Antibiotic Combination Therapy: A Strategy to Overcome Bacterial Resistance to Aminoglycoside Antibiotics

Overcoming antibiotic resistance: the potential and pitfalls of drug repurposing

Since its emergence shortly after the discovery of penicillin, antibiotic resistance has escalated dramatically, posing a significant health threat and economic burden. Combating antibiotic resistance, especially in Gram-negative bacteria (GNB) and drug-resistant Mycobacterium tuberculosis, necessitates innovative research, substantial financial investment, and global cooperation to safeguard public health and develop sustainable solutions. Drug repositioning, or drug repurposing, involves identifying new therapeutic applications for existing drugs, utilizing their established safety profiles and pharmacological data to swiftly provide effective treatments against resistant pathogens. Several drugs, including otilonium bromide, penfluridol, eltrombopag, ibuprofen, and ceritinib, have demonstrated potent antibacterial activity against multidrug-resistant (MDR) bacteria. These drugs can disrupt biofilms, damage bacterial membranes, and inhibit bacterial growth. Furthermore, the combination of repurposed drugs with conventional antibiotics can reduce the required dosage of individual drugs, mitigate side effects, and delay the development of resistance, making it a promising strategy against MDR bacteria such as Staphylococcus aureus, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Escherichia coli. Despite its promise, drug repurposing faces challenges such as potential off-target effects, toxicity, and regulatory and intellectual property issues, necessitating rigorous evaluations and strategic solutions. This article aims to explore the potential of drug repurposing as a strategy to combat antibiotic resistance, examining its benefits, challenges, and future prospects. We address the legal, economic, and practical challenges associated with repurposing existing drugs, highlight successful examples, and propose solutions to enhance the efficacy and viability of this approach in combating MDR bacterial infections.

Combinatorial biosynthesis of novel aminoglycoside antibiotics via pathway engineering

With the current spread of clinically relevant multidrug-resistant (MDR) pathogens, insufficient unearthing of new anti-infectives, and the high cost required for approval of new antimicrobial agents, a strong need for getting these agents via more economic and other alternative routes has emerged. With the discovery of the biosynthetic pathways of various antibiotics pointing out the role of each gene/protein in their antibiotic-producing strains, it became apparent that the biosynthetic gene clusters can be manipulated to produce modified antibiotics. This new approach is known as the combinatorial biosynthesis of new antibiotics which can be employed for obtaining novel derivatives of these valuable antibiotics using genetically modified antibiotic-producing strains (pathway engineering). In this review and based on the available biosynthetic gene clusters of the major aminoglycoside antibiotics (AGAs), the possible alterations or modifications that could be done by co-expression of certain gene(s) previously known to be involved in unique biosynthetic steps have been discussed. In this review defined novel examples of modified AGA using this approach were described and the information provided will act as a platform of researchers to get and develop new antibiotics by the antibiotic-producing bacterial strains such as Streptomyces, Micromonospora,…etc. This way, novel antibiotics with new biological activities could be isolated and used in the treatment of infectious diseases conferring resistance to existing antibiotics.

Gallic acid synergistically enhances the antibacterial activity of azithromycin in MRSA

The rise of antibiotic resistance in existing pathogens has been identified as a major threat to global healthcare in the twenty-first century. This resistance has consequences such as increased cost and prolonged hospital stays, treatment failure, and ultimately increased risk of patient mortality. It is therefore imperative to develop strategies to combat drug resistance. Combined treatment of common antibiotics and natural compounds is one of the most effective methods against resistant bacterial infections. Gallic acid (GA) is a natural secondary metabolite abundantly found in plants and has significant medicinal effects in various aspects of health. In this research, the antibacterial effects of azithromycin (AZM) and GA alone and in combination with each other were investigated on planktonic and biofilm forms of methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant Staphylococcus aureus (MRSA), and Pseudomonas aeruginosa (P. aeruginosa). The results showed that the combination of AZM/GA had an additive effect against MSSA and P. aeruginosa and a synergistic effect against MRSA. In addition, combining these two agents significantly reduced the minimum biofilm inhibitory concentration (MBIC) of AZM and GA in the MRSA strain. Finally, the level of ROS generation in the effect of AZM plus GA was evaluated in the bacteria. Among the studied strains, ROS production was significantly increased in combination treatment compared to AZM alone in MRSA. The results show that the combination of AZM and GA has a significant effect against MRSA and can be considered as an effective treatment option.

Stimuli-Responsive NO Delivery Platforms for Bacterial Infection Treatment

The prevalence of drug-resistant bacterial infections has emerged as a grave threat to clinical treatment and global human health, presenting one of the foremost challenges in medical care. Thus, there is an urgent imperative to develop safe and efficacious novel antimicrobial strategies. Nitric oxide (NO) is a recognized endogenous signaling molecule, which plays a pivotal role in numerous pathological processes. Currently, NO has garnered significant interest as an antibacterial agent due to its capability to eradicate bacteria, disrupt biofilms, and facilitate wound healing, all while circumventing the emergence of drug resistance. However, the inherently unstable characteristic of NO therapeutic gas renders the controlled administration of NO gases exceedingly challenging. Hence, in this review, the current challenge of bacterial infection is discussed; then it is briefly elucidated the antibacterial mechanism of NO and comprehensively delineate the recent advancements in stimulus-responsive NO delivery platforms, along with their merits, obstacles, and prospective avenues for clinical application. This review offers guidance for future advancements in NO-medicated anti-infection therapy is hoped.

Antimicrobial activity of metal-based nanoparticles: a mini-review

The resistance of pathogenic microorganisms to antibiotics is one of the main problems of world health. Of particular concern are multidrug-resistant (MDR) bacteria. Infections caused by these microorganisms affect the appearance of acute or chronic diseases. In this regard, modern technologies, such as nanomaterials (NMs), especially promising nanoparticles (NPs), can possess antimicrobial properties or improve the effectiveness and delivery of known antibiotics. Their diversity and characteristics, combined with surface functionalization, enable multivalent interactions with microbial biomolecules. This article presents an overview of the most current research on replacing antibiotics with NPs, including the prospects and risks involved.

Prevalence and mechanisms of aminoglycoside resistance among drug-resistant Pseudomonas aeruginosa clinical isolates in Iran

BACKGROUND

Aminoglycosides have been a cornerstone of the treatment of nosocomial infections caused by Pseudomonas aeruginosa for over 80 years. However, escalating emergence of resistance poses a significant challenge. Therefore, this study aimed to investigate the prevailing patterns of aminoglycoside resistance among clinical isolates of P. aeruginosa in Iran; as well as the underlying resistance mechanisms observed in patients referred to Ardabil hospitals.

METHODS

A total of 200 isolates from five hospitals were evaluated. The resistance profiles of P. aeruginosa isolates to tobramycin, amikacin, and netilmicin were determined using the disk diffusion method. The capacity of aminoglycoside-resistant isolates to form biofilms was assessed through a phenotypic assay, and the results were confirmed using the gene amplification technique. The presence of genes associated with aminoglycoside resistance was detected using polymerase chain reaction (PCR). Quantitative reverse transcription PCR (qRT-PCR) was performed to measure the expression levels of genes encoding the MexXY-OprM efflux pump and PhoPQ two-component system (TCS).

RESULTS

The prevalence of aminoglycoside-resistant P. aeruginosa isolates was 48%, with 94.7% demonstrating multidrug resistance (MDR). All aminoglycoside-resistant P. aeruginosa strains exhibited biofilm-forming capabilities and harbored all the genes associated with biofilm production. Among the nine genes encoding 16S rRNA methylase and aminoglycoside-modifying enzymes, three genes were detected in these isolates: aac(6')-Ib (85.4%), ant(2'')-Ia (18.7%), and aph(3')-VI (3.1%). Additionally, all aminoglycoside-resistant P. aeruginosa isolates carried mexY and phoP genes, although the expression levels of mexY and phoP were 75% and 87.5%, respectively.

CONCLUSION

Given the considerably high prevalence of aminoglycoside-resistant P. aeruginosa strains, urgent measures are warranted to transition towards the use of novel aminoglycosides and to uphold vigilant surveillance of resistance patterns.

Investigating the antimicrobial potential of bovine lactoferrin against the neonatal pathogen, Staphylococcus capitis

Lactoferrin is an antimicrobial glycoprotein that demonstrates a broad-spectrum of activity against a wide variety of clinical pathogens. This study investigated the potential of bovine lactoferrin (bLf) against multidrug resistant Staphylococcus capitis (S. capitis) strains. Growth curve analysis and time-kill curves demonstrated that at 750 µg ml-1 lactoferrin significantly inhibited (50.6%, P < 0.05) the growth of most isolates tested (90%), and this effect was based on a bacteriostatic mechanism. At the same concentration, bLf also significantly inhibited (30%, P < 0.05) biofilm formation in 40% of strains tested. Combinations of bLf with selected antibiotics were assessed for enhanced antimicrobial activity using growth curves. BLf combined with β-lactam antibiotics reduced the growth of S. capitis strains, however, the effects were not significant. BLf displays antimicrobial effects against multidrug resistant S. capitis isolates, but with strain-specific effects.

Anti-Biofilm Perspectives of Propolis against Staphylococcus epidermidis Infections

Staphylococcus epidermis has emerged as the main causative agent of medical device-related infections. Their major pathogenicity factor lies in its ability to adhere to surfaces and proliferate into biofilms, which increase their resistance to antibiotics. The main objective of this study was to evaluate the use and the mechanism of action of an ethanolic extract of Spanish propolis (EESP) as a potential alternative for preventing biofilm-related infections caused by S. epidermidis. The chemical composition of propolis is reported and its antibacterial activity against several strains of S. epidermidis with different biofilm-forming capacities evaluated. The influence of sub-inhibitory concentrations (sub-MICs) of EESP on their growth, physicochemical surface properties, adherence, and biofilm formation were studied. EESP interferes with planktonic cells, homogenizing their physicochemical surface properties and introducing a significant delay in their growth. The adherence and biofilms at the EESP concentrations investigated were decreased up to 90.5% among the strains. Microscopic analysis indicated that the planktonic cells that survived the treatment were the ones that adhere and proliferate on the surfaces. The results obtained suggest that the EESP has a high potential to be used as an inhibitor of both the adhesion and biofilm formation of S. epidermidis.

Antimicrobial Peptide Screening for Designing Custom Bactericidal Hydrogels

Staphylococcus aureus (S. aureus) is an opportunistic pathogen that lives on surfaces and skin and can cause serious infections inside the body. Antimicrobial peptides (AMPs) are part of the innate immune system and can eliminate pathogens, including bacteria and viruses, and are a promising alternative to antibiotics. Although studies have reported that AMP-functionalized hydrogels can prevent bacterial adhesion and biofilm formation, AMP dosing and the combined effects of multiple AMPs are not well understood. Here, three AMPs with different antibacterial properties were synthesized and the soluble minimum inhibitory concentrations (MICs) of each AMP against methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) were determined. Hydrogels with immobilized AMPs at their MIC (DD13-RIP 27.5 µM; indolicidin 43.8 µM; P10 120 µM) were effective in preventing MRSA adhesion and biofilm formation. Checkerboard AMP screens identified synergy between indolicidin (3.1 µM) and P10 (12.5 µM) based on soluble fractional inhibitory concentration indices (FICIs) against MRSA, and hydrogels formed with these AMPs at half of their synergistic concentrations (total peptide concentration, 7.8 µM) were highly efficacious in killing MRSA. Mammalian cells cultured atop these hydrogels were highly viable, demonstrating that these AMP hydrogels are biocompatible and selectively eradicate bacteria, based on soluble checkerboard-screening data.

A smooth vetch (Vicia villosa var.) strain endogenous to the broad-spectrum antagonist Bacillus siamensis JSZ06 alleviates banana wilt disease

Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense Tropical Race 4 (Foc TR4), poses a significant threat to banana production globally, thereby necessitating effective biocontrol methods to manage this devastating disease. This study investigates the potential of Bacillus siamensis strain JSZ06, isolated from smooth vetch, as a biocontrol agent against Foc TR4. To this end, we conducted a series of in vitro and in vivo experiments to evaluate the antifungal activity of strain JSZ06 and its crude extracts. Additionally, genomic analyses were performed to identify antibiotic synthesis genes, while metabolomic profiling was conducted to characterize bioactive compounds. The results demonstrated that strain JSZ06 exhibited strong inhibitory activity against Foc TR4, significantly reducing mycelial growth and spore germination. Moreover, scanning and transmission electron microscopy revealed substantial ultrastructural damage to Foc TR4 mycelia treated with JSZ06 extracts. Genomic analysis identified several antibiotic synthesis genes, and metabolomic profiling revealed numerous antifungal metabolites. Furthermore, in pot trials, the application of JSZ06 fermentation broth significantly enhanced banana plant growth and reduced disease severity, achieving biocontrol efficiencies of 76.71% and 79.25% for leaves and pseudostems, respectively. In conclusion, Bacillus siamensis JSZ06 is a promising biocontrol agent against Fusarium wilt in bananas, with its dual action of direct antifungal activity and plant growth promotion underscoring its potential for integrated disease management strategies.

Developing antibacterial peptides as a promising therapy for combating antibiotic-resistant Pseudomonas aeruginosa infections

Background and Aim

Antibiotic-resistant Pseudomonas aeruginosa poses a serious health threat. This study aimed to investigate the antibacterial activity of peptide KW-23 against drug-resistant P. aeruginosa and its potential for enhancing the efficacy of conventional antibiotics.

Materials and Methods

KW-23 was synthesized from nine amino acids, specifically three tryptophans and three lysines. The purity of the substance was analyzed using reverse-phase high-performance liquid chromatography. The peptide was identified through mass spectrometry using electrospray ionization. The minimum inhibitory concentration (MIC) values of KW-23 in combination with conventional antibiotics against control and multidrug-resistant P. aeruginosa were determined utilizing broth microdilution. The erythrocyte hemolytic assay was used to measure toxicity. The KW-23 effect was analyzed using the time-kill curve.

Results

The peptide exhibited strong antibacterial activity against control and multidrug-resistant strains of P. aeruginosa, with MICs of 4.5 μg/mL and 20 μg/mL, respectively. At higher concentration of 100 μg/mL, KW-23 exhibited a low hemolytic impact, causing no more than 3% damage to red blood. The cytotoxicity assay demonstrates KW-23's safety, while the time-kill curve highlights its rapid and sustained antibacterial activity. The combination of KW-23 and gentamicin exhibited synergistic activity against both susceptible and resistant P. aeruginosa, with fractional inhibitory concentration index values of 0.07 and 0.27, respectively.

Conclusion

The KW-23 synthesized in the laboratory significantly combats antibiotic-resistant P. aeruginosa. Due to its strong antibacterial properties and low toxicity to cells, KW-23 is a promising alternative to traditional antibiotics in combating multidrug-resistant bacteria.

Nanotechnology-driven strategies to enhance the treatment of drug-resistant bacterial infections

The misuse of antibiotics has led to increased bacterial resistance, posing a global public health crisis and seriously endangering lives. Currently, antibiotic therapy remains the most common approach for treating bacterial infections, but its effectiveness against multidrug-resistant bacteria is diminishing due to the slow development of new antibiotics and the increase of bacterial drug resistance. Consequently, developing new a\ntimicrobial strategies and improving antibiotic efficacy to combat bacterial infection has become an urgent priority. The emergence of nanotechnology has revolutionized the traditional antibiotic treatment, presenting new opportunities for refractory bacterial infection. Here we comprehensively review the research progress in nanotechnology-based antimicrobial drug delivery and highlight diverse platforms designed to target different bacterial resistance mechanisms. We also outline the use of nanotechnology in combining antibiotic therapy with other therapeutic modalities to enhance the therapeutic effectiveness of drug-resistant bacterial infections. These innovative therapeutic strategies have the potential to enhance bacterial susceptibility and overcome bacterial resistance. Finally, the challenges and prospects for the application of nanomaterial-based antimicrobial strategies in combating bacterial resistance are discussed. This article is categorized under: Biology-Inspired Nanomaterials > Nucleic Acid-Based Structures Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease.

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.

Murepavadin promotes the killing efficacies of aminoglycoside antibiotics against Pseudomonas aeruginosa by enhancing membrane potential

Murepavadin is a peptidomimetic that specifically targets the lipopolysaccharide transport protein LptD of Pseudomonas aeruginosa. Here, we found that murepavadin enhances the bactericidal efficacies of tobramycin and amikacin. We further demonstrated that murepavadin enhances bacterial respiration activity and subsequent membrane potential, which promotes intracellular uptake of aminoglycoside antibiotics. In addition, the murepavadin-amikacin combination displayed a synergistic bactericidal effect in a murine pneumonia model.

Identification of a novel DNA repair inhibitor using an in silico driven approach shows effective combinatorial activity with genotoxic agents against multidrug-resistant Escherichia coli

Increasing antimicrobial drug resistance represents a global existential threat. Infection is a particular problem in immunocompromised individuals, such as patients undergoing cancer chemotherapy, due to the targeting of rapidly dividing cells by antineoplastic agents. We recently developed a strategy that targets bacterial nucleotide excision DNA repair (NER) to identify compounds that act as antimicrobial sensitizers specific for patients undergoing cancer chemotherapy. Building on this, we performed a virtual drug screening of a ~120,000 compound library against the key NER protein UvrA. From this, numerous target compounds were identified and of those a candidate compound, Bemcentinib (R428), showed a strong affinity toward UvrA. This NER protein possesses four ATPase sites in its dimeric state, and we found that Bemcentinib could inhibit UvrA's ATPase activity by ~90% and also impair its ability to bind DNA. As a result, Bemcentinib strongly diminishes NER's ability to repair DNA in vitro. To provide a measure of in vivo activity we discovered that the growth of Escherichia coli MG1655 was significantly inhibited when Bemcentinib was combined with the DNA damaging agent 4-NQO, which is analogous to UV. Using the clinically relevant DNA-damaging antineoplastic cisplatin in combination with Bemcentinib against the urological sepsis-causing E. coli strain EC958 caused complete growth inhibition. This study offers a novel approach for the potential development of new compounds for use as adjuvants in antineoplastic therapy.

Unraveling resistance mechanisms in combination therapy: A comprehensive review of recent advances and future directions

Antimicrobial resistance is a global health threat. Misuse and overuse of antimicrobials are the main drivers in developing drug-resistant bacteria. The emergence of the rapid global spread of multi-resistant bacteria requires urgent multisectoral action to generate novel treatment alternatives. Combination therapy offers the potential to exploit synergistic effects for enhanced antibacterial efficacy of drugs. Understanding the complex dynamics and kinetics of drug interactions in combination therapy is crucial. Therefore, this review outlines the current advances in antibiotic resistance's evolutionary and genetic dynamics in combination therapies-exposed bacteria. Moreover, we also discussed four pivotal future research areas to comprehend better the development of antibiotic resistance in bacteria treated with combination strategies.

Pre-formulation of an additive combination of two antimicrobial agents, clofazimine and nisin A, to boost antimicrobial activity

According to the World Health Organization, antimicrobial resistance is one of the top ten issues that pose a major threat to humanity. The lack of investment by the pharmaceutical industry has meant fewer novel antimicrobial agents are in development, exacerbating the problem. Emerging drug design strategies are exploring the repurposing of existing drugs and the utilization of novel drug candidates, like antimicrobial peptides, to combat drug resistance. This proactive approach is crucial in fighting global health threats. In this study, an additive combination of a repurposed anti-leprosy drug, clofazimine, and an antimicrobial peptide, nisin A, are preformulated using liquid antisolvent precipitation to generate a stable amorphous, ionized nanoparticle system to boost antimicrobial activity. The nanotechnology aims to improve the physicochemical properties of the inherently poorly water-soluble clofazimine molecules while also harnessing the previously unreported additive effect of clofazimine and nisin A. The approach transformed clofazimine into a more water-soluble salt, yielding amorphous nanoparticles stabilized by the antimicrobial peptide; and combined the two drugs into a more soluble and more active formulation. Blending pre-formulation strategies like amorphization, salt formation, and nanosizing to improve the inherent low aqueous solubility of drugs can open many new possibilities for the design of new antimicrobial agents. This fusion of pre-formulation technologies in combination with the multi-hurdle approach of selecting drugs with different effects on microbes could be key in the design platform of new antibiotics in the fight against antimicrobial resistance.

Laboratory Evolution of Antimicrobial Resistance in Bacteria to Develop Rational Treatment Strategies

Laboratory evolution studies, particularly with Escherichia coli, have yielded invaluable insights into the mechanisms of antimicrobial resistance (AMR). Recent investigations have illuminated that, with repetitive antibiotic exposures, bacterial populations will adapt and eventually become tolerant and resistant to the drugs. Through intensive analyses, these inquiries have unveiled instances of convergent evolution across diverse antibiotics, the pleiotropic effects of resistance mutations, and the role played by loss-of-function mutations in the evolutionary landscape. Moreover, a quantitative analysis of multidrug combinations has shed light on collateral sensitivity, revealing specific drug combinations capable of suppressing the acquisition of resistance. This review article introduces the methodologies employed in the laboratory evolution of AMR in bacteria and presents recent discoveries concerning AMR mechanisms derived from laboratory evolution. Additionally, the review outlines the application of laboratory evolution in endeavors to formulate rational treatment strategies.

Antibiotic action and resistance: updated review of mechanisms, spread, influencing factors, and alternative approaches for combating resistance

Antibiotics represent a frequently employed therapeutic modality for the management of bacterial infections across diverse domains, including human health, agriculture, livestock breeding, and fish farming. The efficacy of antibiotics relies on four distinct mechanisms of action, which are discussed in detail in this review, along with accompanying diagrammatic illustrations. Despite their effectiveness, antibiotic resistance has emerged as a significant challenge to treating bacterial infections. Bacteria have developed defense mechanisms against antibiotics, rendering them ineffective. This review delves into the specific mechanisms that bacteria have developed to resist antibiotics, with the help of diagrammatic illustrations. Antibiotic resistance can spread among bacteria through various routes, resulting in previously susceptible bacteria becoming antibiotic-resistant. Multiple factors contribute to the worsening crisis of antibiotic resistance, including human misuse of antibiotics. This review also emphasizes alternative solutions proposed to mitigate the exacerbation of antibiotic resistance.

Enhancing Commercial Antibiotics with Trans-Cinnamaldehyde in Gram-Positive and Gram-Negative Bacteria: An In Vitro Approach

One strategy to mitigate the emergence of bacterial resistance involves reducing antibiotic doses by combining them with natural products, such as trans-cinnamaldehyde (CIN). The objective of this research was to identify in vitro combinations (CIN + commercial antibiotic (ABX)) that decrease the minimum inhibitory concentration (MIC) of seven antibiotics against 14 different Gram-positive and Gram-negative pathogenic bacteria, most of them classified as ESKAPE. MIC values were measured for all compounds using the broth microdilution method. The effect of the combinations on these microorganisms was analyzed through the checkboard assay to determine the type of activity (synergy, antagonism, or addition). This analysis was complemented with a kinetic study of the synergistic combinations. Fifteen synergistic combinations were characterized for nine of the tested bacteria. CIN demonstrated effectiveness in reducing the MIC of chloramphenicol, streptomycin, amoxicillin, and erythromycin (94-98%) when tested on Serratia marcescens, Staphylococcus aureus, Pasteurella aerogenes, and Salmonella enterica, respectively. The kinetic study revealed that when the substances were tested alone at the MIC concentration observed in the synergistic combination, bacterial growth was not inhibited. However, when CIN and the ABX, for which synergy was observed, were tested simultaneously in combination at these same concentrations, the bacterial growth inhibition was complete. This demonstrates the highly potent in vitro synergistic activity of CIN when combined with commercial ABXs. This finding could be particularly beneficial in livestock farming, as this sector witnesses the highest quantities of antimicrobial usage, contributing significantly to antimicrobial resistance issues. Further research focused on this natural compound is thus warranted for this reason.

Combating Aminoglycoside Resistance: From Structural and Functional Characterisation to Therapeutic Challenges with RKAAT

A comprehensive knowledge of aminoglycoside-modifying enzymes (AMEs) and their role in bacterial resistance mechanisms is urgently required due to the rising incidence of antibiotic resistance, particularly in Klebsiella pneumoniae infections. This study explores the essential features of AMEs, including their structural and functional properties, the processes by which they contribute to antibiotic resistance, and the therapeutic importance of aminoglycosides. The study primarily examines the Recombinant Klebsiella pneumoniae Aminoglycoside Adenylyl Transferase (RKAAT), particularly emphasizing its biophysical characteristics and the sorts of resistance it imparts. Furthermore, this study examines the challenges presented by RKAAT-mediated resistance, an evaluation of treatment methods and constraints, and options for controlling infection. The analysis provides a prospective outlook on strategies to address and reduce antibiotic resistance. This extensive investigation seeks to provide vital insights into the continuing fight against bacterial resistance, directing future research efforts and medicinal approaches.

Encapsulating Antibiotic and Protein-Stabilized Nanosilver into Sandwich-Structured Electrospun Nanofibrous Scaffolds for MRSA-Infected Wound Treatment

With the increasing prevalence of microbial infections, which results in prolonged inflammation and delayed wound healing, the development of effective and safe antimicrobial wound dressings of multiple properties remains challenging for public health. Despite their various formats, the available developed dressings with limited functions may not fulfill the diverse demands involved in the complex wound healing process. In this study, multifunctional sandwich-structured electrospinning nanofiber membranes (ENMs) were fabricated. According to the structural composition, the obtained ENMs included a hydrophilic inner layer loaded with curcumin and gentamicin sulfate, an antibacterial middle layer consisting of bovine serum albumin stabilized silver oxide nanoparticles, and a hydrophobic outer layer. The prepared sandwich-structured ENMs (SNM) exhibited good biocompatibility and killing efficacy on Escherichia coli, Staphylococcus aureus, and Methicillin-resistant S. aureus (MRSA). In particular, transcriptomic analysis revealed that SNM inactivated MRSA by inhibiting its carbohydrate and energy metabolism and reduced the bacterial resistance by downregulating mecA. In the animal experiment, SNM showed improved wound healing efficiency by reducing the bacterial load and inflammation. Moreover, 16S rDNA sequencing results indicated that SNM treatment may accelerate wound healing without observed influence on the normal skin flora. Therefore, the constructed sandwich-structured ENMs exhibited promising potential as dressings to deal with the infected wound management.

Antibiotics Coupled with Photothermal Therapy for the Enhanced Killing of Bacteria

In this study, the application of ionic materials as a combination antibiotic drug was investigated. The fluoroquinolone, Norfloxacin, was converted into the ionic form and combined with the cationic dye, IR780+, using an ion-exchange reaction. The resulting ionic combination drug possesses two killing mechanisms in one compound. The antibiotic chemical mechanism along with the photothermal mechanism that was acquired by adding IR780 to the compound led to the development of a combination antibiotic drug. This ionic combination drug consisting of Norfloxacin anion and IR780 cation is easily dispersed in water using sonication waves. The parent compounds and ionic combination drug, dissolved in organic solvent and dispersed in water, were characterized, and the photophysical properties were studied in detail. It was discovered that the aqueous ionic combination drugs exhibited significant changes in absorbance and photoluminescent properties. In aqueous media, the dispersed ionic combination drug exhibited a very broad absorbance with an additional peak around 1000 nm which is advantageous in photothermal. A significant decrease in the quantum yield along with enhanced non-radiative rate constant was observed for the combination drug in the aqueous. The photothermal mechanism is present in both the parent IR780 dye and the ionic combination drug. The ionic combination drug displayed a high light-to-heat conversion efficiency and temperature increase similar to the parent dye. The combination of both killing mechanisms in the ionic combination drug resulted in enhanced antibacterial activity against Escherichia coli as compared to the parent Norfloxacin and IR780-I individually.

Development of Novel Peptide-Modified Silver Nanoparticle-Based Rapid Biosensors for Detecting Aminoglycoside Antibiotics

The detection and monitoring of aminoglycoside antibiotics (AGAs) have become of utmost importance due to their widespread use in human and animal therapy, as well as the associated risks of exposure, toxicity, and the emergence of antimicrobial resistance. In this study, we successfully synthesized casein hydrolysate peptides-functionalized silver nanoparticles (CHPs@AgNPs) and employed them as a novel colorimetric analytical platform to demonstrate remarkable specificity and sensitivity toward AGAs. The colorimetric and spectral response of the CHPs@AgNPs was observed at 405 and 520 nm, showing a linear correlation with the concentration of streptomycin, a representative AGA. The color changes from yellow to orange provided a visual indication of the analyte concentration, enabling quantitative determination for real-world samples. The AgNP assay exhibited excellent sensitivity with dynamic ranges of approximately 200-650 and 100-700 nM for streptomycin-spiked tap water and dairy whey with limits of detection found to be ∼98 and 56 nM, respectively. The mechanism behind the selective aggregation of CHPs@AgNPs in the presence of AGAs involves the amine groups of the target analytes acting as molecular bridges for electrostatic coupling with hydroxyl or carboxyl functionalities of adjacent NPs, driving the formation of stable NP aggregates. The developed assay offers several advantages, making it suitable for various practical applications. It is characterized by its simplicity, rapidity, specificity, sensitivity, and cost-effectiveness. These unique features make the method a promising tool for monitoring water quality, ensuring food safety, and dealing with emergent issues of antibiotic resistance.

Effect of Three Different Amino Acids Plus Gentamicin Against Methicillin-Resistant Staphylococcus aureus

Background

The issue of methicillin-resistant Staphylococcus aureus (MRSA) resistant to many antibiotics and causing serious infectious diseases is a growing healthcare concern.

Purpose

In recent years, exogenous administration of metabolites in combination with antibiotics can re-sensitize resistant bacteria to antibiotics; however, their effects vary, and their underlying mechanism of action remains elusive.

Methods

We assessed the bactericidal effects of the three amino acids in combination with gentamicin in vitro and in vivo. Subsequently, we explored the role of these amino acids on the metabolomics of MRSA using Liquid chromatography-tandem mass spectrometry (LC-MS/MS). Furthermore, we performed the downstream analyses using MetaboAnalyst and Interactive Pathways Explorer.

Results

Exogenous threonine showed the best bactericidal efficacy with gentamicin, followed by glycine, wherein serine had no effect. Amino acid treatments mainly up-regulated the metabolites, increased the amino acid abundance, and significantly activated metabolisms; these effects were consistent with the bactericidal efficacy of the three amino acids. Most amino acids participated in the tricarboxylic acid cycle, and threonine supplementation increased the activities of citrate synthase, isocitrate dehydrogenase and α-ketoglutarate dehydrogenase, whereas glycine increased activities of citrate synthase and α-ketoglutarate dehydrogenase, and serine did not affect the activities of any of the three key enzymes. We identified 24 biomarkers in the three groups, among which glutamic acid and cysteine showed a gradient decrease and increase, respectively. Subsequent analyses revealed that glutamic acid but not cysteine promoted the bactericidal effect of gentamicin synergistically.

Conclusion

Threonine has the best synergistic effect in reversing bacterial resistance compared to glycine and serine. We show that different amino acids combined with an antibiotic mainly affect amino acid metabolism and act via different metabolic regulatory mechanisms, which could help develop effective strategies for tackling MRSA infections.

Identification and characterization of a novel aminoglycoside O-nucleotidyltransferase ANT(6)-If from Paenibacillus thiaminolyticus PATH554

Background

Paenibacillus thiaminolyticus, a species of genus Paenibacillus of the family Paenibacillaceae, exists widely in environments and habitats in various plants and worms, and occasionally causes human infections. This work aimed to characterize the function of a novel aminoglycoside O-nucleotidyltransferase resistance gene, designated ant(6)-If, from a P. thiaminolyticus strain PATH554.

Methods

Molecular cloning, antimicrobial susceptibility testing, enzyme expression and purification, and kinetic analysis were used to validate the function of the novel gene. Whole-genome sequencing and comparative genomic analysis were performed to investigate the phylogenetic relationship of ANT(6)-If and other aminoglycoside O-nucleotidyltransferases, and the synteny of ant(6)-If related sequences.

Results

The recombinant with the cloned ant(6)-If gene (pMD19-ant(6)-If/DH5α) demonstrated a 128-fold increase of minimum inhibitory concentration level against streptomycin, compared with the control strains (DH5α and pMD19/DH5α). The kinetic parameter k_cat/K_m of ANT(6)-If for streptomycin was 9.01 × 10³ M^-1·s^-1. Among the function-characterized resistance genes, ANT(6)-If shared the highest amino acid sequence identity of 75.35% with AadK. The ant(6)-If gene was located within a relatively conserved genomic region in the chromosome.

Conclusion

ant(6)-If conferred resistance to streptomycin. The study of a novel resistance gene in an unusual environmental bacterium in this work contributed to elucidating the resistance mechanisms in the microorganisms.

Conjugates of Aminoglycosides with Stapled Peptides as a Way to Target Antibiotic-Resistant Bacteria

The misuse and overuse of antibiotics led to the development of bacterial resistance to existing aminoglycoside (AMG) antibiotics and limited their use. Consequently, there is a growing need to develop effective antimicrobials against multidrug-resistant bacteria. To target resistant strains, we propose to combine 2-deoxystreptamine AMGs, neomycin (NEO) and amikacin (AMK), with a membrane-active antimicrobial peptide anoplin and its hydrocarbon stapled derivative. The AMG-peptide hybrids were conjugated using the click chemistry reaction in solution to obtain a non-cleavable triazole linker and by disulfide bridge formation on the resin to obtain a linker cleavable in the bacterial cytoplasm. Homo-dimers connected via disulfide bridges between the N-terminus thiol analogues of anoplin and hydrocarbon stapled anoplin were also synthesized. These hybrid compounds show a notable increase in antibacterial and bactericidal activity, as compared to the unconjugated ones or their combinations, against Gram-positive and Gram-negative bacteria, especially for the strains resistant to AMK or NEO. The conjugates and disulfide peptide dimers exhibit low hemolytic activity on sheep red blood erythrocytes.

Exploring antibiotic resistance with chemical tools

Antibiotic resistance is an enormous problem that is accountable for over a million deaths annually, with numbers expected to significantly increase over the coming decades. Although some of the underlying causes leading up to antibiotic resistance are well understood, many of the molecular processes involved remain elusive. To better appreciate at a molecular level how resistance emerges, customized chemical biology tools can offer a solution. This Feature Article attempts to provide an overview of the wide variety of tools that have been developed over the last decade, by highlighting some of the more illustrative examples. These include the use of fluorescent, photoaffinity and activatable antibiotics and bacterial components to start to unravel the molecular mechanisms involved in resistance. The antibiotic crisis is an eminent global threat and requires the continuous development of creative chemical tools to dissect and ultimately counteract resistance.

An Update Review of Approaches to Multiple Action-Based Antibacterials

Many approaches are being pursued to address the major global health challenge posed by the increasing resistance of pathogenic bacteria to antibacterial agents. One of the promising approaches being investigated includes the design and development of multiple action-based small-molecule antibacterials. Aspects of this broad area have been reviewed previously, and recent developments are addressed in this update review covering the literature mainly over the past three years. Considerations encompassing drug combinations, single-molecule hybrids and prodrugs are summarised in regard to the intentional design and development of multiple-action agents with a focus on potential triple or greater activities in bacteria. The hope for such single agents or combinations of single agents is that resistance development will be significantly hindered, and they may be useful in tackling bacterial disease caused by both resistant and non-resistant bacteria.

Discovery of Novel Resistance Mechanisms of Vibrio parahaemolyticus Biofilm against Aminoglycoside Antibiotics

Inappropriate use of antibiotics eventually leads to the emergence of antibiotic-resistant strains and invalidates the treatment of infectious diseases. Aminoglycoside antibiotics (AGAs) are a class of broad-spectrum cationic antibiotics widely used for the treatment of Gram-negative bacterial infections. Understanding the AGA resistance mechanism of bacteria would increase the efficacy of treating these infections. This study demonstrates a significant correlation between AGA resistance and the adaptation of biofilms by Vibrio parahaemolyticus (VP). These adaptations were the result of challenges against the aminoglycosides (amikacin and gentamicin). Confocal laser scanning microscope (CLSM) analysis revealed an enclosure type mechanism where the biological volume (BV) and average thickness (AT) of V. parahaemolyticus biofilm were significantly positively correlated with amikacin resistance (BIC) (p < 0.01). A neutralization type mechanism was mediated by anionic extracellular polymeric substances (EPSs). The biofilm minimum inhibitory concentrations of amikacin and gentamicin were reduced from 32 µg/mL to 16 µg/mL and from 16 µg/mL to 4 µg/mL, respectively, after anionic EPS treatment with DNase I and proteinase K. Here, anionic EPSs bind cationic AGAs to develop antibiotic resistance. Transcriptomic sequencing revealed a regulatory type mechanism, where antibiotic resistance associated genes were significantly upregulated in biofilm producing V. parahaemolyticus when compared with planktonic cells. The three mechanistic strategies of developing resistance demonstrate that selective and judicious use of new antibiotics are needed to win the battle against infectious disease.

Occurrence and Multidrug Resistance in Strains of Listeria monocytogenes Recovered from the Anaerobic Co-Digestion Sludge Contained in a Single Stage Steel Biodigester: Implications for Antimicrobial Stewardship

L. monocytogenes is a zoonotic foodborne pathogen with inherent adaptability to tolerate environmental and physiological stresses, thereby causing severe disease outbreaks. Antibiotic resistant foodborne pathogens are a challenge to the food industry. A total of 18 samples were pooled from a bio-digester co-digesting swine manure/pinewood sawdust, and evaluated for the occurrence of bacterium plus total viable counts using the spread plate method. The recovered bacterial isolates were presumptively identified by growth on selective medium and confirmed by biochemical characterisation, leading to the isolation of 43 L. monocytogenes. The isolates were characterized based on their susceptibility to antibiotics via the Kirby-Bauer disc diffusion technique against a panel of 14 antibiotics. Equally, the multiple antibiotic resistance (MAR) index was calculated, and MAR phenotypes generated. The bacterial counts were between 102 and104 cfu/mL. Complete susceptibility (100%) was demonstrated to ampicillin, gentamicin and sulfamethoxazole, which are the drugs of choice in the treatment of listeriosis. In addition, intermediate sensitivity occurred at 25.58% to cefotaxime, and the highest resistance (51.16%) was exhibited against nalidixic acid. The MAR index ranged from 0 to 0.71. Overall, 41.86% of the Listeria isolates displayed multidrug resistance, with 18 different MAR phenotypes, demonstrating CIP, E, C, TET, AUG, S, CTX, NA, AML, NI as the greatest MAR phenotype. It can be concluded that the isolates yielding MAR > 0.2 originated from the farm, where antibiotics had been in routine use. Therefore, strict monitoring of antibiotics use in the farm is crucial to mitigate further increase in antibiotic resistance amongst these bacterial isolates.

Chemical Basis of Combination Therapy to Combat Antibiotic Resistance

The antimicrobial resistance crisis is a global health issue requiring discovery and development of novel therapeutics. However, conventional screening of natural products or synthetic chemical libraries is uncertain. Combination therapy using approved antibiotics with inhibitors targeting innate resistance mechanisms provides an alternative strategy to develop potent therapeutics. This review discusses the chemical structures of effective β-lactamase inhibitors, outer membrane permeabilizers, and efflux pump inhibitors that act as adjuvant molecules of classical antibiotics. Rational design of the chemical structures of adjuvants will provide methods to impart or restore efficacy to classical antibiotics for inherently antibiotic-resistant bacteria. As many bacteria have multiple resistance pathways, adjuvant molecules simultaneously targeting multiple pathways are promising approaches to combat multidrug-resistant bacterial infections.

Anti-Staphylococcal Activities of Rosmarinus officinalis and Myrtus communis Essential Oils through ROS-Mediated Oxidative Stress

Rosmarinus officinalis and Myrtus communis essential oils (EOs) are well-known for their ethno-pharmaceutical properties. In the present study, we have analyzed the chemical composition of both EOs by gas chromatography-mass spectrometry. Then we assessed their antibacterial, antibiofilm, and anti-virulence actions against the opportunistic pathogen Staphylococcus aureus. The cytotoxic effect of agents tested against this bacterium was investigated by monitoring reactive oxygen-species (ROS) generation and antioxidant-enzyme (catalase) production. Regarding the antistaphylococcal effects, our results showed antibacterial efficacy of both Eos and their combination, where the minimum inhibitory concentrations ranged between 0.7 and 11.25 mg/mL. A combination of tested agents showed the highest anti-hemolytic and anti-protease effects. Additionally, association between EOs displayed more potency against the development of biofilm performed by S. aureus, with percentage of removal reaching 74%. The inhibitory impacts of EOs on S. aureus virulence factors were discovered to be concentration-dependent. Furthermore, our results provide insight on the abilities of R. officinalis and M. communis EOs, as well as their potential in combination, to generate ROS and affect oxidative stress enzyme catalase in S. aureus, leading to their antagonistic effect against this pathogen.

Uracil restores susceptibility of methicillin-resistant Staphylococcus aureus to aminoglycosides through metabolic reprogramming

Background: Methicillin-resistant Staphylococcus aureus (MRSA) has now become a major nosocomial pathogen bacteria and resistant to many antibiotics. Therefore, Development of novel approaches to combat the disease is especially important. The present study aimed to provide a novel approach involving the use of nucleotide-mediated metabolic reprogramming to tackle intractable methicillin-resistant S. aureus (MRSA) infections. Objective: This study aims to explore the bacterial effects and mechanism of uracil and gentamicin in S. aureus. Methods: Antibiotic bactericidal assays was used to determine the synergistic bactericidal effect of uracil and gentamicin. How did uracil regulate bacterial metabolism including the tricarboxylic acid (TCA) cycle by GC-MS-based metabolomics. Next, genes and activity of key enzymes in the TCA cycle, PMF, and intracellular aminoglycosides were measured. Finally, bacterial respiration, reactive oxygen species (ROS), and ATP levels were also assayed in this study. Results: In the present study, we found that uracil could synergize with aminoglycosides to kill MRSA (USA300) by 400-fold. Reprogramming metabolomics displayed uracil reprogrammed bacterial metabolism, especially enhanced the TCA cycle to elevate NADH production and proton motive force, thereby promoting the uptake of antibiotics. Furthermore, uracil increased cellular respiration and ATP production, resulting the generation of ROS. Thus, the combined activity of uracil and antibiotics induced bacterial death. Inhibition of the TCA cycle or ROS production could attenuate bactericidal efficiency. Moreover, uracil exhibited bactericidal activity in cooperation with aminoglycosides against other pathogenic bacteria. In a mouse mode of MRSA infection, the combination of gentamicin and uracil increased the survival rate of infected mice. Conclusion: Our results suggest that uracil enhances the activity of bactericidal antibiotics to kill Gram-positive bacteria by modulating bacterial metabolism.

No more tears from surgical site infections in interventional pain management

As the field of interventional pain management (IPM) grows, the risk of surgical site infections (SSIs) is increasing. SSI is defined as an infection of the incision or organ/space that occurs within one month after operation or three months after implantation. It is also common to find patients with suspected infection in an outpatient clinic. The most frequent IPM procedures are performed in the spine. Even though primary pyogenic spondylodiscitis via hematogenous spread is the most common type among spinal infections, secondary spinal infections from direct inoculation should be monitored after IPM procedures. Various preventive guidelines for SSI have been published. Cefazolin, followed by vancomycin, is the most commonly used surgical antibiotic prophylaxis in IPM. Diagnosis of SSI is confirmed by purulent discharge, isolation of causative organisms, pain/tenderness, swelling, redness, or heat, or diagnosis by a surgeon or attending physician. Inflammatory markers include traditional (C-reactive protein, erythrocyte sedimentation rate, and white blood cell count) and novel (procalcitonin, serum amyloid A, and presepsin) markers. Empirical antibiotic therapy is defined as the initial administration of antibiotics within at least 24 hours prior to the results of blood culture and antibiotic susceptibility testing. Definitive antibiotic therapy is initiated based on the above culture and testing. Combination antibiotic therapy for multidrug-resistant Gram-negative bacteria infections appears to be superior to monotherapy in mortality with the risk of increasing antibiotic resistance rates. The never-ending war between bacterial resistance and new antibiotics is continuing. This article reviews prevention, diagnosis, and treatment of infection in pain medicine.

Resistance-resistant antibacterial treatment strategies

Antibiotic resistance is a major danger to public health that threatens to claim the lives of millions of people per year within the next few decades. Years of necessary administration and excessive application of antibiotics have selected for strains that are resistant to many of our currently available treatments. Due to the high costs and difficulty of developing new antibiotics, the emergence of resistant bacteria is outpacing the introduction of new drugs to fight them. To overcome this problem, many researchers are focusing on developing antibacterial therapeutic strategies that are "resistance-resistant"-regimens that slow or stall resistance development in the targeted pathogens. In this mini review, we outline major examples of novel resistance-resistant therapeutic strategies. We discuss the use of compounds that reduce mutagenesis and thereby decrease the likelihood of resistance emergence. Then, we examine the effectiveness of antibiotic cycling and evolutionary steering, in which a bacterial population is forced by one antibiotic toward susceptibility to another antibiotic. We also consider combination therapies that aim to sabotage defensive mechanisms and eliminate potentially resistant pathogens by combining two antibiotics or combining an antibiotic with other therapeutics, such as antibodies or phages. Finally, we highlight promising future directions in this field, including the potential of applying machine learning and personalized medicine to fight antibiotic resistance emergence and out-maneuver adaptive pathogens.

R R, L. F L, M.C.G DR, N.B C, S.C D, O. L F. Advances and perspectives for antimicrobial peptide and combinatory therapies

Antimicrobial peptides (AMPs) have shown cell membrane-directed mechanisms of action. This specificity can be effective against infectious agents that have acquired resistance to conventional drugs. The AMPs' membrane-specificity and their great potential to combat resistant microbes has brought hope to the medical/therapeutic scene. The high death rate worldwide due to antimicrobial resistance (AMR) has pushed forward the search for new molecules and product developments, mainly antibiotics. In the current scenario, other strategies including the association of two or more drugs have contributed to the treatment of difficult-to-treat infectious diseases, above all, those caused by bacteria. In this context, the synergistic action of AMPs associated with current antibiotic therapy can bring important results for the production of new and effective drugs to overcome AMR. This review presents the advances obtained in the last 5 years in medical/antibiotic therapy, with the use of products based on AMPs, as well as perspectives on the potentialized effects of current drugs combined with AMPs for the treatment of bacterial infectious diseases.

Membrane-Active Cyclic Amphiphilic Peptides: Broad-Spectrum Antibacterial Activity Alone and in Combination with Antibiotics

We designed a library of 24 cyclic peptides containing arginine (R) and tryptophan (W) residues in a sequential manner [R_nW_n] (n = 2-7) to study the impact of the hydrophilic/hydrophobic ratio, charge, and ring size on the antibacterial activity against Gram-positive and Gram-negative strains. Among peptides, 5a and 6a demonstrated the highest antimicrobial activity. In combination with 11 commercially available antibiotics, 5a and 6a showed remarkable synergism against a large panel of resistant pathogens. Hemolysis (HC₅₀ = 340 μg/mL) and cell viability against mammalian cells demonstrated the selective lethal action of 5a against bacteria over mammalian cells. Calcein dye leakage and scanning electron microscopy studies revealed the membranolytic effect of 5a. Moreover, the stability in human plasma (t_1/2 = 3 h) and the negligible ability of pathogens to develop resistance further reflect the potential of 5a for further development as a peptide-based antibiotic.

Drug Repurposing Approaches towards Defeating Multidrug-Resistant Gram-Negative Pathogens: Novel Polymyxin/Non-Antibiotic Combinations

Multidrug-resistant (MDR) Gram-negative pathogens remain an unmet public health threat. In recent times, increased rates of resistance have been reported not only to commonly used antibiotics, but also to the last-resort antibiotics, such as polymyxins. More worryingly, despite the current trends in resistance, there is a lack of new antibiotics in the drug-discovery pipeline. Hence, it is imperative that new strategies are developed to preserve the clinical efficacy of the current antibiotics, particularly the last-line agents. Combining conventional antibiotics such as polymyxins with non-antibiotics (or adjuvants), has emerged as a novel and effective strategy against otherwise untreatable MDR pathogens. This review explores the available literature detailing the latest polymyxin/non-antibiotic combinations, their mechanisms of action, and potential avenues to advance their clinical application.

Artemisinin derivative DHA27 enhances the antibacterial effect of aminoglycosides against Pseudomonas aeruginosa by inhibiting mRNA expression of aminoglycoside-modifying enzymes

Bacterial resistance is becoming increasingly serious, the present study aimed to investigate the mechanism of antibacterial sensitization effect of DHA27 combined with tobramycin in tobramycin-resistant Pseudomonas aeruginosa (PA). We found that DHA27 combined with aminoglycosides had an antibacterial sensitization effect on PA. Tobramycin, owing to its lower toxic and side effects, was selected to further study the molecular mechanism of drug combination. A sublethal-dose bacterial challenge/sepsis mouse model was established to study the protective effect of DHA27 plus tobramycin. Scanning electron microscopy was used to investigate whether DHA27 exerts the antibacterial sensitization effect by directly affecting bacterial morphology. The effect of DHA27 on daunorubicin accumulation in bacteria was studied, and quantitative reverse transcription PCR was used to study the effect of DHA27 plus tobramycin on 16S rRNA methyltransferase and aminoglycoside-modifying enzyme mRNA expression. Twenty clinical isolates of PA were found to be tobramycin resistant; DHA27 plus tobramycin had a significant antibacterial sensitization effect on many of these resistant strains. DHA27 plus tobramycin reduced the bacterial load in the spleen and lungs of sepsis model mice and levels of proinflammatory cytokines interleukin-1β (IL-1β) and interferon-γ (IFN-γ). DHA27 plus tobramycin significantly inhibited the mRNA expression of aminoglycoside-modifying enzymes in bacteria. DHA27 combined with AGs had an antibacterial sensitization effect on PA; the molecular mechanism underlying this effect is closely related to the inhibition of the mRNA expression of aminoglycoside-modifying enzymes, especially aac(3)-II.

In Vitro Assessment of the Combination of Antibiotics against Some Integron-Harbouring Enterobacteriaceae from Environmental Sources

One strategy for combating antimicrobial resistance in many infections is to combine antibacterial compounds to create combinations that outperform each molecule alone. In this study, we examine and study the inhibitory effect of combining two drugs belonging to different antibiotic classes to obtain a possible potentiating effect against some Enterobacteriaceae isolates harbouring integrons recovered from rivers and effluents of hospital and wastewater treatment plants in Eastern Cape Province, South Africa. These integrons could easily enable the isolates to acquire genes that confer additional resistance against conventional antibiotics. The minimum inhibitory concentration of the various antibiotics was determined using the broth microdilution, while the checkerboard method was used to determine the fractional inhibitory concentration indices (FICIs). A total of 26.3% (10/38) of the interactions were categorised as synergistic, while 73.7% (28/38) were indifferent. None of the combinations were antagonistic. The time–kill assays revealed all the synergistic interactions as bactericidal. Therefore, the combinations of gentamicin with tetracycline, ciprofloxacin, and ceftazidime against multidrug-resistant (MDR) Klebsiella pneumoniae, tetracycline–ceftazidime combination against MDR Escherichia coli, colistin combinations with ceftazidime and gentamicin, and tetracycline–gentamicin combinations against MDR Citrobacter freundii may be future therapeutic alternatives. Hence, the synergistic combinations reported in this study must be assessed further in vivo before their clinical applications.