Novel anion liposome-encapsulated antisense oligonucleotide restores susceptibility of methicillin-resistant Staphylococcus aureus and rescues mice from lethal sepsis by targeting mecA

Oligonucleotide probes for imaging and diagnosis of bacterial infections

The rise of infectious diseases as a public health concern has necessitated the development of rapid and precise diagnostic methods. Imaging techniques like nuclear and optical imaging provide the ability to diagnose infectious diseases within the body, eliminating delays caused by sampling and pre-enrichments of clinical samples and offering spatial information that can aid in a more informed diagnosis. Traditional molecular probes are typically created to image infected tissue without accurately identifying the pathogen. In contrast, oligonucleotides can be tailored to target specific RNA sequences, allowing for the identification of pathogens, and even generating antibiotic susceptibility profiles by focusing on drug resistance genes. Despite the benefits that nucleic acid mimics (NAMs) have provided in terms of stabilizing oligonucleotides, the inadequate delivery of these relatively large molecules into the cytoplasm of bacteria remains a challenge for widespread use of this technology. This review summarizes the key advancements in the field of oligonucleotide probes for in vivo imaging, highlighting the most promising delivery systems described in the literature for developing optical imaging through in vivo hybridization.

Efficient systemic CNS delivery of a therapeutic antisense oligonucleotide with a blood-brain barrier-penetrating ApoE-derived peptide

Antisense oligonucleotide (ASO) has emerged as a promising therapeutic approach for treating central nervous system (CNS) disorders by modulating gene expression with high selectivity and specificity. However, the poor permeability of ASO across the blood-brain barrier (BBB) diminishes its therapeutic success. Here, we designed and synthesized a series of BBB-penetrating peptides (BPP) derived from either the receptor-binding domain of apolipoprotein E (ApoE) or a transferrin receptor-binding peptide (THR). The BPPs were conjugated to phosphorodiamidate morpholino oligomers (PMO) that are chemically analogous to the 2'-O-(2-methoxyethyl) (MOE)-modified ASO approved by the FDA for treating spinal muscular atrophy (SMA). The BPP-PMO conjugates significantly increased the level of full-length SMN2 in the patient-derived SMA fibroblasts in a concentration-dependent manner with minimal to no toxicity. Furthermore, the systemic administration of the most potent BPP-PMO conjugates significantly increased the expression of full-length SMN2 in the brain and spinal cord of SMN2 transgenic adult mice. Notably, BPP8-PMO conjugate showed a 1.25-fold increase in the expression of full-length functional SMN2 in the brain. Fluorescence imaging studies confirmed that 78% of the fluorescently (Cy7)-labelled BPP8-PMO reached brain parenchyma, with 11% uptake in neuronal cells. Additionally, the BPP-PMO conjugates containing retro-inverso (RI) D-BPPs were found to possess extended half-lives compared to their L-counterparts, indicating increased stability against protease degradation while preserving the bioactivity. This delivery platform based on BPP enhances the CNS bioavailability of PMO targeting the SMN2 gene, paving the way for the development of systemically administered neurotherapeutics for CNS disorders.

A comparative analysis of peptide-delivered antisense antibiotics using diverse nucleotide mimics

Antisense oligomer (ASO)-based antibiotics that target mRNAs of essential bacterial genes have great potential for counteracting antimicrobial resistance and for precision microbiome editing. To date, the development of such antisense antibiotics has primarily focused on using phosphorodiamidate morpholino (PMO) and peptide nucleic acid (PNA) backbones, largely ignoring the growing number of chemical modalities that have spurred the success of ASO-based human therapy. Here, we directly compare the activities of seven chemically distinct 10mer ASOs, all designed to target the essential gene acpP upon delivery with a KFF-peptide carrier into Salmonella. Our systematic analysis of PNA, PMO, phosphorothioate (PTO)-modified DNA, 2'-methylated RNA (RNA-OMe), 2'-methoxyethylated RNA (RNA-MOE), 2'-fluorinated RNA (RNA-F), and 2'-4'-locked RNA (LNA) is based on a variety of in vitro and in vivo methods to evaluate ASO uptake, target pairing and inhibition of bacterial growth. Our data show that only PNA and PMO are efficiently delivered by the KFF peptide into Salmonella to inhibit bacterial growth. Nevertheless, the strong target binding affinity and in vitro translational repression activity of LNA and RNA-MOE make them promising modalities for antisense antibiotics that will require the identification of an effective carrier.

Promising strategies employing nucleic acids as antimicrobial drugs

Antimicrobial resistance (AMR) is a growing concern because it causes microorganisms to develop resistance to drugs commonly used to treat infections. This results in increased difficulty in treating infections, leading to higher mortality rates and significant economic effects. Investing in new antimicrobial agents is, therefore, necessary to prevent and control AMR. Antimicrobial nucleic acids have arisen as potential key players in novel therapies for AMR infections. They have been designed to serve as antimicrobials and to act as adjuvants to conventional antibiotics or to inhibit virulent mechanisms. This new category of antimicrobial drugs consists of antisense oligonucleotides and oligomers, DNAzymes, and transcription factor decoys, differing in terms of structure, target molecules, and mechanisms of action. They are synthesized using nucleic acid analogs to enhance their resistance to nucleases. Because bacterial envelopes are generally impermeable to oligonucleotides, delivery into the cytoplasm typically requires the assistance of nanocarriers, which can affect their therapeutic potency. Given that numerous factors contribute to the success of these antimicrobial drugs, this review aims to provide a summary of the key advancements in the use of oligonucleotides for treating bacterial infections. Their mechanisms of action and the impact of factors such as nucleic acid design, target sequence, and nanocarriers on the antimicrobial potency are discussed.

Understanding Antisense Oligonucleotide Efficiency in Inhibiting Prokaryotic Gene Expression

Oligonucleotides offer a unique opportunity for sequence specific regulation of gene expression in bacteria. A fundamental question to address is the choice of oligonucleotide, given the large number of options available. Different modifications varying in RNA binding affinities and cellular uptake are available but no comprehensive comparisons have been performed. Herein, the efficiency of blocking expression of β-galactosidase (β-Gal) in E. coli was evaluated utilizing different antisense oligomers (ASOs). Fluorescein (FAM)-labeled oligomers were used to understand their differences in bacterial uptake. Flow cytometry analysis revealed significant differences in uptake, with high fluorescence seen in cells treated with FAM-labeled peptidic nucleic acid (PNA), phosphorodiamidate morpholino oligonucleotide (PMO) and phosphorothioate (PS) oligomers, and low fluorescence observed in cells treated with phosphodiester (PO) oligomers. Thermal denaturation (Tm) of oligomer:RNA duplexes and isothermal titration calorimetry (ITC) studies reveal that ASO binding to target RNA demonstrates a good correlation between Tm and Kd values. There was no correlation between Kd values and reduction of β-Gal activity in bacterial cells. However, cell-free translation assays demonstrated a direct relationship between Kd values and inhibition of gene expression by antisense oligomers, with tight binding oligomers such as LNA being the most efficient. Membrane active compounds such as polymyxin B and A22 further improved the cellular uptake of FAM-PNA and FAM-PS oligomers in wild-type E. coli cells. PNA and PMO were most effective in cellular uptake and reducing β-Gal activity as compared to oligomers with PS or those with PO linkages. Overall, cell uptake of the oligomers is shown as the key determinant in predicting their differences in bacterial antisense inhibition, and the RNA affinity is the key determinant in inhibition of gene expression in cell free systems.

New Weapons to Fight against Staphylococcus aureus Skin Infections

The treatment of Staphylococcus aureus skin and soft tissue infections faces several challenges, such as the increased incidence of antibiotic-resistant strains and the fact that the antibiotics available to treat methicillin-resistant S. aureus present low bioavailability, are not easily metabolized, and cause severe secondary effects. Moreover, besides the susceptibility pattern of the S. aureus isolates detected in vitro, during patient treatment, the antibiotics may never encounter the bacteria because S. aureus hides within biofilms or inside eukaryotic cells. In addition, vascular compromise as well as other comorbidities of the patient may impede proper arrival to the skin when the antibiotic is given parenterally. In this manuscript, we revise some of the more promising strategies to improve antibiotic sensitivity, bioavailability, and delivery, including the combination of antibiotics with bactericidal nanomaterials, chemical inhibitors, antisense oligonucleotides, and lytic enzymes, among others. In addition, alternative non-antibiotic-based experimental therapies, including the delivery of antimicrobial peptides, bioactive glass nanoparticles or nanocrystalline cellulose, phototherapies, and hyperthermia, are also reviewed.

Antisense oligonucleotides: a promising therapeutic option against infectious diseases

Infectious diseases have been one of the biggest health problems of humanity for centuries. Nucleic acid-based therapeutics have received attention in recent years with their effectiveness in the treatment of various infectious diseases and vaccine development studies. This review aims to provide a comprehensive understanding of the basic properties underlying the mechanism of antisense oligonucleotides (ASOs), their applications, and their challenges. The efficient delivery of ASOs is the greatest challenge for their therapeutic success, but this problem is overcome with new-generation antisense molecules developed with chemical modifications. The types, carrier molecules, and gene regions targeted by sequences have been summarized in detail. Research and development of antisense therapy is still in its infancy; however, gene silencing therapies appear to have the potential for faster and longer-lasting activity than conventional treatment strategies. On the other hand, realizing the potential of antisense therapy will require a large initial economic investment to ascertain the pharmacological properties and learn how to optimize them. The ability of ASOs to be rapidly designed and synthesized to target different microbes can reduce drug discovery time from 6 years to 1 year. Since ASOs are not particularly affected by resistance mechanisms, they come to the fore in the fight against antimicrobial resistance. The design-based flexibility of ASOs has enabled it to be used for different types of microorganisms/genes and successful in vitro and in vivo results have been revealed. The current review summarized a comprehensive understanding of ASO therapy in combating bacterial and viral infections.

Evaluation of the synergistic effect of chitosan metal ions (Cu2+/Co2+) in combination with antibiotics to counteract the effects on antibiotic resistant bacteria

The effectiveness of antibiotics that save millions of lives is in danger due to the increasing rise of resistant bacteria around the world. We proposed chitosan-copper ions (CSNP-Cu²⁺) and chitosan-cobalt ion nanoparticles (CSNP-Co²⁺) as biodegradable nanoparticles loaded with metal ions synthesized via an ionic gelation method for treatment of antibiotic resistant bacteria. The nanoparticles were characterized using TEM, FT-IR, zeta potential and ICP-OES. The MIC was evaluated for the NPs in addition to evaluating the synergetic effect of the nanoparticles in combination with cefepime or penicillin for five different antibiotic resistant bacterial strains. In order to investigate the mode of action, MRSA, DSMZ 28766 and Escherichia coli E0157:H7 were selected for further evaluation of antibiotic resistant genes expression upon treatment with NPs. Finally, the cytotoxic activities were investigated using MCF7, HEPG2 and A549 and WI-38 cell lines. The results showed quasi spherical shape and mean particle size of 19.9 ± 5 nm, 21 ± 5 nm and 22.27 ± 5 for CSNP, CSNP-Cu²⁺ and CSNP-Co²⁺ respectively. FT-IR showed slight shifting of the hydroxyl and amine group's peaks of chitosan indicating the adsorption of metal ions. Both nanoparticles had antibacterial activity with MIC ranging between 125 and 62 μg ml^-1 for the used standard bacterial strains. Moreover, the combination of each of the synthesized NP with either cefepime or penicillin not only showed a synergetic effect as antibacterial activity of each NP or antibiotics alone, but also decreased the fold of antibiotic resistance genes expression. The NPs showed potent cytotoxic activities for MCF-7, HepG2 and A549 cancer cell lines with lower cytotoxic values for the WI-38 normal cell line. The NPs' antibacterial activity may be due to penetration and rupture of the cell membrane and the outer membrane of Gram negative and Gram positive bacteria causing bacterial cell death, in addition to, penetration into the bacterial genes and blocking gene expression that is vital to bacterial growth. The fabricated nanoparticles can be an effective, affordable and biodegradable solution to challenge antibiotic resistant bacteria.

Engineered liposomes to deliver nucleic acid mimics in Escherichia coli

Antisense oligonucleotides (ASOs) composed of nucleic acid mimics (NAMs) monomers are considered as potential novel therapeutic drugs against bacterial infections. However, bacterial envelopes are generally impermeable to naked oligonucleotides. Herein, liposomes loaded with NAMs-modified oligonucleotides (LipoNAMs) were evaluated to deliver ASOs in Escherichia coli. Specifically, we tested several surface modifications that included methoxyPEG conjugated to different lipid anchors or modification of the PEG distal ends with maleimide groups and antibodies. MethoxyPEG coated LipoNAMs showed low delivery efficiency for most bacteria, but maleimide-functionalized PEG LipoNAMs were able to deliver ASOs to nearly half of the bacterial population. Conjugation of antibodies to maleimide-functionalized PEG LipoNAMs increased 1.3-fold the delivery efficiency, enhancing the selectivity towards E. coli and biocompatibility. This work demonstrated for the first time that the coupling of antibodies to PEGylated liposomes can significantly improve the delivery of ASOs in E. coli, which might bring alternative routes for the treatment of bacterial infections in the future.

Enhancing activity of β-lactam and fluoroquinolones antibiotics by artemisinin and its derivatives against MDR Escherichia coli

Artemisinin and its derivatives had played a biocidal role in biomedical remedies, while they were expected to enhance the activity of antibiotics against multiple drug-resistant (MDR) bacteria. The current study evaluated the interaction of artemisinin (ART), dihydroartemisinin (DHA), artesunate (AS), and artemisinic acid (AA) with β-lactam and fluoroquinolones antibiotics against Escherichia coli. Antibiotic strip test (E-test), Kirby Bauer's disc test (KB method), and broth microdilution method were adopted for susceptibility analysis, while the checkerboard method was applied to assess synergisms. ART, DHA, AS, and AA showed significantly enhanced antibacterial effects of β-lactam antibiotics against different strains of E. coli. The study showed ciprofloxacin to be most effective by presenting the least MIC (0.017125 ± 0.0022 μg/ml), while oxacillin was least effective (MIC 256 μg/ml) against E. coli. Synergism between AA and penicillin G (75%), ampicillin (25%), and oxacillin (50%) was observed in all isolates tested. AA and AS significantly decreased the MIC of ampicillin (-0.912 ± 0.908 μg/ml) and ciprofloxacin (-0.901 ± 0.893 g/ml), respectively. Artemisinin and its derivatives increased antibiotic accumulation within E. coli in a dose-dependent manner. The time-kill assay significantly reduced the bacterial number within 24 h of incubation. The study thus concludes greater room for improvement in enhancing the efficacy of antibiotics if used with artemisinin and its derivatives.

Amphipathic dendritic poly-peptides carrier to deliver antisense oligonucleotides against multi-drug resistant bacteria in vitro and in vivo

Background

Outbreaks of infection due to multidrug-resistant (MDR) bacteria, especially Gram-negative bacteria, have become a global health issue in both hospitals and communities. Antisense oligonucleotides (ASOs) based therapeutics hold a great promise for treating infections caused by MDR bacteria. However, ASOs therapeutics are strangled because of its low cell penetration efficiency caused by the high molecular weight and hydrophilicity.

Results

Here, we designed a series of dendritic poly-peptides (DPP1 to DPP12) to encapsulate ASOs to form DSPE-mPEG2000 decorated ASOs/DPP nanoparticles (DP-AD1 to DP-AD12) and observed that amphipathic DP-AD2, 3, 7 or 8 with a positive charge ≥ 8 showed great efficiency to deliver ASOs into bacteria, but only the two histidine residues contained DP-AD7 and DP-AD8 significantly inhibited the bacterial growth and the targeted gene expression of tested bacteria in vitro. DP-AD7_anti-acpP remarkably increased the survival rate of septic mice infected by ESBLs-E. coli, exhibiting strong antibacterial effects in vivo.

Conclusions

For the first time, we designed DPP as a potent carrier to deliver ASOs for combating MDR bacteria and demonstrated the essential features, namely, amphipathicity, 8–10 positive charges, and 2 histidine residues, that are required for efficient DPP based delivery, and provide a novel approach for the development and research of the antisense antibacterial strategy.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01384-y.

Oligonucleotide Solid Nucleolipid Nanoparticles against Antibiotic Resistance of ESBL-Producing Bacteria

Antibiotic resistance has become a major issue in the global healthcare system, notably in the case of Gram-negative bacteria. Recent advances in technology with oligonucleotides have an enormous potential for tackling this problem, providing their efficient intrabacterial delivery. The current work aimed to apply this strategy by using a novel nanoformulation consisting of DOTAU, a nucleolipid carrier, in an attempt to simultaneously deliver antibiotic and anti-resistance oligonucleotides. Ceftriaxone, a third-generation cephalosporin, was formulated with DOTAU to form an ion pair, and was then nanoprecipitated. The obtained solid nanocapsules were characterized using FT-IR, XRD, HPLC, TEM and DLS techniques and further functionalized by the anti-resistance ONα sequence. To obtain an optimal anti-resistance activity and encapsulation yield, both the formulation protocol and the concentration of ONα were optimized. As a result, monodispersed negatively charged nanoparticles of CFX–DOTAU-ONα with a molar ratio of 10:24:1 were obtained. The minimum inhibitory concentration of these nanoparticles on the resistant Escherichia coli strain was significantly reduced (by 75%) in comparison with that of non-vectorized ONα. All aforementioned results reveal that our nanoformulation can be considered as an efficient and relevant strategy for oligonucleotide intrabacterial delivery in the fight against antibiotic resistance.

Uptake Dynamics of Cubosome Nanocarriers at Bacterial Surfaces and the Routes for Cargo Internalization

Antibiotic-resistant bacteria pose a significant threat to humanity. Gram-negative strains have demonstrated resistance to last resort antibiotics, partially due to their outer membrane, which hinders transport of antimicrobials into the bacterium. Nanocarrier (NC)-mediated drug delivery is one proposed strategy for combating this emerging issue. Here, the uptake of self-assembled lipid nanocarriers of cubic symmetry (cubosomes) into bacteria revealed fundamental differences in the uptake mechanism between Gram-positive and Gram-negative bacteria. For Gram-positive bacteria, the NCs adhere to the outer peptidoglycan layers and slowly internalize to the bacterium. For Gram-negative bacteria, the NCs interact in two stages, fusion with the outer lipid membrane and then diffusion through the inner wall. The self-assembled nature of the cubosomes imparts a unique ability to transfer payloads via membrane fusion. Remarkably, the fusion uptake mechanism allowed rapid NC internalization by the Gram-negative bacteria, overcoming the outer membrane responsible for their heightened resilience. Here this is demonstrated by the marked reduction in the minimal inhibition concentration required for antibiotics against a pathogenic strain of Gram-negative bacteria, Escherichia coli. These results provide mechanistic insight for the development of lipid NCs as a new tool to combat bacteria.

The Application of Nucleic Acids and Nucleic Acid Materials in Antimicrobial Research

Due to the misuse of antibiotics, multiple drug-resistant pathogenic bacteria have increasingly emerged. This has increased the difficulty of treatment as these bacteria directly affect public health by diminishing the potency of existing antibiotics. Developing alternative therapeutic strategies is the urgent need to reduce the mortality and morbidity related to drug-resistant bacterial infections. In the past 10 to 20 years, nanomedicines have been widely studied and applied as an antibacterial agent. They have become a novel tool for fighting resistant bacteria. The most common innovative substances, metal and metal oxide nanoparticles (NPs), have been widely reported. Until recently, DNA nanostructures were used alone or functionalized with specific DNA sequences by many scholars for antimicrobial purposes which were alternatively selected as therapy for severe bacterial infections. These are a potential candidate for treatments and have a considerable role in killing antibiotic-resistant bacteria. This review involves the dimensions of multidrug resistance and the mechanism of bacteria developing drug resistance. The importance of this article is that we summarized the current study of nano-materials based on nucleic acids in antimicrobial use. Meanwhile, the current progress and the present obstacles for their antibacterial and therapeutic use and special function of stem cells in this field are also discussed.

Peptide nucleic acid restores colistin susceptibility through modulation of MCR-1 expression in Escherichia coli

BACKGROUND

Plasmid-mediated mechanisms of drug resistance accelerate the spread of polymyxin resistance, leaving clinicians with few or no antibacterial options for the treatment of infections caused by MDR bacteria, especially carbapenemase-producing strains.

OBJECTIVES

To evaluate the associations among promoter sequence variation, mcr-1 expression, host factors and levels of colistin resistance and to propose antisense agents such as peptide nucleic acids (PNAs) targeting mcr-1 as a tool to restore colistin susceptibility through modulation of MCR-1 expression in Escherichia coli.

METHODS

A β-galactosidase assay was performed to study mcr-1 promoter activity. Quantitative real-time PCR and western blot assays were used to identify the expression level of MCR-1 in WT strains and transformants. Three PNAs targeting different regions of mcr-1 were designed and synthesized to determine whether they can effectively inhibit MCR-1 expression. MIC was measured to test colistin susceptibility in the presence or absence of PNA-1 in mcr-1-carrying E. coli.

RESULTS

Variation in the mcr-1 promoter sequence and host species affect promoter activity, MCR-1 expression levels and colistin MICs. One PNA targeting the ribosome-binding site fully inhibited the expression of mcr-1 at a concentration of 4 μM, resulting in significantly increased susceptibility to colistin. The MIC90 of colistin decreased from 8 to 2 mg/L (P < 0.05) in the presence of 4 μM PNA.

CONCLUSIONS

These findings suggest that the antisense approach is a possible strategy to combat mcr-1-mediated resistance as well as other causes of emerging global resistance.

Delivery of antisense oligonucleotides using multi-layer coated gold nanoparticles to methicillin-resistant S. aureus for combinatorial treatment

The spread of multidrug-resistant (MDR) bacterial infections has become a serious global threat. We introduce multi-layer coated gold nanoparticles (MLGNPs) delivering antisense oligonucleotides (ASOs) targeting the resistance gene of methicillin-resistant Staphylococcus aureus (MRSA), as a selective antimicrobial by restoring susceptibility. MLGNPs were prepared by multi-step surface immobilization of gold nanoparticles (GNPs) with polyethylenimine (PEI) and loaded with ASO targeting the mecA gene. The MLGNPs were shown to be efficiently internalized into various types of Gram-positive bacteria, including MRSA, Staphylococcus epidermidis, and Bacillus subtilis, which was superior to single-layer coated GNPs and free PEI polymer. The delivery of MLGNPs into MRSA resulted in up to 74% silencing of the mecA gene with high selectivity, in a dose-dependent manner. The treatment of MLGNPs to MRSA in the presence of oxacillin, a beta-lactam antibiotic, showed major suppression (~71%) of bacterial growth, due to the recovery of antibacterial sensitivity. Furthermore, the treatment of MLGNPs in a complex system showed preferential uptake into bacteria over mammalian cells, demonstrating the suitable characteristics of MLGNPs for selective delivery into bacteria. The current approach can be potentially applied for targeting various types of MDR bacterial infections by specific silencing of a resistance gene, as a combinatorial therapeutic used with conventional antibiotics.

Nanobiosystems for Antimicrobial Drug-Resistant Infections

The worldwide increased bacterial resistance toward antimicrobial therapeutics has led investigators to search for new therapeutic options. Some of the options currently exploited to treat drug-resistant infections include drug-associated nanosystems. Additionally, the use of bacteriophages alone or in combination with drugs has been recently revisited; some studies utilizing nanosystems for bacteriophage delivery have been already reported. In this review article, we focus on nine pathogens that are the leading antimicrobial drug-resistant organisms, causing difficult-to-treat infections. For each organism, the bacteriophages and nanosystems developed or used in the last 20 years as potential treatments of pathogen-related infections are discussed. Summarizing conclusions and future perspectives related with the potential of such nano-antimicrobials for the treatment of persistent infections are finally highlighted.

Recent Advances in Peptide Nucleic Acids as Antibacterial Agents

The emergence of antibiotic-resistant bacteria and the slow progress in searching for new antimicrobial agents makes it hard to treat bacterial infections and cause problems for the healthcare system worldwide, including high costs, prolonged hospitalizations, and increased mortality. Therefore, the discovery of effective antibacterial agents is of great importance. One attractive alternative is antisense peptide nucleic acid (PNA), which inhibits or eliminates gene expression by binding to the complementary messenger RNA (mRNA) sequence of essential genes or the accessible and functionally important regions of the ribosomal RNA (rRNA). Following 30 years of development, PNAs have played an extremely important role in the treatment of Gram-positive, Gram-negative, and acidfast bacteria due to their desirable stability of hybrid complex with target RNA, the strong affinity for target mRNA/rRNA, and the stability against nucleases. PNA-based antisense antibiotics can strongly inhibit the growth of pathogenic and antibiotic-resistant bacteria in a sequence-specific and dose-dependent manner at micromolar concentrations. However, several fundamental challenges, such as intracellular delivery, solubility, physiological stability, and clearance still need to be addressed before PNAs become broadly applicable in clinical settings. In this review, we summarize the recent advances in PNAs as antibacterial agents and the challenges that need to be overcome in the future.

Can Vitamin B12 Assist the Internalization of Antisense LNA Oligonucleotides into Bacteria?

The emergence of bacterial resistance to traditional small-molecule antibiotics is fueling the search for innovative strategies to treat infections. Inhibiting the expression of essential bacterial genes using antisense oligonucleotides (ASOs), particularly composed of nucleic acid mimics (NAMs), has emerged as a promising strategy. However, their efficiency depends on their association with vectors that can translocate the bacterial envelope. Vitamin B₁₂ is among the largest molecules known to be taken up by bacteria and has very recently started to gain interest as a trojan-horse vector. Gapmers and steric blockers were evaluated as ASOs against Escherichia coli (E. coli). Both ASOs were successfully conjugated to B₁₂ by copper-free azide-alkyne click-chemistry. The biological effect of the two conjugates was evaluated together with their intracellular localization in E. coli. Although not only B₁₂ but also both B₁₂-ASO conjugates interacted strongly with E. coli, they were mostly colocalized with the outer membrane. Only 6–9% were detected in the cytosol, which showed to be insufficient for bacterial growth inhibition. These results suggest that the internalization of B₁₂-ASO conjugates is strongly affected by the low uptake rate of the B₁₂ in E. coli and that further studies are needed before considering this strategy against biofilms in vivo.

Delivery of Oligonucleotides into Bacteria by Fusogenic Liposomes

Oligonucleotides able to hybridize bacterial RNA via in situ hybridization may potentially act as new antimicrobials, replacing antibiotics, and as fast in vivo diagnostic probes, outperforming current clinical methodologies. Nonetheless, oligonucleotides are not able to efficiently permeate the multi-layered bacterial envelope to reach their target RNA in the cytosol. Cationic fusogenic liposomes are here suggested as vehicles to enable the internalization of oligonucleotides in bacteria. Here, we describe the formulation of DOTAP-DOPE liposomes, their complexation with small negatively charged oligonucleotides, and the evaluation of the intracellular delivery of the oligonucleotides in bacteria. This strategy uncovers the potential of performing FISH in vivo for real-time detection and treatment of infections.

The bactericidal efficacy of femtosecond laser-based therapy on the most common infectious bacterial pathogens in chronic wounds: an in vitro study

We investigated the influence of femtosecond laser irradiation on the growth of the two most common infectious bacterial pathogens in wounds; Staphylococcus aureus and Pseudomonas aeruginosa as an attempt to validate optimum parameters for a laser-based bactericidal modality to be used clinically. Bacterial cultures were exposed to femtosecond laser irradiation at different wavelengths, exposure times, and laser powers. The source of femtosecond laser was INSPIRE HF100 laser system, Spectra-Physics, which is pumped by a mode-locked femtosecond Ti: sapphire laser MAI TAI HP, Spectra-Physics. After irradiation, bacterial cells' survival was monitored by observing the clear zones of inhibition in cultured agar plates. Results for all strains indicated that the exposure to femtosecond laser irradiation with a wavelength ranging from ultraviolet (λ > 350 nm) to blue laser light (λ < 480 nm), for a period above 20 min and with a power density of ≈ 0.063 W/cm², was enough to inhibit both bacterial pathogens with the results maintained for 1 week following irradiation.

Anti-Methicillin-Resistant Staphylococcus aureus Nanoantibiotics

Nanoparticle-based antibiotic constructs have become a popular area of investigation in the biomedical sciences. Much of this work has pertained to human diseases, largely in the cancer therapy arena. However, considerable research has also been devoted to the nanochemistry for controlling infectious diseases. Among these are ones due to bacterial infections, which can cause serious illnesses leading to death. The onset of multi-drug-resistant (MDR) infections such as those caused by the human pathogen Staphylococcus aureus has created a dearth of problems such as surgical complications, persistent infections, and lack of available treatments. In this article, we set out to review the primary literature on the design and development of new nanoparticle materials for the potential treatment of S. aureus infections, and areas that could be further expanded upon to make nanoparticle antibiotics a mainstay in clinical settings.

Cardiolipin-Based Lipopolyplex Platform for the Delivery of Diverse Nucleic Acids into Gram-Negative Bacteria

Antibiotic resistance is a growing public health concern. Because only a few novel classes of antibiotics have been developed in the last 40 years, such as the class of oxazolidinones, new antibacterial strategies are urgently needed [1]. Nucleic acid-based antibiotics are a new type of antimicrobials. However, free nucleic acids cannot spontaneously cross the bacterial cell wall and membrane;consequently, their intracellular delivery into bacteria needs to be assisted. Here, we introduce an original lipopolyplex system named liposome polymer nucleic acid (LPN), capable of versatile nucleic acid delivery into bacteria. We characterized LPN formed with significant therapeutic nucleic acids: 11 nt antisense single-stranded (ss) DNA and double-stranded (ds) DNA of 15 and 95 base pairs (bp), 9 kbp plasmid DNA (pDNA), and 1,000 nt ssRNA. All these complexes were efficiently internalized by two different bacterial species, i.e., Escherichia coli and Pseudomonas aeruginosa, as shown by flow cytometry. Consistent with intracellular delivery, LPN prepared with an antisense oligonucleotide and directed against an essential gene, induced specific and important bacterial growth inhibition likely leading to a bactericidal effect. Our findings indicate that LPN is a versatile platform for efficient delivery of diverse nucleic acids into Gram-negative bacteria.

Alternatives to Conventional Antibiotics in the Era of Antimicrobial Resistance

As more antibiotics are rendered ineffective by drug-resistant bacteria, focus must be shifted towards alternative therapies for treating infections. Although several alternatives already exist in nature, the challenge is to implement them in clinical use. Advancements within biotechnology, genetic engineering, and synthetic chemistry have opened up new avenues towards the search for therapies that can substitute for antibiotics. This review provides an introduction to the various promising approaches that have been adopted in this regard. Whilst the use of bacteriophages and antibodies has been partly implemented, other promising strategies, such as probiotics, lysins, and antimicrobial peptides, are in various stages of development. Propitious concepts such as genetically modified phages, antibacterial oligonucleotides, and CRISPR-Cas9 are also discussed.

Nanomaterials and molecular transporters to overcome the bacterial envelope barrier: Towards advanced delivery of antibiotics

With the dramatic consequences of bacterial resistance to antibiotics, nanomaterials and molecular transporters have started to be investigated as alternative antibacterials or anti-infective carrier systems to improve the internalization of bactericidal drugs. However, the capability of nanomaterials/molecular transporters to overcome the bacterial cell envelope is poorly understood. It is critical to consider the sophisticated architecture of bacterial envelopes and reflect how nanomaterials/molecular transporters can interact with these envelopes, being the major aim of this review. The first part of this manuscript overviews the permeability of bacterial envelopes and how it limits the internalization of common antibiotic and novel oligonucleotide drugs. Subsequently we critically discuss the mechanisms that allow nanomaterials/molecular transporters to overcome the bacterial envelopes, focusing on the most promising ones to this end - siderophores, cyclodextrins, metal nanoparticles, antimicrobial/cell-penetrating peptides and fusogenic liposomes. This review may stimulate drug delivery and microbiology scientists in designing effective nanomaterials/molecular transporters against bacterial infections.

Emerging Nanomedicine Therapies to Counter the Rise of Methicillin-Resistant Staphylococcus aureus

In a recent report, the World Health Organisation (WHO) classified antibiotic resistance as one of the greatest threats to global health, food security, and development. Methicillin-resistant Staphylococcus aureus (MRSA) remains at the core of this threat, with persistent and resilient strains detectable in up to 90% of S. aureus infections. Unfortunately, there is a lack of novel antibiotics reaching the clinic to address the significant morbidity and mortality that MRSA is responsible for. Recently, nanomedicine strategies have emerged as a promising therapy to combat the rise of MRSA. However, these approaches have been wide-ranging in design, with few attempts to compare studies across scientific and clinical disciplines. This review seeks to reconcile this discrepancy in the literature, with specific focus on the mechanisms of MRSA infection and how they can be exploited by bioactive molecules that are delivered by nanomedicines, in addition to utilisation of the nanomaterials themselves as antibacterial agents. Finally, we discuss targeting MRSA biofilms using nano-patterning technologies and comment on future opportunities and challenges for MRSA treatment using nanomedicine.

Advances in the delivery of antisense oligonucleotides for combating bacterial infectious diseases

Discovery and development of new antibacterial drugs against multidrug resistant bacterial strains have become more and more urgent. Antisense oligonucleotides (ASOs) show immense potential to control the spread of resistant microbes due to its high specificity of action, little risk to human gene expression, and easy design and synthesis to target any possible gene. However, efficient delivery of ASOs to their action sites with enough concentration remains a major obstacle, which greatly hampers their clinical application. In this study, we reviewed current progress on delivery strategies of ASOs into bacteria, focused on various non-virus gene vectors, including cell penetrating peptides, lipid nanoparticles, bolaamphiphile-based nanoparticles, DNA nanostructures and Vitamin B12. The current review provided comprehensive understanding and novel perspective for the future application of ASOs in combating bacterial infections.

Advances in therapeutic bacterial antisense biotechnology

Antisense therapeutics are a biotechnological form of antibiotic therapy using chemical analogues of short single-stranded nucleic acid sequences modified to form stable oligomers. These molecules are termed antisense oligonucleotides (ASOs) because their sequence is complementary, via Watson-Crick specific base pairing, to their target messenger RNA (mRNA). ASOs modify gene expression in this sequence-dependent manner by binding to its complementary mRNA and inhibiting its translation into protein through steric blockage and/or through RNase degradation of the ASO/RNA duplex. The widespread use of conventional antibiotics has led to the increasing emergence of multiple drug-resistant pathogenic bacteria. There is an urgent need to develop alternative therapeutic strategies to reduce the morbidity and mortality associated with bacterial infections, and until recently, the use of ASOs as therapeutic agents has been essentially limited to eukaryotic cells, with ASOs as antibacterials having been largely unexplored primarily due to the poor uptake efficiency of antisense molecules by bacteria. There are conceptual advantages to bacterial antisense antibiotic therapies, including a sequence-dependent approach that allows for a rational design to multiple specific molecular targets. This review summarizes the current knowledge of antisense bacterial biotechnology and highlights the recent progress and the current obstacles in their development for therapeutic applications.

Peptide nucleic acids (PNAs): currently potential bactericidal agents

In recent years, the emergence of ESBL-producing and multi-drug resistant bacteria have been increased and designing novel components is necessary for confrontation these bacteria. Peptide nucleic acids (PNAs) are one of the synthetic components that bind to single strand DNA and RNA. Applications of these components are wide while, and one of the important applications of these components is inhibition of gene expression and knock downing the target gene follow as inhibition of bacterial growth. For PNA targeting gene, peptide-PNAs (PPNA) activity cannot be occurred without sequence homology, at the same time, it has been affected by sequence-based specific target and dose-dependent-based manner. Choosing the conserved sequence in different bacterial genus can provide broad-spectrum antimicrobial activity. In this review article, we studied several research papers and extract PNA targeting genes that cause gene knock down and inhibition of bacterial growth. Some novel opportunities for advancement and the design ultra-narrow-spectrum antimicrobial drugs against multi-drug can be accessible by utilizing PNA against necessary genes of pathogens. These results open novel vision for therapeutic intervention. Future researches are required to evaluate the safety, toxicity and pharmacokinetics properties of PPNAs in order to be utilized in clinical treatment.

Intracellular delivery of oligonucleotides in Helicobacter pylori by fusogenic liposomes in the presence of gastric mucus

The rising antimicrobial resistance contributes to 25000 annual deaths in Europe. This threat to the public health can only be tackled if novel antimicrobials are developed, combined with a more precise use of the currently available antibiotics through the implementation of fast, specific, diagnostic methods. Nucleic acid mimics (NAMs) that are able to hybridize intracellular bacterial RNA have the potential to become such a new class of antimicrobials and additionally could serve as specific detection probes. However, an essential requirement is that these NAMs should be delivered into the bacterial cytoplasm, which is a particular challenge given the fact that they are charged macromolecules. We consider these delivery challenges in relation to the gastric pathogen Helicobacter pylori, the most frequent chronic infection worldwide. In particular, we evaluate if cationic fusogenic liposomes are suitable carriers to deliver NAMs across the gastric mucus barrier and the bacterial envelope. Our study shows that DOTAP-DOPE liposomes post-PEGylated with DSPE-PEG (DSPE Lpx) can indeed successfully deliver NAMs into Helicobacter pylori, while offering protection to the NAMs from binding and inactivation in gastric mucus isolated from pigs. DSPE Lpx thus offer exciting new possibilities for in vivo diagnosis and treatment of Helicobacter pylori infections.

Regulation of Pseudomonas aeruginosa Virulence by Distinct Iron Sources

Pseudomonas aeruginosa is a ubiquitous environmental bacterium and versatile opportunistic pathogen. Like most other organisms, P. aeruginosa requires iron for survival, yet iron rapidly reacts with oxygen and water to form stable ferric (FeIII) oxides and hydroxides, limiting its availability to living organisms. During infection, iron is also sequestered by the host innate immune system, further limiting its availability. P. aeruginosa’s capacity to cause disease in diverse host environments is due to its ability to scavenge iron from a variety of host iron sources. Work over the past two decades has further shown that different iron sources can affect the expression of distinct virulence traits. This review discusses how the individual components of P. aeruginosa’s iron regulatory network allow this opportunist to adapt to a multitude of host environments during infection.

Design, challenge, and promise of stimuli-responsive nanoantibiotics

Over the past few years, there have been calls for novel antimicrobials to combat the rise of drug-resistant bacteria. While some promising new discoveries have met this call, it is not nearly enough. The major problem is that although these new promising antimicrobials serve as a short-term solution, they lack the potential to provide a long-term solution. The conventional method of creating new antibiotics relies heavily on the discovery of an antimicrobial compound from another microbe. This paradigm of development is flawed due to the fact that microbes can easily transfer a resistant mechanism if faced with an environmental pressure. Furthermore, there has been some evidence to indicate that the environment of the microbe can provide a hint as to their virulence. Because of this, the use of materials with antimicrobial properties has been garnering interest. Nanoantibiotics, (nAbts), provide a new way to circumvent the current paradigm of antimicrobial discovery and presents a novel mechanism of attack not found in microbes yet; which may lead to a longer-term solution against drug-resistance formation. This allows for environment-specific activation and efficacy of the nAbts but may also open up and create new design methods for various applications. These nAbts provide promise, but there is still ample work to be done in their development. This review looks at possible ways of improving and optimizing nAbts by making them stimuli-responsive, then consider the challenges ahead, and industrial applications.Graphical abstractA graphic detailing how the current paradigm of antibiotic discovery can be circumvented by the use of nanoantibiotics.

Anti-infectives in Drug Delivery-Overcoming the Gram-Negative Bacterial Cell Envelope

Infectious diseases are becoming a major menace to the state of health worldwide, with difficulties in effective treatment especially of nosocomial infections caused by Gram-negative bacteria being increasingly reported. Inadequate permeation of anti-infectives into or across the Gram-negative bacterial cell envelope, due to its intrinsic barrier function as well as barrier enhancement mediated by resistance mechanisms, can be identified as one of the major reasons for insufficient therapeutic effects. Several in vitro, in silico, and in cellulo models are currently employed to increase the knowledge of anti-infective transport processes into or across the bacterial cell envelope; however, all such models exhibit drawbacks or have limitations with respect to the information they are able to provide. Thus, new approaches which allow for more comprehensive characterization of anti-infective permeation processes (and as such, would be usable as screening methods in early drug discovery and development) are desperately needed. Furthermore, delivery methods or technologies capable of enhancing anti-infective permeation into or across the bacterial cell envelope are required. In this respect, particle-based carrier systems have already been shown to provide the opportunity to overcome compound-related difficulties and allow for targeted delivery. In addition, formulations combining efflux pump inhibitors or antimicrobial peptides with anti-infectives show promise in the restoration of antibiotic activity in resistant bacterial strains. Despite considerable progress in this field however, the design of carriers to specifically enhance transport across the bacterial envelope or to target difficult-to-treat (e.g., intracellular) infections remains an urgently needed area of improvement. What follows is a summary and evaluation of the state of the art of both bacterial permeation models and advanced anti-infective formulation strategies, together with an outlook for future directions in these fields.

Oxacillin sensitization of methicillin-resistant Staphylococcus aureus and methicillin-resistant Staphylococcus pseudintermedius by antisense peptide nucleic acids in vitro

Background

Antibiotic resistance genes can be targeted by antisense agents, which can reduce their expression and thus restore cellular susceptibility to existing antibiotics. Antisense inhibitors can be gene and pathogen specific, or designed to inhibit a group of bacteria having conserved sequences within resistance genes. Here, we aimed to develop antisense peptide nucleic acids (PNAs) that could be used to effectively restore susceptibility to β-lactams in methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus pseudintermedius (MRSP).

Results

Antisense PNAs specific for conserved regions of the mobilisable gene mecA, and the growth essential gene, ftsZ, were designed. Clinical MRSA and MRSP strains of high oxacillin resistance were treated with PNAs and assayed for reduction in colony forming units on oxacillin plates, reduction in target gene mRNA levels, and cell size. Anti-mecA PNA at 7.5 and 2.5 μM reduced mecA mRNA in MRSA and MRSP (p < 0.05). At these PNA concentrations, 66 % of MRSA and 92 % of MRSP cells were killed by oxacillin (p < 0.01). Anti-ftsZ PNA at 7.5 and 2.5 μM reduced ftsZ mRNA in MRSA and MRSP, respectively (p ≤ 0.05). At these PNA concentrations, 86 % of MRSA cells and 95 % of MRSP cells were killed by oxacillin (p < 0.05). Anti-ftsZ PNAs resulted in swelling of bacterial cells. Scrambled PNA controls did not affect MRSA but sensitized MRSP moderately to oxacillin without affecting mRNA levels.

Conclusions

The antisense PNAs effects observed provide in vitro proof of concept that this approach can be used to reverse β-lactam resistance in staphylococci. Further studies are warranted as clinical treatment alternatives are needed.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0599-x) contains supplementary material, which is available to authorized users.

The prrF-encoded small regulatory RNAs are required for iron homeostasis and virulence of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen that requires iron to cause infection, but it also must regulate the uptake of iron to avoid iron toxicity. The iron-responsive PrrF1 and PrrF2 small regulatory RNAs (sRNAs) are part of P. aeruginosa's iron regulatory network and affect the expression of at least 50 genes encoding iron-containing proteins. The genes encoding the PrrF1 and PrrF2 sRNAs are encoded in tandem in P. aeruginosa, allowing for the expression of a distinct, heme-responsive sRNA named PrrH that appears to regulate genes involved in heme metabolism. Using a combination of growth, mass spectrometry, and gene expression analysis, we showed that the ΔprrF1,2 mutant, which lacks expression of the PrrF and PrrH sRNAs, is defective for both iron and heme homeostasis. We also identified phuS, encoding a heme binding protein involved in heme acquisition, and vreR, encoding a previously identified regulator of P. aeruginosa virulence genes, as novel targets of prrF-mediated heme regulation. Finally, we showed that the prrF locus encoding the PrrF and PrrH sRNAs is required for P. aeruginosa virulence in a murine model of acute lung infection. Moreover, we showed that inoculation with a ΔprrF1,2 deletion mutant protects against future challenge with wild-type P. aeruginosa. Combined, these data demonstrate that the prrF-encoded sRNAs are critical regulators of P. aeruginosa virulence.

Delivery of antibiotics with polymeric particles

Despite the wide use of antibiotics, bacterial infection is still one of the leading causes of hospitalization and mortality. The clinical failure of antibiotic therapy is linked with low bioavailability, poor penetration to bacterial infection sites, and the side effects of antibiotics, as well as the antibiotic resistance properties of bacteria. Antibiotics encapsulated in nanoparticles or microparticles made up of a biodegradable polymer have shown great potential in replacing the administration of antibiotics in their "free" form. Polymeric particles provide protection to antibiotics against environmental deactivation and alter antibiotic pharmacokinetics and biodistribution. Polymeric particles can overcome tissue and cellular barriers and deliver antibiotics into very dense tissues and inaccessible target cells. Polymeric particles can be modified to target or respond to particular tissues, cells, and even bacteria, and thereby facilitate the selective concentration or release of the antibiotic at infection sites, respectively. Thus, the delivery of antibiotics with polymeric particles augments the level of the bioactive drug at the site of infection while reducing the dosage and the dosing frequency. The end results are improved therapeutic effects as well as decreased "pill burden" and drug side effects in patients. The main objective of this review is to analyze recent advances and current perspectives in the use of polymeric antibiotic delivery systems in the treatment of bacterial infection.

Antisense growth inhibition of methicillin-resistant Staphylococcus aureus by locked nucleic acid conjugated with cell-penetrating peptide as a novel FtsZ inhibitor

Methicillin-resistant Staphylococcus aureus (MRSA) infections are becoming increasingly difficult to treat, owing to acquired antibiotic resistance. The emergence and spread of MRSA limit therapeutic options and require new therapeutic strategies, including novel MRSA-active antibiotics. Filamentous temperature-sensitive protein Z (FtsZ) is a highly conserved bacterial tubulin homologue that is essential for controlling the bacterial cell division process in different species of S. aureus. We conjugated a locked nucleic acid (LNA) that targeted ftsZ mRNA with the peptide (KFF)3K, to generate peptide-LNA (PLNA). The present study aimed to investigate whether PLNA could be used as a novel antibacterial agent. PLNA787, the most active agent synthesized, exhibited promising inhibitory effects on four pathogenic S. aureus strains in vitro. PLNA787 inhibited bacterial growth and resolved lethal Mu50 infections in epithelial cell cultures. PLNA787 also improved the survival rates of Mu50-infected mice and was associated with reductions of bacterial titers in several tissue types. The inhibitory effects on ftsZ mRNA and FtsZ protein expression and inhibition of the bacterial cell division process are considered to be the major mechanisms of PLNA. PLNA787 demonstrated activity against MRSA infections in vitro and in vivo. Our findings suggest that ftsZ mRNA is a promising new target for developing novel antisense antibiotics.

Reversion of antibiotic resistance by inhibiting mecA in clinical methicillin-resistant Staphylococci by antisense phosphorothioate oligonucleotide

Methicillin-resistant Staphylococci (MRS), methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus epidermidis (MRSE) have become a challenging problem in nosocomial infections and are connected with high morbidity and mortality rates. This is due to the increasing incidence of resistance to virtually all β-lactams and a wide variety of antimicrobials. The spread of MRS severely limits therapeutic options and generates the need for novel antibiotics that are able to combat MRS infections. One method of inhibiting bacterial growth is by blocking the expression of conserved bacterial genes and provides potential new avenues for generating a new generation of antimicrobials. The mecA gene is highly conserved among Staphylococcal species, and this makes it an ideal target for antisense inhibition. We had identified a target sequence (854-871 nt) within the mecA mRNA coding region that is particularly sensitive to antisense inhibition. The anti-mecA PS-ODN04 oligonucleotide was encapsulated into an anionic liposome. MRSA01 and MRSE01 clinical strains treated with this antisense sequence became susceptible to existing β-lactam antibiotics, and their growth was inhibited by oxacillin in vitro and in vivo. PS-ODN04 reduced the bacterial titers in the blood of mice infected with MRSA01 and MRSE01 and significantly improved their survival rate. Our data offer a possible new strategy for treating MRS infections.

Opposite effects of cefoperazone and ceftazidime on S‑ribosylhomocysteine lyase/autoinducer-2 quorum sensing and biofilm formation by an Escherichia coli clinical isolate

To investigate the effects of subminimum inhibitory concentrations of cephalosporins on bacterial biofilm formation, the biofilm production of 52 Escherichia (E.) coli strains was examined following treatment with cephalosporin compounds at 1/4 minimum inhibitory concentrations (MICs). Ceftazidime (CAZ) inhibited biofilm formation in seven isolates, while cefoperazone (CFP) enhanced biofilm formation in 18 isolates. Biofilm formation of E. coli E42 was inhibited by CAZ and induced by CFP. Therefore, using reverse transcription-polymerase chain reaction, the expression of the biofilm-modulating genes of this isolate was investigated. To monitor the production of the autoinducer of quorum sensing in E. coli, autoinducer-2 (AI-2) production was detected by measuring the bioluminescence response of Vibrio harveyi BB170. Antisense oligonucleotides (AS-ODNs) targeting S-ribosylhomocysteine lyase (luxS) inhibited the expression of the luxS gene in E. coli. CAZ at 1/4 MIC reduced luxS mRNA levels and the production of AI-2, whereas CFP at 1/4 MIC had the opposite effect. AS-ODNs targeting luxS significantly decreased the aforementioned inhibitory effects of CAZ and the induction effects of CFP on E. coli biofilm formation. Therefore, biofilm formation by the E. coli clinical isolate E42 was evoked by CFP but attenuated by CAZ at sub-MICs, via a luxS/AI-2-based quorum sensing system.

Nanomedicine in the Management of Microbial Infection - Overview and Perspectives

For more than 2 billion years, microbes have reigned on our planet, evolving or outlasting many obstacles they have encountered. In the 20th century, this trend took a dramatic turn with the introduction of antibiotics and vaccines. Nevertheless, since then, microbes have progressively eroded the effectiveness of previously successful antibiotics by developing resistance, and many infections have eluded conventional vaccine design approaches. Moreover, the emergence of resistant and more virulent strains of bacteria has outpaced the development of new antibiotics over the last few decades. These trends have had major economic and health impacts at all levels of the socioeconomic spectrum - we need breakthrough innovations that could effectively manage microbial infections and deliver solutions that stand the test of time. The application of nanotechnologies to medicine, or nanomedicine, which has already demonstrated its tremendous impact on the pharmaceutical and biotechnology industries, is rapidly becoming a major driving force behind ongoing changes in the antimicrobial field. Here we provide an overview on the current progress of nanomedicine in the management of microbial infection, including diagnosis, antimicrobial therapy, drug delivery, medical devices, and vaccines, as well as perspectives on the opportunities and challenges in antimicrobial nanomedicine.

Investigation of the antibacterial activity and efflux pump inhibitory effect of co-loaded piperine and gentamicin nanoliposomes in methicillin-resistant Staphylococcus aureus

OBJECTIVE

Antibiotic resistance has stimulated the research for developing novel strategies that can prevent bacterial growth. Methicillin-resistant Staphylococcus aureus (MRSA), regarded as one of the most serious antibiotic-resistant bacteria which has been conventionally recognized as a nosocomial pathogen.

MATERIALS AND METHODS

Nanoliposomal formulations of piperine and gentamicin were prepared by dehydration-rehydration (DRV) method and characterized for size, zeta potential and encapsulation efficiency. Antibactericidal activities of liposomal and free forms were evaluated against MRSA ATCC 43300 by the determination of minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and fractional inhibitory concentration index (FICI). The time-kill studies were carried out to evaluate the potency of antibacterial agents. The effect of piperine on bacterial efflux pumps was also investigated.

RESULTS

MIC values of gentamicin and piperine were 32 and 100 µg/mL, respectively. Synergetic effects were observed by the combination of gentamicin and piperine and FICI was determined to be 0.5. Following incorporation of gentamicin into liposomal gentamicin and liposomal combination, the MIC values were reduced 16- and 32-fold, respectively. MBC values of gentamicin reduced 4 and 8 times following incorporation into gentamicin and combination liposomes, respectively. In comparison with vancomycin, liposomal combination was more effective in bacterial inhibition and killing. Liposomal combination was the most effective preparations in time-kill study. Our findings indicated that liposomal piperine was able to inhibit the efflux pump sufficiently.

CONCLUSION

The results of this study revealed that liposomal combination is a powerful nano-antibacterial agent to eradicate MRSA infection. This dual-loaded formulation was an effective approach for eradication of MRSA.

Liposome-encapsulated ISMN: a novel nitric oxide-based therapeutic agent against Staphylococcus aureus biofilms

Background

Staphylococcus aureus in its biofilm form has been associated with recalcitrant chronic rhinosinusitis with significant resistance to conventional therapies. This study aims to determine if liposomal-encapsulation of a precursor of the naturally occurring antimicrobial nitric oxide (NO) enhances its desired anti-biofilm effects against S. aureus, in the hope that improving its efficacy can provide an effective topical agent for future clinical use.

Methodology

S. aureus ATCC 25923 biofilms were grown in-vitro using the Minimum Biofilm Eradication Concentration (MBEC) device and exposed to 3 and 60 mg/mL of the NO donor isosorbide mononitrate (ISMN) encapsulated into different anionic liposomal formulations based on particle size (unilamellar ULV, multilamellar MLV) and lipid content (5 and 25 mM) at 24 h and 5 min exposure times. Biofilms were viewed using Live-Dead Baclight stain and confocal scanning laser microscopy and quantified using the software COMSTAT2.

Results

At 3 and 60 mg/mL, ISMN-ULV liposomes had comparable and significant anti-biofilm effects compared to untreated control at 24 h exposure (p = 0.012 and 0.02 respectively). ULV blanks also had significant anti-biofilm effects at both 24 h and 5 min exposure (p = 0.02 and 0.047 respectively). At 5 min exposure, 60 mg/mL ISMN-MLV liposomes appeared to have greater anti-biofilm effects compared to pure ISMN or ULV particles. Increasing liposomal lipid content improved the anti-biofilm efficacy of both MLV and ULVs at 5 min exposure.

Conclusion

Liposome-encapsulated “nitric oxide” is highly effective in eradicating S. aureus biofilms in-vitro, giving great promise for use in the clinical setting to treat this burdensome infection. Further studies however are needed to assess its safety and efficacy in-vivo before clinical translation is attempted.

(Non-)translational medicine: targeting bacterial RNA

The rise and spread of antibiotic resistance is among the most severe challenges facing modern medicine. Despite this fact, attempts to develop novel classes of antibiotic have been largely unsuccessful. The traditional mechanisms by which antibiotics work are subject to relatively rapid bacterial resistance via mutation, and hence have a limited period of efficacy. One promising strategy to ameliorate this problem is to shift from the use of chemical compounds targeting protein structures and processes to a new era of RNA-based therapeutics. RNA-mediated regulation (riboregulation) has evolved naturally in bacteria and is therefore a highly efficient means by which gene expression can be manipulated. Here, we describe recent advances toward the development of effective anti-bacterial therapies, which operate through various strategies centered on RNA.

Penicillin facilitates the entry of antisense constructs into Streptococcus mutans

Antisense oligonucleotides (AS-ODN) target genes in a sequence-specific manner inhibit gene function and have potential use as antimicrobial agents. Cell barriers, such as peptidoglycan, cell surface proteins and lipopolysaccharide membranes, prevent delivery of AS-ODN into the bacterial cell, limiting their use as an effective treatment option. The β-lactam antibiotic penicillin was examined for its ability to deliver phosphorothioate oligodeoxyribonucleotides (PS-ODNs) and γ(32) P-ODN into Streptococcus mutans OMZ175. Treatment of lag-phase S. mutans OMZ175 cells with penicillin and FBA (PS-ODN targeting the fructose-biphosphate aldolase gene), resulted in prolonged suppression of growth (> 24 h) and fba expression (656.9 ± 194.4-fold decrease at 5 h). Suppression of both cell growth and fba expression corresponded with a greater amount of γ(32) P-ODN becoming cell associated, with a maximum γ(32) P-ODN concentration per cell achieved 5 h after penicillin treatment (6.50 ± 1.39 × 10(8) molecules per CFU). This study confirms that for S. mutans OMZ175, the peptidoglycan layer acts as a major barrier preventing AS-ODN penetration and suggests that the use of agents such as penicillin that interfere with peptidoglycan integrity can significantly increase the uptake of PS-ODN by these cells.

Inhibition of cell division induced by external guide sequences (EGS Technology) targeting ftsZ

EGS (external guide sequence) technology is a promising approach to designing new antibiotics. EGSs are short antisense oligoribonucleotides that induce RNase P-mediated cleavage of a target RNA by forming a precursor tRNA-like complex. The ftsZ mRNA secondary structure was modeled and EGSs complementary to two regions with high probability of being suitable targets were designed. In vitro reactions showed that EGSs targeting these regions bound ftsZ mRNA and elicited RNase P-mediated cleavage of ftsZ mRNA. A recombinant plasmid, pEGSb1, coding for an EGS that targets region “b” under the control of the T7 promoter was generated. Upon introduction of this plasmid into Escherichia coli BL21(DE3)(pLysS) the transformant strain formed filaments when expression of the EGS was induced. Concomitantly, E. coli harboring pEGSb1 showed a modest but significant inhibition of growth when synthesis of the EGSb1 was induced. Our results indicate that EGS technology could be a viable strategy to generate new antimicrobials targeting ftsZ.

Targeting RNA polymerase primary σ70 as a therapeutic strategy against methicillin-resistant Staphylococcus aureus by antisense peptide nucleic acid

Background

Methicillin-resistant Staphylococcus aureus (MRSA) causes threatening infection-related mortality worldwide. Currently, spread of multi-drug resistance (MDR) MRSA limits therapeutic options and requires new approaches to “druggable” target discovery, as well as development of novel MRSA-active antibiotics. RNA polymerase primary σ⁷⁰ (encoded by gene rpoD) is a highly conserved prokaryotic factor essential for transcription initiation in exponentially growing cells of diverse S. aureus, implying potential for antisense inhibition.

Methodology/Principal Findings

By synthesizing a serial of cell penetrating peptide conjugated peptide nucleic acids (PPNAs) based on software predicted parameters and further design optimization, we identified a target sequence (234 to 243 nt) within rpoD mRNA conserved region 3.0 being more sensitive to antisense inhibition. A (KFF)₃K peptide conjugated 10-mer complementary PNA (PPNA2332) was developed for potent micromolar-range growth inhibitory effects against four pathogenic S. aureus strains with different resistance phenotypes, including clinical vancomycin-intermediate resistance S. aureus and MDR-MRSA isolates. PPNA2332 showed bacteriocidal antisense effect at 3.2 fold of MIC value against MRSA/VISA Mu50, and its sequence specificity was demonstrated in that PPNA with scrambled PNA sequence (Scr PPNA2332) exhibited no growth inhibitory effect at higher concentrations. Also, PPNA2332 specifically interferes with rpoD mRNA, inhibiting translation of its protein product σ⁷⁰ in a concentration-dependent manner. Full decay of mRNA and suppressed expression of σ⁷⁰ were observed for 40 µM or 12.5 µM PPNA2332 treatment, respectively, but not for 40 µM Scr PPNA2332 treatment in pure culture of MRSA/VISA Mu50 strain. PPNA2332 (≥1 µM) essentially cleared lethal MRSA/VISA Mu50 infection in epithelial cell cultures, and eliminated viable bacterial cells in a time- and concentration- dependent manner, without showing any apparent toxicity at 10 µM.

Conclusions

The present result suggested that RNAP primary σ⁷⁰ is a very promising candidate target for developing novel antisense antibiotic to treat severe MRSA infections.

ε/ζ systems: their role in resistance, virulence, and their potential for antibiotic development

Cell death in bacteria can be triggered by activation of self-inflicted molecular mechanisms. Pathogenic bacteria often make use of suicide mechanisms in which the death of individual cells benefits survival of the population. Important elements for programmed cell death in bacteria are proteinaceous toxin-antitoxin systems. While the toxin generally resides dormant in the bacterial cytosol in complex with its antitoxin, conditions such as impaired de novo synthesis of the antitoxin or nutritional stress lead to antitoxin degradation and toxin activation. A widespread toxin-antitoxin family consists of the ε/ζ systems, which are distributed over plasmids and chromosomes of various pathogenic bacteria. In its inactive state, the bacteriotoxic ζ toxin protein is inhibited by its cognate antitoxin ε. Upon degradation of ε, the ζ toxin is released allowing this enzyme to poison bacterial cell wall synthesis, which eventually triggers autolysis. ε/ζ systems ensure stable plasmid inheritance by inducing death in plasmid-deprived offspring cells. In contrast, chromosomally encoded ε/ζ systems were reported to contribute to virulence of pathogenic bacteria, possibly by inducing autolysis in individual cells under stressful conditions. The capability of toxin-antitoxin systems to kill bacteria has made them potential targets for new therapeutic compounds. Toxin activation could be hijacked to induce suicide of bacteria. Likewise, the unique mechanism of ζ toxins could serve as template for new drugs. Contrarily, inhibition of virulence-associated ζ toxins might attenuate infections. Here we provide an overview of ε/ζ toxin-antitoxin family and its potential role in the development of new therapeutic approaches in microbial defense.