Antisense antimicrobial therapeutics

Antimicrobial antisense RNA delivery to F-pili producing multidrug-resistant bacteria via a genetically engineered bacteriophage

Multidrug-resistant bacteria are a growing issue worldwide. This study developed a convenient and effective method to downregulate the expression of a specific gene to produce a novel antimicrobial tool using a small (140 nucleotide) RNA with a 24-nucleotide antisense (as) region from an arabinose-inducible expression phagemid vector in Escherichia coli. Knockdown effects of rpoS encoding RNA polymerase sigma factor were observed using this inducible artificial asRNA approach. asRNAs targeting several essential E. coli genes produced significant growth defects, especially when targeted to acpP and ribosomal protein coding genes rplN, rplL, and rpsM. Growth inhibited phenotypes were facilitated in hfq^- conditions. Phage lysates were prepared from cells harboring phagemids as a lethal-agent delivery tool. Targeting the rpsM gene by phagemid-derived M13 phage infection of E. coli containing a carbapenem-producing F-plasmid and multidrug-resistant Klebsiella pneumoniae containing an F-plasmid resulted in the death of over 99.99% of infected bacteria. This study provides a possible strategy for treating bacterial infection and can be applied to any F-pilus producing bacterial species.

Highly parallel lab evolution reveals that epistasis can curb the evolution of antibiotic resistance

Genetic perturbations that affect bacterial resistance to antibiotics have been characterized genome-wide, but how do such perturbations interact with subsequent evolutionary adaptation to the drug? Here, we show that strong epistasis between resistance mutations and systematically identified genes can be exploited to control spontaneous resistance evolution. We evolved hundreds of Escherichia coli K-12 mutant populations in parallel, using a robotic platform that tightly controls population size and selection pressure. We find a global diminishing-returns epistasis pattern: strains that are initially more sensitive generally undergo larger resistance gains. However, some gene deletion strains deviate from this general trend and curtail the evolvability of resistance, including deletions of genes for membrane transport, LPS biosynthesis, and chaperones. Deletions of efflux pump genes force evolution on inferior mutational paths, not explored in the wild type, and some of these essentially block resistance evolution. This effect is due to strong negative epistasis with resistance mutations. The identified genes and cellular functions provide potential targets for development of adjuvants that may block spontaneous resistance evolution when combined with antibiotics.

Efficient Delivery of Antisense Oligonucleotides by an Amphipathic Cell-Penetrating Peptide in Acinetobacter baumannii

BACKGROUND

Carbapenem-resistant Acinetobacter baumannii (A. baumannii) was on the top of the list of the most threatening bacteria published by the WHO in 2017. Antisense oligonucleotides (ASOs) based therapy is a promising strategy for combating Multi-Drug Resistant (MDR) bacteria because of its high specificity, easy design and lower induction of resistance, but poor cellular uptake by bacteria has restricted the further utilization of this therapy.

METHODS

Here, we used CADY, a secondary amphipathic peptide of 20 residues that could successfully carry siRNA into mammalian cells, to prepare CADY/ASOs nanoparticles (CADY-NPs) targeting acpP (encoding acyl carrier protein), and evaluated the uptake features, the inhibitory effects of CADY-NPs on gene expression and the growth of MDR-A. baumannii.

RESULTS

We found that CADY-NPs could be quickly internalized by drug-sensitive and MDR-A. baumannii in an energy independent manner, which could be restrained by chlorpromazine (an inhibitor of clathrin mediated endocytosis) significantly. In addition, CADY-NPs targeting acpP concentrationdependently retarded the growth of MDR-A. baumannii, which was associated with the decreased expression of targeted genes in A. baumannii.

CONCLUSION

In conclusion, our research is the first to demonstrate that CADY can deliver ASOs into bacteria and provide a novel strategy for the treatment of MDR-A. baumannii.

How CRISPR-Cas System Could Be Used to Combat Antimicrobial Resistance

Rapid emergence of antibiotic-resistant bacteria has made it harder for us to combat infectious diseases and to develop new antibiotics. The clustered regularly interspaced short palindromic repeats - CRISPR-associated (CRISPR-Cas) system, as a bacterial adaptive immune system, is recognized as one of the new strategies for controlling antibiotic-resistant strains. The programmable Cas nuclease of this system used against bacterial genomic sequences could be lethal or could help reduce resistance of bacteria to antibiotics. Therefore, this study aims to review using the CRISPR-Cas system to promote sensitizing bacteria to antibiotics. We envision that CRISPR-Cas approaches may open novel ways for the development of smart antibiotics, which could eliminate multidrug-resistant (MDR) pathogens and differentiate between beneficial and pathogenic microorganisms. These systems can be exploited to quantitatively and selectively eliminate individual bacterial strains based on a sequence-specific manner, creating opportunities in the treatment of MDR infections, the study of microbial consortia, and the control of industrial fermentation.

Antibacterial Therapeutic Agents Composed of Functional Biological Molecules

Antibacterial agents are a group of materials that selectively destroy bacteria by interfering with bacterial growth or survival. With the emergence of resistance phenomenon of bacterial pathogens to current antibiotics, new drugs are frequently entering into the market along with the existing drugs, and the alternative compounds with antibacterial functions are being explored. Due to the advantages of their inherent biochemical and biophysical properties including precise targeting ability, biocompatibility, biodegradability, long blood circulation time, and low cytotoxicity, biomolecules such as peptides, carbohydrates, and nucleic acids have huge potential for the antimicrobial application and have been extensively studied in recent years. In this review, antimicrobial therapeutic agents composed of three kinds of functional biological molecules were summarized. In addition, the research progress of antibacterial mechanism, chemical modification, and nanoparticle coupling of those biomolecules were also discussed.

Antibacterial Peptide Nucleic Acids-Facts and Perspectives

Antibiotic resistance is an escalating, worldwide problem. Due to excessive use of antibiotics, multidrug-resistant bacteria have become a serious threat and a major global healthcare problem of the 21st century. This fact creates an urgent need for new and effective antimicrobials. The common strategies for antibiotic discovery are based on either modifying existing antibiotics or screening compound libraries, but these strategies have not been successful in recent decades. An alternative approach could be to use gene-specific oligonucleotides, such as peptide nucleic acid (PNA) oligomers, that can specifically target any single pathogen. This approach broadens the range of potential targets to any gene with a known sequence in any bacterium, and could significantly reduce the time required to discover new antimicrobials or their redesign, if resistance arises. We review the potential of PNA as an antibacterial molecule. First, we describe the physicochemical properties of PNA and modifications of the PNA backbone and nucleobases. Second, we review the carriers used to transport PNA to bacterial cells. Furthermore, we discuss the PNA targets in antibacterial studies focusing on antisense PNA targeting bacterial mRNA and rRNA.

Artificial small RNA-mediated growth inhibition in Escherichia coli and Salmonella enterica serovar Typhimurium

We developed a synthetic RNA approach to identify growth inhibition sequences by cloning random 24-nucleotide (nt) sequences into an arabinose-inducible expression vector. This vector expressed a small RNA (sRNA) of ∼140 nt containing a 24 nt random sequence insert. After transforming Escherichia coli with the vector, 10 out of 954 transformants showed strong growth defect phenotypes and two clones caused cell lysis. We then examined growth inhibition phenotypes in the Salmonella Typhimurium LT2 strain using the twelve sRNAs that exerted an inhibitory effect on E. coli growth. Three of these clones showed strong growth inhibition phenotypes in S. Typhimurium LT2. The most effective sRNA contained the same insert (N1) in both bacteria. The 24 nt random sequence insert of N1 was abundant in guanine residues (ten out of 24 nt), and other random sequences causing growth defects were also highly enriched for guanine (G) nucleotides. We, therefore, generated clones that express sRNAs containing a stretch of 16 to 24 continuous guanine sequences (poly-G₁₆, -G₁₈, -G₂₀, -G₂₂, and -G₂₄). All of these clones induced growth inhibition in both liquid and agar plate media and the poly-G₂₀ clone showed the strongest effect in E. coli. These results demonstrate that our sRNA expression system can be used to identify nucleotide sequences that are potential candidates for oligonucleotide antimicrobial drugs.

Current landscape in the discovery of novel antibacterial agents

BACKGROUND

Standard treatments against bacterial infections are becoming ineffective due to the rise of antibacterial resistance worldwide. Classical approaches to develop new antibacterial agents are not sufficient to fulfil the current pipeline, therefore new strategies are currently being devised in the field of antibacterial discovery.

OBJECTIVES

The objective of this narrative review is to compile the most successful strategies for drug discovery within the antibacterial context that are currently being pursued.

SOURCES

Peer-reviewed publications from the MEDLINE database with robust data addressing the discovery of new antibacterial agents in the current pipeline have been selected.

CONTENT

Several strategies to discover new antibacterials are described in this review: (i) derivatives of known antibacterial agents; the activity of a known antimicrobial agent can be improved through two strategies: (a) the modification of the original chemical structure of an antimicrobial agent to circumvent antibacterial resistance mechanisms and (b) the development of a compound that inhibits the mechanisms of resistance to an antibacterial agent; (ii) new antibacterial agents targeting new proteins; (iii) inhibitors of virulence factors; (iv) nanoparticles; (v) antimicrobial peptides and peptidomimetics; (vi) phage therapy and enzybiotics; and (vii) antisense oligonucleotides.

IMPLICATIONS

This review intends to provide a positive message affirming that several different strategies to design new antibacterial agents are currently being developed, and we are therefore confident that in the near future some of the most promising approaches will come to fruition.

Application of 2'-OMethylRNA' Antisense Oligomer to Control Candida albicans EFG1 Virulence Determinant

Antisense oligomers and their analogs have been successfully utilized to silence gene expression for the treatment of many human diseases; however, the control of yeast’s virulence determinants has never been exploited before. In this sense, this work is based on the key hypothesis that if a pathogen’s genetic sequence is a determinant of virulence, it will be possible to synthesize a nucleic acid mimic based on antisense therapy (AST) that will bind to the mRNA produced, blocking its translation into protein and, consequently, reducing the pathogen virulence phenotype. EFG1 is an important determinant of virulence that is involved in the regulation of the Candida albicans switch from yeast to filamentous form. Thus, our main goal was to design and synthesize an antisense oligonucleotide (ASO) targeting the EFG1 mRNA and to validate its in vitro applicability. The results show that the anti-EFG1 2′-OMethylRNA (2′OMe) oligomer was able to significantly reduce the levels of EFG1 gene expression and of Efg1p protein translation (both approximately 60%), as well as effectively prevent filamentation of C. albicans cells (by 80%). Moreover, it was verified that anti-EFG1 2′OMe keeps the efficacy in different simulated human body fluids. Undeniably, this work provides potentially valuable information for future research into the management of Candida infections, regarding the development of a credible and alternative method to control C. albicans infections, based on AST methodology.

A New Antisense Phosphoryl Guanidine Oligo-2'-O-Methylribonucleotide Penetrates Into Intracellular Mycobacteria and Suppresses Target Gene Expression

The worldwide spread of multidrug-resistant Mycobacterium tuberculosis strains prompted the development of new strategies to combat tuberculosis, one of which is antisense therapy based on targeting bacterial mRNA by oligonucleotide derivatives. However, the main limitation of antisense antibacterials is poor cellular uptake because of electrostatic charge. Phosphoryl guanidine oligo-2′-O-methylribonucleotides (2′-OMe PGOs) are a novel type of uncharged RNA analogues with high RNA affinity, which penetrate through the bacterial cell wall more efficiently. In this study, we investigated the uptake and biological effects of 2′-OMe PGO in mycobacteria. The results indicated that 2′-OMe PGO specific for the alanine dehydrogenase-encoding ald gene inhibited the growth of Mycobacterium smegmatis and downregulated ald expression at both the transcriptional and translational levels through an RNase H-independent mechanism, showing higher biological activity than its phosphorothioate oligonucleotide counterpart. Confocal microscopy revealed that the anti-ald 2′-OMe PGO was taken up by intracellular mycobacteria residing in RAW 264.7 macrophages without exerting toxic effects on eukaryotic cells, indicating that 2′-OMe PGO was able to efficiently cross two cellular membranes. In addition, 2′-OMe PGO inhibited the transcription of the target ald gene in M. smegmatis-infected macrophages. Thus, we demonstrated, for the first time, a possibility of targeting gene expression and inhibiting growth of intracellular mycobacteria by antisense oligonucleotide derivatives. Strong antisense activity and efficient uptake of the new RNA analogue, 2′-OMe PGO, by intracellular microorganisms revealed here may promote the development of novel therapeutic strategies to treat TB and prevent the emergence of drug-resistant mycobacterial strains.

AcrAB-TolC Inhibition by Peptide-Conjugated Phosphorodiamidate Morpholino Oligomers Restores Antibiotic Activity in Vitro and in Vivo

Overexpression of bacterial efflux pumps is a driver of increasing antibiotic resistance in Gram-negative pathogens. The AcrAB-TolC efflux pump has been implicated in resistance to a number of important antibiotic classes including fluoroquinolones, macrolides, and β-lactams. Antisense technology, such as peptide-conjugated phosphorodiamidate morpholino oligomers (PPMOs), can be utilized to inhibit expression of efflux pumps and restore susceptibility to antibiotics. Targeting of the AcrAB-TolC components with PPMOs revealed a sequence for acrA, which was the most effective at reducing antibiotic efflux. This acrA-PPMO enhances the antimicrobial effects of the levofloxacin and azithromycin in a panel of clinical Enterobacteriaceae strains. Additionally, acrA-PPMO enhanced azithromycin in vivo in a K. pneumoniae septicemia model. PPMOs targeting the homologous resistance-nodulation-division (RND)-efflux system in P. aeruginosa, MexAB-OprM, also enhanced potency to several classes of antibiotics in a panel of strains and in a cell culture infection model. These data suggest that PPMOs can be used as an adjuvant in antibiotic therapy to increase the efficacy or extend the spectrum of useful antibiotics against a variety of Gram-negative infections.

Bridged Nucleic Acids Reloaded

Oligonucleotides are key compounds widely used for research, diagnostics, and therapeutics. The rapid increase in oligonucleotide-based applications, together with the progress in nucleic acids research, has led to the design of nucleotide analogs that, when part of these oligomers, enhance their efficiency, bioavailability, or stability. One of the most useful nucleotide analogs is the first-generation bridged nucleic acids (BNA), also known as locked nucleic acids (LNA), which were used in combination with ribonucleotides, deoxyribonucleotides, or other analogs to construct oligomers with diverse applications. However, there is still room to improve their efficiency, bioavailability, stability, and, importantly, toxicity. A second-generation BNA, BNANC (2'-O,4'-aminoethylene bridged nucleic acid), has been recently made available. Oligomers containing these analogs not only showed less toxicity when compared to LNA-containing compounds but, in some cases, also exhibited higher specificity. Although there are still few applications where BNANC-containing compounds have been researched, the promising results warrant more effort in incorporating these analogs for other applications. Furthermore, newer BNA compounds will be introduced in the near future, offering great hope to oligonucleotide-based fields of research and applications.

Reversing resistance to counter antimicrobial resistance in the World Health Organisation's critical priority of most dangerous pathogens

The speed at which bacteria develop antimicrobial resistance far outpace drug discovery and development efforts resulting in untreatable infections. The World Health Organisation recently released a list of pathogens in urgent need for the development of new antimicrobials. The organisms that are listed as the most critical priority are all Gram-negative bacteria resistant to the carbapenem class of antibiotics. Carbapenem resistance in these organisms is typified by intrinsic resistance due to the expression of antibiotic efflux pumps and the permeability barrier presented by the outer membrane, as well as by acquired resistance due to the acquisition of enzymes able to degrade β-lactam antibiotics. In this perspective article we argue the case for reversing resistance by targeting these resistance mechanisms - to increase our arsenal of available antibiotics and drastically reduce antibiotic discovery times - as the most effective way to combat antimicrobial resistance in these high priority pathogens.

In Vitro and In Vivo Activity of a Novel Antisense Peptide Nucleic Acid Compound Against Multidrug-Resistant Acinetobacter baumannii

Multidrug-resistant (MDR) Acinetobacter baumannii is a difficult pathogen due to its propensity to develop resistance to antibiotics. Antisense nucleic acid analogs have been proposed as a potential alternative anti-infective approach. We developed a peptide nucleic acid (PNA) compound that targets the essential Acinetobacter gene carA. The PNA oligomer was conjugated to the cell-penetrating peptide (RXR)₄XB. In vitro testing of the PNA conjugate against four clinical strains of MDR-A. baumannii in minimal medium demonstrated that all four strains were inhibited at a concentration of 1.25 μM. In vivo testing of the PNA conjugate was done using a Galleria mellonella model of sepsis caused by one of the clinical strains. Preliminary testing of a variety of inocula demonstrated that an inoculum of 1 × 10⁶ cfu was lethal to the majority of caterpillars by day 3, but not within 24 hours. The PNA compound was administered 30 minutes after an inoculum of 1 × 10⁶ cfu at doses estimated to produce concentrations of ∼5 and 20 μM. The PNA compound had no effect at the lower dose. However, the higher dose reduced mortality from 5/28 (18%) to 0/28 (0%) at day 1 (p = 0.051) and from 19/28 (68%) to 9/28 (32%) at day 6 (p = 0.015). Antisense therapy is a novel approach to dealing with difficult MDR pathogens that could circumvent the problem of progressive resistance to available antibiotics. Further studies need to be done with additional strains and more complex in vivo model systems.

Role of Proline in Pathogen and Host Interactions

SIGNIFICANCE

Proline metabolism has complex roles in a variety of biological processes, including cell signaling, stress protection, and energy production. Proline also contributes to the pathogenesis of various disease-causing organisms. Understanding the mechanisms of how pathogens utilize proline is important for developing new strategies against infectious diseases. Recent Advances: The ability of pathogens to acquire amino acids is critical during infection. Besides protein biosynthesis, some amino acids, such as proline, serve as a carbon, nitrogen, or energy source in bacterial and protozoa pathogens. The role of proline during infection depends on the physiology of the host/pathogen interactions. Some pathogens rely on proline as a critical respiratory substrate, whereas others exploit proline for stress protection.

CRITICAL ISSUES

Disruption of proline metabolism and uptake has been shown to significantly attenuate virulence of certain pathogens, whereas in other pathogens the importance of proline during infection is not known. Inhibiting proline metabolism and transport may be a useful therapeutic strategy against some pathogens. Developing specific inhibitors to avoid off-target effects in the host, however, will be challenging. Also, potential treatments that target proline metabolism should consider the impact on intracellular levels of Δ1-pyrroline-5-carboxylate, a metabolite intermediate that can have opposing effects on pathogenesis.

FUTURE DIRECTIONS

Further characterization of how proline metabolism is regulated during infection would provide new insights into the role of proline in pathogenesis. Biochemical and structural characterization of proline metabolic enzymes from different pathogens could lead to new tools for exploring proline metabolism during infection and possibly new therapeutic compounds.

Solid lipid nanoparticles for the delivery of anti-microbial oligonucleotides

Novel alternatives to antibiotics are urgently needed for the successful treatment of antimicrobial resistant (AMR) infections. Experimental antibacterial oligonucleotide therapeutics, such as transcription factor decoys (TFD), are a promising approach to circumvent AMR. However, the therapeutic potential of TFD is contingent upon the development of carriers that afford efficient DNA protection against nucleases and delivery of DNA to the target infection site. As a carrier for TFD, here we present three prototypes of anionic solid lipid nanoparticles that were coated with either the cationic bolaamphiphile 12-bis-tetrahydroacridinium or with protamine. Both compounds switched particles zeta potential to positive values, showing efficient complexation with TFD and demonstrable protection from deoxyribonuclease. The effective delivery of TFD into bacteria was confirmed by confocal microscopy while SLN-bacteria interactions were studied by flow cytometry. Antibacterial efficacy was confirmed using a model TFD targeting the Fur iron uptake pathway in E. coli under microaerobic conditions. Biocompatibility of TFD-SLN was assessed using in vitro epithelial cell and in vivo Xenopus laevis embryo models. Taken together these results indicate that TFD-SLN complex can offer preferential accumulation of TFD in bacteria and represent a promising class of carriers for this experimental approach to tackling the worldwide AMR crisis.

Does a Conjugation Site Affect Transport of Vitamin B12 -Peptide Nucleic Acid Conjugates into Bacterial Cells?

Gram-negative bacteria develop specific systems for the uptake of scarce nutrients, including vitamin B₁₂ . These uptake pathways may be utilized for the delivery of biologically relevant molecules into cells. Indeed, it was recently reported that vitamin B₁₂ transported an antisense peptide nucleic acid (PNA) into Escherichia coli and Salmonella Typhimurium cells. The present studies indicate that the conjugation site of PNA to vitamin B₁₂ has an impact on PNA transport into bacterial cells. Toward this end, a specifically designed PNA oligomer has been tethered at various positions of vitamin B₁₂ (central Co, R_5' -OH, c and e amide chains, meso position, and at the hydroxy group of cobinamide) by using known or newly developed methodologies and tested for the uptake of the synthesized conjugates by E. coli. Compounds in which the PNA oligonucleotide was anchored at the R_5' -OH position were transported more efficiently than that of other compounds tethered at the peripheral positions around the corrin ring. Of importance is the fact that, contrary to mammalian organisms, E. coli also takes up cobinamide, which is an incomplete corrinoid. This selectivity opens up ways to fight bacterial infections.

Morpholino oligomers tested in vitro, in biofilm and in vivo against multidrug-resistant Klebsiella pneumoniae

Background

Klebsiella pneumoniae is an opportunistic pathogen and many strains are multidrug resistant. KPC is one of the most problematic resistance mechanisms, as it confers resistance to most β-lactams, including carbapenems. A promising platform technology for treating infections caused by MDR pathogens is the nucleic acid-like synthetic oligomers that silence bacterial gene expression by an antisense mechanism.

Objectives

To test a peptide-conjugated phosphorodiamidate morpholino oligomer (PPMO) in a mouse model of K. pneumoniae infection.

Methods

PPMOs were designed to target various essential genes of K. pneumoniae and screened in vitro against a panel of diverse strains. The most potent PPMOs were further tested for their bactericidal effects in broth cultures and in established biofilms. Finally, a PPMO was used to treat mice infected with a KPC-expressing strain.

Results

The most potent PPMOs targeted acpP, rpmB and ftsZ and had MIC75s of 0.5, 4 and 4 μM, respectively. AcpP PPMOs were bactericidal at 1-2 × MIC and reduced viable cells and biofilm mass in established biofilms. In a mouse pneumonia model, therapeutic intranasal treatment with ∼30 mg/kg AcpP PPMO improved survival by 89% and reduced bacterial burden in the lung by ∼3 logs. Survival was proportional to the dose of AcpP PPMO. Delaying treatment by 2, 8 or 24 h post-infection improved survival compared with control groups treated with PBS or scrambled sequence (Scr) PPMOs.

Conclusions

PPMOs have the potential to be effective therapeutic agents against KPC-expressing, MDR K. pneumoniae.

Challenges and Opportunities of Nontraditional Approaches to Treating Bacterial Infections

Due to increasing rates of antimicrobial-resistant infections and the current inadequacy of the antibiotic pipeline, there is increasing interest in nontraditional approaches to antibacterial therapies. We define "traditional" agents as small-molecule agents that directly target bacterial components to exert a bacteriostatic or bactericidal effect, and "nontraditional approaches" as antimicrobial therapeutics that work through other means (ie, not a small molecule and/or utilizes a nontraditional target). Due to their atypical features, such therapies may be less susceptible to the emergence of resistance than traditional antibiotics. They include approaches such as monoclonal antibodies, virulence disruptors, immunomodulators, phage therapies, microbiome-based therapies, antibiotic potentiators, and antisense approaches. This article discusses both the developmental and regulatory advantages and challenges associated with each of these technologies. By identifying existing regulatory and developmental gaps, we hope to provide a sense of where focusing resources may provide the greatest impact on successful product development.

Amikacin: Uses, Resistance, and Prospects for Inhibition

Aminoglycosides are a group of antibiotics used since the 1940s to primarily treat a broad spectrum of bacterial infections. The primary resistance mechanism against these antibiotics is enzymatic modification by aminoglycoside-modifying enzymes that are divided into acetyl-transferases, phosphotransferases, and nucleotidyltransferases. To overcome this problem, new semisynthetic aminoglycosides were developed in the 70s. The most widely used semisynthetic aminoglycoside is amikacin, which is refractory to most aminoglycoside modifying enzymes. Amikacin was synthesized by acylation with the l-(-)-γ-amino-α-hydroxybutyryl side chain at the C-1 amino group of the deoxystreptamine moiety of kanamycin A. The main amikacin resistance mechanism found in the clinics is acetylation by the aminoglycoside 6'-N-acetyltransferase type Ib [AAC(6')-Ib], an enzyme coded for by a gene found in integrons, transposons, plasmids, and chromosomes of Gram-negative bacteria. Numerous efforts are focused on finding strategies to neutralize the action of AAC(6')-Ib and extend the useful life of amikacin. Small molecules as well as complexes ionophore-Zn⁺² or Cu⁺² were found to inhibit the acetylation reaction and induced phenotypic conversion to susceptibility in bacteria harboring the aac(6')-Ib gene. A new semisynthetic aminoglycoside, plazomicin, is in advance stage of development and will contribute to renewed interest in this kind of antibiotics.

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.

The antibacterial effect of topical ozone on the treatment of MRSA skin infection

Skin can be infected by many types of microorganisms, most commonly by gram‑positive strains of Staphylococcus and Streptococcus spp. Treatment of Staphylococcus aureus (S. aureus) infections, particularly that of methicillin resistant Staphylococcus aureus (MRSA), is a challenge in clinical practice. Ozone therapy has proven to be one of the strongest antiseptics against the majority of microorganisms involved in skin infections. The purpose of the present study was to evaluate the microbicidal effects of topical ozone therapy on S. aureus and MRSA, and determine the clinical efficacy of ozone therapy on patients with MRSA skin infection. Microbicidal effects of ozonated oil and ozonated water were determined by plating and Kirby Bauer methods. Clinical efficacy and safety of topical ozone were evaluated in two cases with skin MRSA infection. The killing rates of ozonated oil for S. aureus and MRSA were greater when compared with the control oil group. Almost 100% of S. aureus were eliminated by ozonated oil following 5 min. Almost 100% MRSA were eliminated by ozonated oil following 15 min. In addition, 100% S. aureus and 100% MRSA were eliminated by ozonated water in 1 min. The inhibition zone diameters of ozonated oil for S. aureus and MRSA were 17 and 13 mm, respectively, which were significantly larger than the control group. Both cases of skin MRSA infection were completely healed with ozone therapy. In conclusion, ozone therapy is a potential treatment for S. aureus and MRSA skin infection as it has great efficacy, few side effects and low‑costs.

Evaluation of the electron transfer flavoprotein as an antibacterial target in Burkholderia cenocepacia

There are hundreds of essential genes in multidrug-resistant bacterial genomes, but only a few of their products are exploited as antibacterial targets. An example is the electron transfer flavoprotein (ETF), which is required for growth and viability in Burkholderia cenocepacia. Here, we evaluated ETF as an antibiotic target for Burkholderia cepacia complex (Bcc). Depletion of the bacterial ETF during infection of Caenorhabditis elegans significantly extended survival of the nematodes, proving that ETF is essential for survival of B. cenocepacia in this host model. In spite of the arrest in respiration in ETF mutants, the inhibition of etf expression did not increase the formation of persister cells, when treated with high doses of ciprofloxacin or meropenem. To test if etf translation could be inhibited by RNA interference, antisense oligonucleotides that target the etfBA operon were synthesized. One antisense oligonucleotide was effective in inhibiting etfB translation in vitro but not in vivo, highlighting the challenge of reduced membrane permeability for the design of drugs against B. cenocepacia. This work contributes to the validation of ETF of B. cenocepacia as a target for antibacterial therapy and demonstrates the utility of a C. elegans liquid killing assay to validate gene essentiality in an in vivo infection model.

Next-generation precision antimicrobials: towards personalized treatment of infectious diseases

Antibiotics started to be used almost 90 years ago to eradicate life-threatening infections. The urgency of the problem required rapid, broad-spectrum elimination of infectious agents. Since their initial discovery, these antimicrobials have saved millions of lives. However, they are not exempt from side effects, which include the indiscriminate disruption of the beneficial microbiota. Recent technological advances have enabled the development of antimicrobials that can selectively target a gene, a cellular process, or a microbe of choice. These strategies bring us a step closer to developing personalized therapies that exclusively remove disease-causing infectious agents. Here, we advocate the preservation of our beneficial microbes and provide an overview of promising alternatives to broad-spectrum antimicrobials. Specifically, we emphasize nucleic acid and peptide-based systems as a foundation for next-generation alternatives to antibiotics that do not challenge our microbiota and may help to mitigate the spread of resistance.

Tat-Tagged and Folate-Modified N-Succinyl-chitosan (Tat-Suc-FA) Self-assembly Nanoparticle for Therapeutic Delivery OGX-011 to A549 Cells

The objective of this study was to develop a novel type of an antisense oligonucleotide (OGX-011) loaded Tat-tagged and folate-modified N-succinyl-chitosan (Tat-Suc-FA) nanoparticles (NPs) for improving tumor targetability. In this study, Tat-Suc-FA/OGX-011NPs were prepared and its physicochemical characterizations were also evaluated. The nanoparticles showed an average diameter of 73 ± 16.6 nm, the zeta potential of +23.6 ± 0.3 mV, and a high entrapment efficiency of 89.6 ± 6.6%. Transmission electron microscopy analysis showed the nanoparticles were mostly spherical and well dispersed. The delivery efficiency of this system was investigated both in vitro and in vivo. In comparison with nontargeted Lipofectamin2000/OGX-011 and free OGX-011, Tat-Suc-FA/GOX-011 showed the highest apoptosis rate of 14.2% ± 1.8% and significant uptake in A549 cells. Tat-Suc-FA NPs loaded with GOX-011 induced significant down-regulation of s-CLU mRNA and protein levels in A549 cells. In A549 tumor-bearing mice model, Tat-Suc-FA/GOX-011 produced a more efficient down-regulation of s-CLU compared to Lipofectamin2000/OGX-011. Furthermore, the combined use of Tat-Suc-FA/OGX-011 with DDP chemotherapy showed a most significant inhibition of tumor growth and greatly enhanced the survival rate of A549 tumor-bearing mice. These findings suggested successful application of Tat-Suc-FA NPs for the high efficiency and specificity in therapeutic delivery of OGX-011 to A549 cells.

A Review of Experimental and Off-Label Therapies for Clostridium difficile Infection

In spite of increased awareness and the efforts taken to optimize Clostridium difficile infection (CDI) management, with the limited number of currently available antibiotics for C. difficile the halt of this increasing epidemic remains out of reach. There are, however, close to 80 alternative treatment methods with controversial anti-clostridial efficacy or in experimental phase today. Indeed, some of these therapies are expected to become acknowledged members of the recommended anti-CDI arsenal within the next few years. None of these alternative treatment methods can respond in itself to all the major challenges of CDI management, which are primary prophylaxis in the susceptible population, clinical cure of severe cases, prevention of recurrences, and forestallment of asymptomatic C. difficile carriage and in-hospital spread. Yet, the greater the variety of treatment choices on hand, the better combination strategies can be developed to reach these goals in the future. The aim of this article is to provide a comprehensive summary of these experimental and currently off-label therapeutic options.