Green Synthesized Chitosan Nanoparticles for Controlling Multidrug-Resistant mecA- and blaZ-Positive Staphylococcus aureus and aadA1-Positive Escherichia coli.

Antimicrobial resistance has recently been considered an emerging catastrophe globally. The public health and environmental threats were aggravated by the injudicious use of antibiotics in animal farming, aquaculture, and croup fields, etc. Consequently, failure of antibiotic therapies is common because of the emergence of multidrug-resistant (MDR) bacteria in the environment. Thus, the reduction in antibiotic spillage in the environment could be an important step for overcoming this situation. Bear in mind, this research was focused on the green synthesis of chitosan nanoparticles (ChiNPs) using Citrus lemon (Assam lemon) extract as a cross-linker and application in controlling MDR bacteria to reduce the antibiotic spillage in that sector. For evaluating antibacterial activity, Staphylococcus aureus and Escherichia coli were isolated from environmental specimens, and their multidrug-resistant pattern were identified both phenotypically by disk diffusion and genotypically by detecting methicillin- (mecA), penicillin- (blaZ), and streptomycin (aadA1)-resistance encoding genes. The inhibitory zone's diameter was employed as a parameter for determining the antibacterial effect against MDR bacteria revealing 30 ± 0.4 mm, 34 ± 0.2 mm, and 36 ± 0.8 mm zones of inhibition against methicillin- (mecA) and penicillin (blaZ)-resistant S. aureus, and streptomycin (aadA1)-resistant E. coli, respectively. The minimum inhibitory concentration at 0.31 mg/mL and minimum bactericidal concentration at 0.62 mg/mL of yielded ChiNPs were used as the broad-spectrum application against MDR bacteria. Finally, the biocompatibility of ChiNPs was confirmed by showing a negligible decrease in BHK-21 cell viability at doses less than 2 MIC, suggesting their potential for future application in antibiotic-free farming practices.

Design, synthesis, and bioactivity evaluation of clindamycin derivatives against multidrug-resistant bacterial strains.

Our research aims to reduce the bacterial resistance of clindamycin against Gram-positive bacteria and expand its range of bacterial susceptibility. First, we optimized the structure of clindamycin based on its structure-activity relationship. Second, we employed the fractional inhibitory concentration method to detect drugs suitable for combination with clindamycin derivatives. We then used a linker to connect the clindamycin derivatives with the identified combined therapy drugs. Finally, we tested antibacterial susceptibility testing and conducted in vitro bacterial inhibition activity assays to determine the compounds. with the highest efficacy. The results of our study show that we synthesized clindamycin propionate derivatives and clindamycin homo/heterodimer derivatives, which exhibited superior antibacterial activity compared to clindamycin and other antibiotics against both bacteria and fungi. In vitro bacteriostatic activity testing against four types of Gram-negative bacteria and one type of fungi revealed that all synthesized compounds had bacteriostatic effects at least 1000 times better than clindamycin and sulfonamides. The minimum inhibitory concentration (MIC) values for these compounds ranged from 0.25 to 0.0325 mM. Significantly, compound 5a demonstrated the most potent inhibitory activity against three distinct bacterial strains, displaying MIC values spanning from 0.0625 to 0.0325 mM. Furthermore, our calculations indicate that compound 5a is safe for cellular use. In conclusion, the synthesized compounds hold great promise in addressing bacterial antibiotic resistance.

Membrane-Active All-Hydrocarbon-Stapled α-Helical Amphiphilic Tat Peptides: Broad-Spectrum Antibacterial Activity and Low Incidence of Drug Resistance.

Multidrug resistance against conventional antibiotics has dramatically increased the difficulty of treatment and accelerated the need for novel antibacterial agents. The peptide Tat (47-57) is derived from the transactivating transcriptional activator of human immunodeficiency virus 1, which is well-known as a cell-penetrating peptide in mammalian cells. However, it is also reported that the Tat peptide (47-57) has antifungal activity. In this study, a series of membrane-active hydrocarbon-stapled α-helical amphiphilic peptides were synthesized and evaluated as antibacterial agents against Gram-positive and Gram-negative bacteria, including multidrug-resistant strains. The impact of hydrocarbon staple, the position of aromatic amino acid residue in the hydrophobic face, the various types of aromatic amino acids, and the hydrophobicity on bioactivity were also investigated and discussed in this study. Among those synthesized peptides, analogues P3 and P10 bearing a l-2-naphthylalanine (Φ) residue at the first position and a Tyr residue at the eighth position demonstrated the highest antimicrobial activity and negligible hemolytic toxicity. Notably, P3 and P10 showed obviously enhanced antimicrobial activity against multidrug-resistant bacteria, low drug resistance, high cell selectivity, extended half-life in plasma, and excellent performance against biofilm. The antibacterial mechanisms of P3 and P10 were also preliminarily investigated in this effort. In conclusion, P3 and P10 are promising antimicrobial alternatives for the treatment of the antimicrobial-resistance crisis.

Synergistic interactions of essential oil components with antibiotics against multidrug-resistant Corynebacterium striatum.

AIM: In this study, it was aimed to examine the antibacterial activity of the essential oil components (EOCs), carvacrol (CAR), cinnamaldehyde (CIN), thymol (TH), alpha pinene (α-PN), eucalyptol (EU), limonene (LIM), and the antibiotics, linezolid (LZD), vancomycin (VAN), gentamicin (GEN), ciprofloxacin (CIP), clindamycin (CLN), and penicillin (PEN) against 50 multidrug resistant Corynebacterium striatum strains, and the synergistic interactions of CAR and CIN with the antibiotics against 10 randomly selected Coryne. striatum strains to explore synergistic interactions to determine if their combined use could enhance antibiotic activity and potentially reduce resistance. METHODS AND RESULTS: The activity of the EOCs and the antibiotics against Coryne. striatum strains isolated from clinical specimens, was examined by broth microdilution method. The synergistic interactions of the EOCs with the antibiotics against 10 randomly selected Coryne. striatum strains were determined by checkerboard method. EOCs, CIN, and CAR and antibiotics, LZD, VAN, GEN, CIP, and CLN were detected to have antibacterial activity against Coryne. striatum strains alone and either synergistic interactions were observed in combinations of the antibiotics with EOCs. CONCLUSIONS: All Coryne. striatum strains were determined to be susceptible to VAN and LZD and resistant to GEN, PEN, CIP, and CLN. Synergistic interactions were observed in all combinations of antibiotics tested with CAR and CIN.

Extending the Potency and Lifespan of Antibiotics: Inhibitors of Gram-Negative Bacterial Efflux Pumps.

Efflux is a natural process found in all prokaryotic and eukaryotic cells that removes a diverse range of substrates from inside to outside. Many antibiotics are substrates of bacterial efflux pumps, and modifications to the structure or overexpression of efflux pumps are an important resistance mechanism utilized by many multidrug-resistant bacteria. Therefore, chemical inhibition of bacterial efflux to revitalize existing antibiotics has been considered a promising approach for antimicrobial chemotherapy over two decades, and various strategies have been employed. In this review, we provide an overview of bacterial multidrug resistance (MDR) efflux pumps, of which the resistance nodulation division (RND) efflux pumps are considered the most clinically relevant in Gram-negative bacteria, and describe over 50 efflux inhibitors that target such systems. Although numerous efflux inhibitors have been identified to date, none have progressed into clinical use because of formulation, toxicity, and pharmacokinetic issues or a narrow spectrum of inhibition. For these reasons, the development of efflux inhibitors has been considered a difficult and complex area of research, and few active preclinical studies on efflux inhibitors are in progress. However, recently developed tools, including but not limited to computational tools including molecular docking models, offer hope that further research on efflux inhibitors can be a platform for research and development of new bacterial efflux inhibitors.

Design, Synthesis, and Biological Evaluation of Novel Arylomycins against Multidrug-Resistant Gram-Negative Bacteria.

G0775, an arylomycin-type SPase I inhibitor that is being evaluated in a preclinical study, exhibited potent antibacterial activities against some Gram-negative bacteria but meanwhile suffered defects such as a narrow antibacterial spectrum and poor pharmacokinetic properties. Herein, systematic structural modifications were carried out, including optimization of the macrocyclic skeleton, warheads, and lipophilic regions. The optimization culminated in the discovery of 138f, which showed more potent activity and a broader spectrum against clinically isolated carbapenem-resistant Gram-negative bacteria, especially against Acinetobacter baumannii and Pseudomonas aeruginosa. 162, the free amine of 138f, exhibited an excellent pharmacokinetic profile in rats. In a neutropenic mouse thigh model of infection with multidrug-resistant P. aeruginosa, the potent in vivo antibacterial efficacy of 162 was confirmed and superior to that of G0775 (3.5-log decrease vs 1.1-log decrease in colony-forming unit (CFU)). These results support 162 as a potential antimicrobial agent for further research.

Antibacterial activity of flavonoid extracts from Enteromorpha intestinalis and Caulerpa prolifera against multidrug-resistant foodborne bacterial isolates.

Background: Food poisoning caused by bacterial agents is a worldwide problem, usually accompanied by unpleasant symptoms and may be severe leading to death. Natural compounds from marine algae namely flavonoids may play a role in the remedy of this condition. Aim: This research aims to assess the potency of flavonoids extracted from Enteromorpha intestinalis and Caulerpa prolifera as antibacterial agents. Methods: Enteromorpha intestinalis was collected from Western Libyan Coast and C. prolifera was collected from Farwa Island. The antimicrobial activity and determination of minimum inhibitory concentration of algal flavonoid-containing extracts was performed in vitro against some positive and negative Gram bacteria. Results: Crude extract containing flavonoids from E. intestinalis was more effective than C. prolifera extract against Staphylococcus aureus with antimicrobial essay (25-28 + 1 and 14.5-37.5 + 0.5-1.5), MIC (50 and 50-250 µg/ml), MBC (75 and 75-250 µg/ml). In Bacillus cereus, the antimicrobial assay (19-24.5 + 0.5-1.5: 24 + 1), MIC (50-250 + 100 µg/ml), and MBC (250 and 125 µg/ml). On the other hand, flavonoids containing extract from C. prolifera were more effective than E. intestinalis against Enterohemorrhagic Escherichia coli O157 EHEC O157 (25-28 + 1: 14-18.5 + 0.5-1.5), MIC (100-250:100-500 µg/ml), and MBC (150-250 and 250-500 µg/ml). Salmonella enterica qualitatively combat by flavonoid from E. intestinalis (13.5-14 + 0.5-1: 10.5-13.5 + 0.5-1.5), MIC (100-250: 250 µg/ml), and MBC (100-250: 250 µg/ml). Flavonoids from C. prolifera (4 strains: 2 strains) were effective against S. enterica. Crude flavonoids from both algae were not effective against Bacillus pumilus. Conclusion: Data from this study could conclude that flavonoid extracts from E. intestinalis and C. prolifera could be used against foodborne bacterial agents.

Cylindrospermopsin enhances the conjugative transfer of plasmid-mediated multi-antibiotic resistance genes through glutathione biosynthesis inhibition.

Cylindrospermopsin (CYN), a cyanobacterial toxin, has been detected in the global water environment. However, information concerning the potential environmental risk of CYN is limited, since the majority of previous studies have mainly focused on the adverse health effects of CYN through contaminated drinking water. The present study reported that CYN at environmentally relevant levels (0.1-100 µg/L) can significantly enhance the conjugative transfer of RP4 plasmid in Escherichia coli genera, wherein application of 10 µg/L of CYN led to maximum fold change of ∼6.5- fold at 16 h of exposure. Meanwhile, evaluation of underlying mechanisms revealed that environmental concentration of CYN exposure could increase oxidative stress in the bacterial cells, resulting in ROS overproduction. In turn, this led to an upregulation of antioxidant enzyme-related genes to avoid ROS attack. Further, inhibition of the synthesis of glutathione (GSH) was also detected, which led to the rapid depletion of GSH in cells and thus triggered the SOS response and promoted the conjugative transfer process. Increase in cell membrane permeability, upregulation of expression of genes related to pilus generation, ATP synthesis, and RP4 gene expression were also observed. These results highlight the potential impact on the spread of antimicrobial resistance in water environments.

3-O-Substituted Quercetin: an Antibiotic-Potentiating Agent against Multidrug-Resistant Gram-Negative Enterobacteriaceae through Simultaneous Inhibition of Efflux Pump and Broad-Spectrum Carbapenemases.

The discovery of safe and efficient inhibitors against efflux pumps as well as metallo-ß-lactamases (MBL) is one of the main challenges in the development of multidrug-resistant (MDR) reversal agents which can be utilized in the treatment of carbapenem-resistant Gram-negative bacteria. In this study, we have identified that introduction of an ethylene-linked sterically demanding group at the 3-OH position of the previously reported MDR reversal agent di-F-Q endows the resulting compounds with hereto unknown multitarget inhibitory activity against both efflux pumps and broad-spectrum ß-lactamases including difficult-to-inhibit MBLs. A molecular docking study of the multitarget inhibitors against efflux pump, as well as various classes of ß-lactamases, revealed that the 3-O-alkyl substituents occupy the novel binding sites in efflux pumps as well as carbapenemases. Not surprisingly, the multitarget inhibitors rescued the antibiotic activity of a carbapenem antibiotic, meropenem (MEM), in NDM-1 (New Delhi Metallo-ß-lactamase-1)-producing carbapenem-resistant Enterobacteriaceae (CRE), and they reduced MICs of MEM more than four-fold (synergistic effect) in 8-9 out of 14 clinical strains. The antibiotic-potentiating activity of the multitarget inhibitors was also demonstrated in CRE-infected mouse model. Taken together, these results suggest that combining inhibitory activity against two critical targets in MDR Gram-negative bacteria, efflux pumps, and ß-lactamases, in one molecule is possible, and the multitarget inhibitors may provide new avenues for the discovery of safe and efficient MDR reversal agents.

Broad-spectrum activity of membranolytic cationic macrocyclic peptides against multi-drug resistant bacteria and fungi.

The emergence of multidrug-resistant (MDR) strains causes severe problems in the treatment of microbial infections owing to limited treatment options. Antimicrobial peptides (AMPs) are drawing considerable attention as promising antibiotic alternative candidates to combat MDR bacterial and fungal infections. Herein, we present a series of small amphiphilic membrane-active cyclic peptides composed, in part, of various nongenetically encoded hydrophilic and hydrophobic amino acids. Notably, lead cyclic peptides 3b and 4b showed broad-spectrum activity against drug-resistant Gram-positive (MIC = 1.5-6.2 µg/mL) and Gram-negative (MIC = 12.5-25 µg/mL) bacteria, and fungi (MIC = 3.1-12.5 µg/mL). Furthermore, lead peptides displayed substantial antibiofilm action comparable to standard antibiotics. Hemolysis (HC50 = 230 µg/mL) and cytotoxicity (>70 % cell viability against four different mammalian cells at 100 µg/mL) assay results demonstrated the selective lethal action of 3b against microbes over mammalian cells. A calcein dye leakage experiment substantiated the membranolytic effect of 3b and 4b, which was further confirmed by scanning electron microscopy. The behavior of 3b and 4b in aqueous solution and interaction with phospholipid bilayers were assessed by employing nuclear magnetic resonance (NMR) spectroscopy in conjunction with molecular dynamics (MD) simulations, providing a solid structural basis for understanding their membranolytic action. Moreover, 3b exhibited stability in human blood plasma (t1/2 = 13 h) and demonstrated no signs of resistance development against antibiotic-resistant S. aureus and E. coli. These findings underscore the potential of these newly designed amphiphilic cyclic peptides as promising anti-infective agents, especially against Gram-positive bacteria.

Enhancing effect of natural adjuvant, panduratin A, on antibacterial activity of colistin against multidrug-resistant Acinetobacter baumannii.

Colistin- and carbapenem-resistant Acinetobacter baumannii is a serious multidrug resistant (MDR) bacterium in clinical settings. Discovery of new antibacterial drugs against MDR is facing multiple challenges in drug development. Combination of known antibiotics with a robust adjuvant might be an alternative effective strategy for MDR treatment. In the study herein, we report an antibiotic adjuvant activity of a natural compound panduratin A from fingerroot (Boesenbergia rotunda) as a potent adjuvant to colistin. The present study investigated the antibiotic adjuvant effect of panduratin A against 10 colistin- and carbapenem-resistant A. baumannii. Antibacterial activities were tested by broth microdilution method. Biofilm assay was used to determine the efficacy of panduratin A in biofilm formation inhibition on two representative strains Aci46 and Aci44. Genomic and transcriptomic analyses of colistin- and carbapenem-resistant A. baumannii strains were used to identify potential resistance and tolerance mechanism in the bacteria. Panduratin A-colistin combination showed an increased effect on antibacterial in the A. baumannii. However, panduratin A did not improve the antibacterial activity of imipenem. In addition, panduratin A improves anti-biofilm activity of colistin against Aci44 and Aci46, the colistin- and carbapenem-resistant A. baumannii. Panduratin A markedly enhances bactericidal and anti-biofilm activity of colistin against colistin- resistant A. baumannii. Based on genome comparisons, single nucleotide polymorphism (SNP) patterns in six genes encoding biofilm and lipid A biosynthesis were shared in Aci44 and Aci46. In Aci44, we identified a partial sequence of pmrB encoding a polymyxin resistant component PmrB, whereas a full length of pmrB was observed in Aci46. RNA-seq analyses of Aci44 revealed that panduratin A-colistin combination induced expression of ribosomal proteins and oxidative stress response proteins, whereas iron transporter and MFS-type transporter systems were suppressed. Panduratin A-colistin combination could promote intracellular reactive oxygen species (ROS) accumulation could lead to the cidal effect on colistin-resistant A. baumannii. Combination of panduratin A and colistin showed a significant increase in colistin efficacy against colistin- resistant A. baumannii in comparison of colistin alone. Genomic comparison between Aci44 and Aci46 showed mutations and SNPs that might affect different phenotypes. Additionally, based on RNA-Seq, panduratin A-colistin combination could lead to ROS production and accumulation. These findings confirmed the potency of panduratin as colistin adjuvant against multidrug resistant A. baumannii.

Dihydrophenazine: a multifunctional new weapon that kills multidrug-resistant Acinetobacter baumannii and restores carbapenem and oxidative stress susceptibilities.

AIMS: The current work aims to fully characterize a new antimicrobial agent against Acinetobacter baumannii, which continues to represent a growing threat to healthcare settings worldwide. With minimal treatment options due to the extensive spread of resistance to almost all the available antimicrobials, the hunt for new antimicrobial agents is a high priority. METHODS AND RESULTS: An Egyptian soil-derived bacterium strain NHM-077B proved to be a promising source for a new antimicrobial agent. Bio-guided fractionation of the culture supernatants of NHM-077B followed by chemical structure elucidation identified the active antimicrobial agent as 1-hydroxy phenazine. Chemical synthesis yielded more derivatives, including dihydrophenazine (DHP), which proved to be the most potent against A. baumannii, yet it exhibited a marginally safe cytotoxicity profile against human skin fibroblasts. Proteomics analysis of the cells treated with DHP revealed multiple proteins with altered expression that could be correlated to the observed phenotypes and potential mechanism of the antimicrobial action of DHP. DHP is a multipronged agent that affects membrane integrity, increases susceptibility to oxidative stress, interferes with amino acids/protein synthesis, and modulates virulence-related proteins. Interestingly, DHP in subinhibitory concentrations re-sensitizes the highly virulent carbapenem-resistant A. baumannii strain AB5075 to carbapenems providing great hope in regaining some of the benefits of this important class of antibiotics. CONCLUSIONS: This work underscores the potential of DHP as a promising new agent with multifunctional roles as both a classical and nonconventional antimicrobial agent that is urgently needed.

Discovery of novel dihydronaphthalene-imidazole ligands as potential inhibitors of Staphylococcus aureus multidrug resistant NorA efflux pump: A combination of experimental and in silico molecular docking studies.

Overexpression of the efflux pump is a predominant mechanism by which bacteria show antimicrobial resistance (AMR) and leads to the global emergence of multidrug resistance (MDR). In this work, the inhibitory potential of library of dihydronapthyl scaffold-based imidazole derivatives having structural resemblances with some known efflux pump inhibitors (EPI) were designed, synthesized and evaluated against efflux pump inhibitor against overexpressing bacterial strains to study the synergistic effect of compounds and antibiotics. Out of 15 compounds, four compounds (Dz-1, Dz-3, Dz-7, and Dz-8) were found to be highly active. DZ-3 modulated the MIC of ciprofloxacin, erythromycin, and tetracycline by 128-fold each against 1199B, XU212 and RN4220 strains of S. aureus respectively. DZ-3 also potentiated tetracycline by 64-fold in E. coli AG100 strain. DZ-7 modulated the MIC of both tetracycline and erythromycin 128-fold each in S. aureus XU212 and S. aureus RN4220 strains. DZ-1 and DZ-8 showed the moderate reduction in MIC of tetracycline in E. coli AG100 only by 16-fold and 8-fold, respectively. DZ-3 was found to be the potential inhibitor of NorA as determined by ethidium bromide efflux inhibition and accumulation studies employing NorA overexpressing strain SA-1199B. DZ-3 displayed EPI activity at non-cytotoxic concentration to human cells and did not possess any antibacterial activity. Furthermore, molecular docking studies of DZ-3 was carried out in order to understand the possible binding sites of DZ-3 with the active site of the protein. These studies indicate that dihydronaphthalene scaffolds could serve as valuable cores for the development of promising EPIs.

In vitro and ex vivo activity of the fluoroquinolone DC-159a against mycobacteria.

Antimicrobial resistance is a global health problem. In 2021, it was estimated almost half a million of multidrug-resistant tuberculosis (MDR-TB) cases. Besides, non-tuberculous mycobacteria (NTM) are highly resistant to several drugs and the emergence of fluoroquinolone (FQ) resistant M. tuberculosis (Mtb) is also a global concern making treatments difficult and with variable outcome. The aim of this study was to evaluate the activity of the FQ, DC-159a, against Mtb and NTM and to explore the cross-resistance with the currently used FQs.A total of 12 pre-extensively drug-resistant (XDR) Mtb, 2 XDR, 36 fully drug susceptible strains and 41 NTM isolates were included to estimate the in vitro activity of DC-159a, moxifloxacin (MOX) and levofloxacin (LX), using minimal inhibitory and bactericidal concentration (MIC and MBC). The activity inside the human macrophages and pulmonary epithelial cells were also determined.DC-159a was active in vitro and ex vivo against mycobacteria. Besides, it was more active than MOX/LX. Moreover, no cross-resistance was evidenced between DC-159a and LX/MOX as DC-159a could inhibit Mtb and MAC strains that were already resistant to LX/MOX.DC-159a could be a possible candidate in new therapeutic regimens for MDR/ XDR-TB and mycobacterioses cases.

Efflux pump inhibitor, phenylalanine-arginine beta-naphthylamide analog potentiates the activity of 5-O-mycaminosyltylonolide for multi-drug resistant Pseudomonas aeruginosa.

The emergence and spread of antimicrobial resistance are global threats. Pseudomonas aeruginosa (P. aeruginosa) is responsible for a substantial proportion of this global health issue because of its intrinsic resistance to many antibiotics due to the impermeability of its outer membrane and its multidrug efflux pump systems. Therefore, therapeutic drugs are limited, and the development of new drugs is extremely challenging. As an alternative approach, we focused on a combinational treatment strategy and found that 5-O-mycaminosyltylonolide (OMT) showed potent antibacterial activity against P. aeruginosa in the presence of an efflux pump inhibitor, phenylalanine-arginine beta-naphthylamide (PAßN). In this report, we prepared a PAßN derivative and compared the potentiation activity of OMT by PAßNs against multidrug-resistant P. aeruginosa clinical isolates.

Preventive nasal administration of flagellin restores antimicrobial effect of gentamicin and protects against a multidrug-resistant strain of Pseudomonas aeruginosa.

The increasing prevalence of multidrug-resistant Pseudomonas aeruginosa (PA) is a significant concern for chronic respiratory disease exacerbations. Host-directed drugs, such as flagellin, an agonist of toll-like receptor 5 (TLR5), have emerged as a promising solution. In this study, we evaluated the prophylactic intranasal administration of flagellin against a multidrug-resistant strain of PA (PAMDR) in mice and assessed the possible synergy with the antibiotic gentamicin (GNT). The results indicated that flagellin treatment before infection decreased bacterial load in the lungs, likely due to an increase in neutrophil recruitment, and reduced signs of inflammation, including proinflammatory cytokines. The combination of flagellin and GNT showed a synergistic effect, decreasing even more the bacterial load and increasing mice survival rates, in comparison to mice pre-treated only with flagellin. These findings suggest that preventive nasal administration of flagellin could restore the effect of GNT against MDR strains of PA, paving the way for the use of flagellin in vulnerable patients with chronic respiratory diseases.

Klebicin E, a pore-forming bacteriocin of Klebsiella pneumoniae, exploits the porin OmpC and the Ton system for translocation.

Bacteriocins, which have narrow-spectrum activity and limited adverse effects, are promising alternatives to antibiotics. In this study, we identified klebicin E (KlebE), a small bacteriocin derived from Klebsiella pneumoniae. KlebE exhibited strong efficacy against multidrug-resistant K. pneumoniae isolates and conferred a significant growth advantage to the producing strain during intraspecies competition. A giant unilamellar vesicle leakage assay demonstrated the unique membrane permeabilization effect of KlebE, suggesting that it is a pore-forming toxin. In addition to a C-terminal toxic domain, KlebE also has a disordered N-terminal domain and a globular central domain. Pulldown assays and soft agar overlay experiments revealed the essential role of the outer membrane porin OmpC and the Ton system in KlebE recognition and cytotoxicity. Strong binding between KlebE and both OmpC and TonB was observed. The TonB-box, a crucial component of the toxin-TonB interaction, was identified as the 7-amino acid sequence (E3ETLTVV9) located in the N-terminal region. Further studies showed that a region near the bottom of the central domain of KlebE plays a primary role in recognizing OmpC, with eight residues surrounding this region identified as essential for KlebE toxicity. Finally, based on the discrepancies in OmpC sequences between the KlebE-resistant and sensitive strains, it was found that the 91st residue of OmpC, an aspartic acid residue, is a key determinant of KlebE toxicity. The identification and characterization of this toxin will facilitate the development of bacteriocin-based therapies targeting multidrug-resistant K. pneumoniae infections.

The impact and safety of encapsulated nanomaterials as a new alternative against carbapenem resistant bacteria. a systematic review.

The emergence of multi drug resistant bacterial infections has caused a critical problem with implication on hospitalization and mortality rates. This systematic review aims to review the combined antimicrobial effect of nanoparticles attached to the traditionally used antibiotics, to overcome the antibiotic resistance crisis. In this systematic search we focused on preclinical studies that have used animal models, to test and evaluate the effect of nanomaterials added to antibiotics against gram negative bacteria with carbapenem resistance. Where, this newly formed structure has led to significant decrease in bacterial load in animal model serum. Furthermore, by evaluating nanomaterial cytotoxicity and inflammatory markers, promising results were established, where low toxicity indices were presented, supporting the ability of this new pathway to be used as an alternative to abused antibiotics. Our research collected the various data and showed encouraging preclinical one for using nanomaterials with antibiotics. This undeniable route should be considered, due to its ability to contribute to the treatment of multi drug resistant bacterial infections. These findings provide base for future studies and reinforce the need for more evaluation and testing on the safety of nanomaterials against bacterial infections.

A novel antibiotic class targeting the lipopolysaccharide transporter.

Carbapenem-resistant Acinetobacter baumannii (CRAB) has emerged as a major global pathogen with limited treatment options1. No new antibiotic chemical class with activity against A. baumannii has reached patients in over 50 years1. Here we report the identification and optimization of tethered macrocyclic peptide (MCP) antibiotics with potent antibacterial activity against CRAB. The mechanism of action of this molecule class involves blocking the transport of bacterial lipopolysaccharide from the inner membrane to its destination on the outer membrane, through inhibition of the LptB2FGC complex. A clinical candidate derived from the MCP class, zosurabalpin (RG6006), effectively treats highly drug-resistant contemporary isolates of CRAB both in vitro and in mouse models of infection, overcoming existing antibiotic resistance mechanisms. This chemical class represents a promising treatment paradigm for patients with invasive infections due to CRAB, for whom current treatment options are inadequate, and additionally identifies LptB2FGC as a tractable target for antimicrobial drug development.

Dynamics of Extended-spectrum Beta-lactamase-producing, Third-generation Cephalosporin-resistant and Tetracycline-resistant Escherichia coli in Feedlot Cattle With or Without Tylosin Administration.

The impact of in-feed use of tylosin in feedlot cattle on Gram-negative foodborne bacteria is unknown. We evaluated the effect of continuous in-feed tylosin use on the concentration and prevalence of tetracycline-resistant (TETr)-, third-generation cephalosporin-resistant (3GCr)-, and extended-spectrum ß-lactamase-producing (ESBLs) E. coli in feedlot cattle. A cohort of weaned calves (10 animals/group) were randomized to receive a feed ration with or without tylosin. Fecal samples, regularly collected over the entire feeding period, and pen surface and feed samples, collected at the end of the feeding period, were cultured on selective media. Enumeration and binary outcomes were analyzed by mixed effects linear regression or logistic regression, respectively, using treatment and days on feed as fixed factors, and animal ID as a random variable. Tylosin supplementation did not affect the fecal concentrations of TETrE. coli or fecal prevalence of 3GCrE. coli. However, cattle in the tylosin group were 1.5 times more likely (Odds ratio = 1.5: 95% confidence interval: 1.1-2.0) to harbor ESBLs E. coli than the control cattle. Regardless of tylosin treatment, fecal concentrations of TETrE. coli and the prevalence of 3GCr- and ESBLs-E. coli increased over time. Tylosin-supplemented feed did not affect the prevalence of TETrE. coli; 3GCr and ESBLs-E. coli were not detected from the feed samples. Most of the 3GCr- and ESBLs-E. coli isolates carried the blaCTX-M-15 gene, widely detected among ESBLs-E. coli human isolates. In summary, although in-feed tylosin use in feedlot cattle did not select for TETr- and 3GCr-E. coli, it increased the likelihood of detecting ESBL-producing E. coli. Furthermore, the study indicated that the feedlot production setting gradually increases the levels of E. coli resistant to the critically and/or important antibiotics for public health, indicating an increased risk of their dissemination beyond the feedlot environment.