Daptomycin – a novel antibiotic against Gram-positive pathogens

Daptomycin-Impregnated PMMA Cement against Vancomycin-Resistant Germs: Dosage, Handling, Elution, Mechanical Stability, and Effectiveness

BACKGROUND

The number of periprosthetic joint infections caused by vancomycin-resistant pathogens is increasing. Currently, no PMMA cement is commercially available to cover VRE. Daptomycin shows promising results in treating infection, offering a good safety profile and a reduced risk of developing resistance. The purpose of this in vitro study was to investigate the mechanical stability, handling properties, elution behavior, and antimicrobial effectiveness of PMMA cement loaded with three different daptomycin concentrations in comparison to commercially available antibiotic-loaded bone cement (ALBC).

METHODS

Mechanical properties and handling characteristics (ISO 5833, DIN 53435), HPLC elution, antimicrobial effectiveness with proliferation assay (DIN 17025), and inhibition zone testing were investigated.

RESULTS

All tested daptomycin concentrations met the ISO and DIN standards for mechanical strength. Loading of 40 g of PMMA cement with 0.5 g of daptomycin did not show any antimicrobial effectiveness, in contrast to 1.0 g and 1.5 g. PMMA cement with 1.5 g of daptomycin was the best in terms of elution and effectiveness, and it showed good ISO mechanical strength; ISO doughing was sticky for a little longer and setting was faster compared to the vancomycin-containing reference cement.

CONCLUSION

PMMA cement containing 0.5 g of gentamicin and 1.5 g of daptomycin could be a good alternative to the already established COPAL® (Wehrheim, Germany) G+V for the treatment of PJIs caused by VRE.

Natural products acting against S. aureus through membrane and cell wall disruption

Covering: 2015 to 2022Staphylococcus aureus (S. aureus) is responsible for several community and hospital-acquired infections with life-threatening complications such as bacteraemia, endocarditis, meningitis, liver abscess, and spinal cord epidural abscess. In recent decades, the abuse and misuse of antibiotics in humans, animals, plants, and fungi and the treatment of nonmicrobial diseases have led to the rapid emergence of multidrug-resistant pathogens. The bacterial wall is a complex structure consisting of the cell membrane, peptidoglycan cell wall, and various associated polymers. The enzymes involved in bacterial cell wall synthesis are established antibiotic targets and continue to be a central focus for antibiotic development. Natural products play a vital role in drug discovery and development. Importantly, natural products provide a starting point for active/lead compounds that sometimes need modification based on structural and biological properties to meet the drug criteria. Notably, microorganisms and plant metabolites have contributed as antibiotics for noninfectious diseases. In this study, we have summarized the recent advances in understanding the activity of the drugs or agents of natural origin that directly inhibit the bacterial membrane, membrane components, and membrane biosynthetic enzymes by targeting membrane-embedded proteins. We also discussed the unique aspects of the active mechanisms of established antibiotics or new agents.

Staphylococcus aureus Sensitivity to Membrane Disrupting Antibacterials Is Increased under Microgravity

In a survey of the International Space Station (ISS), the most common pathogenic bacterium identified in samples from the air, water and surfaces was Staphylococcus aureus. While growth under microgravity is known to cause physiological changes in microbial pathogens, including shifts in antibacterial sensitivity, its impact on S. aureus is not well understood. Using high-aspect ratio vessels (HARVs) to generate simulated microgravity (SMG) conditions in the lab, we found S. aureus lipid profiles are altered significantly, with a higher presence of branch-chained fatty acids (BCFAs) (14.8% to 35.4%) with a concomitant reduction (41.3% to 31.4%) in straight-chain fatty acids (SCFAs) under SMG. This shift significantly increased the sensitivity of this pathogen to daptomycin, a membrane-acting antibiotic, leading to 12.1-fold better killing under SMG. Comparative assays with two additional compounds, i.e., SDS and violacein, confirmed S. aureus is more susceptible to membrane-disrupting agents, with 0.04% SDS and 0.6 mg/L violacein resulting in 22.9- and 12.8-fold better killing in SMG than normal gravity, respectively. As humankind seeks to establish permanent colonies in space, these results demonstrate the increased potency of membrane-active antibacterials to control the presence and spread of S. aureus, and potentially other pathogens.

New Mutations in cls Lead to Daptomycin Resistance in a Clinical Vancomycin- and Daptomycin-Resistant Enterococcus faecium Strain

Daptomycin (DAP), a last-resort antibiotic for treating Gram-positive bacterial infection, has been widely used in the treatment of vancomycin-resistant enterococci (VRE). Resistance to both daptomycin and vancomycin leads to difficulties in controlling infections of enterococci. A clinical multidrug-resistant Enterococcus faecium EF332 strain that shows resistance to both daptomycin and vancomycin was identified, for which resistance mechanisms were investigated in this work. Whole-genome sequencing and comparative genomic analysis were performed by third-generation PacBio sequencing, showing that E. faecium EF332 contains four plasmids, including a new multidrug-resistant pEF332-2 plasmid. Two vancomycin resistance-conferring gene clusters vanA and vanM were found on this plasmid, making it the second reported vancomycin-resistant plasmid containing both clusters. New mutations in chromosomal genes cls and gdpD that, respectively, encode cardiolipin synthase and glycerophosphoryl diester phosphodiesterase were identified. Their potential roles in leading to daptomycin resistance were further investigated. Through molecular cloning and phenotypic screening, two-dimensional thin-layer chromatography, fluorescence surface charge test, and analysis of cardiolipin distribution patterns, we found that mutations in cls decrease surface negative charges of the cell membrane (CM) and led to redistribution of lipids of CM. Both events contribute to the DAP resistance of E. faecium EF332. Mutation in gdpD leads to changes in CM phospholipid compositions, but cannot confer DAP resistance. Neither mutation could result in changes in cellular septa. Therefore, we conclude that the daptomycin resistance of E. faecium EF332 is conferred by new cls mutations. This work reports the genetic basis for vancomycin and daptomycin resistance of a multidrug-resistant E. faecium strain, with the finding of new mutations of cls that leads to daptomycin resistance.

PaP1, a Broad-Spectrum Lysin-Derived Cationic Peptide to Treat Polymicrobial Skin Infections

Most skin infections, including those complicating burns, are polymicrobial involving multiple causative bacteria. Add to this the fact that many of these organisms may be antibiotic-resistant, and a simple skin lesion or burn could soon become life-threatening. Membrane-acting cationic peptides from Gram-negative bacteriophage lysins can potentially aid in addressing the urgent need for alternative therapeutics. Such peptides natively constitute an amphipathic region within the structural composition of these lysins and function to permit outer membrane permeabilization in Gram-negative bacteria when added externally. This consequently allows the lysin to access and degrade the peptidoglycan substrate, resulting in rapid hypotonic lysis and bacterial death. When separated from the lysin, some of these cationic peptides kill sensitive bacteria more effectively than the native molecule via both outer and cytoplasmic membrane disruption. In this study, we evaluated the antibacterial properties of a modified cationic peptide from the broad-acting lysin PlyPa01. The peptide, termed PaP1, exhibited potent in vitro bactericidal activity toward numerous high priority Gram-positive and Gram-negative pathogens, including all the antibiotic-resistant ESKAPE pathogens. Both planktonic and biofilm-state bacteria were sensitive to the peptide, and results from time-kill assays revealed PaP1 kills bacteria on contact. The peptide was bactericidal over a wide temperature and pH range and could withstand autoclaving without loss of activity. However, high salt concentrations and complex matrices were found to be largely inhibitory, limiting its use to topical applications. Importantly, unlike other membrane-acting antimicrobials, PaP1 lacked cytotoxicity toward human cells. Results from a murine burn wound infection model using methicillin-resistant Staphylococcus aureus or multidrug-resistant Pseudomonas aeruginosa validated the in vivo antibacterial efficacy of PaP1. In these studies, the peptide enhanced the potency of topical antibiotics used clinically for treating chronic wound infections. Despite the necessity for additional preclinical drug development, the collective data from our study support PaP1 as a potential broad-spectrum monotherapy or adjunctive therapy for the topical treatment of polymicrobial infections and provide a foundation for engineering future lysin-derived peptides with improved antibacterial properties.

Air Ambulance: Antimicrobial Power of Bacterial Volatiles

We are currently facing an antimicrobial resistance crisis, which means that a lot of bacterial pathogens have developed resistance to common antibiotics. Hence, novel and innovative solutions are urgently needed to combat resistant human pathogens. A new source of antimicrobial compounds could be bacterial volatiles. Volatiles are ubiquitous produced, chemically divers and playing essential roles in intra- and interspecies interactions like communication and antimicrobial defense. In the last years, an increasing number of studies showed bioactivities of bacterial volatiles, including antibacterial, antifungal and anti-oomycete activities, indicating bacterial volatiles as an exciting source for novel antimicrobial compounds. In this review we introduce the chemical diversity of bacterial volatiles, their antimicrobial activities and methods for testing this activity. Concluding, we discuss the possibility of using antimicrobial volatiles to antagonize the antimicrobial resistance crisis.

The Emerging Role of β-Lactams in the Treatment of Methicillin-Resistant Staphylococcus aureus Bloodstream Infections

Methicillin-resistant Staphylococcus aureus (MRSA) bloodstream infections (BSI) are associated with substantial morbidity and mortality. Monotherapy with first-line antimicrobials such as vancomycin (VAN; glycopeptide) and daptomycin (DAP; lipopeptide) are inadequate in some cases due to reduced antibiotic susceptibilities or therapeutic failure. In recent years, β-lactam antibiotics have emerged as a potential option for combination therapy with VAN and DAP that may meet an unmet therapeutic need for MRSA BSI. Ceftaroline (CPT), the only commercially available β-lactam in the United States with intrinsic in vitro activity against MRSA, has been increasingly studied in the setting of VAN and DAP failures. Novel combinations of first-line agents (VAN and DAP) with β-lactams have been the subject of many recent investigations due to in vitro findings such as the "seesaw effect," where β-lactam susceptibility may be improved in the presence of decreased glycopeptide and lipopeptide susceptibility. The combination of CPT and DAP, in particular, has become the focus of many scientific evaluations, due to intrinsic anti-MRSA activities and potent in vitro synergistic activity against various MRSA strains. This article reviews the available literature describing these innovative therapeutic approaches for MRSA BSI, focusing on preclinical and clinical studies, and evaluates the potential benefits and limitations of each strategy.

Calculated initial parenteral treatment of bacterial infections: Safety and tolerabilty

This is the fourth chapter of the guideline "Calculated initial parenteral treatment of bacterial infections in adults - update 2018" in the 2nd updated version. The German guideline by the Paul-Ehrlich-Gesellschaft für Chemotherapie e.V. (PEG) has been translated to address an international audience. Safety and tolerability of antimicrobial agents will be discussed in this chapter. Toxic, allergic and biological effects can be differentiated on the basis of their pathogenesis. The question of differences in the tolerability of specific antibiotics is of particular importance. However, due to limitations of the available data, it cannot be answered for most agents with the desired accuracy. For an assessment of rare side effects, results from the postmarketing surveillance have to be used.

Development and Challenges of Antimicrobial Peptides for Therapeutic Applications

More than 3000 antimicrobial peptides (AMPs) have been discovered, seven of which have been approved by the U.S. Food and Drug Administration (FDA). Now commercialized, these seven peptides have mostly been utilized for topical medications, though some have been injected into the body to treat severe bacterial infections. To understand the translational potential for AMPs, we analyzed FDA-approved drugs in the FDA drug database. We examined their physicochemical properties, secondary structures, and mechanisms of action, and compared them with the peptides in the AMP database. All FDA-approved AMPs were discovered in Gram-positive soil bacteria, and 98% of known AMPs also come from natural sources (skin secretions of frogs and toxins from different species). However, AMPs can have undesirable properties as drugs, including instability and toxicity. Thus, the design and construction of effective AMPs require an understanding of the mechanisms of known peptides and their effects on the human body. This review provides an overview to guide the development of AMPs that can potentially be used as antimicrobial drugs.

Efficacy of chimeric ectolysin P128 in drug-resistant Staphylococcus aureus bacteraemia in mice

Objectives

P128 is a recombinant chimeric ectolysin with potent antistaphylococcal activity. P128 was evaluated as monotherapy and in combination with two standard-of-care (SoC) antibiotics, vancomycin and daptomycin, in mouse models of Staphylococcus aureus bacteraemia.

Methods

Healthy BALB/c mice were challenged (intraperitoneally) with 109 cfu of MRSA strain COL or USA300 and treated with a single dose of P128 (0.2-10 mg/kg). Drug synergy was tested using a single dose of P128 (0.2 or 2.5 mg/kg) along with sub-therapeutic dose levels of vancomycin (27.5 or 55 mg/kg) or daptomycin (12.5 mg/kg). Bacterial load was checked in peritoneal fluid and in blood, at different time intervals. Synergy against drug-resistant strains was tested using the P128/vancomycin combination against vancomycin-resistant S. aureus (VRSA).

Results

In MRSA bacteraemia, P128, vancomycin and daptomycin monotherapy resulted in 31%, 46% and 46% survival, respectively. The P128/vancomycin and P128/daptomycin combinations afforded increased survival of 85% and 88%, respectively. P128 showed a rapid bactericidal effect with a reduction of cfu in both the peritoneal fluid and the blood within 1 h. In VRSA bacteraemia, a mouse-equivalent therapeutic dose of vancomycin (110 mg/kg) failed to rescue animals. P128 (1-20 mg/kg) as monotherapy resulted in dose-dependent efficacy. Survival (37%) with 2.5 mg/kg P128 increased to 63% with the P128/vancomycin combination.

Conclusions

P128 exerted a rapid bactericidal effect in vivo and rescued animals from fatal invasive MRSA and VRSA infections. P128/SoC antibiotic combinations exerted a synergistic effect. P128 restored the susceptibility of VRSA to vancomycin. P128 is a novel, potent therapeutic agent for antibiotic-resistant, systemic S. aureus infections.

Evaluation of treatment options for methicillin-resistant Staphylococcus aureus infections in the obese patient

Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as a major cause of infection in both the hospital and community setting. Obesity is a risk factor for infection, and the prevalence of this disease has reached epidemic proportions worldwide. Treatment of infections in this special population is a challenge given the lack of data on the optimal antibiotic choice and dosing strategies, particularly for treatment of MRSA infections. Obesity is associated with various physiological changes that may lead to altered pharmacokinetic parameters. These changes include altered drug biodistribution, elimination, and absorption. This review provides clinicians with a summary of the literature pertaining to the pharmacokinetic and pharmacodynamic considerations when selecting antibiotic therapy for the treatment of MRSA infections in obese patients.

High-Dose Daptomycin Is Effective as an Antibiotic Lock Therapy in a Rabbit Model of Staphylococcus epidermidis Catheter-Related Infection

Long-term catheter-related bloodstream infections (CRBSIs) involving coagulase-negative staphylococci are associated with poor patient outcomes, increased hospitalization, and high treatment costs. The use of vancomycin lock therapy has been an important step forward in treatment of these biofilms, although failures occur in 20% of patients. In this study, we report that a high dose of daptomycin lock therapy may offer a therapeutic advantage for these CRBSIs in just 24 h of treatment.

Therapeutic Drug Monitoring of Daptomycin: A Retrospective Monocentric Analysis

BACKGROUND

Daptomycin dose is adjusted to body weight and renal function and is usually not guided by therapeutic drug monitoring. Daptomycin plasma concentration measurement was established at our institution in January 2009 and is now increasingly being used. The aim of this study was to describe and characterize variability in daptomycin exposure during routine clinical therapy.

METHODS

We collected daptomycin plasma concentrations that were measured at our institution during the period January 2009-July 2012. Additional clinical and demographic data and their association with daptomycin exposure were tested by a multilevel linear regression analysis.

RESULTS

A total of 332 daptomycin plasma concentrations were determined in 86 patients. Sixty-six percent (n = 218) of all determinations were trough concentrations (Cmin), and 34% (n = 114) were peak concentrations (Cmax). Cmin ranged 2-68 mg/L (median, 16.7 mg/L), and Cmax 20-236 mg/L (median, 66.2 mg/L). A significant positive association of total dose, albumin, creatinine and a significant negative association of dose interval and intermittent hemodialysis with Cmin were found in the regression analysis. Total dose and intensive care unit (ICU) stay were significantly associated with Cmax (P < 0.05). However, only 28% (P < 0.005) of Cmin variability and 8% (P = 0.08) of Cmax variability were explained by the factors included in the analysis.

CONCLUSIONS

Daptomycin plasma concentrations are often unpredictable as shown by highly variable drug exposure that is only partially explained by dose administered and underlying renal function.

Daptomycin: an evidence-based review of its role in the treatment of Gram-positive infections

Infections caused by Gram-positive pathogens remain a major public health burden and are associated with high morbidity and mortality. Increasing rates of infection with Gram-positive bacteria and the emergence of resistance to commonly used antibiotics have led to the need for novel antibiotics. Daptomycin, a cyclic lipopeptide with rapid bactericidal activity against a wide range of Gram-positive bacteria including methicillin-resistant Staphylococcus aureus, has been shown to be effective and has a good safety profile for the approved indications of complicated skin and soft tissue infections (4 mg/kg/day), right-sided infective endocarditis caused by S. aureus, and bacteremia associated with complicated skin and soft tissue infections or right-sided infective endocarditis (6 mg/kg/day). Based on its pharmacokinetic profile and concentration-dependent bactericidal activity, high-dose (>6 mg/kg/day) daptomycin is considered an important treatment option in the management of various difficult-to-treat Gram-positive infections. Although daptomycin resistance has been documented, it remains uncommon despite the increasing use of daptomycin. To enhance activity and to minimize resistance, daptomycin in combination with other antibiotics has also been explored and found to be beneficial in certain severe infections. The availability of daptomycin via a 2-minute intravenous bolus facilitates its outpatient administration, providing an opportunity to reduce risk of health care-associated infections, improve patient satisfaction, and minimize health care costs. Daptomycin, not currently approved for use in the pediatric population, has been shown to be widely used for treating Gram-positive infections in children.

Towards a definition of daptomycin optimal dose: Lessons learned from experimental and clinical data

Daptomycin exhibits excellent antibacterial activity against a wide range of Gram-positive bacteria. The on-label standard daily doses for daptomycin are 4 mg/kg for skin infections and 6 mg/kg for bacteraemia or right-sided endocarditis. Daptomycin bactericidal activity is predominantly concentration-dependent and by considering the values of pharmacokinetic targets established by several authors as well as the peak and trough concentrations of daptomycin obtained at various daily dosages, it appears that these targets can easily be reached with a dose of 6 mg/kg but only for a minimum inhibitory concentration (MIC) at 0.1 mg/L, and that for increasing MICs (e.g. 0.5 mg/L or 1 mg/L) these targets may only be attained with higher dosages (i.e. ≥10 mg/kg). High-dose (HD) daptomycin therapy has also been proven to be effective for reducing the risk of selection of daptomycin-resistant strains. Given the concentration-dependent bactericidal activity of daptomycin, the absence of a dose-toxicity relationship and the need to prevent the selection of resistant strains, we propose to consider for staphylococcal (i) skin and soft-tissue infections, daily doses of daptomycin of 6 mg/kg (new standard dose) and (ii) endocarditis or bacteraemia including those associated with intravascular catheter and implant-related infections, ≥10 mg/kg (HD) when the MIC is unknown or >0.25 mg/L, and 6-10 mg/kg (intermediate doses) when the MIC is ≤0.25 mg/L. For severe and deep-seated enterococcal infections, we propose high (≥10 mg/kg) daily doses of daptomycin in combination with another active agent, especially a β-lactam.

Evaluation of High-Dose Daptomycin Versus Vancomycin Alone or Combined with Clarithromycin or Rifampin Against Staphylococcus aureus and S. epidermidis in a Novel In Vitro PK/PD Model of Bacterial Biofilm

INTRODUCTION

Medical device infections are associated with significant morbidity and mortality. These difficult-to-treat infections often result in antibiotic failure and resistance. Combination therapy is often required, however, the most optimal combination is unknown. We evaluated the in vitro activity of daptomycin (DAP) or vancomycin (VAN) alone and in combination with rifampin (RIF) or clarithromycin (CLA) against strains of Staphylococcus aureus and S. epidermidis grown in biofilm on 3 prosthetic device materials.

METHODS

One methicillin-resistant S. aureus (MRSA R5266), one heteroresistant vancomycin-intermediate S. aureus (hVISA R3640), and one methicillin-resistant S. epidermidis (MRSE R461) strain was evaluated in a CDC biofilm reactor with titanium, Teflon®, and steel coupons. Regimens simulated included DAP 10 mg/kg/day, and VAN 1 g q12h alone or in combination with RIF 600 mg q24h or CLA 250 mg q12h. Additional regimens including DAP 12 mg/kg/day or VAN ± RIF 450 mg q12h were evaluated against the hVISA strain.

RESULTS

DAP + RIF or VAN + RIF demonstrated enhanced activity against R3640 in embedded biofilm (EB) cells in all materials versus DAP or VAN alone (P ≤ 0.040). Only DAP + RIF demonstrated sustained bactericidal activity (≥3.80 log10 CFU/cm2 reduction from baseline) against EB and planktonic cells of R5266 and EB cells of R461 in all 3 materials. Of interest, CLA did not appear to enhance DAP or VAN killing activities, and the addition of RIF prevented the emergence of resistance to DAP or VAN in all organisms.

CONCLUSION

Using an in vitro bacterial biofilm model containing three common prosthetic device materials, DAP + RIF and VAN + RIF were the most effective regimens. DAP + RIF displayed the greatest activity and represents a promising combination to evaluate for treatment of biofilm-associated staphylococcal infections.

High-dose daptomycin therapy for staphylococcal endocarditis and when to apply it

Infective endocarditis (IE) continues to present a large burden to the health-care system. Staphylococcus aureus, the leading pathogen associated with the disease, has always proven difficult to treat. Increasing numbers of S. aureus isolates are demonstrating reduced susceptibility to vancomycin, and therapeutic options are limited. Daptomycin is frequently employed when vancomycin therapy proves unsuccessful or when vancomycin minimum inhibitory concentration (MIC) values rise above 1 mg/L. Currently, daptomycin is FDA-approved at a dose of 6 mg/kg/day for the treatment of S. aureus bacteremia and associated right-sided endocarditis. However, numerous in vitro and clinical studies suggest that daptomycin doses up to 12 mg/kg/day may provide improved efficacy and resistance prevention. Additionally, high-dose daptomycin has demonstrated excellent safety. Together, these data suggest a role for high-dose daptomycin in staphylococcal IE patients who are severely ill, previously failed therapy with vancomycin, or possess a S. aureus isolate with an elevated vancomycin MIC.

Simple and validated UHPLC method coupled to UV detection for determination of daptomycin in human plasma and urine

Daptomycin, a lipopeptide antibiotic with excellent activity against Gram-positive bacteria, is excreted primarily by the kidneys. Development of effective chromatographic methodologies for the determination of daptomycin in human specimens is necessary for clinical use. This study developed a simple and validated ultra-high-performance liquid chromatography method coupled to ultraviolet detection for determination of daptomycin in human plasma and urine. After the pretreatments involving protein precipitation, the supernatants were separated using a 2.3 µm particle size octadecylsilyl column, and the run time was 1 min. The calibration curves were linear over the concentration ranges of 2-200 mg/L for plasma and 25-300 mg/L for urine. Intra- and inter-assay precision and accuracy values of plasma were within 13.5 and 92-100% and within 10.7 and 100-107%, respectively. Those of urine were within 5.0 and 101-104% and within 3.7 and 100-101%, respectively. The validated method was applied to the determination of plasma and urine samples in patients receiving 4-6 mg/kg of intravenous daptomycin, resulting in sufficient sensitivity for evaluating the plasma exposure and urinary excretion. In conclusion, the present method with acceptable analytical performance can be helpful for evaluating the pharmacokinetic disposition of daptomycin in clinical settings.

Cyclic lipodepsipeptides: a new class of antibacterial agents in the battle against resistant bacteria

In order to provide effective treatment options for infections caused by multidrug-resistant bacteria, innovative antibiotics are necessary, preferably with novel modes of action and/or belonging to novel classes of drugs. Naturally occurring cyclic lipodepsipeptides, which contain one or more ester bonds along with the amide bonds, have emerged as promising candidates for the development of new antibiotics. Some of these natural products are either already marketed or in advanced stages of clinical development. However, despite the progress in the development of new antibacterial agents, it is inevitable that resistant strains of bacteria will emerge in response to the widespread use of a particular antibiotic and limit its lifetime. Therefore, development of new antibiotics remains our most efficient way to counteract bacterial resistance.

Enhancing the antibiotic antibacterial effect by sub lethal tellurite concentrations: tellurite and cefotaxime act synergistically in Escherichia coli

The emergence of antibiotic-resistant pathogenic bacteria during the last decades has become a public health concern worldwide. Aiming to explore new alternatives to treat antibiotic-resistant bacteria and given that the tellurium oxyanion tellurite is highly toxic for most microorganisms, we evaluated the ability of sub lethal tellurite concentrations to strengthen the effect of several antibiotics. Tellurite, at nM or µM concentrations, increased importantly the toxicity of defined antibacterials. This was observed with both Gram negative and Gram positive bacteria, irrespective of the antibiotic or tellurite tolerance of the particular microorganism. The tellurite-mediated antibiotic-potentiating effect occurs in laboratory and clinical, uropathogenic Escherichia coli, especially with antibiotics disturbing the cell wall (ampicillin, cefotaxime) or protein synthesis (tetracycline, chloramphenicol, gentamicin). In particular, the effect of tellurite on the activity of the clinically-relevant, third-generation cephalosporin (cefotaxime), was evaluated. Cell viability assays showed that tellurite and cefotaxime act synergistically against E. coli. In conclusion, using tellurite like an adjuvant could be of great help to cope with several multi-resistant pathogens.

Update on the appropriate use of linezolid in clinical practice

Multi-antibiotic resistant Gram-positive cocci, which include Staphylococcus aureus, the coagulase-negative staphylococcal group, Enterococcus faecalis and Enterococcus faecium, and other streptococci, represent emerging pathogens especially in the setting of the immunocompromised, hospitalized patients, in particular when surgery, invasive procedures, or prosthetic implants are of concern, patients are admitted in intensive care units, or underlying chronic disorders and immunodeficiency are of concern, and broad-spectrum antibiotics or immunosuppressive drugs are widely administered. During the recent years, the phenomenon of multiresistant Gram-positive cocci is spreading to the community, where the retrieval of such microorganism is progressively increasing. The spectrum of available antimicrobial compounds for an effective management of these relevant infections is significantly impaired in selection and clinical efficacy by the emerging and spread of methicillin-resistant and more recently glycopeptide-resistant Gram-positive microbial strains. The first oxazolidinone derivative linezolid, together with the recently licensed quinupristin–dalfopristin, daptomycin, and tigecycline, followed by a number of glycopeptides, fluoroquinolones, and other experimental compounds on the pipeline, represent an effective response to the great majority of these concerns, due to their innovative mechanisms of action, their maintained or enhanced activity against multiresistant pathogens, their effective pharmacokinetic/pharmacodynamic properties, their frequent possibility of synergistic activity with other compounds effective against Gram-positive pathogens, and a diffuse potential for a safe and easy administration, also when compromised patients are of concern. The main problems related to the epidemiological and clinical features of multiresistant Gram-positive infection, the potential clinical indications of all recently available compounds compared with the standard of care of treatment of resistant Gram-positive infections, and updated data on efficacy and tolerability of linezolid as the golden standard compound for vancomycin-resistant Gram-positive cocci in multiple clinical situations, are outlined and updated on the ground of an extensive review of all the available, recent evidences coming from the international literature.

Update on cutaneous manifestations of infectious diseases

Many emerging pathogens present in the skin and are of interest to dermatologists. Recent epidemics of measles, avian flu, and SARS demonstrated how an organism can rapidly spread worldwide because of airline travel. Travelers are often contagious before they are aware that they have the disease, contributing to the spread. This article reviews bacterial, mycobacterial, fungal, and viral pathogens important to dermatologists.

Chemical genomics in Escherichia coli identifies an inhibitor of bacterial lipoprotein targeting

One of the most significant hurdles to developing new chemical probes of biological systems and new drugs to treat disease is that of understanding the mechanism of action of small molecules discovered with cell-based small-molecule screening. Here we have assembled an ordered, high-expression clone set of all of the essential genes from Escherichia coli and used it to systematically screen for suppressors of growth inhibitory compounds. Using this chemical genomic approach, we demonstrate that the targets of well-known antibiotics can be identified as high copy suppressors of chemical lethality. This approach led to the discovery of MAC13243, a molecule that belongs to a new chemical class and that has a unique mechanism and promising activity against multidrug-resistant Pseudomonas aeruginosa. We show that MAC13243 inhibits the function of the LolA protein and represents a new chemical probe of lipoprotein targeting in bacteria with promise as an antibacterial lead with Gram-negative selectivity.

Microbial drug discovery: 80 years of progress

Microbes have made a phenomenal contribution to the health and well-being of people throughout the world. In addition to producing many primary metabolites, such as amino acids, vitamins and nucleotides, they are capable of making secondary metabolites, which constitute half of the pharmaceuticals on the market today and provide agriculture with many essential products. This review centers on these beneficial secondary metabolites, the discovery of which goes back 80 years to the time when penicillin was discovered by Alexander Fleming.

Pre-clinical experience with daptomycin

Daptomycin is a broad-spectrum, bactericidal agent active against Gram-positive bacteria, acting largely and unusually through membrane depolarization. Activity is markedly affected in vitro by the availability of calcium ions, and its high molecular weight with associated poor diffusion means that conventional disc diffusion testing is not reliable (and as a consequence not available). In order to allow susceptibility categorization, it is recommended that the MIC be determined in the presence of a defined calcium concentration. The activity of daptomycin is concentration-dependent with a prolonged post-antibiotic effect. It has linear pharmacokinetics, with a half-life of 8-9 h, the primary route of excretion is renal, it exhibits serum protein binding of approximately 92% and there is no interaction with the P450 cytochrome. Daptomycin is inactivated by surfactant in the lung and, in consequence, is not recommended for the treatment of respiratory infections. Daptomycin is currently licensed for the treatment of complicated skin and soft tissue infections and for bacteraemia and right-sided endocarditis due to methicillin-susceptible and -resistant Staphylococcus aureus. To date, daptomycin-resistant bacteria have rarely been isolated from patients, although increases in vancomycin MIC may be linked to reduced susceptibility to daptomycin. Close monitoring of resistance is essential to maintain the clinical utility of the drug. Using once-daily dosing, daptomycin has been generally well tolerated; however, weekly monitoring of creatinine phosphokinase is recommended, as myopathy in skeletal muscles has been seen, albeit rarely. The rapid bactericidal action of daptomycin makes it a useful addition to the therapeutic armamentarium for the treatment of Gram-positive infections, providing a valuable alternative to vancomycin when it is inappropriate or resistance is a problem.

R chi-01, a new family of oxazolidinones that overcome ribosome-based linezolid resistance

New and improved antibiotics are urgently needed to combat the ever-increasing number of multidrug-resistant bacteria. In this study, we characterized several members of a new oxazolidinone family, R chi-01. This antibiotic family is distinguished by having in vitro and in vivo activity against hospital-acquired, as well as community-acquired, pathogens. We compared the 50S ribosome binding affinity of this family to that of the only marketed oxazolidinone antibiotic, linezolid, using chloramphenicol and puromycin competition binding assays. The competition assays demonstrated that several members of the R chi-01 family displace, more effectively than linezolid, compounds known to bind to the ribosomal A site. We also monitored binding by assessing whether R chi-01 compounds protect U2585 (Escherichia coli numbering), a nucleotide that influences peptide bond formation and peptide release, from chemical modification by carbodiimide. The R chi-01 oxazolidinones were able to inhibit translation of ribosomes isolated from linezolid-resistant Staphylococcus aureus at submicromolar concentrations. This improved binding corresponds to greater antibacterial activity against linezolid-resistant enterococci. Consistent with their ribosomal A-site targeting and greater potency, the R chi-01 compounds promote nonsense suppression and frameshifting to a greater extent than linezolid. Importantly, the gain in potency does not impact prokaryotic specificity as, like linezolid, the members of the R chi-01 family show translation 50% inhibitory concentrations that are at least 100-fold higher for eukaryotic than for prokaryotic ribosomes. This new family of oxazolidinones distinguishes itself from linezolid by having greater intrinsic activity against linezolid-resistant isolates and may therefore offer clinicians an alternative to overcome linezolid resistance. A member of the R chi-01 family of compounds is currently undergoing clinical trials.

Pharmacokinetic evaluation of single-dose intravenous daptomycin in patients with thermal burn injury

Daptomycin pharmacokinetics were evaluated for burn patients. Burn patients had decreases in the maximum concentration of the drug in serum (44%) and the area under the concentration-time curve (47%) and increases in the volume of distribution (64%) and total clearance (77%) compared to healthy volunteers. In burn patients, daptomycin at 10 to 12 mg/kg of body weight/day would be required to achieve drug exposures similar to those for healthy volunteers receiving 6 mg/kg.

Update on daptomycin: the first approved lipopeptide antibiotic

Daptomycin, the first approved member of the lipopeptide antibiotic class, exhibits potent bactericidal in vitro activity against most Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus species and penicillin-resistant Streptococcus species. Since its approval in 2003 for the treatment of complicated skin and skin structure infections, several review articles have summarised daptomycin's mechanism of action, pharmacokinetics, pharmacodynamics, clinical trials and safety profiles. The objective of this paper is to summarise past information with a focus on the latest susceptibility data of isolates collected worldwide, new pharmacodynamic studies, clinical data regarding bacteraemia/endocarditis and postmarketing surveillance in the treatment of skin and skin-structure infections.

Synthesis, structure analysis, and antibacterial activity of some novel 10-substituted 2-(4-piperidyl/phenyl)-5,5-dioxo[1,2,4]triazolo[1,5-b][1,2,4]benzothiadiazine derivatives

A new series of 10-substituted 5,5-dioxo-5,10-dihydro[1,2,4]triazolo[1,5-b]-[1,2,4]benzothiadiazine arylsulfonamide derivatives (10a-j and 13a-f) was synthesized. The structures of these compounds were confirmed on the basis of spectral data, elemental analysis, X-ray analysis, and quantum chemical calculations. These compounds were evaluated for their efficacy as antibacterial agents against various Gram-positive and Gram-negative strains of bacteria. Amongst these compounds 10f and 10i were the most active compounds against Escherichia coli and 13e against E. coli as well as Bacillus subtilis. Moreover, other compounds also showed potent inhibitory activity in comparison to the standard drugs.

New antimicrobial agents as therapy for resistant gram-positive cocci

Vancomycin- and methicillin-resistant gram-positive cocci have emerged as an increasingly problematic cause of hospital-acquired infections. We conducted a literature review of newer antibiotics with activity against vancomycin-resistant and methicillin-resistant gram-positive cocci. Quinupristin/dalfopristin, linezolid, daptomycin, and tigecycline have in vitro activity for methicillin-resistant staphylococci and are superior to vancomycin for vancomycin-resistant isolates. Dalbavancin, telavancin, and oritavancin are new glycopeptides that have superior pharmacodynamic properties compared to vancomycin. We review the antibacterial spectrum, clinical indications and contraindications, pharmacologic properties, and adverse events associated with each of these agents. Daptomycin has rapid bactericidal activity for Staphylococcus aureus and is approved for use in bacteremia and right-sided endocarditis. Linezolid is comparable to vancomycin in patients with methicillin-resistant S. aureus (MRSA) pneumonia and has pharmacoeconomic advantages given its oral formulation. Quinupristin/dalfopristin is the drug of choice for vancomycin-resistant Enterococcus faecium infections but has no activity against Enterococcus faecalis. Tigecycline has activity against both enterococcus species and MRSA; it is also active against Enterobacteriaceae and anaerobes which allows for use in intra-abdominal and diabetic foot infections. A review of numerous in vitro and animal model studies shows that interaction between these newer agents and other antistaphylococcal agents for S. aureus are usually indifferent (additive).

Community-acquired methicillin-resistant Staphylococcus aureus

Published data confirm that community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections are increasing in incidence in both urban and rural settings. The statistical risk is higher for athletes, military personnel, prison inmates, intravenous drug abusers, the homeless, children in daycare, and certain Native American groups, but the infections are by no means restricted to these populations. Roughly 85% of the infections involve the skin and subcutaneous tissue, with the most common presentations being an abscess or folliculitis. The typical associated gene cassette is quite small and codes only for methicillin resistance. Abscesses generally respond to drainage.

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should recognize groups at high risk for community-acquired MSRA infections and manage these infections appropriately.

Management of cSSTIs: the role of daptomycin

BACKGROUND

Skin and soft tissue infections (SSTIs) and complicated SSTIs (cSSTIs), particularly those caused by Gram-positive pathogens, are among the most common human bacterial infections. The emergence of resistance to antibiotics such as methicillin and vancomycin has compromised treatment options for these infections and stimulated the search for new antimicrobial therapies. Daptomycin, the first in a class of agents known as cyclic lipopeptides, is a novel antibiotic with potent activity against most Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus.

SCOPE

This review examines the novel properties of daptomycin and describes its therapeutic efficacy and tolerability, particularly in the treatment of cSSTIs. The data search strategy included identification of original research papers, review articles, meeting reports and editorials by searches of MEDLINE and references from relevant articles.

FINDINGS

In vitro studies have demonstrated that daptomycin has superior bactericidal activity compared with vancomycin and the newer anti-Gram-positive agents, quinupristin/dalfopristin and linezolid. Robust, randomised, phase III clinical trials have shown daptomycin to be effective and well tolerated for the treatment of cSSTIs caused by Gram-positive bacteria, with equivalent clinical success rates and a similar safety profile to those of comparator agents. Data from these studies suggest a trend toward shorter duration of therapy and faster resolution of symptoms with daptomycin.

CONCLUSIONS

Given the pressing need for new antibiotics to combat infections caused by Gram-positive organisms, and to overcome the problem of resistance to conventional antibiotics, daptomycin is a welcome addition to the treatment options for the management of cSSTIs.

4-Pyridone derivatives as new inhibitors of bacterial enoyl-ACP reductase FabI

Bacterial FAS provides essential fatty acids for use in the assembly of key cellular components. Among them, FabI is an enoyl-ACP reductase which catalyzes the final and rate-limiting step of bacterial FAS. It is a potential target for selective antibacterial action, because it shows low overall sequence homology with mammalian enzymes. Until today, various compounds have been reported as inhibitors of bacterial FabI-inhibitory compounds. To discover novel small-molecular FabI inhibitors, we initially screened our compound library for inhibitory activity toward FabI of Escherichia coli. And discovered 4-pyridone derivatives as a lead compound. Structure optimization studies yielded 4-pyridone derivatives 7n having strong FabI-inhibitory and antibacterial activities against Staphylococcus aureus. There have been no reports concerning 4-pyridone derivatives as FabI inhibitor.

Daptomycin is more efficacious than vancomycin against a methicillin-susceptible Staphylococcus aureus in experimental meningitis

OBJECTIVES

To test the efficacy of daptomycin, a cyclic lipopeptide antibiotic, against a methicillin-susceptible Staphylococcus aureus strain in experimental rabbit meningitis and to determine its penetration into non-inflamed and inflamed meninges

RESULTS

Over a treatment period of 8 h, daptomycin (15 mg/kg) was significantly superior to the comparator regimen vancomycin (-4.54 +/- 1.12 log(10)/mL for daptomycin versus -3.43 +/- 1.17 log(10)/mL for vancomycin). Daptomycin managed to sterilize 6 out of 10 CSFs compared with 4 out of 10 for vancomycin. The penetration of daptomycin into inflamed meninges was approximately 5% and approximately 2% into non-inflamed meninges.

CONCLUSIONS

The superior bactericidal activity of daptomycin was confirmed in vivo and in time-killing assays in vitro.

Structure-based drug design meets the ribosome

The high-resolution structures of the bacterial ribosomal subunits and those of their complexes with antibiotics have advanced significantly our understanding of small-molecule interactions with RNA. The wealth of RNA structural data generated by these structures has allowed computational chemists to employ a drug discovery paradigm focused on RNA-based targets. The structures also show how target-based resistance affects antibiotics acting at the level of the ribosome. Not only are the sites pinpointed where different classes of antibiotics inhibit protein synthesis, but their orientations, relative dispositions, and unique mechanisms of action are also revealed at the atomic level. Both the 30S and the 50S ribosomal subunits have been shown to be "targets of targets", offering several adjacent, functionally relevant binding pockets for antibiotics. It is the detailed knowledge of these validated locations, or ribofunctional loci, plus the mapping of the resistance hot-spots that allow the rational design of next-generation antibacterials. When the structural information is combined with a data-driven computational toolkit able to describe and predict molecular properties appropriate for bacterial cell penetration and drug-likeness, a structure-based drug design approach for novel antibacterials shows great promise.

When will the genomics investment pay off for antibacterial discovery?

Effective solutions to antibacterial resistance are among the key unmet medical needs driving the antibacterial industry. A major thrust in a number of companies is the development of agents with new modes of action in order to bypass the increasing emergence of antibacterial resistance. However, few antibacterials marketed in the last 30 years have novel modes of action. Most recently, genomics and target-based screening technologies have been emphasized as a means to facilitate this and expedite the antibacterial discovery process. And although no new antibacterials have yet been marketed as result of these technologies, genomics has delivered well-validated novel bacterial targets as well as a host of genetic approaches to support the antibacterial discovery process. Likewise, high throughput screening technologies have delivered the capacity to perform robust screenings of large compound collections to identify target inhibitors for lead generation. One of the principal challenges still facing antibacterial discovery is to become proficient at optimizing target inhibitors into broad-spectrum antibacterials with appropriate in vivo properties. Genomics-based technologies clearly have the potential for additional application throughout the discovery process especially in the areas of structural biology and safety assessment.

The efficacy and safety of daptomycin: first in a new class of antibiotics for Gram-positive bacteria

In the face of increasing resistance to currently available antibiotics, there is a continued interest in the development of new drugs to treat Gram-positive infections. One such agent is the cyclic lipopeptide daptomycin-licensed in the USA for treatment of Gram-positive complicated skin and skin structure infections (cSSSIs) in 2003 and currently awaiting European approval for a similar indication (complicated skin and soft tissue infections). Daptomycin exerts its rapid bactericidal effect through insertion into and subsequent depolarisation of the bacterial cell membrane, a mode of action unlike that of any other available antibiotic. This novel mechanism of action makes the development of cross-resistance between daptomycin and other antibiotic classes unlikely. Daptomycin is highly active in vitro against a range of Gram-positive pathogens, including both susceptible and multidrug-resistant staphylococci and enterococci. Bactericidal activity has also been demonstrated against both growing and stationary-phase organisms, suggesting potential utility in the treatment of deep-seated infections. Two pivotal clinical studies comparing daptomycin 4 mg/kg per day intravenously with vancomycin or oxacillin-class antibiotics demonstrated the efficacy of daptomycin for treatment of cSSSIs. Daptomycin was well tolerated, with most adverse events considered to be unrelated to study medication, of mild-to-moderate intensity, and with a frequency and distribution similar to those associated with comparator antibiotics. The favourable clinical profile and low potential for development of resistance combine to make daptomycin a promising alternative to current agents for treatment of Gram-positive bacterial infections.