacted biofilm growth, kill/removal, and subsequent regrowth of a mixed species biofilm. The tubing was conditioned to simulate one, two, and five years of use. The data collected demonstrates a clear trend between simulated age of the tubing and biofilm accumulation on the surface. Bacterial log densities ranged from 5.6 Log10(CFU/cm2) for the new tubing to 6.6 Log10(CFU/cm2) for tubing aged to simulate five years of use. The counts for the yeast were similar. Caustic cleaning of the tubing, regardless of starting biofilm coverage, left less than 2.75 Log10(CFU/cm2) viable bacteria and yeast cells remaining on the tubing surface. This demonstrated the effectiveness of the caustic at controlling biofilm accumulation in the simulated beer draught line. The biofilm that accumulated in the five-year aged tubing was able to recover more quickly, reaching 3.6 Log10(CFU/cm2) within 24 h indicating the treatment did not fully eradicate the biofilm, suggesting that the strong chemistry used in this study would cease to be as effective over time.

Carbon dots for staining bacterial dead cells and distinguishing dead/alive bacteria

The small molecular dyes such as propidium iodide (PI) always suffer from photo-bleaching and potential toxicity. To tackle the problems, a type of nontoxic carbon dots (CDs) was obtained for dead/alive bacterial distinguishing. This kind of carbon dots has an average size of 1.91 nm and owns carboxyl groups, emerging as excellent candidates for imaging bacterial cells. The negative charges of carboxyl groups lead their avoidance of alive cells while their small size facilitates penetration of dead cells. This kind of nontoxic CDs has effectively differentiated between and alive ones, presenting a highly promising green dye comparing with traditional small molecular dyes.

Different traits for cold tolerance of extremely thermophilic Calditerricola strains isolated from mesothermal municipal sewage sludge and its hyperthermal compost

Extreme thermophiles Calditerricola satsumensis DD2 and D3 were isolated from mesothermal municipal sludge, a material used for hyperthermal composting. To understand the ecologically anomalous findings, their behavior at various temperatures, membrane fatty acid composition, and draft genome sequences were compared with those of C. satsumensis YMO81T and Calditerricola yamamurae YMO722T, already isolated from hyperthermal compost. All four strains grew between 56 and 83 °C. However, strains DD2 and D3 were stable for ≥48 h at a wide range of temperatures (20-75 °C), while strains YMO81T and YMO722T were highly labile at lower temperatures. The former strains maintained their colony-forming ability for >180 days at 20 °C, while the latter strains lost it within 1 d. All four strains showed similar composition of membrane fatty acid, which were not affected by 20 °C treatment. Comparative draft genome analyses showed that 13 candidate genes were present only in strains DD2 and D3, and the specific expression of six gene homologs was confirmed. A DNA chaperone, site-specific recombinase XerD homolog, had tetra adenine sequence at its upper gene region, and was up-regulated by 20 °C treatment in DD2 and D3, suggesting a possible role in the cold tolerance of sludge-derived strains. In addition, the lack of another possible DNA chaperone, a homolog of the ATP-dependent DNA helicase, in the compost-derived strains may accelerate their sensitivity to cold shock. In conclusion, we speculate that the specific phenotypic and genotypic characteristics of sludge-derived strains are responsible for their unusual ecological distribution at ambient temperatures.

Highly biocidal poly(vinyl alcohol)-hydantoin/starch hybrid gels: A "Trojan Horse" for Bacillus subtilis

HYPOTHESIS

Poly (vinyl alcohol) (PVA) cryogels can be functionalized with n-Halamines to confer biocidal features useful for their application as wound-dressing tools. Their efficacy can be boosted by stably embedding a polymeric bacterial food source (e.g., starch) in the gel matrix. The bioavailability of the food source lures bacteria inside the gel network via chemotactic mechanisms, promoting their contact with the biocidal functionalities and their consequent inactivation.

EXPERIMENTS

The synthesis of a novel hydantoin-functionalized PVA (H-PVA-hyd) is proposed. The newly synthesized H-PVA-hyd polymer was introduced in the formulation of H-PVA-based cryogels. To promote the cryogelation of the systems we exploited phase-separation mechanisms employing either a PVA carrying residual acetate groups (L-PVA) or starch as phase-segregating components. The permanence of the biocidal functionality after swelling was investigated via proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FT-IR) microscopy. The activated H-PVA-hyd cryogels have been tested against bacteria with amylolytic activity (Bacillus subtilis) and the outcomes were analyzed by direct observation via confocal laser scanning microscopy (CLSM).

FINDINGS

The cryogels containing starch resulted in being the most effective (up to 90% bacterial killing), despite carrying a lower amount of hydantoin groups than their starch-free counterparts, suggesting that their improved efficacy relies on a "Trojan Horse" type of mechanism.

The selenium-independent phospholipid hydroperoxide glutathione peroxidase from Theobroma cacao (TcPHGPX) protects plant cells against damages and cell death

Proteins from the glutathione peroxidase (GPX) family, such as GPX4 or PHGPX in animals, are extensively studied for their antioxidant functions and apoptosis inhibition. GPXs can be selenium-independent or selenium-dependent, with selenium acting as a potential cofactor for GPX activity. However, the relationship of plant GPXs to these functions remains unclear. Recent research indicated an upregulation of Theobroma cacao phospholipid hydroperoxide glutathione peroxidase gene (TcPHGPX) expression during early witches' broom disease stages, suggesting the use of antioxidant mechanisms as a plant defense strategy to reduce disease progression. Witches' broom disease, caused by the hemibiotrophic fungus Moniliophthora perniciosa, induces cell death through elicitors like MpNEP2 in advanced infection stages. In this context, in silico and in vitro analyses of TcPHGPX's physicochemical and functional characteristics may elucidate its antioxidant potential and effects against cell death, enhancing understanding of plant GPXs and informing strategies to control witches' broom disease. Results indicated TcPHGPX interaction with selenium compounds, mainly sodium selenite, but without improving the protein function. Protein-protein interaction network suggested cacao GPXs association with glutathione and thioredoxin metabolism, engaging in pathways like signaling, peroxide detection for ABA pathway components, and anthocyanin transport. Tests on tobacco cells revealed that TcPHGPX reduced cell death, associated with decreased membrane damage and H2O2 production induced by MpNEP2. This study is the first functional analysis of TcPHGPX, contributing to knowledge about plant GPXs and supporting studies for witches' broom disease control.

Illuminating Bacterial Contamination in Water Sources: The Power of Fluorescence-Based Methods

Bacterial contamination of water sources is a significant public health concern, and therefore, it is important to have accurate and efficient methods for monitoring bacterial concentration in water samples. Fluorescence-based methods, such as SYTO 9 and PI staining, have emerged as a promising approach for real-time bacterial quantification. In this review, we discuss the advantages of fluorescence-based methods over other bacterial quantification methods, including the plate count method and the most probable number (MPN) method. We also examine the utility of fluorescence arrays and linear regression models in improving the accuracy and reliability of fluorescence-based methods. Overall, fluorescence-based methods offer a faster, more sensitive, and more specific option for real-time bacterial quantification in water samples.

Fluorescent Chiral Quantum Dots to Unveil Origin-Dependent Exosome Uptake and Cargo Release

Exosomes are promising nanocarriers for drug delivery. Yet, it is challenging to apply exosomes in clinical use due to the limited understanding of their physiological functions. While cellular uptake of exosomes is generally known through endocytosis and/or membrane fusion, the mechanisms of origin-dependent cellular uptake and subsequent cargo release of exosomes into recipient cells are still unclear. Herein, we investigated the intricate mechanisms of exosome entry into recipient cells and the intracellular cargo release. In this study, we utilized chiral graphene quantum dots (GQDs) as representatives of exosomal cargo, taking advantage of the superior permeability of chiral GQDs into lipid membranes, as well as their excellent optical properties for tracking analysis. We observed a higher uptake rate of exosomes in their parental recipient cells. However, these exosomes were predominantly entrapped in lysosomes through endocytosis (intraspecies endocytic uptake). On the other hand, in non-parental recipient cells, exosomes exhibited a greater inclination for cellular uptake through membrane fusion, followed by direct cargo release into the cytosol (cross-species direct fusion uptake). We revealed the underlying mechanisms involved in the cellular uptake and the subsequent cargo release of exosomes depending on their cell-of-origin and recipient cell types. This study envisions valuable insights into further advancements in the effective drug delivery using exosomes, as well as a comprehensive understanding of cellular communication, including disease pathogenesis.

In situ formation of ferrous sulfide in glycyrrhizic acid hydrogels to promote healing of multi-drug resistant Staphylococcus aureus-infected diabetic wounds

Diabetic wound treatment faces great challenges in clinic. Staphylococcus aureus (S. aureus) is one of the most frequently isolated pathogens from the diabetic infections, which can severely impede wound healing time. Herein, ferrous sulfide (FeS) nanoparticles were fabricated through an in situ reaction between Fe2+ and S2- in glycyrrhizic acid (GA) solution. As the FeS nanoparticles aged, the solution gradually transformed into a gel, exhibiting excellent mechanical strength, injectability, and biocompatibility as a wound dressing. In addition to its own pharmacological effects, GA could act as the protector for FeS from oxidation of air. It also provided a weak acidic microenvironment, facilitating the pH-dependent dissolution reaction of FeS to release H2S and Fe2+. Notably, the effective antibacterial performance of the FeS/GA hydrogels towards S. aureus and multi-drug resistant S. aureus (MRSA) was achieved via the degradedly released Fe2+ and H2S through combination of ferroptosis damage and energy metabolism disruption. Moreover, FeS/GA hydrogels effectively modulated the proportion of M1/M2 macrophages, reduced the secretion of inflammatory cytokines, and significantly enhanced the proliferation and migration of fibroblasts in vitro. Importantly, in an MRSA-infected diabetic wound model, the FeS/GA hydrogels efficiently eradicated bacteria and regulated the inflammatory microenvironment, thereby promoting the diabetic wound repair. Overall, our study establishes a novel strategy for developing multifunctional hydrogels that serve as an effective therapeutic platform for managing bacteria-infected diabetic wounds.

Collaborative cytometric inter-laboratory ring test for probiotics quantification

Introduction

Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. From this definition, accurate enumeration of probiotic products is a necessity. Nonetheless, this definition does not specify the methods for assessing such viability. Colony forming units is the de facto gold standard for enumerating viable in probiotic products. The notion of microbial viability has been anchored in the concept of cultivability, which refers to a cell's capacity to replicate and form colonies on agar media. However, there is a growing consensus that the term "viability" should not be exclusively tied to the ability to cultivate cells. For example, bacterial cells can exist in a Viable But Non-Culturable (VBNC) state, characterized by the maintenance of characteristics such as membrane integrity, enzymatic activity, pH gradients, and elevated levels of rRNA, despite losing the ability to form colonies.

Methods

Herein we present the results of a collaborative inter-laboratory ring test for cytometric bacterial quantification. Specifically, membrane integrity fluorescence flow cytometry (FFC) method and the newer impedance flow cytometry (IFC) method have been used. Both methods interrogate single cells in solution for the presence of intact membranes. FFC exploits fluorochromes that reflect the presence or absence of an intact membrane. IFC probes membrane integrity in a label-free approach by detecting membrane-induced hindrances to the propagation of electricity.

Results

A performance ring-test and comparison design on the FFC method showed that the method is robust against the exchange of equipment, procedures, materials, and operators. After initial method optimization with assessments of rehydration medium, wake-up duration, and phase shift gating on the individual strains, the IFC method showed good agreement with the FFC results. Specifically, we tested 6 distinct species of probiotic bacteria (3 Lactobacillus and 3 Bifidobacterium strains) finding good agreement between FFC and IFC results in terms of total and live cells.

Discussion

Together, these results demonstrate that flow cytometry is a reliable, precise, and user-friendly culture-independent method for bacterial enumeration.

Bactericidal efficacy difference between air and nitrogen cold atmospheric plasma on Bacillus cereus: Inactivation mechanism of Gram-positive bacteria at the cellular and molecular level

As an emerging food processing technology, cold atmospheric plasma (CAP) has attracted great attention in the field of microbial inactivation. Although CAP has been proven to effectively inactivate a variety of foodborne pathogens, there is less research on the inactivation of Bacillus cereus, and the exact inactivation mechanism is still unclear. Elucidating the inactivation mechanism will help to develop and optimize this sterilization method, with the prospective application in industrialized food production. This study aims to explore the bactericidal efficacy difference between air and nitrogen CAP on B. cereus, a typical Gram-positive bacterium, and reveals the inactivation mechanism of CAP at the cellular and molecular level, by observing the change of the cell membrane, cell morphological damage, intracellular antioxidant enzyme activity and cellular biomacromolecules changes. The results showed that both air CAP and nitrogen CAP could effectively inactivate B. cereus, which was due to the reactive oxygen and nitrogen species (RONS) generated by the plasma causing bacterial death. The damage pathways of CAP on Gram-positive bacteria could be explained by disrupting the bacterial cell membrane and cell morphology, disturbing the intracellular redox homeostasis, and destroying biomacromolecules in the cells. The differences in active species generated by the plasma were the main reason for the different bactericidal efficiencies of air CAP and nitrogen CAP, where air CAP producing RONS with stronger oxidative capacity in a shorter time. This study indicates that air CAP is an effective, inexpensive and green technology for B. cereus inactivation, providing a basis for industrial application in food processing.

Applied Methods to Assess the Antimicrobial Activity of Metallic-Based Nanoparticles

With the rise of antibiotic resistance, the drive to discover novel antimicrobial substances and standard testing methods with the aim of controlling transmissive diseases are substantially high. In healthcare sectors and industries, although methods for testing antibiotics and other aqueous-based reagents are well established, methods for testing nanomaterials, non-polar and other particle-based suspensions are still debatable. Hence, utilities of ISO standard validations of such substances have been recalled where corrective actions had to be taken. This paper reports a serial analysis obtained from testing the antimicrobial activities of 10 metallic-based nanomaterials against 10 different pathogens using five different in vitro assays, where the technique, limitation and robustness of each method were evaluated. To confirm antimicrobial activities of metallic-based nanomaterial suspensions, it was found that at least two methods must be used, one being the agar well diffusion method, which was found to be the most reliable method. The agar well diffusion method provided not only information on antimicrobial efficacy through the size of the inhibitory zones, but it also identified antimicrobial ions and synergistic effects released by the test materials. To ascertain the effective inhibitory concentration of nanoparticles, the resazurin broth dilution method is recommended, as MIC can be determined visually without utilising any equipment. This method also overcomes the limit of detection (LoD) and absorbance interference issues, which are often found in the overexpression of cell debris and nanoparticles or quantum dots with optical profiles. In this study, bimetallic AgCu was found to be the most effective antimicrobial nanoparticle tested against across the bacterial (MIC 7 µg/mL) and fungal (MIC 62.5 µg/mL) species.

Metabolomic Differences between Viable but Nonculturable and Recovered Lacticaseibacillus paracasei Zhang

The fermentation process can be affected when the starter culture enters the viable but nonculturable (VBNC) state. Therefore, it is of interest to investigate how VBNC cells change physiologically. Lacticaseibacillus (L.) paracasei Zhang is both a probiotic and a starter strain. This study aimed to investigate the metabolomic differences between VBNC and recovered L. paracasei Zhang cells. First, L. paracasei Zhang was induced to enter the VBNC state by keeping the cells in a liquid de Man-Rogosa-Sharpe (MRS) medium at 4 °C for 220 days. Flow cytometry was used to sort the induced VBNC cells, and three different types of culture media (MRS medium, skim milk with 1% yeast extract, and skim milk) were used for cell resuscitation. Cell growth responses in the three types of recovery media suggested that the liquid MRS medium was the most effective in reversing the VBNC state in L. paracasei Zhang. Metabolomics analysis revealed 25 differential metabolites from five main metabolite classes (amino acid, carbohydrate, lipid, vitamin, and purine and pyrimidine). The levels of L-cysteine, L-alanine, L-lysine, and L-arginine notably increased in the revived cells, while cellulose, alginose, and guanine significantly decreased. This study confirmed that VBNC cells had an altered physiology.

Synthesis and evaluation of water-soluble imidazolium salt chitin with broad-spectrum antimicrobial activity and excellent biocompatibility for infected wound healing

Infections caused by bacteria have long constituted a major threat to human health and the economy. Therefore, there is an urgent need to design broad-spectrum antibacterial materials possessing good biocompatibility to treat such infections. Herein, inspired by the good biocompatibility of chitin and antibacterial properties of imidazolium salts, a polysaccharide-based material, imidazolium salt chitin (IMSC), was homogeneously prepared using a facile method with epichlorohydrin as a chemical crosslinker to combine chitin with imidazole to enhance Staphylococcus aureus (S. aureus)-infected wound healing. The characteristics, antimicrobial properties, and biosafety of IMSC were evaluated. The results demonstrated successful grafting of imidazole onto chitin. Furthermore, IMSC exhibited good water solubility, broad-spectrum antimicrobial activity, hemocompatibility, and biocompatibility. Moreover, IMSC enabled complete healing of S. aureus-infected wound in Sprague-Dawley rats within 15 days of application, thus demonstrating that IMSC could reduce wound inflammation and remarkably accelerate wound healing owing to its efficient antibacterial activity and ability to promote collagen deposition in and around the wound area. Therefore, this study provides a promising and potential therapeutic strategy for infected wound healing by synthesizing a water-soluble and broad-spectrum antimicrobial material exhibiting good biocompatibility.

Inactivation effects and mechanism of ohmic heating on Bacillus cereus

The inactivation effects and mechanism of ohmic heating (OH) on Bacillus cereus ATCC 11778 were investigated in this study, conventional heating (CH) was also carried out and served as control. All OH treatments (10 V/cm 50 Hz, 10 V/cm 500 Hz, 5 V/cm 50 Hz and 5 V/cm 500 Hz) could achieve a comparable inactivation effect with CH, while OH treatments significantly shortened the processing time. OH treated cells exhibited significantly higher leakage of metal ions (Mg²⁺ and K⁺) and biomacromolecules (nucleic acids and proteins) than those treated with CH when bacterial suspensions were heated to the same temperature. Moreover, OH treatment caused more damage on membrane structure, greatly decreased the cell membrane potential and endogenous enzyme activity than that of CH. The results of this study indicated that OH is more efficient in the inactivation of bacteria.

Current Perspectives on Viable but Non-Culturable Foodborne Pathogenic Bacteria: A Review

Foodborne diseases caused by foodborne pathogens pose risks to food safety. Effective detection and efficient inactivation of pathogenic bacteria has always been a research hotspot in the field of food safety. Complicating these goals, bacteria can be induced to adopt a viable but non-culturable (VBNC) state under adverse external environmental stresses. When in the VBNC state, pathogens cannot form visible colonies during traditional culture but remain metabolically active and toxic. The resulting false negative results in growth-related assays can jeopardize food safety. This review summarizes the latest research on VBNC foodborne pathogens, including induction conditions, detection methods, mechanism of VBNC formation, and possible control strategies. It is hoped that this review can provide ideas and methods for future research on VBNC foodborne pathogenic bacteria.

Cytoprotection of Probiotic Lactobacillus acidophilus with Artificial Nanoshells of Nature-Derived Eggshell Membrane Hydrolysates and Coffee Melanoidins in Single-Cell Nanoencapsulation

One-step fabrication method for thin films and shells is developed with nature-derived eggshell membrane hydrolysates (ESMHs) and coffee melanoidins (CMs) that have been discarded as food waste. The nature-derived polymeric materials, ESMHs and CMs, prove highly biocompatible with living cells, and the one-step method enables cytocompatible construction of cell-in-shell nanobiohybrid structures. Nanometric ESMH-CM shells are formed on individual probiotic Lactobacillus acidophilus, without any noticeable decrease in viability, and the ESMH-CM shells effectively protected L. acidophilus in the simulated gastric fluid (SGF). The cytoprotection power is further enhanced by Fe³⁺-mediated shell augmentation. For example, after 2 h of incubation in SGF, the viability of native L. acidophilus is 30%, whereas nanoencapsulated L. acidophilus, armed with the Fe³⁺-fortified ESMH-CM shells, show 79% in viability. The simple, time-efficient, and easy-to-process method developed in this work would contribute to many technological developments, including microbial biotherapeutics, as well as waste upcycling.

Leveraging microfluidic dielectrophoresis to distinguish compositional variations of lipopolysaccharide in E. coli

Lipopolysaccharide (LPS) is the unique feature that composes the outer leaflet of the Gram-negative bacterial cell envelope. Variations in LPS structures affect a number of physiological processes, including outer membrane permeability, antimicrobial resistance, recognition by the host immune system, biofilm formation, and interbacterial competition. Rapid characterization of LPS properties is crucial for studying the relationship between these LPS structural changes and bacterial physiology. However, current assessments of LPS structures require LPS extraction and purification followed by cumbersome proteomic analysis. This paper demonstrates one of the first high-throughput and non-invasive strategies to directly distinguish Escherichia coli with different LPS structures. Using a combination of three-dimensional insulator-based dielectrophoresis (3DiDEP) and cell tracking in a linear electrokinetics assay, we elucidate the effect of structural changes in E. coli LPS oligosaccharides on electrokinetic mobility and polarizability. We show that our platform is sufficiently sensitive to detect LPS structural variations at the molecular level. To correlate electrokinetic properties of LPS with the outer membrane permeability, we further examined effects of LPS structural variations on bacterial susceptibility to colistin, an antibiotic known to disrupt the outer membrane by targeting LPS. Our results suggest that microfluidic electrokinetic platforms employing 3DiDEP can be a useful tool for isolating and selecting bacteria based on their LPS glycoforms. Future iterations of these platforms could be leveraged for rapid profiling of pathogens based on their surface LPS structural identity.

Antimicrobial activity and mechanism of preservatives against Alicyclobacillus acidoterrestris and its application in apple juice

Alicyclobacillus acidoterrestris has great influence on the quality of apple juice products. In this study, the antibacterial activity of five preservatives (ε-polylysine, propylparaben, monocaprin, octyl gallate and heptylparaben) against A. acidoterrestris and its underlying mechanism were investigated. Results showed that these five preservatives all exerted antibacterial activity through a multiple bactericidal mechanism, and monocaprin and octyl gallate had the highest antibacterial activity, with the minimum inhibitory concentration (MIC) values of 22.5 and 6.25 mg/L, respectively. Five preservatives all changed the permeability of the cell membrane and destroyed the complete cell morphology, with the leakages of the intracellular electrolytes. Moreover, the treatment of ε-polylysine, propylparaben and monocaprin increased the leakage of intracellular protein; propylparaben and octyl gallate reduced the levels of cellular adenosine triphosphate. Also, monocaprin and octyl gallate may stimulate bacteria to release a large amount of reactive oxygen species, so that certain oxidative damage can kill the bacteria. Furthermore, monocaprin and octyl gallate could effectively inactivate the contamination of A. acidoterrestris in apple juices, with the slightly decrease of soluble sugars and organic acids, without significant adverse effects on total sugars and titratable acids. This research highlights the great promise of using monocaprin and octyl gallate as the safe multi-functionalized food additives for food preservations.

Primary Amine Functionalized Carbon Dots for Dead and Alive Bacterial Imaging

Small molecular dyes are commonly used for bacterial imaging, but they still meet a bottleneck of biological toxicity and fluorescence photobleaching. Carbon dots have shown high potential for bio-imaging due to their low cost and negligible toxicity and anti-photobleaching. However, there is still large space to enhance the quantum yield of the carbon quantum dots and to clarify their mechanisms of bacterial imaging. Using carbon dots for dyeing alive bacteria is difficult because of the thick density and complicated structure of bacterial cell walls. In this work, both dead or alive bacterial cell imaging can be achieved using the primary amine functionalized carbon dots based on their small size, excellent quantum yield and primary amine functional groups. Four types of carbon quantum dots were prepared and estimated for the bacterial imaging. It was found that the spermine as one of precursors can obviously enhance the quantum yield of carbon dots, which showed a high quantum yield of 66.46% and high fluorescence bleaching-resistance (70% can be maintained upon 3-h-irradiation). Furthermore, a mild modifying method was employed to bound ethylenediamine on the surface of the spermine-carbon dots, which is favorable for staining not only the dead bacterial cells but also the alive ones. Investigations of physical structure and chemical groups indicated the existence of primary amine groups on the surface of spermine-carbon quantum dots (which own a much higher quantum yield) which can stain alive bacterial cells visibly. The imaging mechanism was studied in detail, which provides a preliminary reference for exploring efficient and environment-friendly carbon dots for bacterial imaging.

To decipher the phytochemical agent and mechanism for Urginea indica mediated green synthesis of Ag nanoparticles and investigation of its antibacterial activity against Methicillin-resistant Staphylococcus aureus

Globally, Methicillin-Resistant Staphylococcus aureus bacteraemia is one of the commonest bloodstream infections associated with clinical complications and high mortality. Thence, devising effective and targeted biogenic silver based strategies are in great demand. However, limited insights regarding the biosynthesis methodologies impedes the possible scale up and commercial potentials. We, hereby demonstrate the biosynthesis of Ag nanoparticles using the phytochemical agent extracted and purified from bulb extract of Urginea indica. The chemical structure of the phytochemical agent is investigated by various chromatographic and spectroscopic techniques and was found closely relatable to N-ethylacetamide. Ag nanoparticles synthesis by this agent was found to have a strong Surface Plasmon band at 402 nm. X-ray diffraction and transmission electron microscopy further validated the formation of Ag nanoparticles with face-centred cubic structure with a size range of 20-30 nm. The biogenic metal nanoparticles have shown potential antibacterial activity against S. aureus and MRSA (within a range of 10-50 μg/mL). The nanoparticles have also shown promising anti-biofim activity against the above mentioned strains. The nanoparticles were expected to induce ROS mediated bactericidal mechamism. Cell viability and in-vitro infection studies advocate noticeable biocompatibility and future clinical potential of the developed nanoparticles against Staphylococcus infections.

Communication Breakdown: Into the Molecular Mechanism of Biofilm Inhibition by CeO2 Nanocrystal Enzyme Mimics and How It Can Be Exploited

Bacterial biofilm formation is a huge problem in industry and medicine. Therefore, the discovery of anti-biofilm agents may hold great promise. Biofilm formation is usually a consequence of bacterial cell-cell communication, a process called quorum sensing (QS). CeO₂ nanocrystals (NCs) have been established as haloperoxidase (HPO) mimics and ecologically beneficial biofilm inhibitors. They were suggested to interfere with QS, a mechanism termed quorum quenching (QQ), but their molecular mechanism remained elusive. We show that CeO₂ NCs are effective QQ agents, inactivating QS signals by bromination. Catalytic bromination of 3-oxo-C₁₂-AHL a QS signaling compound used by Pseudomonas aeruginosa, was detected in the presence of CeO₂ NCs, bromide ions, and hydrogen peroxide. Brominated acyl-homoserine lactones (AHLs) no longer act as QS signals but were not detected in the bacterial cultures. Externally added brominated AHLs also disappeared in P. aeruginosa cultures within minutes of their addition, indicating that they are rapidly degraded by the bacteria. Moreover, we detected the catalytic bromination of 2-heptyl-1-hydroxyquinolin-4(1H)-one (HQNO), a multifunctional non-AHL QS signal from P. aeruginosa with antibacterial and algicidal properties controlling the expression of many virulence genes. Brominated HQNO was not degraded by the bacteria in vivo. The repression of the Pseudomonas quinolone signal (PQS) production and biofilm formation in P. aeruginosa through the catalytic formation of Br-HQNO on surfaces with coatings containing CeO₂ enzyme mimics validates the non-toxic strategy for the development of anti-infectives.

Dialdehyde modification of laminarin for facile synthesis of ultrafine silver nanoparticles with excellent antibacterial and wound healing properties

Laminarin is a promising marine biopolymer that is abundant, non-toxic, and biodegradable. However, laminarin has a weak reduction potential for metal ions, resulting in the synthesis of a lower content of large-sized silver nanoparticles (AgNPs). Here, we showed that after the introduction of aldehyde groups, the reduction potential of laminarin increased, decreasing the synthesis time and increasing the density of AgNPs. ¹H NMR and FT-IR confirmed the addition of aldehyde groups on laminarin. The dialdehyde-modified laminarin (DLAM) showed in situ, simple, and rapid synthesis of ultrasmall-sized spherical AgNPs (<10 nm), as revealed by TEM images. The aldehyde and carboxyl groups of DLAM act as synchronized reducing and anchoring agents. The conversion of Ag ions into AgNPs-DLAM was confirmed by UV-Vis spectrophotometer, FTIR, XRD, and XPS analysis. The AgNPs-DLAM showed significantly enhanced antibacterial activities than silver ions against Escherichia coli and Staphylococcus aureus via causing morphological changes and pore formations in bacterial cells. The AgNPs-DLAM also inhibited bacterial biofilm formation. In contrast, the AgNPs-DLAM showed negligible toxicity toward human keratinocytes. Furthermore, AgNPs-DLAM increased the migration of human keratinocytes, indicating efficient wound healing properties. Thus, signifying the importance of AgNPs-DLAM in clinical applications.

Optimized Protocol for Microalgae DNA Staining with SYTO9/SYBR Green I, Based on Flow Cytometry and RSM Methodology: Experimental Design, Impacts and Validation

Multiple fluorochromes are extensively used to investigate different microalgal aspects, such as viability and physiology. Some of them can be used to stain nucleic acids (DNA). Well-known examples are SYBR Green I and SYTO 9, the latter of which offers several advantages, especially when combined with flow cytometry (FCM)—a powerful method for studying microalgal population heterogeneity and analyzing their cell cycles. However, the effects of these dyes on the microalgae cell physiology have not been fully elucidated yet. A statistical experimental design, using response surface methodology (RSM) with FCM was applied in this study to optimize the DNA staining of a non-conventional microalgae, Chromochloris zofingiensis, with SYBR Green I and SYTO 9, and to optimize the variables affecting staining efficiency, i.e., the dye concentration, incubation time and staining temperature. We found that none of these factors affects the staining efficiency, which was not less than 99.65%. However, for both dyes, the dye concentration was shown to be the most significant factor causing cell damage (p-values: 0.0003; <0.0001) for SYBR Green I and SYTO 9, respectively. The staining temperature was only significant for SYTO 9 (p-value: 0.0082), and no significant effect was observed regarding the incubation time for both dyes. The values of the optimized parameters (0.5 µM, 05 min and 25 °C) for SYTO 9 and (0.5 X, 5 min and 25 °C) for SYBR Green I resulted in the maximum staining efficiency (99.8%; 99.6%), and the minimum damaging effects (12.86%; 13.75%) for SYTO 9 and SYBR Green I, respectively. These results offer new perspectives for improving the use of DNA staining fluorochromes and provides insights into their possible side effects on microalgae.

Modification of polyacrylonitrile-derived carbon nanofibers and bacteriophages on screen-printed electrodes: A portable electrochemical biosensor for rapid detection of Escherichia coli

A facile method was developed for fabricating a disposable phage-based electrochemical biosensor for the detection of Escherichia coli. Bare screen-printed electrodes (SPEs) were modified using a two-step drop-casting method, in which polyacrylonitrile-derived electrospun carbon nanofibers (CNFs) were deposited, followed by E. coli bacteriophage immobilization. The deposition of CNFs increased the surface area for bacteriophage immobilization while maintaining a conductive link for ferro/ferricyanide redox transitions. Cyclic voltammetry and electrochemical impedance spectroscopy confirmed that the CNF modification increased the electron-transfer rate, whereas bacteriophages and E. coli blocked electron transfer at the electrode. The biosensor achieved a response within 10 min and a linear response in the E. coli concentration range of 10²-10⁶ CFU/mL. A limit of detection (LOD) of 36 CFU/mL in phosphate-buffered saline was achieved, which is the lowest LOD reported thus far for phage-based disposable SPE sensors. The biosensor exhibited recovery rates between 106 % and 119 % for E. coli detection in apple juice. The proposed fabrication method allowed electrodes to be obtained from different production batches with remarkable consistency and reproducibility, and they remained stable at room temperature for one month. Thus, a phage-based disposable SPE that can be used for bacterial detection was developed for the first time.

Antibacterial and Antibiofilm Potency of Menadione Against Multidrug-Resistant S. aureus

Menadione is an analogue of 1,4-naphthoquinone (1,4-NQ) that possesses enormous pharmaceutical potential. The minimum inhibitory concentration (MIC) of menadione was determined against eighteen pathogens of the ESKAPE category, including thirteen multidrug-resistant (MDR) and five standard strains. From a total of eighteen pathogens, five strains of S. aureus (four: MDR and one: Standard strain) were considered further for detailed studies. This study included the determination of minimum bactericidal concentration (MBC), time-kill assay, scanning electron microscopic technique (SEM), and detection of reactive oxygen species (ROS). Additionally, the effect of menadione on biofilms of three strains of S. aureus was performed through crystal violet assay, SEM, and confocal laser scanning microscopy (CLSM). Menadione exerted substantial antibacterial activity against S. aureus (S8, S9, NCIM 5021) at a lower MIC (64 µg/mL). Whereas, the MIC of 256 µg/mL was displayed against J2 and J4 (MDR and biofilm-forming strains). The time-killing effect of menadione against S. aureus strains was observed after 9 h at MBCs of 64 µg/mL (NCIM 5021), 128 µg/mL (S8, S9), and 512 µg/mL (J2, J4). Enhanced levels of ROS in all five S. aureus were observed in presence of menadione (MICs and MBCs). The relation of enhanced ROS due to menadione activity invigorated us to explore its effect on S. aureus biofilms. We report menadione-mediated inhibition (> 90%) of biofilm formation (at respective MICs) and effect on preformed biofilms (> 85%) at 1024 µg/mL. Menadione possessing antibacterial and antibiofilm potentials are imperative in the era of multidrug resistance developed by bacterial pathogens.

Silver Ion Loaded Agarose-Hyaluronic Acid Hydrogel as a Potential Antibacterial Wound Dressing

Wound infection, especially chronic ones, not only increases the opportunity to generate superbacteria but also imposes significant burden, both physically and mentally, on the patients. Therefore, the development of suitable wound addressing is an important way to deal with this matter. Here in this study, we employed the good gelling property of agarose (AR) and the wound healing promotion effect of hyaluronic acid (HA) to prepare an agarose-hyaluronic acid hydrogel. The AR-HA gel was loaded with silver ion (Ag+ from AgNO3) upon gelling (AR-HA/Ag) and finally applied as a potential wound dressing for antibacterial treatment and healing promotion of wounds. Our results suggested that the AR-HA/Ag hydrogel maintained the antibacterial efficacy of Ag+ while significantly promoted the healing of human umbilical vein endothelial cells (HUVEC) due to the cell proliferation promotion effect of HA. Taken together, AR-HA/Ag might be a potential antibacterial wound dressing for future application in clinic.

Abundance of Live and Dead Bacteriopsammon Inhabiting Sandy Ecosystems of Recreational Marine Beaches of the Southern Baltic Sea

The study was carried out on four non-tidal sandy marine beaches located on the Polish part of the southern Baltic Sea coast. We applied a LIVE/DEAD™ BacLight™ Bacterial Viability Kit (Invitrogen™) method to determine the abundance of live and dead bacteriopsammon. Live psammon bacteria cells constituted 31-53% of the total number of bacteria inhabiting sand of the studied beaches. Abundance of live and dead psammon bacteria generally differed along the horizontal profile in all beaches. The maximum density of bacteria was noted in the dune and the middle part of the beach (dry zones) and the minimum in wet zones, i.e., under seawater surface and at the swash zone. Generally along the vertical profile, the highest numbers of two studied bacterial groups were noted in the surface sand layer, while with increasing sediment depth their numbers significantly decreased. The abundance of live and dead bacteria showed a distinct seasonal variation.

In-vitro toxicity assessment of Eucalyptus robusta Smith extracts via whole-cell bioreporter

Eucalyptus is widely planted in China for wood industries, and there are increasing concerns about its ecotoxicity in the environment. This study explored the in-vitro toxicity of Eucalyptus extracts by assessing the impacts of water-soluble and dimethylsulfoxide (DMSO)-soluble fractions via a whole-cell bioreporter, Acinetobacter baylyi ADPWH_recA. Compounds identified in Eucalyptus extracts included one tannin, two phenolic acids, four terpenoids, four glycosides, and five flavonoids. The leaf extracts contained more biological-active components than barks and roots. Genotoxicity induced by Eucalyptus extracts was mainly associated with water extracts (e.g., flavonoids, phenolic acids) instead of DMSO extracts. The significant cytotoxicity was explained by programmed cell death (PCD), suggested by the results of propidium iodide (PI) and 2',7'-dichlorofluorescein-diacetate (DCFH-DA) assays. Generally, water-soluble fractions contributed more toxicities than DMSO-soluble fractions, particularly at high concentrations. A robust linear regression was built between the compromised toxicity and PCD index (Compromised toxicity = -2.192 × PCD index + 2.219; R² = 0.8886), suggesting a PCD-dependent compromised toxicity which was greatly underestimated. Our results implied non-neglectable ecotoxicological risks of Eucalyptus extracts, hinting at the possible magnified ecological impacts of its large-scale plantation and the potential adverse outcomes to the surrounding ecosystems.

Strategies to Improve the Potency of Oxazolidinones towards Bacterial Biofilms

Biofilms are part of the natural lifecycle of bacteria and are known to cause chronic infections that are difficult to treat. Most antibiotics are developed and tested against bacteria in the planktonic state and are ineffective against bacterial biofilms. The oxazolidinones, including the last resort drug linezolid, are one of the main classes of synthetic antibiotics progressed to clinical use in the last 50 years. They have a unique mechanism of action and only develop low levels of resistance in the clinical setting. With the aim of providing insight into strategies to design more potent antibiotic compounds with activity against bacterial biofilms, we review the biofilm activity of clinically approved oxazolidinones and report on structural modifications to oxazolidinones and their delivery systems which lead to enhanced anti-biofilm activity.

Novel fluorescence-based method for rapid quantification of live bacteria in river water and treated wastewater

Monitoring bacteria is essential for ensuring microbial safety of water sources, including river water and treated wastewater. The plate count method is common for monitoring bacterial abundance, although it cannot detect all live bacteria such as viable but non-culturable bacteria, causing underestimation of microbial risks. Live/Dead BacLight kit, involving fluorochromes SYTO 9 and propidium iodide (PI), provides an alternative to assess bacterial viability using flow cytometry or microscopy. However, its application is limited due to the high cost of flow cytometry and the inapplicability of microscopy to most environmental waters. Thus, this study introduces the combination of BacLight kit and fluorescence spectroscopy for quantifying live bacteria in river water and treated wastewater. Mixtures of live and dead Escherichia coli (E. coli) with various ratios and total cell concentrations were stained with SYTO 9 and PI and measured by fluorescence spectroscopy. The fluorescence emission peak area of SYTO 9 in the range of 500-510 nm at the excitation wavelength of 470 nm correlates linearly with the viable cell counts (R ² > 0.99, p < 0.0001) with only slight variations in the complex water matrix. The tested method can quantify the live E. coli from 3.67 × 10⁴ to 2.70 × 10⁷ cells per mL. This method is simple, sensitive and reliable for quantifying live bacteria in environmental water, which can be later integrated into real-time monitoring systems.

Phenylboronic acid-functionalized silver nanoparticles for highly efficient and selective bacterial killing

With the widespread use of antibiotics, the number of severe infections caused by unknown pathogens is increasing and novel antibacterial agents with high antibacterial efficiency and selective bacterial killing are urgently needed. In this work, we developed a new kind of functional material based on silver nanoparticles (AgNPs), whose surfaces were functionalized with phenylboronic acid (AgNPs-PBA_n). The phenylboronic acid groups on the surface of AgNPs-PBA_n could form covalent bonds with the cis-diol groups of lipopolysaccharide or teichoic acid on the bacterial surface, which highly promoted the interaction between AgNPs-PBA_n and bacteria, resulting in a very strong enhancement of their antibacterial action via membrane disruption. The scanning electron microscopy images revealed that the accumulation of phenylboronic acid-functionalized AgNPs on the bacterial surface is much more than that of the nonfunctionalized AgNPs. Importantly, the antibacterial efficiency of the phenylboronic acid-functionalized AgNPs on a series of bacteria is 32 times higher than that of bare AgNPs. Moreover, AgNPs-PBA_n showed a high selectivity toward bacteria with an IC₅₀ (half maximal inhibitory concentration to mammalian cells) more than 160 times its MBC (minimum bactericidal concentration). In a model of an E. coli-infected wound in vivo, AgNPs-PBA_n could effectively kill the bacteria with an accelerated wound healing rate. This study demonstrates that phenylboronic acid surface functionalization is an efficient way to drastically promote the antibacterial activity of AgNPs, improving the selectivity of silver-based nanoparticles against a variety of bacteria.

Kocuria Strains from Unique Radon Spring Water from Jachymov Spa

Members of the genus Kocuria are often found in soils contaminated with toxic metals or exposed to high levels of ionizing radiation. The use of classical cultivation technics often leads to the isolation of Kocuria sp. from underground spring waters. These bacterial isolates have to adapt their metabolism to survive in such extreme environments. Four bacterial isolates of the genus Kocuria (Kocuria sp. 101, 208, 301, and 401) were obtained from radon spring water (Jachymov, Czech Republic). These isolates were tested for their ability to withstand stress and extreme conditions. Growth was observed at a temperature range of 10–45 °C with optimal growth temperature between 20 and 30 °C. The content of polyunsaturated fatty acids in all four isolates was proved to be temperature-dependent. The strain Kocuria sp. 301 showed high resistance to all studied extreme conditions (UV radiation, desiccation, and free radicals in medium). The results suggest that isolates from radioactive springs might have developed mechanisms that help them survive under several extreme conditions and could be used in biotechnological production.

Transparent polycarbonate coated with CeO2 nanozymes repel Pseudomonas aeruginosa PA14 biofilms

Highly transparent CeO₂/polycarbonate surfaces were fabricated that prevent adhesion, proliferation, and the spread of bacteria. CeO₂ nanoparticles with diameters of 10-15 nm and lengths of 100-200 nm for this application were prepared by oxidizing aqueous dispersions of Ce(OH)₃ with H₂O₂ in the presence of nitrilotriacetic acid (NTA) as the capping agent. The surface-functionalized water-dispersible CeO₂ nanorods showed high catalytic activity in the halogenation reactions, which makes them highly efficient functional mimics of haloperoxidases. These enzymes are used in nature to prevent the formation of biofilms through the halogenation of signaling compounds that interfere with bacterial cell-cell communication ("quorum sensing"). Bacteria-repellent CeO₂/polycarbonate plates were prepared by dip-coating plasma-treated polycarbonate plates in aqueous CeO₂ particle dispersions. The quasi-enzymatic activity of the CeO₂ coating was demonstrated using phenol red enzyme assays. The monolayer coating of CeO₂ nanorods (1.6 μg cm^-2) and the bacteria repellent properties were demonstrated by atomic force microscopy, biofilm assays, and fluorescence measurements. The engineered polymer surfaces have the ability to repel biofilms as green antimicrobials on plastics, where H₂O₂ is present in humid environments such as automotive parts, greenhouses, or plastic containers for rainwater.

Evaluation of the Membrane Damage Mechanism of Chlorogenic Acid against Yersinia enterocolitica and Enterobacter sakazakii and Its Application in the Preservation of Raw Pork and Skim Milk

Plant-derived antimicrobial agents have adequate antimicrobial effects on food-borne pathogens, which can be used as food preservatives. The purpose of this study was to evaluate the antibacterial mechanism of chlorogenic acid (CA) against Yersinia enterocolitica and Enterobacter sakazakii. The minimum inhibitory concentration (MIC) of CA was determined by employing the broth microdilution method. Then, the cell function and morphological changes of Y. enterocolitica and E. sakazakii treated with CA were characterized. Finally, the growth inhibition models of Y. enterocolitica in raw pork and E. sakazakii in skim milk were constructed through the response surface methodology. The results demonstrated that CA has a satisfactory inhibitory effect against Y. enterocolitica and E. sakazakii with a MIC of 2.5 mg/mL. In addition, CA inhibited the growth of Y. enterocolitica and E. sakazakii via cell membrane damage, such as depolarization of the cell membrane, reduction in intracellular adenosine triphosphate (ATP) and pH levels, and destruction of cell morphology. Moreover, CA reduced two log cycles of Y. enterocolitica in raw pork and E. sakazakii in skim milk at a certain temperature. According to the corresponding findings, CA has the potential to be developed as an effective preservative to control Y. enterocolitica and E. sakazakii-associated foodborne diseases.

Preliminary Study on Citrus Oils Antibacterial Activity Measured by Flow Cytometry: A Step-by-Step Development

Essential oils of Citrus sinensis and Citrus latifolia have shown biological functions as antiseptics, anti-inflammatories, antioxidants, antifungal and antimutagenic, so the evaluation of their antibacterial capacity, by themselves or in combination with standard antibiotics, presents an alternative for infection treatment. Flow cytometry opens the door for the design of faster and more accurate measurement of antibacterial activity. We use a SYTO9/PI staining system on E. coli ATCC 25922 to determine antibacterial activity by counting live and dead cells through flow cytometry. We found that dual staining showed highly variable results due to wavelength overlapping and instead we used fluorochrome individual staining that highly correlated with viable counts. Chloramphenicol and cefotaxime treatments did not present a dose-response behavior, rendered diffuse readings and/or gave filament formation on fluorescence microscopy. Amikacin was a better comparison standard because it presented a dose-response behavior. Essential oils had low antibacterial activity as compared to amikacin, with a maximum of 10% and 20% for C. latifolia and C. sinensis, respectively. Combinations of essential oils with antibiotic resulted in an unforeseen strong inhibition of amikacin activity. Although a low antibacterial activity was found, a series of standardization steps are proposed for antibacterial activity measurement by flow cytometry.

Microbial Biofilms in the Food Industry-A Comprehensive Review

Biofilms, present as microorganisms and surviving on surfaces, can increase food cross-contamination, leading to changes in the food industry’s cleaning and disinfection dynamics. Biofilm is an association of microorganisms that is irreversibly linked with a surface, contained in an extracellular polymeric substance matrix, which poses a formidable challenge for food industries. To avoid biofilms from forming, and to eliminate them from reversible attachment and irreversible stages, where attached microorganisms improve surface adhesion, a strong disinfectant is required to eliminate bacterial attachments. This review paper tackles biofilm problems from all perspectives, including biofilm-forming pathogens in the food industry, disinfectant resistance of biofilm, and identification methods. As biofilms are largely responsible for food spoilage and outbreaks, they are also considered responsible for damage to food processing equipment. Hence the need to gain good knowledge about all of the factors favouring their development or growth, such as the attachment surface, food matrix components, environmental conditions, the bacterial cells involved, and electrostatic charging of surfaces. Overall, this review study shows the real threat of biofilms in the food industry due to the resistance of disinfectants and the mechanisms developed for their survival, including the intercellular signalling system, the cyclic nucleotide second messenger, and biofilm-associated proteins.