Integrity Of Bacterial Cell Membrane Research Articles

Macrolactin XY, a Macrolactin Antibiotic from Marine-Derived Bacillus subtilis sp. 18.

Two new compounds, macrolactin XY (1) and (5R, 9S, 10S)-5-(hydroxymethyl)-1,3,7-decatriene-9,10-diol (2), together with nine known compounds (3-11) were isolated from the marine Bacillus subtilis sp. 18 by the OSMAC strategy. These compounds were evaluated for antibacterial activity against six tested microorganisms. Compounds 1-5 and 7-10 showed varied antibacterial activity, with the minimum inhibitory concentration (MIC) ranging from 3 to 12 μg/mL. Macrolactin XY (1) was found to possess superior antibacterial activity, especially exhibiting significant effectiveness against Enterococcus faecalis. The antibacterial activity mechanism against E. faecalis was investigated. The mechanism may disrupt bacterial cell membrane integrity and permeability, and also inhibit the expression of genes associated with bacterial energy metabolism, as established by the experiments concerning cell membrane potential, SDS-PAGE electrophoresis, cell membrane integrity, and key gene expressions. This study offers valuable insights and serves as a theoretical foundation for the future development of macrolactins as antibacterial precursors.

Natural Prenylflavonoids from Sophora flavescens Root Bark against Multidrug-Resistant Methicillin-Sensitive Staphylococcus aureus Targeting the Membrane Permeability.

The overuse of antibiotics in animal farming and aquaculture has led to multidrug-resistant methicillin-sensitive Staphylococcus aureus (MR-MSSA) becoming a common pathogen in foodborne diseases. Sophora flavescens Ait. serves as a traditional plant antibacterial agent and functional food ingredient. A total of 30 compounds (1-30) were isolated from the root bark of S. flavescens, consisting of 20 new compounds (1-20). In the biological activity assay, compound 1 demonstrated a remarkable inhibitory effect on MR-MSSA, with an MIC of 2 μg/mL. Furthermore, 1 was found to rapidly eliminate bacteria, inhibit biofilm growth, and exhibit exceptionally low cytotoxicity. Mechanistic studies have revealed that 1 possesses an enhanced membrane-targeting ability, binding to the bacterial cell membrane components phosphatidylglycerol (PG), phosphatidylethanolamine (PE), and cardiolipin (CL). This disruption of bacterial cell membrane integrity increases intracellular reactive oxygen species, protein and DNA leakage, reduced bacterial metabolism, and ultimately bacterial death. In summary, these findings suggest that compound 1 holds promise as a lead compound against MR-MSSA.

Structure–activity relationships of the intramolecular disulphide bonds in LEAP2, an antimicrobial peptide from Acrossocheilus fasciatus

BackgroundThe liver-expressed antimicrobial peptide 2 (LEAP2) plays a pivotal role in the host’s immune response against pathogenic microorganisms. Numerous such antimicrobial peptides have recently been shown to mitigate infection risk in fish, and studying those harboured by the economically important fish Acrossocheilus fasciatus is imperative for enhancing its immune responses against pathogenic microorganisms. In this study, we cloned and sequenced LEAP2 cDNA from A. fasciatus to examine its expression in immune tissues and investigate the structure–activity relationships of its intramolecular disulphide bonds.ResultsThe predicted amino acid sequence of A. fasciatus LEAP2 was found to include a signal peptide, pro-domain, and mature peptide. Sequence analysis indicated that A. fasciatus LEAP2 is a member of the fish LEAP2A cluster and is closely related to Cyprinus carpio LEAP2A. A. fasciatus LEAP2 transcripts were expressed in various tissues, with the head kidney exhibiting the highest mRNA levels. Upon exposure to Aeromonas hydrophila infection, LEAP2 expression was significantly upregulated in the liver, head kidney, and spleen. A mature peptide of A. fasciatus LEAP2, consisting of two disulphide bonds (Af-LEAP2-cys), and a linear form of the LEAP2 mature peptide (Af-LEAP2) were chemically synthesised. The circular dichroism spectroscopy result shows differences between the secondary structures of Af-LEAP2 and Af-LEAP2-cys, with a lower proportion of alpha helix and a higher proportion of random coil in Af-LEAP2. Af-LEAP2 exhibited potent antimicrobial activity against most tested bacteria, including Acinetobacter guillouiae, Pseudomonas aeruginosa, Staphylococcus saprophyticus, and Staphylococcus warneri. In contrast, Af-LEAP2-cys demonstrated weak or no antibacterial activity against the tested bacteria. Af-LEAP2 had a disruptive effect on bacterial cell membrane integrity, whereas Af-LEAP2-cys did not exhibit this effect. Additionally, neither Af-LEAP2 nor Af-LEAP2-cys displayed any observable ability to hydrolyse the genomic DNA of P. aeruginosa.ConclusionsOur study provides clear evidence that linear LEAP2 exhibits better antibacterial activity than oxidised LEAP2, thereby confirming, for the first time, this phenomenon in fish.

Assessment of antibacterial activity, modes of action, and synergistic effects of Origanum vulgare hydroethanolic extract with antibiotics against avian pathogenic Escherichia coli

This study evaluates the antibacterial effectiveness of Origanum vulgare hydroethanolic extract, both independently and in combination with antibiotics, against Escherichia coli strains associated with avian colibacillosis—a significant concern for the poultry industry due to the rise of antibiotic-resistant E. coli. The urgent demand for new treatments is addressed by analyzing the extract's phytochemical makeup via High-Performance Liquid Chromatography (HPLC), which identified sixteen phenolic compounds. Antibacterial activity was determined through agar diffusion and the measurement of minimum inhibitory and bactericidal concentrations (MIC and MBC), showing moderate efficacy (MIC: 3.9 to 7.8 mg/mL, MBC: 31.2 to 62.4 mg/mL). Combining the extract with antibiotics like ampicillin and tetracycline amplified antibacterial activity, indicating a synergistic effect and highlighting the importance of combinatory treatments against resistant strains. Further analysis revealed the extract's mechanisms of action include disrupting bacterial cell membrane integrity and inhibiting ATPase/H+ proton pumps, essential for bacterial survival.Moreover, the extract effectively inhibited and eradicated biofilms, crucial for preventing bacterial colonization. Regarding cytotoxicity, the extract showed no hemolytic effect at 1 to 9 mg/mL concentrations. These results suggest Origanum vulgare extract, particularly when used with antibiotics, offers a promising strategy for managing avian colibacillosis, providing both direct antibacterial benefits and moderating antibiotic resistance, thus potentially reducing the economic impact of the disease on the poultry industry.

Differential mechanism between Listeria monocytogenes strains with different virulence contaminating ready-to-eat sausages during the simulated gastrointestinal tract

Listeria monocytogenes exhibits varying levels of pathogenicity when entering the host through contaminated food. However, little is known regarding the stress response and environmental tolerance mechanism of different virulence strains to host gastrointestinal (GI) stimuli. This study analyzed the differences in the survival and genes of stress responses among two strains of L. monocytogenes 10403S (serotype 1/2a, highly virulent strain) and M7 (serotype 4a, low-virulence strain) during simulated gastrointestinal digestion. The results indicated that L. monocytogenes 10403S showed greater acid and bile salt tolerance than L. monocytogenes M7, with higher survival rates and less cell deformation and cell membrane permeability during the in vitro digestion. KEGG analysis of the transcriptomes indicated that L. monocytogenes 10403S displayed significant activity in amino acid metabolism, such as glutamate and arginine, associated with acid tolerance. Additionally, L. monocytogenes 10403S demonstrated a higher efficacy in promoting activities that preserve bacterial cell membrane integrity and facilitate flagellar protein synthesis. These findings will contribute valuable practical insights into the tolerance distinctions among different virulence strains of L. monocytogenes in the GI environment.

Antibacterial Textile Coating Armoured with Aggregation-Induced Emission Photosensitisers to Prevent Healthcare-Associated Infections.

In the quest to curtail the spread of healthcare-associated infections, this work showcases the fabrication of a cutting-edge antibacterial textile coating armoured with aggregation-induced emission photosensitisers (AIE PS) to prevent bacterial colonisation on textiles. The adopted methodology includes a multi-step process using plasma polymerisation and subsequent integration of AIE PS on their surface. The antibacterial effectiveness of the coating was tested against Pseudomonas aeruginosa and Staphylococcus aureus after light irradiation for 1 h. Furthermore, antibacterial mechanistic studies revealed their ability to generate reactive oxygen species that can damage bacterial cell membrane integrity. The results of this investigation can be used to develop ground-breaking explanations for infection deterrence, principally in situations where hospital fabrics play a critical part in the transmission of diseases. The antibacterial coating for textiles developed in this study holds great promise as an efficient strategy to promote public health and reduce the danger of bacterial diseases through regular contact with fabrics.

The capacity of Lamiaceae essential oils, extracts and hydrolats against pathogenic biofilms

The study aimed to analyse the potential of Lamiaceae essential oils, extracts, and hydrolats against bacterial biofilms. Bacterial cells Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus cereus were exposed to Thymus vulgaris L. (thyme), Salvia officinalis L. (sage), Mentha × piperita L. (mint) essential oils, extracts, and hydrolats. The result of the minimal inhibitory concentration assessment shows the highest antibacterial potential for essential oils, followed by extracts and hydrolats respectively. The anti-biofouling capacity revealed that thyme essential oil has the highest potential for biofilm prevention for all tested bacteria, reducing up to 91% of biofilm, followed by mint (88%) and sage (87%) essential oil. While the thyme extract (84%), sage extract (83%) and hydrolat (77%) we less effective. The chemical composition of thyme essential oil showed a high percentage of monoterpene hydrocarbons and oxygenated monoterpenes, among which p-cymene and thymol were the most predominant. The bacterial cell membrane integrity assessment shows a significant increase in dead cells by increasing the concentration of thyme essential oil. The findings of our research indicate that the choice of herbal preparation significantly affects the active components, thereby influencing both antibacterial and anti-biofouling capabilities. Lamiaceae essential oils show great potential for biofilm management and represent a good candidate for antibacterial application in pharmacy, medicine, and industry.

Novel silver nanoparticle-antibiotic combinations as promising antibacterial and anti-biofilm candidates against multiple-antibiotic resistant ESKAPE microorganisms

HypothesisThe emergence of Multiple Antibiotic Resistance (MAR) in ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) pathogens is a global challenge to public health. The inherent antimicrobial nature of silver nanoparticles (AgNPs) makes them promising antimicrobial candidates against antibiotic-resistant pathogens. This study explores the combination of AgNPs with antibiotics (SACs) to create new antimicrobial agents effective against MAR ESKAPE microorganisms. MethodsAgNPs were synthesized using Streptococcus pneumoniae ATCC 49619 and characterized for structure and surface properties. The SACs were tested against ESKAPE microorganisms using growth kinetics and time-kill curve methods. The effect of SACs on bacterial biofilms and the disruption of cell membranes was determined. The in-vitro cytotoxicity effect of the AgNPs was also studied. FindingsThe synthesized AgNPs (spherical, 7.37±4.55 nm diameter) were antimicrobial against MAR ESKAPE microorganisms. The SACs showed synergy with multiple conventional antibiotics, reducing their antibacterial concentrations up to 32-fold. Growth kinetics and time-kill studies confirmed the growth retardation effect and bactericidal activity of SACs. Mechanistic studies suggested that these biofilm-eradicating SACs probably resulted in the loss of bacterial cell membrane integrity, leading to leakage of the cytoplasmic content. The AgNPs were highly cytotoxic against skin melanoma cells but non-cytotoxic to normal Vero cells.

Metal-amplified sonodynamic therapy of Ti-based chitosan-polyvinyl alcohol hybrid hydrogel dressing against subcutaneous Staphylococcus aureus infection

Ultrasound (US)-mediated sonodynamic therapy (SDT) has received extensive attention in pathogen elimination for non-invasiveness and high spatial and temporal accuracy. Considering that hydrogel can provide a healing-friendly environment for wounds, in this work, hybrid hydrogels are constructed by embedding Ag doped TiO2 nanoparticles in chitosan-polyvinyl alcohol hydrogels for enhanced sonodynamic antibacterial therapy. With metal silver doped, TiO2 nanoparticles sonosensitivity is improved to generate more reactive oxygen species (ROS), which endows hybrid hydrogels with high-efficient antibacterial properties. In vivo results show that hybrid hydrogel dressing can prevent infection and promote wound closure within 2 days. The healing ratio excess 95 % with no pus produced at the end of treatment. The therapeutic mechanism was identified that heterojunction formed in Ag doped TiO2 facilitates the separation of charge carriers under US irradiation, leading to elevating ROS generation. The generated ROS promote hybrid hydrogels sonodynamic antibacterial therapeutic efficacy to thoroughly eliminate pathogen via disrupting bacterial cell membrane integrity, decreasing membrane fluidity and increasing membrane permeability. Besides, biofilm formation could be effectively inhibited. This work developed a hybrid hydrogel with amplified SDT effect for wound healing, which is expected to provide inspiration of hybrid hydrogels design and Ti-based nanomaterials sonosensitivity enhancement.

Hydantoin derivative dimers as broad-spectrum antimicrobial agents against ESKAPE pathogens with enhanced killing rate and stability.

A new series of hydantoin derivative dimers as potential broad-spectrum antibiotic agents is designed and synthesized to combat ESKAPE pathogens. As membrane-active antimicrobial agents, in addition to cationic charged and hydrophobic groups that mimic AMPs (antimicrobial peptides), hydantoin backbones and aromatic linkers increased the rigidity and lipophilicity of the designed compounds, thus improving the stability and bactericidal killing rate. After whole cell phenotypic screening against eight bacterial strains, including MRSA (methicillin-resistant S. aureus), compound 18 was chosen as the lead compound with overall excellent broad-spectrum antibacterial activity (GM = 7.32 μg mL-1) and good selectivity. Kill-kinetic studies of compound 18 showed that the bacterial growth of both Gram-positive and Gram-negative was completely inhibited within one hour, which demonstrated excellent sterilization efficiency of 18. Furthermore, drug resistance and mechanism studies showed that compound 18 exhibited a steady antibacterial performance during 25 passages and could disrupt bacterial cell membrane integrity and cause cell death. Along with the facile synthesis procedures in solution, this series of hydantoin derivative dimer compounds could be an appealing next generation of antibiotic agents to combat emergent drug resistance.

Anti bacterial function of secreted human FABP3

FABP3 belongs to a large family of cytoplasmic fatty acid binding proteins that are expressed in a tissue-specific manner. It is predominantly expressed in breast, muscle and heart. During our exploratory studies on the role of FABP3 in tumorigenesis and our consequent attempts to study the molecular mechanism responsible for the oncogenic potential of FABP3, we came across an unexpected role of FABP3 as an anti-bacterial protein. Presence of the protein was detected in culture media of cell lines stably over-expressing human FABP3. Conditioned medium from these FABP3 over-expressing cells exerted a distinct anti-bacterial activity against E. coli. Our results indicate that binding of FABP3 to the bacterial cell surface contributes to its anti-bacterial activity. Incubation of E. coli bacterial cells with FABP3 protein led to disruption of the physical integrity of bacterial cell membrane causing leakage of cellular components. Further, in silico analysis predicted strong binding of FABP3 to the antibiotic binding sites on the bacterial ribosome. Interestingly, we found that FABP3 is a naturally occurring secretory protein present in milk in abundance as confirmed by western blot and ELISA. Thus, our experimental data together with in silico analysis suggests that FABP3 is secreted in milk, has an anti-bacterial function, shows activity against E. coli by disrupting bacterial membrane and targeting the ribosome, and may play a protective role against bacterial infection in newborns.

Ru-Based Organometallic Agents Bearing Phenyl Hydroxide: Synthesis and Antibacterial Mechanism Study against Staphylococcus aureus.

The development of antimicrobial agents with novel model of actions is a promising strategy to combat multiple resistant bacteria. Here, three ruthenium-based complexes, which acted as potential antimicrobial agents, were synthesized and characterized. Importantly, three complexes all showed strong bactericidal potency against Staphylococcus aureus. In particular, the most active one has a MIC of 6.25 μg/mL. Mechanistic studies indicated that ruthenium complex killed S. aureus by releasing ROS and damaging the integrity of bacterial cell membrane. In addition, the most active complex not only could inhibit the biofilm formation and hemolytic toxin secretion of S. aureus, but also serve as a potential antimicrobial adjuvant as well, which showed synergistic effects with eight traditional antibiotics. Finally, both G. mellonella larva infection model and mouse skin infection model all demonstrated that ruthenium complex also showed significant efficacy against S. aureus in vivo. In summary, our study suggested that ruthenium-based complexes bearing a phenyl hydroxide are promising antimicrobial agents for combating S. aureus.

The Mechanism of Antimicrobial Activity of Conjugated Bile Acids against Lactic Acid Bacilli.

The mechanism underlying antimicrobial activity of conjugated bile acids against strains of lactic acid bacilli is not well understood. The purpose of this study was to investigate two typical conjugated bile acids (glycochenodeoxycholic acid and taurochenodeoxycholic acid) for their mechanisms of antimicrobial activity against four strains of different species of lactic acid bacilli at the physiological pH of the small intestine of humans. The bacterial cell membrane integrity, transmembrane potential, and transmembrane pH gradient were examined using the fluorescence probes SYTO 9 plus propidium iodide, 3,3'-dipropylthiadicarbocyanine iodide, and 5(6)-carboxyfluorescein diacetate N-succinimidyl ester, respectively. The intracellular ATP levels were measured by the firefly luciferase-based bioluminescence method. It was found that the antimicrobial activity of conjugated bile acids against the strains of lactic acid bacilli is strain-specific, and glycochenodeoxycholic acid showed significantly greater antimicrobial activity than taurochenodeoxycholic acid against the strains of lactic acid bacilli. The conjugated bile acids inhibited the growth of strains of lactic acid bacilli by disrupting membrane integrity, dissipating transmembrane potential, reducing the transmembrane pH gradient, and depleting intracellular ATP. In conclusion, the antimicrobial activity of conjugated bile acids against lactic acid bacilli is a multifactorial phenomenon. This study will provide valuable information for developing strategies to improve the ability of lactic acid bacilli to tolerate bile in vivo.

Bithionol Restores Sensitivity of Multidrug-Resistant Gram-Negative Bacteria to Colistin with Antimicrobial and Anti-biofilm Effects.

Being among the few last-resort antibiotics, colistin (COL) has been used to treat severe infectious diseases, such as those caused by multidrug-resistant Gram-negative bacteria (MDR GNB). However, the appearance of colistin-resistant (COL-R) GNB has been frequently reported. Therefore, novel antimicrobial strategies need to be urgently sought to address this resistance challenge. In the present study, antimicrobial drug screening conducted revealed that bithionol (BT), approved by the Food and Drug Administration and used as an anthelminthic drug for paragonimiasis, exhibited a synergistic antibacterial effect with COL. Clinically isolated COL-R GNB were used as candidates to evaluate the synergistic antibacterial activity. The results revealed that BT could significantly reverse the sensitivity of COL-R GNB to COL. Furthermore, the combined application of BT and COL can reduce bacterial biofilm formation and have a scavenging effect on the mature biofilm in vitro. The damage caused to the bacterial cell membrane integrity by the BT/COL combination was observed under a fluorescence microscope. The fluorescence intensity of reactive oxygen species also increased in the experimental group. The BT/COL combination also exhibited a synergistic antibacterial effect in vivo. Importantly, BT was confirmed to be safe at the highest concentrations that exerted synergistic effects on all tested strains. In conclusion, our findings demonstrated that BT exerted synergistic antimicrobial and anti-biofilm effects when combined with COL against MDR organisms, especially COL-R GNB, in vitro and in vivo. The findings thus provide a reference for the clinical response to the serious challenge of MDR GNB and the exploitation of the potential antibacterial activities of existing clinical non-antibacterial drugs.

Effect of combined zinc oxide nanoparticles using citric acid and microwave heating on the quality of animal fat

The processing method of animal fat as a non-negligible food resource has attracted attention. ZnO nanoparticles (ZnONPs) are a widely studied inorganic antimicrobial agent. In this paper, citric acid modified ZnO nanoparticles (CA-ZnO) were prepared using citric acid for surface modification of ZnO nanoparticles. The surface modification reduced the agglomeration of ZnONPs in the water, and the particle size of CA-ZnO particles was reduced by about 4 times compared to the ZnONPs after dispersion in the water. CA-ZnO also showed a good inhibitory effect against Bacillus cereus, Escherichia coli, and Staphylococcus aureus at the concentration of 0.05 g/kg. Microwave heating combined with CA-ZnO (MCCZ) had a good bactericidal effect and disrupted the integrity of bacterial cell membrane leading to leakage of cell materials and altering the secondary structure of bacterial proteins such as the reduction of α-helix. Using this method for sterilization of animal fats (a mix of same amount of chicken oil and lard), the sterilization rate of animal fats reached 99.97% after 90 s of MCCZ treatment. And MCCZ resulted in less flavor change and quality deterioration compared to traditional high temperature treatment. Therefore, MCCZ could be used as a new method to preserve the product quality of mixed chicken oil and lard.

Antibacterial Activity and Possible Mechanism of Litsea cubeba Essential Oil Against Shigella sonnei and Its Application in Lettuce.

Shigella sonnei, the causative agents of bacillary dysentery, remains a significant threat to public health. Litsea cubeba essential oil (LC-EO), one of the natural essential oils, exhibited promising biological activities. In this study, the antibacterial effects and possible mechanisms of LC-EO on S. sonnei and its application in lettuce medium were investigated. The minimum inhibitory concentration (MIC) of LC-EO against S. sonnei ATCC 25931 and CMCC 51592 was 4 and 6 μL/mL, respectively. The LC-EO could inhibit the growth of S. sonnei, and decreased S. sonnei to undetectable levels with 4 μL/mL for 1 h in Luria-Bertani broth. The antibacterial mechanism indicated that after the treatment of LC-EO, the production of reactive oxygen species and the activity of superoxide dismutase were significantly elevated in S. sonnei cells, and eventually led to the lipid oxidation product, the malondialdehyde content that significantly increased. Moreover, LC-EO at 2 MIC could destroy 96.51% of bacterial cell membrane integrity, and made S. sonnei cells to appear wrinkled with a rough surface, so that the intracellular adenosine triphosphate leakage was about 0.352-0.030 μmol/L. Finally, the results of application evaluation indicated that the addition of LC-EO at 4 μL/mL in lettuce leaves and 6 μL/mL in lettuce juice could decrease the number of S. sonnei to undetectable levels without remarkable influence on the lettuce leaf sensory quality. In summary, LC-EO exerted strong antibacterial activity and has the potential to control S. sonnei in food industry.

Synthesis and biological evaluation of ruthenium complexes containing phenylseleny against Gram-positive bacterial infection by damage membrane integrity and avoid drug-resistance

Compounds modified with selenium atom as potential antibacterial agents have been exploited to combat the nondrug-resistant bacterial infection. In this study, we designed and synthesized four ruthenium complexes retouching of selenium-ether. Fortunately, those four ruthenium complexes shown excellent antibacterial bioactive (MIC: 1.56–6.25 μg/mL) against Staphylococcus aureus (S. aureus), and the most active complex Ru(II)-4 could kill S. aureus by targeting the membrane integrity and avoid the bacteria to evolve drug resistance. Moreover, Ru(II)-4 was found to significantly inhibit the formation of biofilms and biofilm eradicate capacity. In toxicity experiments, Ru(II)-4 exhibited poor hemolysis and low mammalian toxicity. To illustrate the antibacterial mechanism: we conducted scanning electron microscope (SEM), fluorescent staining, membrane rupture and DNA leakage assays. Those results demonstrated that Ru(II)-4 could destroy the integrity of bacterial cell membrane. Furthermore, both G. mellonella wax worms infection model and mouse skin infection model were established to evaluate the antibacterial activity of Ru(II)-4 in vivo, the results indicated that Ru(II)-4 was a potential candidate for combating S. aureus infections, and almost non-toxic to mouse tissue. Thus, all the results indicated that introducing selenium-atom into ruthenium compounds were a promising strategy for developing interesting antibacterial agents.

Defect-Engineered Functionalized MoS2 Quantum Dots with Enhanced Antibacterial Activity

The rapid development of multidrug-resistant bacterial strains creates a global threat and warrants advanced strategies to control infectious diseases. Surface-modified two-dimensional molybdenum disulfide (MoS2) nanomaterials have great potential to eradicate pathogenic bacteria. In MoS2 nanosheets, the presence of atomic defects plays a crucial role in determining their physical and electronic properties. The presence of defects not only improves the extent of surface modification but also affects the generation of reactive oxygen species (ROS), which play a pivotal role in antibacterial activity. Hence, the facile preparation of MoS2 nanomaterials with a controlled degree of defects would prompt their utilization as an efficient antibacterial agent. Herein, we have demonstrated the preparation of different defect-engineered MoS2 quantum dots (QDs), followed by surface modification with thiol ligands. The extent of ligand conjugation on the MoS2 QDs highly depends on the degree of defects, and that can also enhance the aqueous stability. The functionalized MoS2 QDs possessing a higher degree of defects showed remarkably high antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) compared to the lower defect-containing MoS2 QDs. This is due to the generation of a large amount of ROS along with the increased cellular interactions of functionalized MoS2 QDs. This could potentially disrupt the bacterial cell membrane integrity to show enhanced bactericidal activity. The MRSA bacterial growth has been completely suppressed in the presence of only 0.65 μg/mL of functionalized MoS2 QDs.

In vitro safety assessment of electrohydrodynamically encapsulated Lactiplantibacillus plantarum CRD7 and Lacticaseibacillus rhamnosus CRD11 for probiotics use

The current study aimed to validate the safety of electrohydrodynamically encapsulated Lactiplantibacillus plantarum CRD7 and Lacticaseibacillus rhamnosus CRD11 in accordance with guidelines of FAO/WHO and ICMR/DBT. In vitro assays such as mucin degradation, hemolysis of blood cells, antimicrobial susceptibility pattern, possession of virulence factors, biogenic amine, and ammonia production were assessed. In results, the cross-streak and co-culture techniques revealed that CRD7 and CRD11 were compatible in vitro. Upon visual inspection through scanning electron and fluorescence microscopy, the integrity of bacterial cell membrane was confirmed even after the encapsulation process. CRD7 and CRD11 were non-hemolytic and showed negative responses to gelatinase, urease, and DNase activities. Non-mucinolytic activity of CRD7 and CRD11 was verified by measuring cell growth rate (p < 0.05) in different modified media followed by SDS-PAGE. High-performance liquid chromatography analysis revealed that both the strains did not produce biogenic amines (putrescine, cadaverine, histamine, and tyramine). Neither of the Lactobacillus strains produced ammonia after growing in BHI broth for 5 days at 37 °C. L-lactate production was highest (p < 0.05) in CRD11 (8.83 g/L), followed by CRD7 (8.16 g/L), whereas the lowest (p < 0.05) D-lactate was registered for encapsulated CRD11 (0.33 g/L) and CRD7 (0.49 g/L). The antibiogram profile determined through minimum inhibitory concentration showed that CRD7 and CRD11 were sensitive to key antibiotics suggested by EFSA except for gentamycin and kanamycin. PCR data on virulence genes demonstrated that both strains were safe for probiotic use. Moreover, CRD7 and CRD11 strains caused insignificant (p > 0.05) changes in the cell viability of Caco-2 cells as estimated by MTT (98.94–99.50%) and NR uptake (95.42–97.03%) assays and showed sensitivity to human serum. According to the results of these evaluated attributes, it is concluded that L. plantarum CRD7 and L. rhamnosus CRD11 are safe, non-toxic to human epithelial cells, and thus may be potentially suitable for various food/feed applications.

Mechanism of antimicrobials immobilized on packaging film inhabiting foodborne pathogens

Non-migrating active packaging can provide long-lasting and safe antibacterial effects; however, the underlying antibacterial mechanism remains unclear. In this study, chitosan (CS) and lysozyme (LYS) were covalently immobilized on a polylactic acid (PLA) film to produce functional packaging films, chitosan-graft-polylactic acid (CS-g-PLA) and lysozyme-graft-polylactic acid (LYS-g-PLA). The antimicrobial effects and mechanisms of action of these films against Staphylococcus aureus and Escherichia coli were investigated. The minimum inhibitory concentrations (MICs) of the CS and LYS against S. aureus were both 1.25 mg/mL; the MIC against E. coli was 1.25 mg/mL for CS and 2.5 mg/mL for LYS. Scanning and transmission electron microscopy revealed physical damage, significant morphological changes, and intracellular component leakage from bacterial cells after treatment with antimicrobial agents. Cell integrity and conductivity tests showed that bacterial cell membrane integrity was destroyed, and its permeability changed. The gel retardation assay showed that the CS-g-PLA film affected the bacteria by binding to genomic DNA. The results showed that the grafted films effectively inhibited S. aureus and E. coli. CS-g-PLA and LYS-g-PLA films inhibited bacterial growth by destroying the integrity of bacterial cell membranes and promoting changes in membrane wall permeability. In addition, immobilized CS can enter bacterial cells and bind with DNA, thus inhibiting the growth and reproduction of bacteria.