Comparative Pharmacodynamics of Single-Dose Oritavancin and Daily High-Dose Daptomycin Regimens against Vancomycin-Resistant Enterococcus faecium Isolates in an In Vitro Pharmacokinetic/Pharmacodynamic Model of Infection

There are limited therapeutic options to treat infections caused by vancomycin-resistant Enterococcus faecium (VREfm). The lipoglycopeptide oritavancin exhibits in vitro activity against this pathogen, although its utility against infections caused by VREfm has not been clinically established. In this study, the pharmacodynamic activity of free-drug levels associated with 12 mg/kg/day of daptomycin and a single 1,200-mg dose of oritavancin were determined against three VanA VREfm isolates in an in vitro pharmacokinetic/pharmacodynamic model.

Targeting a cell wall biosynthesis hot spot

Covering: up to 2017History points to the bacterial cell wall biosynthetic network as a very effective target for antibiotic intervention, and numerous natural product inhibitors have been discovered. In addition to the inhibition of enzymes involved in the multistep synthesis of the macromolecular layer, in particular, interference with membrane-bound substrates and intermediates essential for the biosynthetic reactions has proven a valuable antibacterial strategy. A prominent target within the peptidoglycan biosynthetic pathway is lipid II, which represents a particular "Achilles' heel" for antibiotic attack, as it is readily accessible on the outside of the cytoplasmic membrane. Lipid II is a unique non-protein target that is one of the structurally most conserved molecules in bacterial cells. Notably, lipid II is more than just a target molecule, since sequestration of the cell wall precursor may be combined with additional antibiotic activities, such as the disruption of membrane integrity or disintegration of membrane-bound multi-enzyme machineries. Within the membrane bilayer lipid II is likely organized in specific anionic phospholipid patches that form a particular "landing platform" for antibiotics. Nature has invented a variety of different "lipid II binders" of at least 5 chemical classes, and their antibiotic activities can vary substantially depending on the compounds' physicochemical properties, such as amphiphilicity and charge, and thus trigger diverse cellular effects that are decisive for antibiotic activity.

Vancomycin-Resistant Enterococci: Therapeutic Challenges in the 21st Century

Vancomycin-resistant enterococci are serious health threats due in part to their ability to persist in rugged environments and their propensity to acquire antibiotic resistance determinants. Enterococci have now established a home in our hospitals and possess mechanisms to defeat most currently available antimicrobials. This article reviews the history of the struggle with this pathogen, what is known about the traits associated with its rise in the modern medical environment, and the current understanding of therapeutic approaches in severe infections caused by these microorganisms. As the 21st century progresses, vancomycin-resistant enterococci continue to pose a daunting clinical challenge.

Emergence of dalbavancin non-susceptible, vancomycin-intermediate Staphylococcus aureus (VISA) after treatment of MRSA central line-associated bloodstream infection with a dalbavancin- and vancomycin-containing regimen

OBJECTIVES

Dalbavancin is a long-acting lipoglycopeptide with activity against gram-positives, including methicillin-resistant Staphylococcus aureus (MRSA). The potential for lipoglycopeptides, with half-lives greater than 1 week, to select for resistance is unknown. Here we explore a case of MRSA central line-associated bloodstream infection in which dalbavancin and vancomycin non-susceptibility emerged in a urine isolate collected after the patient was treated with vancomycin and dalbavancin sequentially.

METHODS

Isolates from blood and urine underwent susceptibility testing, and whole genome sequencing (WGS). The blood isolate was subjected to successive passage in vitro in the presence of escalating dalbavancin concentrations and the emergent isolate was subjected to repeat susceptibility testing and WGS.

RESULTS

The blood isolate was fully susceptible to vancomycin; however, MICs of the urine isolate to dalbavancin, vancomycin, telavancin, and daptomycin were at least fourfold higher than the blood-derived strain. Both strains were indistinguishable by spa and variable number tandem repeat (VNTR) typing, and WGS revealed only seven variants, indicating clonality. Four variants affected genes, including a 3bp in-frame deletion in yvqF, a gene which has been implicated in glycopeptide resistance. Vancomycin and dalbavancin non-susceptibility emerged in the blood isolate after successive passage in vitro in the presence of dalbavancin, and WGS identified a single non-synonymous variant in yvqF.

CONCLUSIONS

This is the first case in which VISA has emerged in the context of a dalbavancin-containing regimen. The selection for cross-resistance to vancomycin in vitro by dalbavancin exposure alone is troubling. Clinicians should be aware of the possibility for emergence of dalbavancin non-susceptibility and glycopeptide cross-resistance arising following therapy.

Peripheral modifications of [Ψ[CH2NH]Tpg4]vancomycin with added synergistic mechanisms of action provide durable and potent antibiotics

Subsequent to binding pocket modifications designed to provide dual d-Ala-d-Ala/d-Ala-d-Lac binding that directly overcome the molecular basis of vancomycin resistance, peripheral structural changes have been explored to improve antimicrobial potency and provide additional synergistic mechanisms of action. A C-terminal peripheral modification, introducing a quaternary ammonium salt, is reported and was found to provide a binding pocket-modified vancomycin analog with a second mechanism of action that is independent of d-Ala-d-Ala/d-Ala-d-Lac binding. This modification, which induces cell wall permeability and is complementary to the glycopeptide inhibition of cell wall synthesis, was found to provide improvements in antimicrobial potency (200-fold) against vancomycin-resistant Enterococci (VRE). Furthermore, it is shown that this type of C-terminal modification may be combined with a second peripheral (4-chlorobiphenyl)methyl (CBP) addition to the vancomycin disaccharide to provide even more potent antimicrobial agents [VRE minimum inhibitory concentration (MIC) = 0.01-0.005 μg/mL] with activity that can be attributed to three independent and synergistic mechanisms of action, only one of which requires d-Ala-d-Ala/d-Ala-d-Lac binding. Finally, it is shown that such peripherally and binding pocket-modified vancomycin analogs display little propensity for acquired resistance by VRE and that their durability against such challenges as well as their antimicrobial potency follow now predictable trends (three > two > one mechanisms of action). Such antibiotics are expected to display durable antimicrobial activity not prone to rapidly acquired clinical resistance.

Managing acute bacterial skin and skin structure infections: Focus on new lipoglycopeptides

Acute bacterial skin and skin structure infections (ABSSSI) are some of the most commonly encountered infections worldwide. Hospitalizations as a result of ABSSSI are associated with high mortality. This article discusses the role of oritavancin and dalbavancin, two new lipoglycopeptides, in the context of the other I.V. available standard therapy options.

Single-Dose Dalbavancin: A Review in Acute Bacterial Skin and Skin Structure Infections

Intravenous dalbavancin (Dalvance^®, Xydalba^®), first approved as a two-dose regimen for the treatment of acute bacterial skin and skin structure infections (ABSSSI), has now been additionally approved as a single-dose regimen. This narrative review discusses the pharmacological properties of intravenous dalbavancin and its clinical efficacy and tolerability as a single-dose regimen in the treatment of adult patients with ABSSSI. Single-dose dalbavancin is an effective and generally well tolerated treatment option for adults with ABSSSI, with noninferior efficacy to the two-dose dalbavancin regimen with regard to early clinical response (at 48-72 h) and low rates of adverse events. Clinical success rates at days 14 and 28 also did not significantly differ between the single- and two-dose dalbavancin regimens; neither did clinical success rates at day 14 when analysed by baseline pathogen. It has a broad spectrum of activity against common ABSSSI-related pathogens, and a favourable pharmacokinetic profile allowing for the convenience of single-dose administration. Thus, dalbavancin presents a promising alternative to conventional antibacterials for the treatment of ABSSSI in adult patients.

Telavancin: a novel semisynthetic lipoglycopeptide agent to counter the challenge of resistant Gram-positive pathogens

Telavancin (TD-6424), a semisynthetic lipoglycopeptide vancomycin-derivative, is a novel antimicrobial agent developed by Theravance for overcoming resistant Gram-positive bacterial infections, specifically methicillin-resistant Staphylococcus aureus (MRSA). The US Food and Drug Administration (USFDA) had approved telavancin in 2009 for the treatment of complicated skin and skin structure infections (cSSSIs) caused by Gram-positive bacteria, including MRSA (S. aureus, Streptococcus agalactiae, Streptococcus pyogenes, Streptococcus anginosus group, or Enterococcus faecalis). Telavancin has two proposed mechanisms of action. In vitro, telavancin has a rapid, concentration-dependent bactericidal effect, due to disruption of cell membrane integrity. Telavancin has demonstrable in vitro activity against aerobic and anaerobic Gram-positive bacteria. Telavancin and vancomycin have similar spectra of activity. Gram-negative bacteria are usually non-susceptible to telavancin. Telavancin has been successfully tested in various animal models of bacteremia, endocarditis, meningitis, and pneumonia. Phase II Telavancin versus Standard Therapy for Treatment of Complicated Skin and Soft-Tissue Infections due to Gram-Positive Bacteria (FAST 1 and FAST 2) and phase III [Assessment of Telavancin in Complicated Skin and Skin Structure Infections 1 (ATLAS 1 and ATLAS 2)] clinical trials have been conducted for evaluating telavancin's efficacy and safety in cSSSIs. Phase III clinical trials have been carried out for evaluating telavancin's safety and efficacy in nosocomial pneumonia [Assessment of Telavancin for Treatment of Hospital acquired Pneumonia 1 and 2 (ATTAIN 1 and ATTAIN 2)]. A phase II randomized, double-blind, clinical trial has been carried out for evaluating telavancin's safety and efficacy in uncomplicated S. aureus bacteremia [Telavancin for Treatment of Uncomplicated S. aureus Bacteremia (ASSURE)]. Pacemaker lead-related infective endocarditis due to a vancomycin intermediate S. aureus (VISA) strain (non-daptomycin susceptible) was successfully treated with parenteral telavancin for 8 weeks. Telavancin extensively binds to serum albumin (~93%) and has a relatively small volume of distribution. Telavancin is not biotransformed by any cytochrome P450 microsomal enzymes and excreted mainly in the urine. Though well-tolerated, worrisome adverse effects, including renal dysfunction and QTc prolongation are of potential concern. Given its extensive binding to plasma proteins, long half-life, and a long post-antibiotic effect, it represents a promising addition to the therapeutic armamentarium in combating infections caused by resistant Gram-positive pathogens, namely, MRSA.

A review on cell wall synthesis inhibitors with an emphasis on glycopeptide antibiotics

Cell wall biosynthesis inhibitors (CBIs) have historically been one of the most effective classes of antibiotics. They are the most extensively used class of antibiotics and their importance is exemplified by the β-lactams and glycopeptide antibiotics. However, this class of antibiotics has not received impunity from resistance development. In the wake of this predicament, this review presents the progress of CBIs, especially glycopeptide derivatives as antibiotics to confront antibacterial resistance. The various strategies used for the development of CBIs, their clinical status and possible directions in which this field can evolve have also been discussed.

What's new in multidrug-resistant pathogens in the ICU?

Over the last several decades, antibacterial drug use has become widespread with their misuse being an ever-increasing phenomenon. Consequently, antibacterial drugs have become less effective or even ineffective, resulting in a global health security emergency. The prevalence of multidrug-resistant organisms (MDROs) varies widely among regions and countries. The primary aim of antibiotic stewardship programs is to supervise the three most influential factors contributing to the development and transmission of MDROs, namely: (1) appropriate antibiotic prescribing; (2) early detection and prevention of cross-colonization of MDROs; and (3) elimination of reservoirs. In the future, it is expected that a number of countries will experience a rise in MDROs. These infections will be associated with a high consumption of healthcare resources manifested by a prolonged hospital stay and high mortality. As a counteractive strategy, minimization of broad-spectrum antibiotic use and prompt antibiotic administration will aid in reduction of antibiotic resistance. Innovative management approaches include development and implementation of rapid diagnostic tests that will help in both shortening the duration of therapy and allowing early targeted therapy. The institution of more accessible therapeutic drug monitoring will help to optimize drug administration and support a patient-specific approach. Areas where further research is required are investigation into the heterogeneity of critically ill patients and the need for new antibacterial drug development.

Approved Glycopeptide Antibacterial Drugs: Mechanism of Action and Resistance

The glycopeptide antimicrobials are a group of natural product and semisynthetic glycosylated peptides that show antibacterial activity against Gram-positive organisms through inhibition of cell-wall synthesis. This is achieved primarily through binding to the d-alanyl-d-alanine terminus of the lipid II bacterial cell-wall precursor, preventing cross-linking of the peptidoglycan layer. Vancomycin is the foundational member of the class, showing both clinical longevity and a still preferential role in the therapy of methicillin-resistant Staphylococcus aureus and of susceptible Enterococcus spp. Newer lipoglycopeptide derivatives (telavancin, dalbavancin, and oritavancin) were designed in a targeted fashion to increase antibacterial activity, in some cases through secondary mechanisms of action. Resistance to the glycopeptides emerged in delayed fashion and occurs via a spectrum of chromosome- and plasmid-associated elements that lead to structural alteration of the bacterial cell-wall precursor substrates.

Glycopeptide resistance: Links with inorganic phosphate metabolism and cell envelope stress

Antimicrobial resistance is a critical health issue today. Many pathogens have become resistant to many or all available antibiotics and limited new antibiotics are in the pipeline. Glycopeptides are used as a 'last resort' antibiotic treatment for many bacterial infections, but worryingly, glycopeptide resistance has spread to very important pathogens such as Enterococcus faecium and Staphylococcus aureus. Bacteria confront multiple stresses in their natural environments, including nutritional starvation and the action of cell-wall stressing agents. These stresses impact bacterial susceptibility to different antimicrobials. This article aims to review the links between glycopeptide resistance and different stresses, especially those related with cell-wall biosynthesis and inorganic phosphate metabolism, and to discuss promising alternatives to classical antibiotics to avoid the problem of antimicrobial resistance.

Newly approved antibiotics and antibiotics reserved for resistant infections: Implications for emergency medicine

Millions of patients are evaluated every year in the emergency department (ED) for bacterial infections. Emergency physicians often diagnose and prescribe initial antibiotic therapy for a variety of bacterial infections, ranging from simple urinary tract infections to severe sepsis. In life-threatening infections, inappropriate choice of initial antibiotic has been shown to increase morbidity and mortality. As such, initiation of appropriate antibiotic therapy on the part of the emergency physician is critical. Increasing rates of antibiotic resistance, drug allergies, and antibiotic shortages further complicates the choice of antibiotics. Patients may have a history of prior resistant infections or culture data indicating that common first-line antibiotics used in the ED may be ineffective. In recent years, there have been several new antibiotic approvals as well as renewed interest in second and third line antibiotics because of the aforementioned concerns. In addition, several newly approved antibiotics have the advantage of being administered once weekly or even as a single infusion, which has the potential to decrease hospitalizations and healthcare costs. This article reviews newly approved antibiotics and antibiotics used to treat resistant infections with a focus on implications for emergency medicine.

History of antimicrobial drug discovery: Major classes and health impact

The introduction of antibiotics into clinical practice revolutionized the treatment and management of infectious diseases. Before the introduction of antibiotics, these diseases were the leading cause of morbidity and mortality in human populations. This review presents a brief history of discovery of the main antimicrobial classes (arsphenamines, β-lactams, sulphonamides, polypeptides, aminoglycosides, tetracyclines, amphenicols, lipopeptides, macrolides, oxazolidinones, glycopeptides, streptogramins, ansamycins, quinolones, and lincosamides) that have changed the landscape of contemporary medicine. Given within a historical timeline context, the review discusses how the introduction of certain antimicrobial classes affected the morbidity and mortality rates due to bacterial infectious diseases in human populations. Problems of resistance to antibiotics of different classes are also extensively discussed.

Reprofiled anthelmintics abate hypervirulent stationary-phase Clostridium difficile

Prolonged use of broad-spectrum antibiotics disrupts the indigenous gut microbiota, which consequently enables toxigenic Clostridium difficile species to proliferate and cause infection. The burden of C. difficile infections was exacerbated with the outbreak of hypervirulent strains that produce copious amounts of enterotoxins and spores. In recent past, membrane-active agents have generated a surge of interest due to their bactericidal property with a low propensity for resistance. In this study, we capitalized on the antimicrobial property and low oral bioavailability of salicylanilide anthelmintics (closantel, rafoxanide, niclosamide, oxyclozanide) to target the gut pathogen. By broth microdilution techniques, we determined the MIC values of the anthelmintics against 16 C. difficile isolates of defined PCR-ribotype. The anthelmintics broadly inhibited C. difficile growth in vitro via a membrane depolarization mechanism. Interestingly, the salicylanilides were bactericidal against logarithmic- and stationary-phase cultures of the BI/NAP1/027 strain 4118. The salicylanilides were poorly active against select gut commensals (Bacteroides, Bifidobacterium and Lactobacillus species), and were non-hemolytic and non-toxic to mammalian cell lines HepG2 and HEK 293T/17 within the range of their in vitro MICs and MBCs. The salicylanilide anthelmintics exhibit desirable properties for repositioning as anti-C. difficile agents.

Clinical pathway for moderate to severe acute bacterial skin and skin structure infections from a US perspective: a roundtable discussion

This article was written with the aim to establish a consensus clinical pathway for long-acting lipoglycopeptide antibiotics such as oritavancin (Orbactiv®) and dalbavancin (Dalvance®) for the treatment of acute bacterial skin and skin structure infections (ABSSSI). Seven infectious diseases pharmacy specialists from a variety of facilities across the United States (US) participated in a roundtable discussion to consider the use of newer single-dose long-acting lipoglycopeptides, and integrate them into clinical pathways for ABSSSI. They identified two ways of treating with these drugs: first, to facilitate discharge from the hospital by switching from initial therapy (e.g., with intravenous (IV) vancomycin) and second, to avoid hospital admission altogether, since the product can be administered in several outpatient settings of care including the emergency department (ED), observation unit (OU) or outpatient infusion center. The participants used existing literature on classification and treatment of ABSSSI and their experience in the clinical setting as bases for their discussion and came to a consensus on the considerations for patient inclusion and exclusion as well as a pathway for outpatient treatment with long-acting lipoglycopeptides. As a result of the discussion, we concluded that the current treatment paradigm for ABSSSI is ripe for re-evaluation and reconfiguration in order to more closely align with the changing healthcare landscape. Hospital stakeholders are constantly searching for new strategies that can improve quality of care while simultaneously reducing overall expenses. The availability of single-dose long-acting lipoglycopeptides is an opportunity to opt for lower-cost outpatient treatment of appropriate ABSSSI patients. This article proposes the inclusion and exclusion considerations, along with a consensus treatment pathway, that could provide a solid foundation for facilities to construct and adapt their own effective clinical pathways for ABSSSI.

Evaluation of Pharmacodynamic Interactions Between Telavancin and Aztreonam or Piperacillin/Tazobactam Against Pseudomonas aeruginosa, Escherichia coli and Methicillin-Resistant Staphylococcus aureus

Introduction

In clinical trials comparing telavancin (TLV) with vancomycin for treatment of hospital-acquired pneumonia, TLV demonstrated lower clinical cure rates than vancomycin in patients who had mixed gram-positive and -negative infections and were concomitantly treated with either aztreonam (ATM) or piperacillin/tazobactam (PTZ). Here, we investigated therapeutic interactions between TLV and ATM or PTZ in an in vitro pharmacokinetic/pharmacodynamic (PK/PD) model under simulated reduced renal function conditions.

Methods

In vitro one-compartment PK/PD models were run over 96 h simulating TLV 10 mg/kg every 48 h, ATM 500 mg every 8 h and PTZ continuous infusion 13.5 g over 24 h alone and in combination against P. aeruginosa, E. coli and methicillin-resistant S. aureus (MRSA). The efficacy of antimicrobials was evaluated by plotting time-kill curves and calculating the reduction in log₁₀ cfu/ml over 96 h.

Results

Against both MRSA strains, TLV was rapidly bactericidal at 4 h and maintained its activity over 96 h with no observed antagonism by either ATM or PTZ. PTZ maintained bacteriostatic and bactericidal activities against E. coli ATCC 25922 and clinical strain R1022 at 96 h, whereas both strains regrew as soon as 24 h in ATM models. Against P. aeruginosa ATCC 27853, regrowth was noted at 24 h in models simulating ATM and PTZ. The addition of TLV to ATM or PTZ had no appreciable impact on activity against the two E. coli strains and P. aeruginosa strain.

Conclusions

The combinations of TLV and either ATM or PTZ did not demonstrate any antagonistic activity. Clinical variables and patient characteristics should be further explored to determine possible reasons for discrepancies in outcomes.

Funding

Theravance Biopharma Antibiotics, Inc.

New Approaches to Antibiotic Use and Review of Recently Approved Antimicrobial Agents

Antimicrobial drug-resistance continues to force adaptation in our clinical practice. We explore new evidence regarding adjunctive antibiotic therapy for skin and soft tissue abscesses as well as duration of therapy for intra-abdominal abscesses. As new evidence refines optimal practice, it is essential to support clinicians in adopting practice patterns concordant with evidence-based guidelines. We review a simple approach that can 'nudge' clinicians towards concordant practices. Finally, the use of novel antimicrobials will play an increasingly important role in contemporary therapy. We review five new antimicrobials recently FDA-approved for use in drug-resistant infections: dalbavancin, oritavancin, ceftaroline, ceftolozane-tazobactam, and ceftazidime-avibactam.

Antibiotics in the clinical pipeline at the end of 2015

There is growing global recognition that the continued emergence of multidrug-resistant bacteria poses a serious threat to human health. Action plans released by the World Health Organization and governments of the UK and USA in particular recognize that discovering new antibiotics, particularly those with new modes of action, is one essential element required to avert future catastrophic pandemics. This review lists the 30 antibiotics and two β-lactamase/β-lactam combinations first launched since 2000, and analyzes in depth seven new antibiotics and two new β-lactam/β-lactamase inhibitor combinations launched since 2013. The development status, mode of action, spectra of activity and genesis (natural product, natural product-derived, synthetic or protein/mammalian peptide) of the 37 compounds and six β-lactamase/β-lactam combinations being evaluated in clinical trials between 2013 and 2015 are discussed. Compounds discontinued from clinical development since 2013 and new antibacterial pharmacophores are also reviewed.

Comparative In Vitro Activities of Oritavancin, Dalbavancin, and Vancomycin against Methicillin-Resistant Staphylococcus aureus Isolates in a Nondividing State

Antibacterial agents that kill nondividing bacteria may be of utility in treating persistent infections. Oritavancin and dalbavancin are bactericidal lipoglycopeptides that are approved for acute bacterial skin and skin structure infections in adults caused by susceptible Gram-positive pathogens. Using time-kill methodology, we demonstrate that oritavancin exerts bactericidal activity against methicillin-resistant Staphylococcus aureus (MRSA) isolates that are maintained in a nondividing state in vitro, whereas dalbavancin and the glycopeptide vancomycin do not.

Telavancin: mechanisms of action, in vitro activity, and mechanisms of resistance

Telavancin is a semisynthetic lipoglycopeptide derivative of vancomycin. Telavancin has a dual mechanism of antibacterial action, disrupting peptidoglycan synthesis and cell membrane function. In 2014, the Clinical and Laboratory Standards Institute (CLSI) revised the antimicrobial susceptibility testing method for telavancin, resulting in minimum inhibitory concentration (MIC) determinations that are more accurate and reproducible and demonstrate greater in vitro potency than shown with the previous testing method. The CLSI testing method changes coincided with revised telavancin MIC interpretive break point criteria for susceptibility approved by the US Food and Drug Administration for Staphylococcus aureus (≤0.12 µg/mL), Streptococcus pyogenes (≤0.12 µg/mL), Streptococcus agalactiae (≤0.12 µg/mL), Streptococcus anginosus group (≤0.06 µg/mL), and Enterococcus faecalis (vancomycin susceptible, ≤0.25 µg/mL). Telavancin is equally potent against methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). It demonstrates activity against isolates of heterogeneous vancomycin-intermediate S. aureus and vancomycin-intermediate S. aureus but is poorly active against vancomycin-resistant S. aureus. It also demonstrates potent activity against Staphylococcus epidermidis and Streptococcus spp. (MIC90 ≤0.03 µg/mL). Thus far, it has not been possible to select for high-level telavancin resistance in the laboratory using serially passaged clinical isolates of MRSA and MSSA.

Evolving resistance among Gram-positive pathogens

Antimicrobial therapy is a key component of modern medical practice and a cornerstone for the development of complex clinical interventions in critically ill patients. Unfortunately, the increasing problem of antimicrobial resistance is now recognized as a major public health threat jeopardizing the care of thousands of patients worldwide. Gram-positive pathogens exhibit an immense genetic repertoire to adapt and develop resistance to virtually all antimicrobials clinically available. As more molecules become available to treat resistant gram-positive infections, resistance emerges as an evolutionary response. Thus, antimicrobial resistance has to be envisaged as an evolving phenomenon that demands constant surveillance and continuous efforts to identify emerging mechanisms of resistance to optimize the use of antibiotics and create strategies to circumvent this problem. Here, we will provide a broad perspective on the clinical aspects of antibiotic resistance in relevant gram-positive pathogens with emphasis on the mechanistic strategies used by these organisms to avoid being killed by commonly used antimicrobial agents.

Clinical efficacy of dalbavancin for the treatment of acute bacterial skin and skin structure infections (ABSSSI)

Acute bacterial skin and skin structure infections (ABSSSI) are a common disease causing patients to seek treatment through the health care system. With the continued increase of drug-resistant bacterial pathogens, these infections are becoming more difficult to successfully cure. Lipoglycopeptides have unique properties that allow the drug to remain active toward both common and challenging pathogens at the infected site for lengthy periods of time. Dalbavancin, a new lipoglycopeptide, provides two unique dosing regimens for the treatment of ABSSSI. The original regimen of 1,000 mg intravenous infusion followed by a 500 mg intravenous infusion after a week has been shown as safe and effective in multiple, randomized noninferiority trials. These studies also demonstrated that dalbavancin was similar to standard regimens in terms of both safety and tolerability. Recently a single 1,500 mg dose was demonstrated to be equivalent to the dalbavancin two-dose regimen for treating ABSSSI. With the introduction of dalbavancin, clinicians have the option to provide an intravenous antimicrobial agent shown to be as effective as traditional therapies, without requiring admission into the hospitals or prescribing a medication which may not be utilized optimally. Further understanding of dalbavancin and its unusual properties can provide unique treatment situations with potential benefits for both the patient and the overall health care system, which should be further explored.

Bacteremia due to Methicillin-Resistant Staphylococcus aureus: New Therapeutic Approaches

This article reviews recent clinical evidence for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) bacteremia. Vancomycin remains the initial antibiotic of choice for the treatment of patients with MRSA bacteremia and endocarditis due to isolates with vancomycin minimum inhibitory concentration ≤2 μg/mL, whereas daptomycin is an effective alternative, and ceftaroline seems promising. Treatment options for persistent MRSA bacteremia or bacteremia due to vancomycin-intermediate or vancomycin-resistant strains include daptomycin, ceftaroline, and combination therapies. There is a critical need for high-level evidence from clinical trials to allow optimally informed decisions in the treatment of MRSA bacteremia and endocarditis.

Dalbavancin Activity When Tested against Streptococcus pneumoniae Isolated in Medical Centers on Six Continents (2011 to 2014)

Dalbavancin, a novel lipoglycopeptide, was approved for use in 2014 by regulatory agencies in the United States and Europe for the treatment of skin and skin structure infections. The activity of dalbavancin was also widely assessed by determination of its activity against Streptococcus pneumoniae clinical isolates collected from patients on six continents monitored during two time intervals (2011 to 2013 and 2014). A total of 18,186 pneumococcal isolates were obtained from 49 nations and submitted to a monitoring laboratory as part of the SENTRY Antimicrobial Surveillance Program for reference susceptibility testing. The potency of dalbavancin against S. pneumoniae was consistent across the years that it was monitored, with the MIC50 and MIC90 being 0.015 and 0.03 μg/ml, respectively, and all isolates were inhibited by ≤0.12 μg/ml. The activity of dalbavancin was not adversely influenced by nonsusceptibility to β-lactams (ceftriaxone or penicillin), macrolides, clindamycin, fluoroquinolones, or tetracyclines or multidrug resistance (MDR). Regional variations in dalbavancin activity were not detected, but S. pneumoniae strains isolated in the Asia-Pacific region were more likely to be nonsusceptible to penicillin and ceftriaxone as well as to be MDR than strains isolated in North or South America and Europe. Direct comparisons of potency illustrated that dalbavancin (MIC50 and MIC90, 0.015 and 0.03 μg/ml, respectively) was 16-fold or more active than vancomycin (MIC50, 0.25 μg/ml), linezolid (MIC50, 1 μg/ml), levofloxacin (MIC50, 1 μg/ml), ceftriaxone (MIC90, 1 μg/ml), and penicillin (MIC90, 2 μg/ml). In conclusion, dalbavancin had potent and consistent activity against this contemporary (2011 to 2014) collection of S. pneumoniae isolates.

Reversing resistance: The next generation antibacterials

Irrational antibiotic usage has led to vast spread resistance to available antibiotics, but we refuse to slide back to “preantibiotic era.” The threat is serious with the “Enterococcus, Staphylococcous, Klebsiella, Acinetobacter, Pseudomonas and Enterobacter” organisms causing nosocomial infections that are difficult to treat because of the production of extended spectrum β-lactamases, carbapenamases and metallo-β-lactamases. Facing us is a situation where soon multidrug resistance would have spread across the globe with no antibiotics to withstand it. The infectious disease society of America and Food and Drug Administration have taken initiatives like the 10 × ‘20 where they plan to develop 10 new antibiotics by the year 2020. Existing classes of antibiotics against resistant bacteria include the carbapenems, oxazolidinones, glycopeptides, monobactams, streptogramins and daptomycin. Newer drugs in existing classes of antibiotics such as cephalosporins, aminoglycosides, tetracyclines, glycopeptides and β-lactamase inhibitors continue to get synthesized. The situation demands newer targets against bacterial machinery. Some of them include the peptidoglycantransferase, outer membrane protein of Pseudomonas, tRNA synthase, fatty acid synthase and mycobacterial ATP synthase. To curb the irrational and excessive usage of presently available antibiotics should be a priority if they are still to be kept in usage for the future.

New Is Old, and Old Is New: Recent Advances in Antibiotic-Based, Antibiotic-Free and Ethnomedical Treatments against Methicillin-Resistant Staphylococcus aureus Wound Infections

Staphylococcus aureus is the most common pathogen of wound infections. Thus far, methicillin-resistant S. aureus (MRSA) has become the major causative agent in wound infections, especially for nosocomial infections. MRSA infections are seldom eradicated by routine antimicrobial therapies. More concerning, some strains have become resistant to the newest antibiotics of last resort. Furthermore, horizontal transfer of a polymyxin resistance gene, mcr-1, has been identified in Enterobacteriaceae, by which resistance to the last group of antibiotics will likely spread rapidly. The worst-case scenario, "a return to the pre-antibiotic era", is likely in sight. A perpetual goal for antibiotic research is the discovery of an antibiotic that lacks resistance potential, such as the recent discovery of teixobactin. However, when considering the issue from an ecological and evolutionary standpoint, it is evident that it is insufficient to solve the antibiotic dilemma through the use of antibiotics themselves. In this review, we summarized recent advances in antibiotic-based, antibiotic-free and ethnomedical treatments against MRSA wound infections to identify new clues to solve the antibiotic dilemma. One potential solution is to use ethnomedical drugs topically. Some ethnomedical drugs have been demonstrated to be effective antimicrobials against MRSA. A decline in antibiotic resistance can therefore be expected, as has been demonstrated when antibiotic-free treatments were used to limit the use of antibiotics. It is also anticipated that these drugs will have low resistance potential, although there is only minimal evidence to support this claim to date. More clinical trials and animal tests should be conducted on this topic.

Kisameet Clay Isolated from the Central Coast of British Columbia, Canada, Demonstrates Broad-Spectrum Antimicrobial Activity

Clay minerals are naturally occurring layered phyllosilicates which consist of fine particles and possess antimicrobial activity. In a recent article, Behroozian et al. obtained Kisameet clay (KC) from Kisameet, from the central coast of British Columbia, Canada, northwest of Vancouver and assessed its antimicrobial activity versus 16 selected ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) possessing a variety of different resistance profiles [S. Behroozian, S. L. Svensson, and J. Davies, mBio 7(1):e01842-15, 2016, http://dx.doi.org/10.1128/mBio.01842-15]. KC demonstrated complete bacterial eradication of Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Staphylococcus aureus within 24 h. For Enterobacter spp., the organisms were eradicated with 1% KC within 5 h, while for Enterococcus faecium, it took 48 h to kill all organisms. Although many questions need to be answered, these exciting findings highlight the importance of testing natural substances/products from around the globe to assess whether they possess antimicrobial activity and potential for usage as topical, oral, or systemic agents for the treatment of multidrug-resistant pathogens.

New drugs for the treatment of complicated intra-abdominal infections in the era of increasing antimicrobial resistance

The continuing increase in multidrug-resistant organisms (MDROs) worldwide has created new challenges in treating complicated intra-abdominal infections (cIAIs). A number of novel antimicrobial agents have been developed against resistant pathogens. To target extended-spectrum β-lactamase (ESBL)-producing pathogens, novel β-lactam antibiotics, such as ceftolozane/tazobactam, ceftazidime/avibactam, aztreonam/avibactam, imipenem/relebactam and S-649266, are antimicrobial alternatives for cIAIs. Two new drugs, eravacycline and plazomicin, have activity against Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae, carbapenem-resistant Acinetobacter baumannii and ESBL-producers. New lipoglycopeptides and oxazolidinones provide feasible options against resistant Gram-positive pathogens. These novel antimicrobials may play a role in improving the clinical outcomes of cIAIs caused by MDROs.

New developments in the treatment of acute bacterial skin and skin structure infections: considerations for the effective use of dalbavancin

Dalbavancin, an intravenous glycopeptide, was approved by the US Food and Drug Administration in May 2014 for use in adult patients with acute bacterial skin and skin structure infections. The recommended dosing regimen for effective use of dalbavancin is 1,000 mg followed by a 500 mg dose after 1 week. Two multinational, identically designed, non-inferiority trials, DISCOVER 1 and 2, demonstrated similar early clinical success with dalbavancin compared to vancomycin with an option to switch to oral linezolid. In a recently published non-inferiority trial, a single-dose regimen of dalbavancin was compared to the traditional two-dose administration and was found to have a non-inferior clinical response. In the aforementioned trials, dalbavancin was well tolerated, with patients experiencing transient adverse events of mild to moderate severity. The prolonged half-life, excellent skin and soft tissue penetration, bactericidal activity against Gram-positive bacteria including methicillin-resistant Staphylococcus aureus, and convenient dosing make dalbavancin a reasonable option for the treatment of acute bacterial skin and skin structure infections in adult patients who have tried and failed other therapies.

Intracellular activity of a membrane-active glycopeptide antibiotic against meticillin-resistant Staphylococcus aureus infection

Staphylococcus aureus is a facultative intracellular pathogen and there are limited options for the treatment of severe intracellular bacterial infections. The membrane-active glycopeptide antibiotic Van-QC8 is a permanent positively charged lipophilic vancomycin analogue that demonstrates high activity against clinically relevant drug-resistant Gram-positive bacteria both in vitro and in vivo. In this study, the intracellular activity of Van-QC8 was evaluated against meticillin-resistant S. aureus (MRSA) infection in RAW macrophages. Furthermore, the mechanism of intracellular uptake of Van-QC8 was investigated. Van-QC8 showed time- and concentration-dependent bactericidal activity against intracellular MRSA. Van-QC8 displayed significantly higher intracellular activity compared with vancomycin and linezolid. Cellular uptake of Van-QC8 was found to be through clathrin-dependent and -independent and caveolin-dependent and -independent endocytic pathways. The findings of this study suggest that Van-QC8 could be translated clinically for the treatment of intracellular infections due to MRSA.

Glycopeptide antibiotic analogs for selective inactivation and two-photon imaging of vancomycin-resistant strains

Theranostic divalent vancomycin systems exhibit selective antibacterial activity against vancomycin-resistant strains and can be applied for two-photon fluorescence imaging.

Insights into the Mechanism of Action of Bactericidal Lipophosphonoxins

The advantages offered by established antibiotics in the treatment of infectious diseases are endangered due to the increase in the number of antibiotic-resistant bacterial strains. This leads to a need for new antibacterial compounds. Recently, we discovered a series of compounds termed lipophosphonoxins (LPPOs) that exhibit selective cytotoxicity towards Gram-positive bacteria that include pathogens and resistant strains. For further development of these compounds, it was necessary to identify the mechanism of their action and characterize their interaction with eukaryotic cells/organisms in more detail. Here, we show that at their bactericidal concentrations LPPOs localize to the plasmatic membrane in bacteria but not in eukaryotes. In an in vitro system we demonstrate that LPPOs create pores in the membrane. This provides an explanation of their action in vivo where they cause serious damage of the cellular membrane, efflux of the cytosol, and cell disintegration. Further, we show that (i) LPPOs are not genotoxic as determined by the Ames test, (ii) do not cross a monolayer of Caco-2 cells, suggesting they are unable of transepithelial transport, (iii) are well tolerated by living mice when administered orally but not peritoneally, and (iv) are stable at low pH, indicating they could survive the acidic environment in the stomach. Finally, using one of the most potent LPPOs, we attempted and failed to select resistant strains against this compound while we were able to readily select resistant strains against a known antibiotic, rifampicin. In summary, LPPOs represent a new class of compounds with a potential for development as antibacterial agents for topical applications and perhaps also for treatment of gastrointestinal infections.

A stepwise dechlorination/cross-coupling strategy to diversify the vancomycin 'in-chloride'

In an effort to rapidly access vancomycin analogues bearing diverse functionality at the 6c-Cl (the 'in-chloride') position, a two-step dechlorination/cross-coupling protocol was developed. Conditions for efficient cross-coupling of the relatively unreactive 6c-Cl group were found that ensure high conversion with minimal product decomposition. A set of 2c-dechloro-6c-functionalized vancomycin derivatives was prepared, and antibiotic activities of the compounds were evaluated against a panel of vancomycin-resistant and vancomycin-susceptible strains. Results from biological testing further underscore the steric sensitivity of vancomycin's binding pocket.

Tedizolid: a novel oxazolidinone with potent activity against multidrug-resistant gram-positive pathogens

Tedizolid phosphate is a novel oxazolidinone prodrug (converted to the active form tedizolid by phosphatases in vivo) that has been developed and recently approved (June 2014) by the United States FDA for the treatment of acute bacterial skin and skin structure infections (ABSSSIs) caused by susceptible Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). Tedizolid is an oxazolidinone, but differs from other oxazolidinones by possessing a modified side chain at the C-5 position of the oxazolidinone nucleus which confers activity against certain linezolid-resistant pathogens and has an optimized C- and D-ring system that improves potency through additional binding site interactions. The mechanism of action of tedizolid is similar to other oxazolidinones and occurs through inhibition of bacterial protein synthesis by binding to 23S ribosomal RNA (rRNA) of the 50S subunit of the ribosome. As with other oxazolidinones, the spontaneous frequency of resistance development to tedizolid is low. Tedizolid is four- to eightfold more potent in vivo than linezolid against all species of staphylococci, enterococci, and streptococci, including drug-resistant phenotypes such as MRSA and vancomycin-resistant enterococci (VRE) and linezolid-resistant phenotypes. Importantly, tedizolid demonstrates activity against linezolid-resistant bacterial strains harboring the horizontally transmissible cfr gene, in the absence of certain ribosomal mutations conferring reduced oxazolidinone susceptibility. With its half-life of approximately 12 h, tedizolid is dosed once daily. It demonstrates linear pharmacokinetics, has a high oral bioavailability of approximately 90 %, and is primarily excreted by the liver as an inactive, non-circulating sulphate conjugate. Tedizolid does not require dosage adjustment in patients with any degree of renal dysfunction or hepatic dysfunction. Studies in animals have demonstrated that the pharmacodynamic parameter most closely associated with the efficacy of tedizolid is fAUC(0-24h)/MIC. In non-neutropenic animals, a dose-response enhancement was observed with tedizolid and lower exposures were required compared to neutropenic cohorts. Two Phase III clinical trials have demonstrated non-inferiority of a once-daily tedizolid 200 mg dose for 6-10 days versus twice-daily 600 mg linezolid for the treatment of ABSSSIs. Both trials used the primary endpoint of early clinical response at 48-72 h; however, one trial compared oral formulations while the other initiated therapy with the parenteral formulation and allowed oral sequential therapy following initial clinical response. Throughout its development, tedizolid has demonstrated that it is well tolerated and animal studies have shown a lower propensity for neuropathies with long-term use than its predecessor linezolid. Data from the two completed Phase III clinical trials demonstrated that the studied tedizolid regimen (200 mg once daily for 6 days) had significantly less impact on hematologic parameters as well as significantly less gastrointestinal treatment-emergent adverse effects (TEAEs) than its comparator linezolid. As with linezolid, tedizolid is a weak, reversible MAO inhibitor; however, a murine head twitch model validated to assess serotonergic activity reported no increase in the number of head twitches with tedizolid even at doses that exceeded the C max in humans by up to 25-fold. Tyramine and pseudoephedrine challenge studies in humans have also reported no meaningful MAO-related interactions with tedizolid. With its enhanced in vitro activity against a broad-spectrum of Gram-positive aerobic bacteria, convenient once-daily dosing, a short 6-day course of therapy, availability of both oral and intravenous routes of administration, and an adverse effect profile that appears to be more favorable than linezolid, tedizolid is an attractive agent for use in both the hospital and community settings. Tedizolid is currently undergoing additional Phase III clinical trials for the treatment of hospital-acquired bacterial pneumonia (HABP) and ventilated nosocomial pneumonia (VNP).

Lipophilic vancomycin aglycon dimer with high activity against vancomycin-resistant bacteria

Antibiotic-resistant superbugs such as vancomycin-resistant Enterococci (VRE) and Staphylococci have become a major global health hazard. To address this issue, we synthesized vancomycin aglycon dimers to systematically probe the impact of a linker on biological activity. A dimer having a pendant lipophilic moiety in the linker showed ∼300-fold more activity than vancomycin against VRE. The high activity of the compound is attributed to its enhanced binding affinity to target peptides which resulted in improved peptidoglycan (cell wall) biosynthesis inhibition. Therefore, our studies suggest that these compounds, prepared by using facile synthetic methodology, can be used to combat vancomycin-resistant bacterial infections.