Understanding antibiotic resistance via outer membrane permeability

N-acetylcysteine promotes doxycycline resistance in the bacterial pathogen Edwardsiella tarda

Bacterial resistance poses a significant threat to both human and animal health. N-acetylcysteine (NAC), which is used as an anti-inflammatory, has been shown to have distinct and contrasting impacts on bacterial resistance. However, the precise mechanism underlying the relationship between NAC and bacterial resistance remains unclear and requires further investigation. In this study, we study the effect of NAC on bacterial resistance and the underlying mechanisms. Specifically, we examine the effects of NAC on Edwardsiella tarda ATCC15947, a pathogen that exhibits resistance to many antibiotics. We find that NAC can promote resistance of E. tarda to many antibiotics, such as doxycycline, resulting in an increase in the bacterial survival rate. Through proteomic analysis, we demonstrate that NAC activates the amino acid metabolism pathway in E. tarda, leading to elevated intracellular glutathione (GSH) levels and reduced reactive oxygen species (ROS). Additionally, NAC reduces antibiotic influx while enhancing efflux, thus maintaining low intracellular antibiotic concentrations. We also propose that NAC promotes protein aggregation, thus contributing to antibiotic resistance. Our study describes the mechanism underlying E. tarda resistance to doxycycline and cautions against the indiscriminate use of metabolite adjuvants.

Unitig-centered pan-genome machine learning approach for predicting antibiotic resistance and discovering novel resistance genes in bacterial strains

In current genomic research, the widely used methods for predicting antimicrobial resistance (AMR) often rely on prior knowledge of known AMR genes or reference genomes. However, these methods have limitations, potentially resulting in imprecise predictions owing to incomplete coverage of AMR mechanisms and genetic variations. To overcome these limitations, we propose a pan-genome-based machine learning approach to advance our understanding of AMR gene repertoires and uncover possible feature sets for precise AMR classification. By building compacted de Brujin graphs (cDBGs) from thousands of genomes and collecting the presence/absence patterns of unique sequences (unitigs) for Pseudomonas aeruginosa, we determined that using machine learning models on unitig-centered pan-genomes showed significant promise for accurately predicting the antibiotic resistance or susceptibility of microbial strains. Applying a feature-selection-based machine learning algorithm led to satisfactory predictive performance for the training dataset (with an area under the receiver operating characteristic curve (AUC) of > 0.929) and an independent validation dataset (AUC, approximately 0.77). Furthermore, the selected unitigs revealed previously unidentified resistance genes, allowing for the expansion of the resistance gene repertoire to those that have not previously been described in the literature on antibiotic resistance. These results demonstrate that our proposed unitig-based pan-genome feature set was effective in constructing machine learning predictors that could accurately identify AMR pathogens. Gene sets extracted using this approach may offer valuable insights into expanding known AMR genes and forming new hypotheses to uncover the underlying mechanisms of bacterial AMR.

Inosine reverses multidrug resistance in Gram-negative bacteria carrying mobilized RND-type efflux pump gene cluster tmexCD-toprJ

Antimicrobial resistance is rapidly increasing worldwide, highlighting the urgent need for pharmaceutical and nonpharmaceutical interventions to tackle different-to-treat bacterial infections. Tigecycline, a semi-synthesis glycylcycline for parenteral administration, is widely recognized as one of the few effective therapies available against pan-drug resistant Gram-negative pathogens. Regrettably, the efficacy of multiple drugs, including tigecycline, is currently being undermined due to the emergence of a recently discovered mobilized resistance-nodulation-division-type efflux pump gene cluster tmexCD1-toprJ1. Herein, by employing untargeted metabolomic approaches, we reveal that the expression of tmexCD1-toprJ1 disrupts bacterial purine metabolism, with inosine being identified as a crucial biomarker. Notably, the supplementation of inosine effectively reverses tigecycline resistance in tmexCD1-toprJ1-positive bacteria. Mechanistically, exogenous inosine enhanced bacterial proton motive force, which promotes the uptake of tigecycline. Furthermore, inosine enhances succinate biosynthesis by stimulating the tricarboxylic acid cycle. Succinate interacts with the two-component system EnvZ/OmpR and upregulates OmpK 36, thereby promoting the influx of tigecycline. These actions collectively lead to the increased intracellular accumulation of tigecycline. Overall, our study offers a distinct combinational strategy to manage infections caused by tmexCD-toprJ-positive bacteria.

IMPORTANCE

TMexCD1-TOprJ1, a mobilized resistance-nodulation-division-type efflux pump, confers phenotypic resistance to multiple classes of antibiotics. Nowadays, tmexCD-toprJ has disseminated among diverse species of clinical pathogens, exacerbating the need for novel anti-infective strategies. In this study, we report that tmexCD1-toprJ1-negative and -positive bacteria exhibit significantly different metabolic flux and characteristics, especially in purine metabolism. Intriguingly, the addition of inosine, a purine metabolite, effectively restores the antibacterial activity of tigecycline by promoting antibiotic uptake. Our findings highlight the correlation between bacterial mechanism and antibiotic resistance, and offer a distinct approach to overcome tmexCD-toprJ-mediated multidrug resistance.

Albumin as a functional carrier solubilizing and facilitating fusidic acid transmembrane delivery into Gram-negative bacteria

Reversing the bacterial resistance is of great significance and importance. Fusidic acid (FA) is commonly effective against Gram-positive bacterial infections, but most Gram-negative bacteria have intrinsic resistance to FA, primarily due to the strong cell membrane-FA interactions, which highly inhibit the intracellular transport of FA. Herein, we use albumin (bovine serum albumin, BSA) as a bifunctional carrier to solubilize FA and facilitate its transmembrane delivery into Gram-negative bacterial cells. The water solubility of FA is significantly enhanced from 11.87 to 442.20 μg/mL by 5 mg/mL BSA after forming FA-BSA complex. Furthermore, FA-BSA (200 μg/mL) causes 99.96 % viability loss to the model pathogen E. coli upon incubation for 3 h, while free FA or BSA alone shows little activity. Elongation of E. coli cells after treated by FA-BSA is demonstrated by SEM, and the transmembrane transport of FA-BSA is demonstrated by CLSM. Interestingly, increasing the BSA amount substantially reduce the antibacterial activity of FA-BSA, implying an albumin-based transmembrane delivery mechanism may exist. This is the first report regarding successfully reversing the intrinsic resistance of Gram-negative bacteria to FA in the form of FA-BSA. The ready availability of albumin and the simple preparation allows FA-BSA to have great potentials for clinical use.

An Overview of the Recent Advances in Antimicrobial Resistance

Antimicrobial resistance (AMR), frequently considered a major global public health threat, requires a comprehensive understanding of its emergence, mechanisms, advances, and implications. AMR's epidemiological landscape is characterized by its widespread prevalence and constantly evolving patterns, with multidrug-resistant organisms (MDROs) creating new challenges every day. The most common mechanisms underlying AMR (i.e., genetic mutations, horizontal gene transfer, and selective pressure) contribute to the emergence and dissemination of new resistant strains. Therefore, mitigation strategies (e.g., antibiotic stewardship programs-ASPs-and infection prevention and control strategies-IPCs) emphasize the importance of responsible antimicrobial use and surveillance. A One Health approach (i.e., the interconnectedness of human, animal, and environmental health) highlights the necessity for interdisciplinary collaboration and holistic strategies in combating AMR. Advancements in novel therapeutics (e.g., alternative antimicrobial agents and vaccines) offer promising avenues in addressing AMR challenges. Policy interventions at the international and national levels also promote ASPs aiming to regulate antimicrobial use. Despite all of the observed progress, AMR remains a pressing concern, demanding sustained efforts to address emerging threats and promote antimicrobial sustainability. Future research must prioritize innovative approaches and address the complex socioecological dynamics underlying AMR. This manuscript is a comprehensive resource for researchers, policymakers, and healthcare professionals seeking to navigate the complex AMR landscape and develop effective strategies for its mitigation.

Green synthesis of polyethylene glycol coated, ciprofloxacin loaded CuO nanoparticles and its antibacterial activity against Staphylococcus aureus

Antibacterial resistance requires an advanced strategy to increase the efficacy of current therapeutics in addition to the synthesis of new generations of antibiotics. In this study, copper oxide nanoparticles (CuO-NPs) were green synthesized using Moringa oleifera root extract. CuO-NPs fabricated into a form of aspartic acid-ciprofloxacin-polyethylene glycol coated copper oxide-nanotherapeutics (CIP-PEG-CuO) to improve the antibacterial activity of NPs and the efficacy of the drug with controlled cytotoxicity. These NPs were charachterized by Fourier transform infrared spectroscopy (FTIR), x-rays diffraction spectroscopy (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). Antibacterial screening and bacterial chemotaxis investigations demonstrated that CIP-PEG-CuO NPs show enhanced antibacterial potential against Gram-positive and Gram-negative clinically isolated pathogenic bacterial strains as compared to CuO-NPs. In ex-vivo cytotoxicity CIP-PEG-CuO-nano-formulates revealed 88% viability of Baby Hamster Kidney 21 cell lines and 90% RBCs remained intact with nano-formulations during hemolysis assay. An in-vivo studies on animal models show that Staphylococcus aureus were eradicated by this newly developed formulate from the infected skin and showed wound-healing properties. By using specially designed nanoparticles that are engineered to precisely transport antimicrobial agents, these efficient nano-drug delivery systems can target localized infections, ensure targeted delivery, enhance efficacy through increased drug penetration through physical barriers, and reduce systemic side effects for more effective treatment.

Carbapenemase producing Gram negative bacteria: Review of resistance and detection methods

Gram negative bacilli that are carbapenem resistant have emerged and are spreading worldwide. Infections caused by carbapenem resistant isolates posses a significant threat due to their high morbidity and mortality rates. Carbapenemases production by multi-drug resistant pathogens severely restricts treatment choices for illnesses caused by bacteria that are resistant to both carbapenems and majority of β-lactam antibiotics. Various phenotypic and genotypic methods for identification can distinguish between different classes of carbapenemase and identify pathogens that are resistant to carbapenems. The establishment of a quick, accurate and reliable test for identifying the clinical strains that produce the carbapenemase enzyme is essential for optimum diagnosis of microbial pathogens and management of the global rise in the prevalence of carbapenemase producing bacterial strains. The aim of this review was to summarize the mechanisms of carbapenem resistance and to provide an overview of different carbapenemase detection methods for carbapenem resistant Gram negative bacilli.

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

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

Coumarin derivatives ameliorate the intestinal inflammation and pathogenic gut microbiome changes in the model of infectious colitis through antibacterial activity

Coumarin, a phenolic compound, is a secondary metabolite produced by plants such as Tanga and Lime. Coumarin derivatives were prepared via Pechmann condensation. In this study, we performed in vitro and in vivo experiments to determine the antimicrobial and gut immune-regulatory functions of coumarin derivatives. For the in vitro antimicrobial activity assay, coumarin derivatives C1 and C2 were selected based on their pathogen-killing activity against various pathogenic microbes. We further demonstrated that the selected coumarin derivatives disrupted bacterial cell membranes. Next, we examined the regulatory function of the coumarin derivatives in gut inflammation using an infectious colitis model. In an in vivo infectious colitis model, administration of selected C1 coumarin derivatives reduced pathogen loads, the number of inflammatory immune cells (Th1 cells and Th17 cells), and inflammatory cytokine levels (IL-6 and IL-1b) in the intestinal tissue after pathogen infection. In addition, we found that the administration of C1 coumarin derivatives minimized abnormal gut microbiome shift-driven pathogen infection. Potential pathogenic gut microbes, such as Enterobacteriaceae and Staphylococcaceae, were increased by pathogen infection. However, this pathogenic microbial expansion was minimized and beneficial bacteria, such as Ligilactobacillus and Limosilactobacillus, increased with C1 coumarin derivative treatment. Functional gene enrichment assessment revealed that the relative abundance of genes associated with lipid and nucleotide metabolism was reduced by pathogen infection; however, this phenomenon was not observed in C1 coumarin derivative-treated animals. Collectively, our data suggest that C1 coumarin derivative is effective antibacterial agents that minimize pathogen-induced gut inflammation and abnormal gut microbiome modulation through their antibacterial activity.

An evaluation of conventional and nature-based technologies for controlling antibiotic-resistant bacteria and antibiotic-resistant genes in wastewater treatment plants

Antibiotic resistance is a globally recognized health concern which leads to longer hospital stays, increased morbidity, increased mortality, and higher medical costs. Understanding how antibiotic resistance persists and exchanges in environmental systems like soil, water, and wastewater are critically important for understanding the emergence of pathogens with new resistance profiles and the subsequent exposure of people who indirectly/directly come in contact with these pathogens. There are concerns about the widespread application of prophylactic antibiotics in the clinical and agriculture sectors, as well as chemicals/detergents used in food and manufacturing industries, especially the quaternary ammonium compounds which have been found responsible for the generation of resistant genes in water and soil. The rates of horizontal gene transfer increase where there is a lack of proper water/wastewater infrastructure, high antibiotic manufacturing industries, or endpoint users - such as hospitals and intensive agriculture. Conventional wastewater treatment technologies are often inefficient in the reduction of ARB/ARGs and provide the perfect combination of conditions for the development of antibiotic resistance. The wastewater discharged from municipal facilities may therefore be enriched with bacterial communities/pathogens and provide a suitable environment (due to the presence of nutrients and other pollutants) to enhance the transfer of antibiotic resistance. However, facilities with tertiary treatment (either traditional/emerging technologies) provide higher rates of reduction. This review provides a synthesis of the current understanding of wastewater treatment and antibiotic resistance, examining the drivers that may accelerate their possible transmission to a different environment, and highlighting the need for tertiary technologies used in treatment plants for the reduction of resistant bacteria/genes.

The pearl jubilee of microcin J25: thirty years of research on an exceptional lasso peptide

Covering: 1992 up to 2023Since their discovery, lasso peptides went from peculiarities to be recognized as a major family of ribosomally synthesized and post-translationally modified peptide (RiPP) natural products that were shown to be spread throughout the bacterial kingdom. Microcin J25 was first described in 1992, making it one of the earliest known lasso peptides. No other lasso peptide has since then been studied to such an extent as microcin J25, yet, previous review articles merely skimmed over all the research done on this exceptional lasso peptide. Therefore, to commemorate the 30th anniversary of its first report, we give a comprehensive overview of all literature related to microcin J25. This review article spans the early work towards the discovery of microcin J25, its biosynthetic gene cluster, and the elucidation of its three-dimensional, threaded lasso structure. Furthermore, the current knowledge about the biosynthesis of microcin J25 and lasso peptides in general is summarized and a detailed overview is given on the biological activities associated with microcin J25, including means of self-immunity, uptake into target bacteria, inhibition of the Gram-negative RNA polymerase, and the effects of microcin J25 on mitochondria. The in vitro and in vivo models used to study the potential utility of microcin J25 in a (veterinary) medicine context are discussed and the efforts that went into employing the microcin J25 scaffold in bioengineering contexts are summed up.

Goethite adaptation prompts alterations in antibiotic susceptibility and suppresses development of antibiotic resistance in bacteria

Understanding the impact of environmental factors on antibiotic sensitivity and the emergence of antibiotic resistance in microorganism is crucial for antibiotics management and environmental risk assessment. Natural materials, like mineral particles, are prevalent in aquatic and terrestrial ecosystems. However, it remains unclear how microorganism adapt to the physical stress of mineral particles and whether this adaptation influences antibiotic sensitivity and the evolution of antibiotic resistance. In this study, the model bacterium Escherichia coli (E. coli) was exposed to the mineral particle goethite for 30 generations. Adaptive morphogenesis, including an increase in the fraction of spherical bacteria, variations in bacterial mobility, a slightly increased cell membrane thickness, and genome-wide changes in the transcriptomic profile, were observed in adapted E. coli samples to counteract the stress. Moreover, the goethite adapted E. coli showed increased susceptibility to antibiotics including amoxicillin and tetracycline, and decreased susceptibility to kanamycin compared to its ancestral counterparts. These alterations in antibiotic susceptibility in the adapted E. coli were not heritable, as evidenced by the gradual recovery of antibiotic tolerance in cells with the cessation of goethite exposure. Transcriptomic data and a series of experiments suggested that these changes may be associated with variations in cell membrane property and iron metabolism. In addition, the evolution of antibiotic resistance in adapted cells occurred at a slower rate compared to their ancestral counterparts. For instance, E. coli adapted to goethite at a concentration of 1 mg/mL did not acquire antibiotic resistance even after 13 generations, probably due to its poor biofilm-formation capacity. Our findings underscore the occurrence of microbial adaptation to goethite, which influenced antibiotic sensitivity and decelerated the development of resistance in microorganisms. This insight contributes to our comprehension of the natural dynamics surrounding the evolution of antibiotic resistance and opens new perspectives for addressing this issue through nanotechnology-based approaches.

Current developments and prospects of the antibiotic delivery systems

Antibiotics have remained the cornerstone for the treatment of bacterial infections ever since their discovery in the twentieth century. The uproar over antibiotic resistance among bacteria arising from genome plasticity and biofilm development has rendered current antibiotic therapies ineffective, urging the development of innovative therapeutic approaches. The development of antibiotic resistance among bacteria has further heightened the clinical failure of antibiotic therapy, which is often linked to its low bioavailability, side effects, and poor penetration and accumulation at the site of infection. In this review, we highlight the potential use of siderophores, antibodies, cell-penetrating peptides, antimicrobial peptides, bacteriophages, and nanoparticles to smuggle antibiotics across impermeable biological membranes to achieve therapeutically relevant concentrations of antibiotics and combat antimicrobial resistance (AMR). We will discuss the general mechanisms via which each delivery system functions and how it can be tailored to deliver antibiotics against the paradigm of mechanisms underlying antibiotic resistance.

Phenotypic, molecular, and in silico characterization of coumarin as carbapenemase inhibitor to fight carbapenem-resistant Klebsiella pneumoniae

BACKGROUND

Carbapenems represent the first line treatment of serious infections caused by drug-resistant Klebsiella pneumoniae. Carbapenem-resistant K. pneumoniae (CRKP) is one of the urgent threats to human health worldwide. The current study aims to evaluate the carbapenemase inhibitory potential of coumarin and to test its ability to restore meropenem activity against CRKP. Disk diffusion method was used to test the antimicrobial susceptibility of K. pneumoniae clinical isolates to various antibiotics. Carbapenemase genes (NDM-1, VIM-2, and OXA-9) were detected using PCR. The effect of sub-MIC of coumarin on CRKP isolates was performed using combined disk assay, enzyme inhibition assay, and checkerboard assay. In addition, qRT-PCR was used to estimate the coumarin effect on expression of carbapenemase genes. Molecular docking was used to confirm the interaction between coumarin and binding sites within three carbapenemases.

RESULTS

K. pneumoniae clinical isolates were found to be multi-drug resistant and showed high resistance to meropenem. All bacterial isolates harbor at least one carbapenemase-encoding gene. Coumarin significantly inhibited carbapenemases in the crude periplasmic extract of CRKP. The checkerboard assay indicated that coumarin-meropenem combination was synergistic exhibiting a fractional inhibitory concentration index ≤ 0.5. In addition, qRT-PCR results revealed that coumarin significantly decreased carbapenemase-genes expression. Molecular docking revealed that the binding energies of coumarin to NDM1, VIM-2, OXA-48 and OXA-9 showed a free binding energy of -7.8757, -7.1532, -6.2064 and - 7.4331 Kcal/mol, respectively.

CONCLUSION

Coumarin rendered CRKP sensitive to meropenem as evidenced by its inhibitory action on hydrolytic activity and expression of carbapenemases. The current findings suggest that coumarin could be a possible solution to overcome carbapenems resistance in CRKP.

Proguanil and chlorhexidine augment the antibacterial activities of clarithromycin and rifampicin against Acinetobacter baumannii

The emergence of Acinetobacter baumannii infections as a significant healthcare concern in hospital settings, coupled with their association with poorer clinical outcomes, has prompted extensive investigation into novel therapeutic agents and innovative treatment strategies. Proguanil and chlorhexidine, both categorized as biguanide compounds, have displayed clinical efficacy as antimalarial and topical antibacterial agents, respectively. In this study, we conducted an investigation to assess the effectiveness of combining proguanil and chlorhexidine with clarithromycin or rifampicin against both laboratory strains and clinical isolates of A. baumannii. The combination therapy demonstrated rapid bactericidal activity against planktonic multidrug-resistant A. baumannii, exhibiting efficacy in eradicating mature biofilms and impeding the development of antibiotic resistance in vitro. Additionally, when administered in conjunction with clarithromycin or rifampicin, proguanil enhanced the survival rate of mice afflicted with intraperitoneal A. baumannii infections, and chlorhexidine expedited wound healing in mice with skin infections. These findings are likely attributable to the disruption of A. baumannii cell membrane integrity by proguanil and chlorhexidine, resulting in heightened membrane permeability and enhanced intracellular accumulation of clarithromycin and rifampicin. Overall, this study underscores the potential of employing proguanil and chlorhexidine in combination with specific antibiotics to effectively combat A. baumannii infections and improve treatment outcomes in clinically challenging scenarios.

Study on seed-borne cultivable bacterial diversity and antibiotic resistance of Poa pratensis L

In order to study the difference of cultivable seed-borne bacterial diversity between commercial varieties and wild species of Poa pratensis L., and their antibiotic resistance to sulfadiazine, tetracycline, oxytetracycline, ciprofloxacin, gentamicin, oxytetracycline and rifampin. In this study, 60 bacterium isolates were isolated by dilution-coated plate method. Through 16S rRNA sequence analysis, 40 representative isolates with different morphological characteristics were identified and phylogenetic tree was constructed. The results of diversity analysis showed that the seed-borne bacterial diversity of commercial varieties was richer than that of wild species. The antibiotic resistance of the isolated bacterial strains was studied by agar dilution method, and it was concluded that the antibiotic resistance of the seed-borne bacteria carried by commercial varieties was stronger than that of the wild species. Finally, the biofilm formation ability and swimming motility of the bacterial strain were measured, and the correlation between the two and the antibiotic resistance of the bacterial strain was analyzed. The analysis showed that the antibiotic resistance of bacterial strains in Poa pratensis L. was significantly correlated with their swimming motility. In addition, the swimming motility of the bacterial strains was significantly correlated with the biofilm formation ability. It is worth mentioning that this is the first time to study the drug-resistant bacteria distributed in the seed-borne bacteria of Poa pratensis L.

Antimicrobial activity of nature-inspired molecules against multidrug-resistant bacteria

Multidrug-resistant bacterial infections present a serious challenge to global health. In addition to the spread of antibiotic resistance, some bacteria can form persister cells which are tolerant to most antibiotics and can lead to treatment failure or relapse. In the present work, we report the discovery of a new class of small molecules with potent antimicrobial activity against Gram-positive bacteria and moderate activity against Gram-negative drug-resistant bacterial pathogens. The lead compound SIMR 2404 had a minimal inhibitory concentration (MIC) of 2 μg/mL against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-intermediate Staphylococcus aureus (VISA). The MIC values against Gram-negative bacteria such as Escherichia coli and Actinobacteria baumannii were between 8-32 μg/mL. Time-kill experiments show that compound SIMR 2404 can rapidly kill tested bacteria. Compound SIMR 2404 was also found to rapidly kill MRSA persisters which display high levels of tolerance to conventional antibiotics. In antibiotic evolution experiments, MRSA quickly developed resistance to ciprofloxacin but failed to develop resistance to compound SIMR 2404 even after 24 serial passages. Compound SIMR 2404 was not toxic to normal human fibroblast at a concentration of 4 μg/mL which is twice the MIC concentration against MRSA. However, at a concentration of 8 μg/mL or higher, it showed cytotoxic activity indicating that it is not ideal as a candidate against Gram-negative bacteria. The acceptable toxicity profile and rapid antibacterial activity against MRSA highlight the potential of these molecules for further studies as anti-MRSA agents.

In Silico and In Vitro Identification of 1,8-Dihydroxy-4,5-dinitroanthraquinone as a New Antibacterial Agent against Staphylococcus aureus and Enterococcus faecalis

Increasing rates of bacterial resistance to antibiotics are a growing concern worldwide. The search for potential new antibiotics has included several natural products such as anthraquinones. However, comparatively less attention has been given to anthraquinones that exhibit functional groups that are uncommon in nature. In this work, 114 anthraquinones were evaluated using in silico methods to identify inhibitors of the enzyme phosphopantetheine adenylyltransferase (PPAT) of Staphylococcus aureus, Enterococcus faecalis, and Escherichia coli. Virtual screenings based on molecular docking and the pharmacophore model, molecular dynamics simulations, and free energy calculations pointed to 1,8-dihydroxy-4,5-dinitroanthraquinone (DHDNA) as the most promising inhibitor. In addition, these analyses highlighted the contribution of the nitro group to the affinity of this anthraquinone for the nucleotide-binding site of PPAT. Furthermore, DHDNA was active in vitro towards Gram-positive bacteria with minimum inhibitory concentration (MIC) values of 31.25 µg/mL for S. aureus and 62.5 µg/mL for E. faecalis against both antibiotic-resistant isolates and reference strains but was ineffective against E. coli. Experiments on kill-time kinetics indicated that, at the tested concentrations, DHDNA produced bacteriostatic effects on both Gram-positive bacteria. Overall, our results present DHDNA as a potential PPAT inhibitor, showing antibacterial activity against antibiotic-resistant isolates of S. aureus and E. faecalis, findings that point to nitro groups as key to explaining these results.

Cell-Based Assay to Determine Type 3 Secretion System Translocon Assembly in Pseudomonas aeruginosa Using Split Luciferase

Multi-drug-resistant Pseudomonas aeruginosa poses a serious threat to hospitalized patients. This organism expresses an arsenal of virulence factors that enables it to readily establish infections and disseminate in the host. The Type 3 secretion system (T3SS) and its associated effectors play a crucial role in the pathogenesis of P. aeruginosa, making them attractive targets for the development of novel therapeutic agents. The T3SS translocon, composed of PopD and PopB, is an essential component of the T3SS secretion apparatus. In the properly assembled translocon, the N-terminus of PopD protrudes into the cytoplasm of the target mammalian cell, which can be exploited as a molecular indicator of functional translocon assembly. In this article, we describe a novel whole-cell-based assay that employs the split NanoLuc luciferase detection system to provide a readout for translocon assembly. The assay demonstrates a favorable signal/noise ratio (13.6) and robustness (Z' = 0.67), making it highly suitable for high-throughput screening of small-molecule inhibitors targeting T3SS translocon assembly.

Outer Membrane Proteins and Efflux Pumps Mediated Multi-Drug Resistance in Salmonella: Rising Threat to Antimicrobial Therapy

Despite colossal achievements in antibiotic therapy in recent decades, drug-resistant pathogens have remained a leading cause of death and economic loss globally. One such WHO-critical group pathogen is Salmonella. The extensive and inappropriate treatments for Salmonella infections have led from multi-drug resistance (MDR) to extensive drug resistance (XDR). The synergy between efflux-mediated systems and outer membrane proteins (OMPs) may favor MDR in Salmonella. Differential expression of the efflux system and OMPs (influx) and positional mutations are the factors that can be correlated to the development of drug resistance. Insights into the mechanism of influx and efflux of antibiotics can aid in developing a structurally stable molecule that can be proficient at escaping from the resistance loops in Salmonella. Understanding the strategic responsibilities and developing policies to address the surge of drug resistance at the national, regional, and global levels are the needs of the hour. In this Review, we attempt to aggregate all the available research findings and delineate the resistance mechanisms by dissecting the involvement of OMPs and efflux systems. Integrating major OMPs and the efflux system's differential expression and positional mutation in Salmonella may provide insight into developing strategic therapies for one health application.

Drug-ionic surfactant interactions: density, sound speed, spectroscopic, and electrochemical studies

The failure of antibiotics against infectious diseases has become a global health issue due to the incessant use of antibiotics in the community and a lack of entry of new antibacterial drugs onto the market. The limited knowledge of biophysical interactions of existing antibiotics with bio-membranes is one of the major hurdles to design and develop more effective antibiotics. Surfactant systems are the simplest biological membrane models that not only mimic the cell membrane functions but are also used to investigate the biophysical interactions between pharmaceutical drugs and bio-membranes at the molecular level. In this work, volumetric and acoustic studies were used to investigate the molecular interactions of moxifloxacin (MXF), a potential antibacterial drug, with ionic surfactants (dodecyl-tri-methyl-ammonium bromide (DTAB), a cationic surfactant and sodium dodecyl sulfate (SDS), an anionic surfactant) under physiological conditions (phosphate buffer, pH 7.4) at T = 298.15-313.15 K at an interval of 5 K. Various volumetric and acoustic parameters were computed from the density and sound speed data and interpreted in terms of MXF-ionic surfactant interaction using electrostriction effect and co-sphere overlap model. Absorption spectroscopy and cyclic voltammetry were further used to determine the binding, partitioning, and related free energies of MXF with ionic micelles.

Antibacterial, bacteriolytic, antibiofilm, and synergistic effects of the peel oils of Citrus microcarpa and Citrus x amblycarpa with tetracycline against foodborne Escherichia coli

Citrus essential oils (EOs) have shown significant antibacterial activity. The present study was undertaken to evaluate the antibacterial activity of the peel oils of Citrus microcarpa and C. x amblycarpa against Escherichia coli. The minimum inhibition concentration (MIC) was determined by using the broth microdilution assay. The checkerboard method was used to identify synergistic effects of the EOs with tetracycline, while bacteriolysis was assessed by calculating the optical density of the bacterial supernatant, crystal violet assay was used to assess their antibiofilm. Ethidium bromide accumulation test was employed to assess efflux pump inhibition. Electron microscope analysis was performed to observe its morphological changes. The EOs of C. microcarpa and C. x amblycarpa were found to contain D-limonene major compound at 55.78% and 46.7%, respectively. Citrus microcarpa EOs exhibited moderate antibacterial against E. coli with a MIC value of 200 μg/mL. The combination of C. microcarpa oil (7.8 μg/mL) and tetracycline (62.5 μg/mL) exhibited a synergy with FICI of 0.5. This combination inhibited biofilm formation and disrupt bacterial cell membranes. Citrus microcarpa EOs blocked the efflux pumps in E. coli. Citrus microcarpa EOs demonstrated promising antibacterial activity, which can be further explored for the development of drugs to combat E. coli.

Combined metabolomics and transcriptomics analysis reveals the mechanism of antibiotic resistance of Salmonella enterica serovar Typhimurium after acidic stress

Drug-resistant Salmonella is widely distributed in the meat production chain, endangering food safety and public health. Acidification of meat products during processing can induce acid stress, which may alter antibiotic resistance. Our study investigated the effects of acid stress on the antibiotic resistance and metabolic profile of Salmonella Typhimurium, and explored the underlying mechanisms using metabolomic and transcriptomic analysis. We found that acid-stressed 14028s was more sensitive to small molecule hydrophobic antibiotics (SMHA) while more resistant to meropenem (MERO). Metabolomic analysis revealed that enhanced sensitivity to SMHA was correlated with increased purine metabolism and tricarboxylic acid cycle. Transcriptomic analysis revealed the downregulation of chemotaxis-related genes, which are also associated with SMHA sensitivity. We also found a significant downregulation of the ompF gene, which encodes a major outer membrane protein OmpF of Salmonella. The decreased expression of OmpF porin hindered the influx of MERO, leading to enhanced resistance of the bacteria to the drug. Our findings contribute to greatly improve the understanding of the relationship between Salmonella metabolism, gene expression, and changes in drug resistance after acid stress, while providing a structural framework for exploring the relationship between bacterial stress responses and antibiotic resistance.

Antimicrobial Resistance: A Growing Serious Threat for Global Public Health

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

How do freshwater microalgae and cyanobacteria respond to antibiotics?

Antibiotic pollution is an emerging environmental challenge. Residual antibiotics from various sources, including municipal and industrial wastewater, sewage discharges, and agricultural runoff, are continuously released into freshwater environments, turning them into reservoirs that contribute to the development and spread of antibiotic resistance. Thus, it is essential to understand the impacts of antibiotic residues on aquatic organisms, especially microalgae and cyanobacteria, due to their crucial roles as primary producers in the ecosystem. This review summarizes the effects of antibiotics on major biological processes in freshwater microalgae and cyanobacteria, including photosynthesis, oxidative stress, and the metabolism of macromolecules. Their adaptive mechanisms to antibiotics exposure, such as biodegradation, bioadsorption, and bioaccumulation, are also discussed. Moreover, this review highlights the important factors affecting the antibiotic removal pathways by these organisms, which will promote the use of microalgae-based technology for the removal of antibiotics. Finally, we offer some perspectives on the opportunities for further studies and applications.

Bioengineered materials with selective antimicrobial toxicity in biomedicine

Fungi and bacteria afflict humans with innumerous pathogen-related infections and ailments. Most of the commonly employed microbicidal agents target commensal and pathogenic microorganisms without discrimination. To distinguish and fight the pathogenic species out of the microflora, novel antimicrobials have been developed that selectively target specific bacteria and fungi. The cell wall features and antimicrobial mechanisms that these microorganisms involved in are highlighted in the present review. This is followed by reviewing the design of antimicrobials that selectively combat a specific community of microbes including Gram-positive and Gram-negative bacterial strains as well as fungi. Finally, recent advances in the antimicrobial immunomodulation strategy that enables treating microorganism infections with high specificity are reviewed. These basic tenets will enable the avid reader to design novel approaches and compounds for antibacterial and antifungal applications.

Antimicrobial Peptide Mastoparan-AF Kills Multi-Antibiotic Resistant Escherichia coli O157:H7 via Multiple Membrane Disruption Patterns and Likely by Adopting 3-11 Amphipathic Helices to Favor Membrane Interaction

We investigated the antimicrobial activity and membrane disruption modes of the antimicrobial peptide mastoparan-AF against hemolytic Escherichia coli O157:H7. Based on the physicochemical properties, mastoparan-AF may potentially adopt a 3-11 amphipathic helix-type structure, with five to seven nonpolar or hydrophobic amino acid residues forming the hydrophobic face. E. coli O157:H7 and two diarrheagenic E. coli veterinary clinical isolates, which are highly resistant to multiple antibiotics, are sensitive to mastoparan-AF, with minimum inhibitory and bactericidal concentrations (MIC and MBC) ranging from 16 to 32 μg mL^-1 for E. coli O157:H7 and four to eight μg mL^-1 for the latter two isolates. Mastoparan-AF treatment, which correlates proportionally with membrane permeabilization of the bacteria, may lead to abnormal dents, large perforations or full opening at apical ends (hollow tubes), vesicle budding, and membrane corrugation and invagination forming irregular pits or pores on E. coli O157:H7 surface. In addition, mRNAs of prepromastoparan-AF and prepromastoparan-B share a 5'-poly(A) leader sequence at the 5'-UTR known for the advantage in cap-independent translation. This is the first report about the 3-11 amphipathic helix structure of mastoparans to facilitate membrane interaction. Mastoparan-AF could potentially be employed to combat multiple antibiotic-resistant hemolytic E. coli O157:H7 and other pathogenic E. coli.

SAR investigation and optimization of benzimidazole-based derivatives as antimicrobial agents against Gram-negative bacteria

Antibiotic-resistant bacteria represent a serious threat to modern medicine and human life. Only a minority of antibacterial agents are active against Gram-negative bacteria. Hence, the development of novel antimicrobial agents will always be a vital need. In an effort to discover new therapeutics against Gram-negative bacteria, we previously reported a structure-activity-relationship (SAR) study on 1,2-disubstituted benzimidazole derivatives. Compound III showed a potent activity against tolC-mutant Escherichia coli with an MIC value of 2 μg/mL, representing a promising lead for further optimization. Building upon this study, herein, 49 novel benzimidazole compounds were synthesized to investigate their antibacterial activity against Gram-negative bacteria. Our design focused on three main goals, to address the low permeability of our compounds and improve their cellular accumulation, to expand the SAR study to the unexplored ring C, and to optimize the lead compound (III) by modification of the methanesulfonamide moiety. Compounds (25a-d, 25f-h, 25k, 25l, 25p, 25r, 25s, and 26b) exhibited potent activity against tolC-mutant E. coli with MIC values ranging from 0.125 to 4 μg/mL, with compound 25d displaying the highest potency among the tested compounds with an MIC value of 0.125 μg/mL. As its predecessor, III, compound 25d exhibited an excellent safety profile without any significant cytotoxicity to mammalian cells. Time-kill kinetics assay indicated that 25d exhibited a bacteriostatic activity and significantly reduced E. coli JW55031 burden as compared to DMSO. Additionally, combination of 25d with colistin partially restored its antibacterial activity against Gram-negative bacterial strains (MIC values ranging from 4 to 16 μg/mL against E. coli BW25113, K. pneumoniae, A. baumannii, and P. aeruginosa). Furthermore, formulation of III and 25d as lipidic nanoparticles (nanocapsules) resulted in moderate enhancement of their antibacterial activity against Gram-negative bacterial strains (A. Baumannii, N. gonorrhoeae) and compound 25d demonstrated superior activity to the lead compound III. These findings establish compound 25d as a promising candidate for treatment of Gram-negative bacterial infections and emphasize the potential of nano-formulations in overcoming poor cellular accumulation in Gram-negative bacteria where further optimization and investigation are warranted to improve the potency and broaden the spectrum of our compounds.

The Influence of Outer Membrane Protein on Ampicillin Resistance of Vibrio parahaemolyticus

The antibiotic resistance of the food-borne pathogen Vibrio parahaemolyticus has attracted researchers' attention in recent years, but its molecular mechanism remains poorly understood. In this study, 7 genes encoding outer membrane proteins (OMPs) were individually deleted in V. parahaemolyticus ATCC33846, and the resistance of these 7 mutants to 14 antibiotics was investigated. The results revealed that the resistance of the 7 mutants to ampicillin was significantly increased. Further exploration of 20-gene transcription changes by real time-qPCR (RT-qPCR) demonstrated that the higher ampicillin resistance might be attributed to the expression of β-lactamase and reduced peptidoglycan (PG) synthesis activity through reduced transcription of penicillin-binding proteins (PBPs), increased transcription of l,d-transpeptidases, downregulated d,d-carboxypeptidase, and alanine deficiency. This study provides a new perspective on ampicillin resistance in OMP mutants with respect to PG synthesis.

An Explorative Review on Advanced Approaches to Overcome Bacterial Resistance by Curbing Bacterial Biofilm Formation

The continuous emergence of multidrug-resistant pathogens evoked the development of innovative approaches targeting virulence factors unique to their pathogenic cascade. These approaches aimed to explore anti-virulence or anti-infective therapies. There are evident concerns regarding the bacterial ability to create a superstructure, the biofilm. Biofilm formation is a crucial virulence factor causing difficult-to-treat, localized, and systemic infections. The microenvironments of bacterial biofilm reduce the efficacy of antibiotics and evade the host's immunity. Producing a biofilm is not limited to a specific group of bacteria; however, Pseudomonas aeruginosa, Acinetobacter baumannii, and Staphylococcus aureus biofilms are exemplary models. This review discusses biofilm formation as a virulence factor and the link to antimicrobial resistance. In addition, it explores insights into innovative multi-targeted approaches and their physiological mechanisms to combat biofilms, including natural compounds, phages, antimicrobial photodynamic therapy (aPDT), CRISPR-Cas gene editing, and nano-mediated techniques.

Current Promising Strategies against Antibiotic-Resistant Bacterial Infections

Infections caused by antibiotic-resistant bacteria (ARB) are one of the major global health challenges of our time. In addition to developing new antibiotics to combat ARB, sensitizing ARB, or pursuing alternatives to existing antibiotics are promising options to counter antibiotic resistance. This review compiles the most promising anti-ARB strategies currently under development. These strategies include the following: (i) discovery of novel antibiotics by modification of existing antibiotics, screening of small-molecule libraries, or exploration of peculiar places; (ii) improvement in the efficacy of existing antibiotics through metabolic stimulation or by loading a novel, more efficient delivery systems; (iii) development of alternatives to conventional antibiotics such as bacteriophages and their encoded endolysins, anti-biofilm drugs, probiotics, nanomaterials, vaccines, and antibody therapies. Clinical or preclinical studies show that these treatments possess great potential against ARB. Some anti-ARB products are expected to become commercially available in the near future.

Cefmetazole Resistance Mechanism for Escherichia Coli Including ESBL-Producing Strains

Purpose

Cefmetazole (CMZ), a cephamycin antibiotic, is primarily used as a definitive therapy for Extended Spectrum β-Lactamase (ESBL)-producing Escherichia coli infections. However, the mechanism of CMZ resistance in E. coli is still unknown. To elucidate the resistance mechanism and to determine combined drugs for prevention of resistance acquisition.

Methods

Clinical isolates of 14 ESBL-producing E. coli and non-producing 12 isolates were used in in vitro testing of CMZ resistance acquisition. After 10-day of CMZ exposure (1st subculture), these strains were incubated in an antibacterial-free medium for 14-day. These strains were again exposed to CMZ for 10-day (2nd subculture) and confirmed for changes in MIC. For each strain detected after 1st subculture, each mRNA expression level of porin, chromosomal ampC, and drug-efflux pump was measured using real-time RT-PCR. Relebactam (REL) has the potency to recover antimicrobial activity against carbapenem-resistant Enterobacterales that has porin deficiency. REL was added to the CMZ dilution series, and MIC changes and those of porin were confirmed.

Results

Of these 26 strains, 15 strains (57.7%) acquired resistance after 1st subculture, but after passage culture on the antibacterial-free medium, 11 strains recovered susceptibility. These 11 strains showed resistance after 2nd subculture. The expression levels of ompF and ompC were significantly decreased in these strains (P<0.05). When REL was added, all strains suppressed resistance acquisition after 1st subculture. The mechanism was the activation of ompF.

Conclusion

Our results showed that the mRNA expression levels of genes encoding porin were decreased in the strains that acquired resistance due to CMZ exposure, and that ompF and ompC in particular were thought to be involved in the acquisition of resistance. The CMZ acquisition of resistance was also suppressed by the concomitant use of REL and actually suppressed the decrease in mRNA expression in ompF. It was confirmed that porin reactivated by REL.

Protective effect of two new nanovaccines against Pseudomonas aeruginosa based on LPS and OPS: A comparison study

Pseudomonas aeruginosa is one of the most important infectious pathogens in medicine. This bacterium causes various infections, especially in patients with severe burns and people with defective immune systems. The purpose of this study was to develop a nanovaccine based on PLGA nanoparticles and lipopolysaccharide and oligopolysaccharide antigens for appropriate stimulation of the humoral and cellular immune systems against P. aeruginosa. LPS-PLGA and OPS-PLGA conjugates were synthesized using the carbodiimide reaction. The prepared conjugates of as well as the pure antigens of LPS and OPS were injected to BALB/c mice in three periods at 2 week intervals. The ELISA test showed that the IgM, IgA, IgG, IgG1, IgG2b, IgG2a and IgG3 antibodies produced against LPS-PLGA or OPS-PLGA conjugates were tens of times higher than the pure antigens. Also, the opsonophagocytosis test showed that the performance and the effect of produced anti-LPS-PLGA antibodies were higher than other groups. In addition, the mice treated with LPS-PLGA conjugate were more resistant to P. aeruginosa infection than other groups. These findings indicated that LPS and OPS antigens in conjugation with PLGA nanoparticles have the ability to create and effective immunity against P. aeruginosa and LPS-PLGA is more effective than OPS-PLGA.

Synergy by Perturbing the Gram-Negative Outer Membrane: Opening the Door for Gram-Positive Specific Antibiotics

New approaches to target antibacterial agents toward Gram-negative bacteria are key, given the rise of antibiotic resistance. Since the discovery of polymyxin B nonapeptide as a potent Gram-negative outer membrane (OM)-permeabilizing synergist in the early 1980s, a vast amount of literature on such synergists has been published. This Review addresses a range of peptide-based and small organic compounds that disrupt the OM to elicit a synergistic effect with antibiotics that are otherwise inactive toward Gram-negative bacteria, with synergy defined as a fractional inhibitory concentration index (FICI) of <0.5. Another requirement for the inclusion of the synergists here covered is their potentiation of a specific set of clinically used antibiotics: erythromycin, rifampicin, novobiocin, or vancomycin. In addition, we have focused on those synergists with reported activity against Gram-negative members of the ESKAPE family of pathogens namely, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and/or Acinetobacter baumannii. In cases where the FICI values were not directly reported in the primary literature but could be calculated from the published data, we have done so, allowing for more direct comparison of potency with other synergists. We also address the hemolytic activity of the various OM-disrupting synergists reported in the literature, an effect that is often downplayed but is of key importance in assessing the selectivity of such compounds for Gram-negative bacteria.

Medicinal Chemistry of Inhibitors Targeting Resistant Bacteria

The discovery of antibiotics was a revolutionary feat that provided countless health benefits. The identification of penicillin by Alexander Fleming initiated the era of antibiotics, represented by constant discoveries that enabled effective treatments for the different classes of diseases caused by bacteria. However, the indiscriminate use of these drugs allowed the emergence of resistance mechanisms of these microorganisms against the available drugs. In addition, the constant discoveries in the 20th century generated a shortage of new molecules, worrying health agencies and professionals about the appearance of multidrug-resistant strains against available drugs. In this context, the advances of recent years in molecular biology and microbiology have allowed new perspectives in drug design and development, using the findings related to the mechanisms of bacterial resistance to generate new drugs that are not affected by such mechanisms and supply new molecules to be used to treat resistant bacterial infections. Besides, a promising strategy against bacterial resistance is the combination of drugs through adjuvants, providing new expectations in designing new antibiotics and new antimicrobial therapies. Thus, this manuscript will address the main mechanisms of bacterial resistance under the understanding of medicinal chemistry, showing the main active compounds against efflux mechanisms, and also the application of the use of drug delivery systems, and finally, the main potential natural products as adjuvants or with promising activity against resistant strains.

Wearable adjunct ozone and antibiotic therapy system for treatment of Gram-negative dermal bacterial infection

The problematic combination of a rising prevalence of skin and soft tissue infections and the growing rate of life-threatening antibiotic resistant infections presents an urgent, unmet need for the healthcare industry. These evolutionary resistances originate from mutations in the bacterial cell walls which prevent effective diffusion of antibiotics. Gram-negative bacteria are of special consideration due to the natural resistance to many common antibiotics due to the unique bilayer structure of the cell wall. The system developed here provides one solution to this problem through a wearable therapy that delivers and utilizes gaseous ozone as an adjunct therapy with topical antibiotics through a novel dressing with drug-eluting nanofibers (NFs). This technology drastically increases the sensitivity of Gram-negative bacteria to common antibiotics by using oxidative ozone to bypass resistances created by the bacterial cell wall. To enable simple and effective application of adjunct therapy, ozone delivery and topical antibiotics have been integrated into a single application patch. The drug delivery NFs are generated via electrospinning in a fast-dissolve PVA mat without inducing decreasing gas permeability of the dressing. A systematic study found ozone generation at 4 mg/h provided optimal ozone levels for high antimicrobial performance with minimal cytotoxicity. This ozone treatment was used with adjunct therapy delivered by the system in vitro. Results showed complete eradication of Gram-negative bacteria with ozone and antibiotics typically used only for Gram-positive bacteria, which showed the strength of ozone as an enabling adjunct treatment option to sensitize bacteria strains to otherwise ineffective antibiotics. Furthermore, the treatment is shown through biocompatibility testing to exhibit no cytotoxic effect on human fibroblast cells.

Effect of sub-minimum inhibitory concentration of ceftriaxone on the expression of outer membrane proteins in Salmonella enterica serovar Typhi

Multi-drug resistance (MDR) in Salmonella is one of the major reasons for foodborne outbreaks worldwide. Decreased susceptibility of Salmonella Typhi to first-line drugs such as ceftriaxone, ciprofloxacin, and azithromycin has raised concern. Reduced outer membrane proteins (OMPs) permeability and increased efflux pump transportation are considered to be the main reasons for the emergence of antibiotic resistance in Salmonella. The present study aimed to assess the expression of OMPs at sub-lethal concentrations of ceftriaxone in S. Typhi (Sl5037/BC, and Sl05). The S. Typhi strains were exposed to sub-MIC and half of the sub-MIC concentrations of ceftriaxone at three different time intervals (0 min, 40 min, and 180 min) and analyzed for differential expression of OMPs. Further, the expression variation of OMP encoding genes (yaeT, ompX, lamb, ompA, and ybfM) in response to ceftriaxone was evaluated using real-time PCR. The genes like lamB, ompX, and yaeT showed significant downregulation (p < 0.05) compared to the control without antibiotic exposure, whereas ybfM and ompA showed a moderate downregulation. The expression of omp genes such as lamB, ompA, ompX, ybfM, and yaeT were found to be low in the presence of ceftriaxone, followed by time and dose-dependent. The study provides insights into the possible involvement of OMPs in drug resistance of S. Typhi, which could help develop a therapeutic strategy to combat MDR isolates of S. Typhi.

Salmonella Typhimurium outer membrane protein A (OmpA) renders protection from nitrosative stress of macrophages by maintaining the stability of bacterial outer membrane

Bacterial porins are highly conserved outer membrane proteins used in the selective transport of charged molecules across the membrane. In addition to their significant contributions to the pathogenesis of Gram-negative bacteria, their role(s) in salmonellosis remains elusive. In this study, we investigated the role of outer membrane protein A (OmpA), one of the major outer membrane porins of Salmonella, in the pathogenesis of Salmonella Typhimurium (STM). Our study revealed that OmpA plays an important role in the intracellular virulence of Salmonella. An ompA deficient strain of Salmonella (STM ΔompA) showed compromised proliferation in macrophages. We found that the SPI-2 encoded virulence factors such as sifA and ssaV are downregulated in STM ΔompA. The poor colocalization of STM ΔompA with LAMP-1 showed that disruption of SCV facilitated its release into the cytosol of macrophages, where it was assaulted by reactive nitrogen intermediates (RNI). The enhanced recruitment of nitrotyrosine on the cytosolic population of STM ΔompAΔsifA and ΔompAΔssaV compared to STM ΔsifA and ΔssaV showed an additional role of OmpA in protecting the bacteria from host nitrosative stress. Further, we showed that the generation of greater redox burst could be responsible for enhanced sensitivity of STM ΔompA to the nitrosative stress. The expression of several other outer membrane porins such as ompC, ompD, and ompF was upregulated in STM ΔompA. We found that in the absence of ompA, the enhanced expression of ompF increased the outer membrane porosity of Salmonella and made it susceptible to in vitro and in vivo nitrosative stress. Our study illustrates a novel mechanism for the strategic utilization of OmpA by Salmonella to protect itself from the nitrosative stress of macrophages.

Salmonella Typhimurium majorly uses SPI-1 and SPI-2 encoded T3SS and virulence factors for thriving in the host macrophages. But the role of non-SPI genes in Salmonella pathogenesis remains unknown. This article illustrates a novel mechanism of how a non-SPI virulent protein, OmpA, helps Salmonella Typhimurium to survive in murine macrophages. Our data revealed that Salmonella lacking OmpA (STM ΔompA) is deficient in producing SPI-2 effector proteins and has a severe defect in maintaining the stability of its outer membrane. It is released into the cytosol of macrophages during infection after disrupting the SCV membrane. STM ΔompA was severely challenged with reactive nitrogen intermediates in the cytosol, which reduced their proliferation in macrophages. We further showed that the deletion of OmpA increased the expression of other larger porins (ompC, ompD, and ompF) on the surface of Salmonella. It was observed that the enhanced expression of OmpF in STM ΔompA increased the outer membrane permeability and made the bacteria more susceptible to in vitro and in vivo nitrosative stress. Altogether our study proposes new insights into the role of Salmonella OmpA as an essential virulence factor.

Antibiotics and Carbohydrate-Containing Drugs Targeting Bacterial Cell Envelopes: An Overview

Certain bacteria constitute a threat to humans due to their ability to escape host defenses as they easily develop drug resistance. Bacteria are classified into gram-positive and gram-negative according to the composition of the cell membrane structure. Gram-negative bacteria have an additional outer membrane (OM) that is not present in their gram-positive counterpart; the latter instead hold a thicker peptidoglycan (PG) layer. This review covers the main structural and functional properties of cell wall polysaccharides (CWPs) and PG. Drugs targeting CWPs are discussed, both noncarbohydrate-related (β-lactams, fosfomycin, and lipopeptides) and carbohydrate-related (glycopeptides and lipoglycopeptides). Bacterial resistance to these drugs continues to evolve, which calls for novel antibacterial approaches to be developed. The use of carbohydrate-based vaccines as a valid strategy to prevent bacterial infections is also addressed.

Fast slow folding of an outer membrane porin

SignificanceOuter membrane porins play a crucial role in processes as varied as energy production, photosynthesis, and nutrient transport. They act as the gatekeepers between a gram-negative bacterium and its environment. Understanding how these proteins fold and function is important in improving our understanding and control of these processes. Here we use single-molecule methods to help resolve the apparent differences between the fast folding expected on a molecular scale and the slow kinetics observed in ensemble measurements in the laboratory.

Impedance sensing of antibiotic interactions with a pathogenic E. coli outer membrane supported bilayer

Antibiotic resistance is a growing global health concern due to the decreasing number of antibiotics available for therapeutic use as more drug-resistant bacteria develop. Changes in the membrane properties of Gram-negative bacteria can influence their response to antibiotics and give rise to resistance. Thus, understanding the interactions between the bacterial membrane and antibiotics is important for elucidating microbial membrane properties to use for designing novel antimicrobial drugs. To study bacterial membrane-antibiotic interactions, we created a surface-supported planar bacterial outer membrane model on an optically-transparent, conducting polymer surface (poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)). This model enables membrane characterization using fluorescence microscopy and electrochemical impedance spectroscopy (EIS). The membrane platform is fabricated using outer membrane vesicles (OMVs) isolated from clinically relevant Gram-negative bacteria, enterohemorrhagic Escherichia coli. This approach enables us to mimic the native components of the bacterial membrane by incorporating native lipids, membrane proteins, and lipopolysaccharides. Using EIS, we determined membrane impedance and captured membrane-antibiotic interactions using the antibiotics polymyxin B, bacitracin, and meropenem. This sensor platform incorporates aspects of the biological complexity found in bacterial outer membranes and, by doing so, offers a powerful, biomimetic approach to the study of antimicrobial drug interactions.

Microbial Resistance to Antibiotics and Effective Antibiotherapy

Currently, the efficacy of antibiotics is severely affected by the emergence of the antimicrobial resistance phenomenon, leading to increased morbidity and mortality worldwide. Multidrug-resistant pathogens are found not only in hospital settings, but also in the community, and are considered one of the biggest public health concerns. The main mechanisms by which bacteria develop resistance to antibiotics include changes in the drug target, prevention of entering the cell, elimination through efflux pumps or inactivation of drugs. A better understanding and prediction of resistance patterns of a pathogen will lead to a better selection of active antibiotics for the treatment of multidrug-resistant infections.

HopE and HopD Porin-Mediated Drug Influx Contributes to Intrinsic Antimicrobial Susceptibility and Inhibits Streptomycin Resistance Acquisition by Natural Transformation in Helicobacter pylori

Helicobacter pylori is a human pathogen competent for natural transformation. Intrinsic and acquired antibiotic resistance contribute to the survival and multiplication of H. pylori under antibiotics. While drug-resistance dissemination by natural transformation (NT)-mediated horizontal gene transfer remains poorly understood in H. pylori. The purpose of the study was to investigate the role of H. pylori porins (HopA, HopB, HopC, HopD, and HopE) in the intrinsic antibiotic resistance and to preliminarily reveal the potential effect of HopE and HopD porins in streptomycin resistance acquisition after NT in the presence of antibiotics. Using traditional antibiotic susceptibility tests and growth curve analysis, we found the MIC values of metronidazole, clarithromycin, levofloxacin, tetracycline, rifampin, and streptomycin in mutants lacking HopE and/or HopD were significantly elevated compare to those in wild-type strain. The quantitative analysis of the tetramethyl rhodamine isothiocyanate (TRITC)-labeled streptomycin accumulation at the single-cell level showed reduced streptomycin intracellular fluorescence in ΔhopE and ΔhopD mutant cells. Furthermore, in the presence of translation-inhibiting antibiotic streptomycin, the resistance acquisition frequency was decreased in the wild-type strain, which could be reversed by mutants lacking HopE and HopD that restored relatively high resistance acquisition frequencies. By transforming a pUC19-rpsLmut-sfgfp linear plasmid carrying a streptomycin conferring mutation, we observed that the impaired ability of rpsLmut synthesis in the wild-type strain was restored in the ΔhopE and ΔhopD mutant transformants. Our study revealed that in the presence of streptomycin, resistance acquisition at least partially relied on the deletion of the hopE and hopD genes, because their loss reduced streptomycin concentration in the cell and thus restored the expression of the resistance-conferring gene, which was inhibited by streptomycin in wild-type strain. The loss of HopE and HopD influx activity may also preserve resistance acquisition by transformation in the presence of antibiotics with other modes of action. IMPORTANCE Helicobacter pylori is constitutively competent for natural transformation (NT) and possesses an efficient system for homologous recombination, which could be utilized to study the NT-mediated horizontal gene transfer induced antibiotic resistance acquisition. Bacterial porins have drawn renewed attention because of their crucial role in antibiotic susceptibility. From the perspective of porin-mediated influx in H. pylori, our study preliminarily revealed the important role of HopE and HopD porins not only in preserving the intrinsic susceptibility to specific antibiotic but also in evading acquired antibiotic resistance by NT in the presence of translation-inhibiting antimicrobial. Therefore, the loss of HopE or HopD porin in H. pylori genomes, combined with the large number of secreted or cell-free genetic elements carrying mutations conferring antibiotic resistance, may raise the possibility that this mechanism plays a potential role in the propagation of antibiotic resistance within H. pylori communities.

Cholic Acid-Based Antimicrobial Peptide Mimics as Antibacterial Agents

There is a significant and urgent need for the development of novel antibacterial agents to tackle the increasing incidence of antibiotic resistance. Cholic acid-based small molecular antimicrobial peptide mimics are reported as potential new leads to treat bacterial infection. Here, we describe the design, synthesis and biological evaluation of cholic acid-based small molecular antimicrobial peptide mimics. The synthesis of cholic acid analogues involves the attachment of a hydrophobic moiety at the carboxyl terminal of the cholic acid scaffold, followed by the installation of one to three amino acid residues on the hydroxyl groups present on the cholic acid scaffold. Structure–activity relationship studies suggest that the tryptophan moiety is important for high antibacterial activity. Moreover, a minimum of +2 charge is also important for antimicrobial activity. In particular, analogues containing lysine-like residues showed the highest antibacterial potency against Gram-positive S. aureus. All di-substituted analogues possess high antimicrobial activity against both Gram-positive S. aureus as well as Gram-negative E. coli and P. aeruginosa. Analogues 17c and 17d with a combination of these features were found to be the most potent in this study. These compounds were able to depolarise the bacterial membrane, suggesting that they are potential antimicrobial pore forming agents.

Antibacterial efficacy and possible mechanism of action of 2-hydroxyisocaproic acid (HICA)

The exploitation of natural antimicrobial compounds that can be used in food preservation has been fast tracked by the development of antimicrobial resistance to existing antimicrobials and the increasing consumer demand for natural food preservatives. 2-hydroxyisocaproic acid (HICA) is a natural compound produced through the leucine degradation pathway and is produced in humans and by certain microorganisms such as lactic acid bacteria and Clostridium species. The present study investigated the antibacterial efficacy of HICA against some important bacteria associated with food quality and safety and provided some insights into its possible antimicrobial mechanisms against bacteria. The results revealed that HICA was effective in inhibiting the growth of tested Gram-positive and Gram-negative bacteria including a multi-drug resistant P. aeruginosa strain in this study. The underlying mechanism was investigated by measuring the cell membrane integrity, membrane permeability, membrane depolarisation, and morphological and ultrastructural changes after HICA treatment in bacterial cells. The evidence supports that HICA exerts its activity via penetration of the bacterial cell membranes, thereby causing depolarisation, rupture of membranes, subsequent leakage of cellular contents and cell death. The current study suggests that HICA has potential to be used as an antibacterial agent against food spoilage and food-borne pathogenic bacteria, targeting the bacterial cell envelope.

Mechanisms of Action of Carbapenem Resistance

Carbapenem antibiotics are the most effective antimicrobials for the treatment of infections caused by the most resistant bacteria. They belong to the category of β-lactams that include the penicillins, cephalosporins, monobactams and carbapenems. This class of antimicrobials has a broader spectrum of activity than most other beta-lactams antibiotics and are the most effective against Gram-positive and Gram-negative bacteria. All β-lactams antibiotics have a similar molecular structure: the carbapenems together with the β-lactams. This combination gives an extraordinary stability to the molecule against the enzymes inactivating the β-lactams. They are safe to use and therefore widespread use in many countries has given rise to carbapenem resistance which is a major global public health problem. The carbapenem resistance in some species is intrinsic and consists of the capacity to resist the action of antibiotics with several mechanisms: for the absence of a specific target, or an intrinsic difference in the composition of cytoplasmatic membrane or the inability to cross the outer membrane. In addition to intrinsic resistance, bacteria can develop resistance to antibiotics with several mechanisms that can be gathered in three main groups. The first group includes antibiotics with poor penetration into the outer membrane of bacterium or antibiotic efflux. The second includes bacteria that modify the target of the antibiotics through genetic mutations or post-translational modification of the target. The third includes bacteria that act with enzyme-catalyzed modification and this is due to the production of beta-lactamases, that are able to inactivate carbapenems and so called carbapenemases. In this review, we focus on the mode of action of carbapenem and the mechanisms of carbapenem resistance.

An Outer Membrane Vesicle-Based Permeation Assay (OMPA) for Assessing Bacterial Bioavailability

When searching for new antibiotics against Gram-negative bacterial infections, a better understanding of the permeability across the cell envelope and tools to discriminate high from low bacterial bioavailability compounds are urgently needed. Inspired by the phospholipid vesicle-based permeation assay (PVPA), which is designed to predict non-facilitated permeation across phospholipid membranes, outer membrane vesicles (OMVs) of Escherichia coli either enriched or deficient of porins are employed to coat filter supports for predicting drug uptake across the complex cell envelope. OMVs and the obtained in vitro model are structurally and functionally characterized using cryo-TEM, SEM, CLSM, SAXS, and light scattering techniques. In vitro permeability, obtained from the membrane model for a set of nine antibiotics, correlates with reported in bacterio accumulation data and allows to discriminate high from low accumulating antibiotics. In contrast, the correlation of the same data set generated by liposome-based comparator membranes is poor. This better correlation of the OMV-derived membranes points to the importance of hydrophilic membrane components, such as lipopolysaccharides and porins, since those features are lacking in liposomal comparator membranes. This approach can offer in the future a high throughput screening tool with high predictive capacity or can help to identify compound- and bacteria-specific passive uptake pathways.