Treatment Of Multidrug-resistant Infections Research Articles

Sonoactivated Nanoantimicrobials: A Potent Armament in the Postantibiotic Era.

Recent research on antibiotic-free therapies has demonstrated remarkable effectiveness in preventing and controlling multi-drug-resistant (MDR) bacterial infection. Antimicrobial sonodynamic therapy (aSDT) developed from photodynamic therapy (PDT) is of particular interest to researchers and clinicians as it is a promising noninvasive treatment of less accessible infections. However, several aSDT-related challenges need to be addressed. These involve companion imaging and diagnosis of aSDT in vivo, insufficient efficacy of aSDT due to the limited oxygen level in the site of infection, infection in the immunocompromised host, and the synergetic approaches for enhanced ROS-mediated antimicrobial activity. This Spotlight on Applications presents the recent approaches in the development of sonoactivated nanoantimicrobials. These developed strategies including bacterial enzyme-responsive sonotheranostics, the ultrasound-switchable nanoenzyme-augmented aSDT, sono-immunomodulating therapy, and sonoactivated chemodynamic therapy (CDT) have shown positive outcomes in the treatment of MDR infections. However, despite the promising results of these approaches, a deeper understanding of the nanoantimicrobial SDT mechanisms in the more precise preclinical model is essential for future optimization regarding efficacy and safety.

Target-Based Design of Promysalin Analogues Identifies a New Putative Binding Cleft in Succinate Dehydrogenase.

Promysalin is a small-molecule natural product that specifically inhibits growth of the Gram-negative pathogen Pseudomonas aeruginosa (PA). This activity holds promise in the treatment of multidrug resistant infections found in immunocompromised patients with chronic illnesses, such as cystic fibrosis. In 2015, our lab completed the first total synthesis; subsequent analogue design and SAR investigation enabled identification of succinate dehydrogenase (Sdh) as the biological target in PA. Herein, we report the target-guided design of new promysalin analogues with varying alkyl chains, one of which is on par with our most potent analogue to date. Computational docking revealed that some analogues have a different orientation in the Sdh binding pocket, placing the terminal carbon proximal to a tryptophan residue. This inspired the design of an extended side chain analogue bearing a terminal phenyl moiety, providing a basis for the design of future analogues.

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.

Genetic and Biochemical Characterization of VMB-1, a Novel Metallo-β-Lactamase Encoded by a Conjugative, Broad-Host Range IncC Plasmid from Vibrio spp.

The increasing incidence of phenotypic resistance to carbapenems in recent years is mainly attributed to acquisition of mobile carbapenemase-encoding genetic elements by major bacterial pathogens. Here, a novel carbapenemase known as Vibrio metallo-β-lactamase 1 (VMB-1), which is encoded by a gene (blaVMB-1 ) located in an integron-bearing, highly transmissible IncC type plasmid, namely pVB1796, is identified and characterized, both genetically and functionally. Recovered from a foodborne Vibrio alginolyticus strain that exhibits resistance to all known β-lactam antibiotics, pVB1796 is found to possess a hybrid backbone that exhibits unique features of both type 1 and type 2 IncC elements. VMB-1 exhibits 94% sequence homology with several recently reported but poorly characterized metallo-β-lactamases (MBLs) produced by the marine organisms Alteromonadaceae, Glaciecola, and Thalassomonas actiniarum. Sequence alignment analysis shows that VMB-1 shares a structurally identical active site with subclass B1 MBLs. Importantly, pVB1796 is found to be efficiently transferred from Vibrio to other Gram-negative bacterial pathogens, including Salmonella typhimurium, Klebsiella pneumoniae, and Acinetobacter baumanni, via conjugation. These findings suggest that blaVMB-1 -bearing plasmids have the potential to be disseminated to other Gram-negative bacterial pathogens in the near future and render carbapenems useless in treatment of multidrug resistant infections.

Chinese expert consensus on polymyxins in the clinical practice

Polymyxin, a polypeptide antibiotic, derived from the culture of bacillus polymucilis, was introduced in the 1950s and used in clinical practice, but was replaced by safer antimicrobials due to its renal toxicity. In the recent years, with the increasing incidence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) bacilli infections, polymyxin is reintroduced into the clinic because it is assumed an important role in the treatment of MDR infections and XDR infections. In order to regulate the clinical applications of polymyxin, we organized experts in relevant fields to develop expert consensus on polymyxin for reference, including parameters like pharmacokinetics and pharmacodynamics, dosage and usage, contraindications and relative contraindications, clinical applications and adverse reactions.

Cathelicidin-Derived Synthetic Peptide Improves Therapeutic Potential of Vancomycin Against Pseudomonas aeruginosa.

Pseudomonas aeruginosa (PA) is the leading cause of corneal blindness worldwide. A constant increase in multi-drug resistant PA strains have heightened the challenge of effectively managing corneal infections with conventional antibiotics. Antimicrobial peptides are promising antibiotic analogs with a unique mode of action. Cathelicidin-derived shorter peptides (FK13 and FK16) have previously been shown to kill a range of pathogens in both in vitro and in vivo systems. Here, our aim was to exploit the potential of FK13 or FK16 to enhance the anti-Pseudomonas activity of vancomycin, which normally has low clinical efficacy against PA. Our results have demonstrated that FK16 is more potent than FK13 against different PA strains including a clinical isolate from a patient’s ocular surface. FK16 was shown to enhance the membrane permeability of PAO1 at sub-inhibitory concentrations. Moreover, FK16 at lower concentrations was shown to increase the antibacterial susceptibility of vancomycin against PA strains up to eightfold. The bactericidal synergism between FK16 and vancomycin was shown to be stable in the presence of physiological tear salt concentration and did not cause toxic effects on the human corneal epithelial cells and human red blood cells. Our results have revealed that sub-inhibitory concentration of FK16 could augment the antimicrobial effects of vancomycin against PA. It is anticipated that the future exploitation of the peptide design approach may enhance the effectiveness of FK16 and its application as an adjuvant to antibiotic therapy for the treatment of multi-drug resistant infections.

Novel Antibiotics for Multidrug-Resistant Gram-Positive Microorganisms.

Increasing multidrug-resistance to Gram-positive pathogens, particularly to staphylococci, enterococci and streptococci, is a major problem, resulting in significant morbidity, mortality and healthcare costs. In recent years, only a small number of novel antibiotics effective against Gram-positive bacteria has been approved. This review will discuss the current evidence for novel branded antibiotics that are highly effective in the treatment of multidrug-resistant infections by Gram-positive pathogens, namely ceftobiprole, ceftaroline, telavancin, oritavancin, dalbavancin, tedizolid, besifloxacin, delafloxacin, ozenoxacin, and omadacycline. The mechanism of action, pharmacokinetics, microbiological spectrum, efficacy and safety profile will be concisely presented. As for any emerging antibiotic agent, resistance is likely to develop against these highly effective antibiotics. Only through appropriate dosing, utilization and careful resistance development monitoring will these novel antibiotics continue to treat Gram-positive pathogens in the future.

Alarmone Ap4A is elevated by aminoglycoside antibiotics and enhances their bactericidal activity

Second messenger molecules play important roles in the responses to various stimuli that can determine a cell's fate under stress conditions. Here, we report that lethal concentrations of aminoglycoside antibiotics result in the production of a dinucleotide alarmone metabolite-diadenosine tetraphosphate (Ap4A), which promotes bacterial cell killing by this class of antibiotics. We show that the treatment of Escherichia coli with lethal concentrations of kanamycin (Kan) dramatically increases the production of Ap4A. This elevation of Ap4A is dependent on the production of a hydroxyl radical and involves the induction of the Ap4A synthetase lysyl-tRNA synthetase (LysU). Ectopic alteration of intracellular Ap4A concentration via the elimination of the Ap4A phosphatase diadenosine tetraphosphatase (ApaH) and the overexpression of LysU causes over a 5,000-fold increase in bacterial killing by aminoglycosides. This increased susceptibility to aminoglycosides correlates with bacterial membrane disruption. Our findings provide a role for the alarmone Ap4A and suggest that blocking Ap4A degradation or increasing its synthesis might constitute an approach to enhance aminoglycoside killing potency by broadening their therapeutic index and thereby allowing lower nontoxic dosages of these antibiotics to be used in the treatment of multidrug-resistant infections.

New possibilities in antibacterial treatment of intra-abdominal infections caused by multiresistant microflora

To determine the place of new drugs with activity against multidrug resistant strains of microorganisms in the treatment of complicated intraabdominal infections. The incidence and distribution of pathogens isolated from intra-abdominal specimens in patients with intra-abdominal infections are analyzed. The current situation on the growth of resistant strains among pathogens causing intra-abdominal infections is rewied. New combined drugs for the treatment of multidrug resistant infections - ceftolozane/tazobactam and ceftazidim/avibactam plus metronidazole, has been suggested. Their potential role in empiric and targeted antibacterial treatment of complicated intraabdominal infections is defined. Taking into consideration local monitoring data and risk factors of multi resistant strains Ceftolozane/tazobactam in combination with metronidazole can be used in empiric regime of treatment. Due to the high activity on carbapenem resistant strains of Klebsiella pneumonia and the lack of alternatives, it is advisable to use Ceftazidim/avibactam for the targeted therapy.

Combination versus monotherapy for the treatment of infections due to carbapenem-resistant Enterobacteriaceae.

Combination therapy is a common strategy for treatment of multidrug resistant infections. Despite the strong twin rationales of improving efficacy and reducing resistance development, the evidence supporting this strategy remains controversial. The aims of this review are to assess the most recent studies supporting the use of combination therapy for treating infections because of carbapenem-resistant Enterobacteriaceae (CRE) and to highlight relevant areas for further research. Evidence supporting the use of combination therapy for the treatment of CRE remains limited to in-vitro experiments and observational studies with considerable risk of bias. Very few antibiotic combinations have been tested in well designed randomized controlled trials, making it difficult to draw general conclusions for clinical practice. Further studies are urgently needed to test the most promising synergistic combinations. New drugs potentially active against CRE should also to be tested in studies with adequate sample size and truly representative of the general patient population.

A Quantitative Model of Daptomycin Binding to Lipid Bilayers.

Daptomycin is a cyclic lipopeptide of clinical importance in the treatment of multidrug resistant infections, including those caused by methicillin-resistant S. aureus strains. Similar to many other antimicrobial peptides, daptomycin binds with preference to anionic membranes such as those typically found in prokaryotes. However, in contrast to most linear α-helical peptides, daptomycin binds to lipid bilayers only in the presence of calcium ions, and its activity in vivo is absolutely Ca2+-dependent. Here, we describe the early events that occur in the binding of daptomycin to lipid bilayers using a quantitative model to analyze both equilibrium and kinetic binding data. The goal of the analysis was to obtain a precise description of the early events that occur in the interaction of daptomycin with lipid and calcium ions at low daptomycin concentrations. In the course of the analysis, we also determined the rate and equilibrium constants for binding of daptomycin to lipid and Ca2+. The model used to describe the experimental data comprises a soluble daptomycin monomer that binds calcium ions in solution with low affinity, a soluble, Ca2+-bound dimer, and a 1:1 daptomycin-lipidCa complex. A strong interaction of daptomycin with Ca2+-complexed lipid, the amount of which depends on the availability of calcium ions in the bulk solution, appears central to its function.

The primary transcriptome, small RNAs and regulation of antimicrobial resistance in Acinetobacter baumannii ATCC 17978.

We present the first high-resolution determination of transcriptome architecture in the priority pathogen Acinetobacter baumannii. Pooled RNA from 16 laboratory conditions was used for differential RNA-seq (dRNA-seq) to identify 3731 transcriptional start sites (TSS) and 110 small RNAs, including the first identification in A. baumannii of sRNAs encoded at the 3′ end of coding genes. Most sRNAs were conserved among sequenced A. baumannii genomes, but were only weakly conserved or absent in other Acinetobacter species. Single nucleotide mapping of TSS enabled prediction of −10 and −35 RNA polymerase binding sites and revealed an unprecedented base preference at position +2 that hints at an unrecognized transcriptional regulatory mechanism. To apply functional genomics to the problem of antimicrobial resistance, we dissected the transcriptional regulation of the drug efflux pump responsible for chloramphenicol resistance, craA. The two craA promoters were both down-regulated >1000-fold when cells were shifted to nutrient limited medium. This conditional down-regulation of craA expression renders cells sensitive to chloramphenicol, a highly effective antibiotic for the treatment of multidrug resistant infections. An online interface that facilitates open data access and visualization is provided as ‘AcinetoCom’ (http://bioinf.gen.tcd.ie/acinetocom/).

Phenotypic changes associated with Colistin resistance due to Lipopolysaccharide loss in Acinetobacter baumannii

ABSTRACTAcinetobacter baumannii can acquire resistance to colistin via complete loss of lipopolysaccharide (LPS) biosynthesis due to mutations in the lpxA, lpxC and lpxD genes. However, although colistin is increasingly being used for the treatment of multidrug resistant infections, very few A. baumannii clinical isolates develop colistin resistance through loss of LPS biosynthesis. This may suggest that LPS loss affects virulence traits that play a role in the transmission and pathogenesis of A. baumannii. In this study we characterize multiple virulence phenotypes of colistin resistant, LPS-deficient derivatives of the ATCC 19606 strain and five multidrug resistant clinical isolates and their colistin resistant, LPS-deficient derivatives. Our results indicate that LPS loss results in growth defects compared to the parental strain in vitro both in laboratory media and human serum (competition indices of 0.58 and 7.0 × 10−7, respectively) and reduced ability to grow and disseminate in vivo (competition index 6.7 × 10−8). Infection with the LPS-deficient strain resulted in lower serum levels of pro-inflammatory cytokines TNF-α and IL-6 compared to the parent strain, and was less virulent in a mouse model of disseminated sepsis. LPS loss also significantly affected biofilm production, surface motility, growth under iron limitation and susceptibility to multiple disinfectants used in the clinical setting. These results demonstrate that LPS loss has a significant effect on multiple virulence traits, and may provide insight into the low incidence of colistin resistant strains lacking LPS that have been reported in the clinical setting.

An Exact Model of Daptomycin Binding to Lipid Bilayers: An Update

Daptomycin is a cyclic lipopeptide of clinical importance in the treatment of multi-drug resistant infections, including those caused by methicillin-resistant S. aureus (MRSA) strains. Similar to other antimicrobial peptides, daptomycin binds with preference to the anionic cytoplasmic membranes typically found in prokaryotes. However, in contrast to most linear, alpha-helical peptides, daptomycin binds to lipid bilayers only in the presence of calcium ions and its activity is absolutely calcium-dependent. We measured the interaction of daptomycin with anionic lipid membranes using kinetic binding experiments and equilibrium titrations. The data were analyzed using an exact model describing the interactions of daptomycin with the lipid bilayer that includes solution and membrane-bound states, and the influence of calcium ions on daptomycin-lipid interactions. A preliminary version of the model was presented at the Biophysical Society Meeting in 2017. Here, we present a more complete analysis.

Bacterial sepsis : Diagnostics and calculated antibiotic therapy.

The mortality of patients with sepsis and septic shock is still unacceptably high. An effective calculated antibiotic treatment within 1h of recognition of sepsis is an important target of sepsis treatment. Delays lead to an increase in mortality; therefore, structured treatment concepts form a rational foundation, taking relevant diagnostic and treatment steps into consideration. In addition to the assumed infection and individual risks of each patient, local resistance patterns and specific problem pathogens must be taken into account during the selection of anti-infective treatment. Many pathophysiologic alterations influence the pharmacokinetics (PK) of antibiotics during sepsis. The principle of standard dosing should be abandoned and replaced by an individual treatment approach with stronger weighting of the pharmacokinetics/pharmacodynamics (PK/PD) index of the substance groups. Although this is not yet the clinical standard, prolonged (or continuous) infusion of β‑lactam antibiotics and therapeutic drug monitoring (TDM) can help to achieve defined PK targets. Prolonged infusion is sufficient without TDM, but for continuous infusion, TDM is generally necessary. Afurther argument for individual PK/PD-oriented antibiotic approaches is the increasing number of infections due to multidrug-resistant (MDR) pathogens in the intensive care unit. For effective treatment, antibiotic stewardship teams (ABS teams) are becoming more established. Interdisciplinary cooperation of the ABS team with infectious disease (ID) specialists, microbiologists, and clinical pharmacists leads not only to rational administration of antibiotics, but also has a positive influence on treatment outcome. The gold standards for pathogen identification are still culture-based detection and microbiologic resistance testing for the various antibiotic groups. Despite the rapid investigation time, novel polymerase chain reaction(PCR)-based procedures for pathogen identification and resistance determination are currently only an adjunct to routine sepsis diagnostics, due to the limited number of studies, high costs, and limited availability. In complicated septic courses with multiple anti-infective therapies or recurrent sepsis, PCR-based procedures can be used in addition to treatment monitoring and diagnostics. Novel antibiotics represent potent alternatives in the treatment of MDR infections. Due to the often defined spectrum of pathogens and the practically (still) absent resistance, they are suitable for targeted treatment of severe MDR infections (therapy escalation). (Contribution available free of charge by "Free Access" [ https://link.springer.com/article/10.1007/s00101-017-0396-z ].).

Emergence of NDM-1-Producing Escherichia coli in Iran

Introduction: Carbapenems are a broad-spectrum class of beta-lactam antibiotics, which are used in treatment of multi-drug resistant infections. Unfortunately, global emerging and spreading of carbapenemase, especially New Delhi metallo β lactamase 1 (blaNDM-1), is a concern in the treatment of multi drug-resistant agents. Here, we report the appearance of blaNDM-1producing Escherichia coli (E. coli) in Iran for the first time. Case Presentation: In this study, 2 blaNDM-1producing E. coli strains were isolated from 2 burn wounds of patients in the Motahari hospital, Tehran. The isolates were resistant to carbapenems (imipenem, meropenem and ertapenem) and other common antibiotics except nitrofurantoin. Combined Disk Test showed that the isolates could not produce blaAmpC and blaKPC carbapenemase, whereas they can produce metallo-β-lactamases (MBL). However, genetic detection using Polymerase Chain Reaction amplification with specific primers for blaKPC, blaIMP, blaVIM-1, blaVIM-1 – blaVIM-37, and blaNDM-1genes showed that only the blaNDM-1gene is amplified from the resistant isolates. Further sequencing of PCR products confirmed the presence of the blaNDM-1gene in these isolates. Conclusions: The emerging of blaNDM-1producing E. coli is a new threat for to the health system in Iran, due to the spreading of the blaNDM-1gene among pathogenic bacteria, which resulted in the emergence of multi drug resistant photogenes. Therefore, early identification of these isolates is mandatory.

Pharmaceutical Approaches to Target Antibiotic Resistance Mechanisms.

There is urgent need for new therapeutic strategies to fight the global threat of antibiotic resistance. The focus of this Perspective is on chemical agents that target the most common mechanisms of antibiotic resistance such as enzymatic inactivation of antibiotics, changes in cell permeability, and induction/activation of efflux pumps. Here we assess the current landscape and challenges in the treatment of antibiotic resistance mechanisms at both bacterial cell and community levels. We also discuss the potential clinical application of chemical inhibitors of antibiotic resistance mechanisms as add-on treatments for serious drug-resistant infections. Enzymatic inhibitors, such as the derivatives of the β-lactamase inhibitor avibactam, are closer to the clinic than other molecules. For example, MK-7655, in combination with imipenem, is in clinical development for the treatment of infections caused by carbapenem-resistant Enterobacteriaceae and Pseudomonas aeruginosa, which are difficult to treat. In addition, other molecules targeting multidrug-resistance mechanisms, such as efflux pumps, are under development and hold promise for the treatment of multidrug resistant infections.

The intensive care medicine research agenda on multidrug-resistant bacteria, antibiotics, and stewardship.

To concisely describe the current standards of care, major recent advances, common beliefs that have been contradicted by recent trials, areas of uncertainty, and clinical studies that need to be performed over the next decade and their expected outcomes with regard to the management of multidrug-resistant (MDR) bacteria, antibiotic use, and antimicrobial stewardship in the intensive care unit (ICU) setting. Narrative review based on a systematic analysis of the medical literature, national and international guidelines, and expert opinion. The prevalence of infection of critically ill patients by MDR bacteria is rapidly evolving. Clinical studies aimed at improving understanding of the changing patterns of these infections in ICUs are urgently needed. Ideal antibiotic utilization is another area of uncertainty requiring additional investigations aimed at better understanding of dose optimization, duration of therapy, use of combination treatment, aerosolized antibiotics, and the integration of rapid diagnostics as a guide for treatment. Moreover, there is an imperative need to develop non-antibiotic approaches for the prevention and treatment of MDR infections in the ICU. Finally, clinical research aimed at demonstrating the beneficial impact of antimicrobial stewardship in the ICU setting is essential. These and other fundamental questions need to be addressed over the next decade in order to better understand how to prevent, diagnose, and treat MDR bacterial infections. Clinical studies described in this research agenda provide a template and set priorities for investigations that should be performed in this field.

An Exact Model of Daptomycin Binding to Lipid Bilayers

Daptomycin is a cyclic lipopeptide of clinical importance in the treatment of multi-drug resistant infections, including those caused by methicillin-resistant S. aureus (MRSA) strains. Similar to other antimicrobial peptides, daptomycin binds with preference to the anionic cytoplasmic membranes typically found in prokaryotes. However, in contrast to most linear, alpha-helical peptides, daptomycin binds to lipid bilayers only in the presence of calcium ions and its activity is absolutely calcium-dependent. We measured the interaction of daptomycin with anionic lipid membranes using kinetic binding experiments and equilibrium titrations. The data were analyzed using an exact model describing the interactions of daptomycin with the lipid bilayer that includes solution and membrane-bound states, and the influence of calcium ions on daptomycin-lipid interactions.

Characterization of antimicrobial activity and mechanisms of low amphipathic peptides with different α-helical propensity

Antimicrobial peptides (AMPs) serve as a defense mechanism within multicellular organisms and are attracting increasing attention because of their potential application in the treatment of multidrug-resistant infections. Amphipathicity has long been believed to be the most important consideration for the structural modification and design of both naturally occurring and synthetic AMPs. Previous studies indicated that disruptive amphipathicity formed by replacing the paired charged amino acid residues on the polar face of an amphipathic helix with tryptophan residues linked with hydrogen bonds on the basis of α-helical protein folding principles endowed the AMPs with increased cell selectivity. In an attempt to augment and hone this strategy further, we designed a series of imperfect amphipathic peptides by placing different types of amino acid residues at the hydrogen bond linked positions of α-helix structures to characterize their antimicrobial properties and mechanism of action. The d-Trp-substituted sequence (PRW4-d) showed greater antimicrobial potency than Cys-(C4), Asp-(D4), Ile-(I4), and Pro-(P4) substituted sequences, comparable to the l-Trp-substituted parent sequence (PRW4). Furthermore, the total replacement of Lys residues with Arg residues along the peptide sequence (PRW4-R) exhibited enhanced antimicrobial activity and cell selectivity. In addition, no cytotoxicity was observed among these synthetic peptides. PRW4-d and PRW4-R maintained their activities in the presence of physiological salts and human serum. The fluorescence spectroscopy, flow cytometry, and electron microscopy observations indicated that the optimized sequences exhibited excellent antimicrobial potency by inducing cytoplasmic membrane potential loss, membrane permeabilization and disruption. Collectively, the results could be useful for designing short AMPs with great antimicrobial activity and cell selectivity.