Experience with expanded use of oritavancin in a tertiary hospital: indications, tolerability and outcomes

Background

Oritavancin is a lipoglycopeptide antibacterial agent used to treat infections caused by Gram-positive organisms. It is FDA-approved for the treatment of acute bacterial skin and soft tissue infections (ABSSIs) but is increasingly being used off-label to treat invasive bacterial infections such as osteomyelitis, prosthetic joint infection and infective endocarditis.

Objectives

This study describes the clinical outcomes and adverse reactions related to oritavancin.

Patients and methods

This was a retrospective study conducted over a 5 year period at a tertiary care medical centre. Ninety-five adult patients were included in this study and were followed for 1 year after the last dose of oritavancin.

Results

The most common indication for oritavancin at our institution was osteomyelitis, followed by ABSSI. Other indications were vertebral infection, hardware-associated infection, bacteraemia and infective endocarditis. Fourteen percent (13/95) of patients developed an adverse reaction to oritavancin during the study period. Cure with no recurrence up to 1 year after the last dose of oritavancin was achieved in 74% (53/71) of patients, and the treatment failure rate was 19% (14/71 patients).

Conclusions

Oritavancin is an effective agent that can be used to treat invasive Gram-positive bacterial infections other than ABSSI. Adverse events requiring drug discontinuation were common.

The Clinical Efficacy of Multidose Oritavancin: A Systematic Review

Oritavancin (ORI) is a semisynthetic lipoglycopeptide approved as a single 1200 mg dose intravenous infusion for the treatment of acute bacterial skin and skin structure infections (ABSSSIs) caused by Gram-positive organisms in adults. The pharmacokinetic/pharmacodynamic (PK/PD) linear kinetic profile and long terminal half-life (~393 h) of ORI make it therapeutically attractive for the treatment of other Gram-positive infections for which prolonged therapy is needed. Multidose regimens are adopted in real-world clinical practice with promising results, but aggregated efficacy data are still lacking. A comprehensive search on PubMed/Medline, Scopus, Cochrane and Google Scholar databases was performed to include papers published up to the end of January 2023. All articles on ORI multiple doses usage, including case reports, with quantitative data and relevant clinical information were included. Two reviewers independently assessed papers against the inclusion/exclusion criteria and for methodological quality. Differences in opinion were adjudicated by a third party. From 1751 potentially relevant papers identified by this search, a total of 16 studies met the inclusion criteria and were processed further in the final data analysis. We extracted data concerning clinical response, bacteriologic response, mortality and adverse events (AEs). From the 16 included papers, 301 cases of treatment with multidose ORIs were identified. Multidose regimens comprised an initial ORI dose of 1200 mg followed by 1200 mg or 800 mg subsequent doses with a varying total number and frequency of reinfusions. The most often treated infections and isolates were osteomyelitis (148; 54.4%), ABSSSI (35; 12.9%) and cellulitis (14; 5.1%); and MRSA (121), MSSA (66), CoNS (17), E. faecalis (13) and E. faecium (12), respectively. Clinical cure and improvement by multidose ORI regimens were observed in 85% (231/272) and 8% (22/272) patients, respectively. Multidose ORI was safe and well tolerated; the most frequent AEs were infusion-related reactions and hypoglycemia. A multidose ORI regimen may be beneficial in treating other Gram-positive infections besides ABSSSIs, with a good safety profile. Further studies are warranted to ascertain the superiority of one multidose ORI scheme or posology over the other.

Rapid bacteriolysis of Staphylococcus aureus by lysin exebacase

Lysins (peptidoglycan hydrolases) are promising new protein-based antimicrobial candidates under development to address rising antibiotic resistance encountered among pathogenic bacteria. Exebacase is an antistaphylococcal lysin and the first member of the lysin class to have entered clinical trials in the United States. In this study, the bacteriolytic activity of exebacase was characterized with time-kill assays, turbidity reduction assays, and microscopy. Three methicillin-susceptible Staphylococcus aureus and three methicillin-resistant S. aureus isolates were tested in time-kill assays over a range of concentrations from 0.25 to 8 × MIC. Exebacase demonstrated a concentration-dependent killing and showed bactericidal activity (≥3 log10 kill achieved relative to the starting inoculum) within 3 h at 1 × MIC against all strains tested. Dose-dependent lysis by exebacase was, furthermore, observed in the turbidity reduction assay, wherein decreases in initial OD600 of 50% were observed within ~15 min at concentrations as low as 4 µg/mL. Membrane dissolution, loss of cytoplasmic material, and lysis were confirmed by video and electron microscopy. The demonstrated rapid bacteriolytic effect of exebacase is an important distinguishing feature of this novel modality. IMPORTANCE To guide the development of an investigational new antibacterial entity, microbiological data are required to evaluate the killing kinetics against target organism(s). Exebacase is a lysin (peptidoglycan hydrolase) that represents a novel antimicrobial modality based on degradation of the cell wall of Staphylococcus aureus. Killing by exebacase was determined in multiple assay formats including time-kill assays, wherein reductions of viability of ≥3 log10 colony-forming units/mL were observed within 3 h for multiple different isolates tested, consistent with very rapid bactericidal activity. Rapid reductions in optical density were likewise observed in exebacase-treated cultures, which were visually consistent with microscopic observations of rapid lysis. Overall, exebacase provides a novel antimicrobial modality against S. aureus, characterized by a rapid cidal and lytic activity.

Comparative In Vitro Activity of New Lipoglycopeptides and Vancomycin Against Ocular Staphylococci and Their Toxicity on the Human Corneal Epithelium

PURPOSE

The purpose of this study was to assess the potential of new lipoglycopeptides as novel topical therapies for improved treatment of recalcitrant ocular infections. We evaluated the in vitro antimicrobial activity of oritavancin, dalbavancin, and telavancin compared with vancomycin (VAN) against a large collection of ocular staphylococcal isolates and their cytotoxicity on human corneal epithelial cells (HCECs).

METHODS

Antimicrobial susceptibility testing was performed by broth microdilution against 223 Staphylococcus spp. clinical isolates. Time-kill kinetics were determined for methicillin-resistant strains of Staphylococcus aureus (MRSA) (n = 2) and Staphylococcus epidermidis (MRSE) (n = 1). In vitro cytotoxicity assays were performed with AlamarBlue and live/dead staining on HCECs.

RESULTS

All new lipoglycopeptides showed strong in vitro potency against ocular staphylococci, including multidrug-resistant MRSA strains, with dalbavancin showing a slightly higher potency overall [minimum inhibitory concentration (MIC) 90 0.06 μg/mL] compared with telavancin and oritavancin (MIC 90 0.12 μg/mL), whereas VAN had the lowest potency (MIC 90 2 μg/mL). Oritavancin exerted rapid bactericidal activity within 1 h for MRSA and 2 h for MRSE. All other drugs were bactericidal within 24 h. At a concentration commonly used for topical preparations (25 mg/mL), cytotoxicity was observed for VAN after 5 min of incubation, whereas reduction in HCEC viability was not seen for telavancin and was less affected by oritavancin and dalbavancin. Cytotoxicity at 25 mg/mL was seen for all drugs at 30 and 60 min but was significantly reduced or undetected for lower concentrations.

CONCLUSIONS

Our study demonstrates that new lipoglycopeptides have substantially better in vitro antimicrobial activity against ocular staphylococcal isolates compared with VAN, with a similar or improved toxicity profile on HCECs.

Novel xanthone antibacterials: Semi-synthesis, biological evaluation, and the action mechanisms

α-Mangostin (α-MG) has demonstrated to display potent activities against Gram-positive bacterial. However, the contribution of phenolic hydroxyl groups of α-MG to the antibacterial activity remains obscure, severely hampering selection of structure modification to develop more potential α-MG-based anti-bacterial derivatives. Herein, twenty-one α-MG derivatives are designed, synthesized and evaluated for the antibacterial activities. The structure activity relationships (SARs) reveal that the contribution of the phenolic groups ranks as C3 > C6 > C1, and the phenolic hydroxyl group at C3 is essential to the antibacterial activity. Of note, compared to the parent compound α-MG, 10a with one acetyl at C1 exhibits the higher safety profiles due to its higher selectivity and no hemolysis, and the more potent antibacterial efficacy in an animal skin abscess model. Our evidences further present that, in comparison with α-MG, 10a has a stronger ability in depolarizing membrane potentials and leads to more leakage of bacterial proteins, consistent with the results observed by transmission electron microscopy (TEM). Transcriptomics analysis demonstrates those observations possibly relate to disturbed synthesis of proteins participating in the biological process of membrane permeability and integrity. Collectively, our findings provide a valuable insight for developing α-MG-based antibacterial agents with little hemolysis and new action mechanism via structural modifications at C1.

Differences in Pharmacokinetic/Pharmacodynamic Parameters of Tedizolid Against VRE and MRSA

PURPOSE

Vancomycin-resistant enterococci (VRE) have recently become a major cause of nosocomial infections and a global public health concern. Tedizolid exhibits powerful antibacterial activity against VRE in vitro, but its pharmacokinetic/pharmacodynamic (PK/PD) parameters remain unclear. Therefore, we aimed to determine the PK/PD indices of tedizolid action on VRE and the mechanisms underlying the PK/PD indices differences of tedizolid against VRE and methicillin-resistant Staphylococcus aureus (MRSA).

METHODS

Optimal PK/PD target values of tedizolid were determined in vitro, based on time-kill curves and post-antibiotic effects (PAEs), and in vivo, using mouse models of thigh infection with VRE and MRSA strains.

RESULTS

The tedizolid bactericidal activity on VRE and MRSA was time-dependent. Correlations were closest between fAUC₂₄/MIC and the tedizolid PK/PD index against MRSA and VRE. To achieve 1 log₁₀ kill tedizolid fAUC₂₄/MIC in neutropenic mouse models of thigh infection with VRE and MRSA should be 14.2 and 138.5, respectively. The PAEs of tedizolid against VRE and MRSA were 2.39 and 0.99 h, respectively.

CONCLUSION

Tedizolid showed bactericidal effects against VRE even in neutropenic mice unlike MRSA, which could be attributed to its longer PAE against VRE. Hence, we hypothesize that tedizolid treatment against VRE infections is promising for achieving therapeutic success in clinical.

Mitigating the toxicity of palmitoylated analogue of α-melanocyte stimulating hormone(11-13) by conjugation with gold nanoparticle: characterisation and antibacterial efficacy against methicillin sensitive and resistant Staphylococccus aureus

In an attempt to develop potent and non-toxic antimicrobial agent, the palmitoylated analogue of α-melanocyte stimulating hormone(11-13), Pal-α-MSH(11-13) was conjugated with gold nanoparticles (GNPs) for the first time and the efficacy of derived complex was investigated against two strains of Staphylococccus aureus. The GNPs were synthesized using tri-sodium citrate as reductant and Pal-α-MSH(11-13) was conjugated thereafter. The particles were characterised by UV-vis spectroscopy, transmission electron microscopy, dynamic light scattering, fourier transform infrared spectroscopy etc. Conjugation occurred via electrostatic interaction between anionic GNPs and cationic Pal-α-MSH(11-13). The zeta potential of GNP-Pal-α-MSH(11-13) was - 26.91, indicating its stability. The antibacterial activity was determined by minimal inhibitory concentration (MIC) and killing kinetics assay, whereas, inhibition of biofilm formation was studied by determining the biofilm biomass by crystal violet dye binding method, viability of biofilm-embedded cells by counting CFUs and metabolic activity by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. The toxicity was analysed by hemolysis assay against murine RBCs and cytotoxicity against 3T3 fibroblasts. The MIC was 18 µM for GNP-Pal-α-MSH(11-13) and 12 µM for Pal-α-MSH(11-13). The killing kinetics and biofilm inhibition studies indicated the comparable efficacy of peptide before and after nano-conjugation. Importantly, the conjugation resulted in diminished toxicity, as evidenced by 0.29 ± 0.03% hemolysis and 100% viable fibroblasts at 72 µM compared to the Pal-α-MSH(11-13), showing 74.99 ± 1.59% hemolysis and 59.39 ± 1.06% viable fibroblasts. The nano-fabrication drastically reduced the peptide toxicity without compromising its antibacterial efficacy. The anionicity of the conjugate may be responsible for non-toxicity that makes them suitable for pharmaceutical applications.

Recent Advances in the Development of Semisynthetic Glycopeptide Antibiotics: 2014-2022

The accelerated appearance of drug-resistant bacteria poses an ever-growing threat to modern medicine's capacity to fight infectious diseases. Gram-positive species such as methicillin-resistant Staphylococcus aureus (MRSA) and Streptococcus pneumoniae continue to contribute significantly to the global burden of antimicrobial resistance. For decades, the treatment of serious Gram-positive infections relied upon the glycopeptide family of antibiotics, typified by vancomycin, as a last line of defense. With the emergence of vancomycin resistance, the semisynthetic glycopeptides telavancin, dalbavancin, and oritavancin were developed. The clinical use of these compounds is somewhat limited due to toxicity concerns and their unusual pharmacokinetics, highlighting the importance of developing next-generation semisynthetic glycopeptides with enhanced antibacterial activities and improved safety profiles. This Review provides an updated overview of recent advancements made in the development of novel semisynthetic glycopeptides, spanning the period from 2014 to today. A wide range of approaches are covered, encompassing innovative strategies that have delivered semisynthetic glycopeptides with potent activities against Gram-positive bacteria, including drug-resistant strains. We also address recent efforts aimed at developing targeted therapies and advances made in extending the activity of the glycopeptides toward Gram-negative organisms.

Proteomic Comparison of Ivermectin Sensitive and Resistant Staphylococcus aureus Clinical Isolates Reveals Key Efflux Pumps as Possible Resistance Determinants

Ivermectin (IVM) is a versatile drug used against many microorganisms. Staphylococcus aureus is one of the most devastating microorganisms. IVM sensitive and resistant S. aureus strains were recently reported. However, the underlying molecular mechanisms of resistance are unknown. Clinical isolates of S. aureus were used for determination of the sensitivities against IVM by growth curve analysis and time-kill kinetics. Then, proteomic, and biochemical approaches were applied to investigate the possible mechanisms of resistance. Proteomic results showed a total of 1849 proteins in the dataset for both strains, 425 unique proteins in strain O9 (IVM sensitive), and 354 unique proteins in strain O20 (IVM resistant). Eight proteins with transport functions were differentially expressed in the IVM resistant strain. Among them, three efflux pumps (mepA, emrB, and swrC) were confirmed by qPCR. The IVM resistant S. aureus may overexpress these proteins as a key resistance determinant. Further experiments are required to confirm the exact mechanistic relationship. Nevertheless, the possibility of blocking these transporters to reverse or delay the onset of resistance and reduce selection pressure is potentially appealing.

Molecular dynamics simulations of the secondary-binding site in disaccharide-modified glycopeptide antibiotics

Oritavancin is a semisynthetic glycopeptide antibiotic used to treat severe infections by multidrug-resistant Gram-positive pathogens. Oritavancin is known to be a thousand times more potent than vancomycin against Gram-positive bacteria due to the additional interactions with bacterial peptidoglycan (PG) facilitated by a secondary-binding site. The presence of this secondary-binding site is evident in desleucyl-oritavancin, an Edman degradation product of oritavancin, still retaining its potency against Gram-positive bacteria, whereas desleucyl-vancomycin is devoid of any antimicrobial activities. Herein, using explicit solvent molecular dynamics (MD) simulations, steered MD simulations, and umbrella sampling, we show evidence of a secondary-binding site mediated by the disaccharide-modified hydrophobic sidechain of oritavancin interactions with the pentaglycyl-bridge segment of the PG. The interactions were characterized through comparison to the interaction of PG with chloroeremomycin, vancomycin, and the desleucyl analogs of the glycopeptides. Our results show that the enhanced binding of oritavancin to PG over the binding of the other complexes studied is due to an increase in the hydrophobic effect, electrostatic and van der Waals interactions, and not the average number of hydrogen bonds. Our ranking of the binding interactions of the biomolecular complexes directly correlates with the order based on their experimental minimum inhibitory concentrations. The results of our simulations provide insight into the modification of glycopeptides to increase their antimicrobial activities or the design of novel antibiotics against pathogenic Gram-positive bacteria.

Kimyrsa, An Oritavancin-Containing Product: Clinical Study and Review of Properties

Background

There is a need for improved antibiotic formulations for the treatment of acute bacterial skin and soft structure infection (ABSSSI), especially with the rise of antimicrobial resistance among Gram-positive bacteria. A new formulation of oritavancin was developed to reduce intravenous infusion volume (from 1000 mL to 250 mL), shorten infusion time (from 3 hours to 1 hour), and provide pharmacies with flexibility in oritavancin preparation (from 5% dextrose in sterile water to either normal saline or 5% dextrose in sterile water) compared with the current formulation.

Methods

A total of 102 adult patients with a diagnosis of ABSSSI suspected or confirmed to be caused by a Gram-positive pathogen were randomized 1:1 to receive either the new formulation of oritavancin or the current formulation. After a single 1200-mg intravenous infusion of oritavancin, the relative area-under-the-curve exposure of the new formulation and current formulation groups were compared. Safety and tolerability of the new formulation were assessed for treatment-emergent adverse events, serious adverse events, and changes to laboratory parameters.

Results

The area under the curve for 0 hour to 72 hours postdose was very similar in the new formulation group compared with the current formulation group. No differences in treatment-emergent adverse events were observed between the current and new formulation groups, and all treatment-emergent adverse events were consistent with the known safety profile of the current formulation.

Conclusions

The new formulation of oritavancin with reduced volume and duration of intravenous infusion demonstrates a safety profile and pharmacokinetics similar to that of the original formulation.

Current and future options for treating complicated skin and soft tissue infections: focus on fluoroquinolones and long-acting lipoglycopeptide antibiotics

Bacterial skin and soft tissue infections are among the most common bacterial infections and constitute a major burden for patients and healthcare systems. Care is complicated by the variety of potential pathogens, some with resistance to previously effective antimicrobial agents, the wide spectrum of clinical presentations and the risk of progression to life-threatening forms. More-efficient care pathways are needed that can reduce hospital admissions and length of stay, while maintaining a high quality of care and adhering to antimicrobial stewardship principles. Several agents approved recently for treating acute bacterial skin and skin structure infections have characteristics that meet these requirements. We address the clinical and pharmacological characteristics of the fourth-generation fluoroquinolone delafloxacin, and the long-acting lipoglycopeptide agents dalbavancin and oritavancin.

Identification of simple arylfluorosulfates as potent agents against resistant bacteria

Sulfur fluoride exchange (SuFEx), a next generation of click chemistry, opens an avenue for drug discovery. We report here the discovery and structure-activity relationship studies of a series of arylfluorosulfates, synthesized via SuFEx, as antibacterial agents. Arylfluorosulfates 3, 81, and 101 showed potency to overcome multidrug resistance and were not susceptible to the generation of resistance. They exhibited rapid bactericidal potency and selectively killed gram-positive bacterial strains. These compounds also exhibited the ability to disrupt established bacterial biofilm and kill persisters derived from biofilm. Furthermore, arylfluorosulfate 3 had a synergistic effect with streptomycin and gentamicin. In addition, their anti-MRSA potency was evaluated and determined by the Caenorhabditis elegans model.

The Minimum Inhibitory Concentration of Antibiotics: Methods, Interpretation, Clinical Relevance

Inefficiency of medical therapies used in order to cure patients with bacterial infections requires not only to actively look for new therapeutic strategies but also to carefully select antibiotics based on variety of parameters, including microbiological. Minimal inhibitory concentration (MIC) defines in vitro levels of susceptibility or resistance of specific bacterial strains to applied antibiotic. Reliable assessment of MIC has a significant impact on the choice of a therapeutic strategy, which affects efficiency of an infection therapy. In order to obtain credible MIC, many elements must be considered, such as proper method choice, adherence to labeling rules, and competent interpretation of the results. In this paper, two methods have been discussed: dilution and gradient used for MIC estimation. Factors which affect MIC results along with the interpretation guidelines have been described. Furthermore, opportunities to utilize MIC in clinical practice, with pharmacokinetic /pharmacodynamic parameters taken into consideration, have been investigated. Due to problems related to PK determination in individual patients, statistical estimation of the possibility of achievement of the PK/PD index, based on the Monte Carlo, was discussed. In order to provide comprehensive insights, the possible limitations of MIC, which scientists are aware of, have been outlined.

Discerning the role of polymicrobial biofilms in the ascent, prevalence, and extent of heteroresistance in clinical practice

Antimicrobial therapy is facing a worrisome and underappreciated challenge, the phenomenon of heteroresistance (HR). HR has been gradually documented in clinically relevant pathogens (e.g. Pseudomonas aeruginosa, Staphylococcus aureus, Burkholderia spp., Acinetobacter baumannii, Klebsiella pneumoniae, Candida spp.) towards several drugs and is believed to complicate the clinical picture of chronic infections. This type of infections are typically mediated by polymicrobial biofilms, wherein microorganisms inherently display a wide range of physiological states, distinct metabolic pathways, diverging refractory levels of stress responses, and a complex network of chemical signals exchange. This review aims to provide an overview on the relevance, prevalence, and implications of HR in clinical settings. Firstly, related terminologies (e.g. resistance, tolerance, persistence), sometimes misunderstood and overlapped, were clarified. Factors generating misleading HR definitions were also uncovered. Secondly, the recent HR incidences reported in clinically relevant pathogens towards different antimicrobials were annotated. The potential mechanisms underlying such occurrences were further elucidated. Finally, the link between HR and biofilms was discussed. The focus was to recognize the presence of heterogeneous levels of resistance within most biofilms, as well as the relevance of polymicrobial biofilms in chronic infectious diseases and their role in resistance spreading. These topics were subject of a critical appraisal, gaining insights into the ascending clinical implications of HR in antimicrobial resistance spreading, which could ultimately help designing effective therapeutic options.

Molecular Dynamics Simulation of Atomic Interactions in the Vancomycin Binding Site

Vancomycin is a glycopeptide antibiotic produced by Amycolaptopsis orientalis used to treat serious infections by Gram-positive pathogens including methicillin-resistant Staphylococcus aureus. Vancomycin inhibits cell wall biosynthesis by targeting lipid II, which is the membrane-bound peptidoglycan precursor. The heptapeptide aglycon structure of vancomycin binds to the d-Ala-d-Ala of the pentapeptide stem structure in lipid II. The third residue of vancomycin aglycon is asparagine, which is not directly involved in the dipeptide binding. Nonetheless, asparagine plays a crucial role in substrate recognition, as the vancomycin analogue with asparagine substituted by aspartic acid (V_D) shows a reduction in antibacterial activities. To characterize the function of asparagine, binding of vancomycin and its aspartic-acid-substituted analogue V_D to l-Lys-d-Ala-d-Ala and l-Lys-d-Ala-d-Lac was investigated using molecular dynamic simulations. Binding interactions were analyzed using root-mean-square deviation (RMSD), two-dimensional (2D) contour plots, hydrogen bond analysis, and free energy calculations of the complexes. The analysis shows that the aspartate substitution introduced a negative charge to the binding cleft of V_D, which altered the aglycon conformation that minimized the repulsive lone pair interaction in the binding of a depsipeptide. Our findings provide new insight for the development of novel glycopeptide antibiotics against the emerging vancomycin-resistant pathogens by chemical modification at the third residue in vancomycin to improve its binding affinity to the d-Ala-d-Lac-terminated peptidoglycan in lipid II found in vancomycin-resistant enterococci and vancomycin-resistant S. aureus.

Lipidated Short Analogue of α-Melanocyte Stimulating Hormone Exerts Bactericidal Activity against the Stationary Phase of Methicillin-Resistant Staphylococcus aureus and Inhibits Biofilm Formation

Stationary phase Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA), has been widely associated with many persistent infections as well as biofilm-associated infections, which are challenging due to their increasing antibiotic resistance. α-Melanocyte stimulating hormone (α-MSH) is an antimicrobial peptide (AMP) with well-established potent activity against S. aureus , but little is known about its antimicrobial efficacy against the stationary phase of the bacteria. We investigated the in vitro activities of two palmitoylated analogues, Pal-α-MSH(6-13) and Pal-α-MSH(11-13), of the C-terminal fragments of α-MSH against biofilm-producing strains of methicillin-sensitive S. aureus (MSSA) and MRSA. While both the peptides demonstrated anti-staphylococcal efficacy, Pal-α-MSH(11-13) emerged as the most effective AMP as palmitoylation led to a remarkable enhancement in its activity against stationary phase bacteria. Similar to α-MSH, both the designed analogues were membrane-active and exhibited improved bacterial membrane depolarization and permeabilization, as further confirmed via electron microscopy studies. Of the two peptides, Pal-α-MSH(11-13) was able to retain its activity in the presence of standard microbiological media, which otherwise is a major limiting factor toward the therapeutic use of α-MSH-based peptides. More importantly, Pal-α-MSH(11-13) was also highly effective in inhibiting the formation of biofilms. Furthermore, it did not lead to resistance development in MRSA cells even upon 18 serial passages at sub-MIC concentrations. These observations support the potential use of Pal-α-MSH(11-13) in the treatment of planktonic as well as sessile S. aureus infections.

Antimicrobial effects of cinnamon essential oil and cinnamaldehyde combined with EDTA against canine otitis externa pathogens

AIMS

The antimicrobial activity of cinnamon essential oil and cinnamaldehyde against bacterial and fungal pathogens associated with canine otitis externa, as well as the effect of their combination with EDTA were investigated.

METHODS AND RESULTS

Antimicrobial susceptibility testing was performed using the broth microdilution method while spot-plating technique was used to determine their bactericidal activity. Time-kill kinetics and checkerboard assays were performed to confirm the bactericidal activity and combination effects of the compounds. Cinnamon oil and cinnamaldehyde exhibited antimicrobial activity against Gram-positive and Gram-negative pathogens, as well as Malassezia pachydermatis. Synergistic interaction was shown when EDTA (672 μg ml^-1 ) was combined with cinnamon oil (41 μg ml^-1 ) and cinnamaldehyde (22 μg ml^-1 ) against Pseudomonas aeruginosa. Cinnamaldehyde exhibited significantly stronger antimicrobial activity than cinnamon bark oil.

CONCLUSIONS

Cinnamon essential oil and cinnamaldehyde, either used alone or in combination with EDTA, were effective against the causative micro-organisms of canine otitis externa. The data suggest that cinnamaldehyde could be a promising antimicrobial agent against canine otitis externa.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows that cinnamon essential oil and cinnamaldehyde, especially the latter, could be used in combination with EDTA as novel treatment for sensitive and resistant bacterial and fungal pathogens involved in canine otitis externa.

Antibiotic Resistance and the MRSA Problem

Staphylococcus aureus is capable of becoming resistant to all classes of antibiotics clinically available and resistance can develop through de novo mutations in chromosomal genes or through acquisition of horizontally transferred resistance determinants. This review covers the most important antibiotics available for treatment of S. aureus infections and a special emphasis is dedicated to the current knowledge of the wide variety of resistance mechanisms that S. aureus employ to withstand antibiotics. Since resistance development has been inevitable for all currently available antibiotics, new therapies are continuously under development. Besides development of new small molecules affecting cell viability, alternative approaches including anti-virulence and bacteriophage therapeutics are being investigated and may become important tools to combat staphylococcal infections in the future.

The Antistaphylococcal Lysin, CF-301, Activates Key Host Factors in Human Blood To Potentiate Methicillin-Resistant Staphylococcus aureus Bacteriolysis

Bacteriophage-derived lysins are cell-wall-hydrolytic enzymes that represent a potential new class of antibacterial therapeutics in development to address burgeoning antimicrobial resistance. CF-301, the lead compound in this class, is in clinical development as an adjunctive treatment to potentially improve clinical cure rates of Staphylococcus aureus bacteremia and infective endocarditis (IE) when used in addition to antibiotics. In order to profile the activity of CF-301 in a clinically relevant milieu, we assessed its in vitro activity in human blood versus in a conventional testing medium (cation-adjusted Mueller-Hinton broth [caMHB]). CF-301 exhibited substantially greater potency (32 to ≥100-fold) in human blood versus caMHB in three standard microbiologic testing formats (e.g., broth dilution MICs, checkerboard synergy, and time-kill assays). We demonstrated that CF-301 acted synergistically with two key human blood factors, human serum lysozyme (HuLYZ) and human serum albumin (HSA), which normally have no nascent antistaphylococcal activity, against a prototypic methicillin-resistant S. aureus (MRSA) strain (MW2). Similar in vitro enhancement of CF-301 activity was also observed in rabbit, horse, and dog (but not rat or mouse) blood. Two well-established MRSA IE models in rabbit and rat were used to validate these findings in vivo by demonstrating comparable synergistic efficacy with standard-of-care anti-MRSA antibiotics at >100-fold lower lysin doses in the rabbit than in the rat model. The unique properties of CF-301 that enable bactericidal potentiation of antimicrobial activity via activation of "latent" host factors in human blood may have important therapeutic implications for durable improvements in clinical outcomes of serious antibiotic-resistant staphylococcal infections.

In vitro activity of oritavancin in combination with rifampin or gentamicin against prosthetic joint infection-associated methicillin-resistant Staphylococcus epidermidis biofilms

This study evaluated the in vitro activity of oritavancin in combination with rifampin or gentamicin against methicillin-resistant Staphylococcus epidermidis (MRSE) biofilms. Oritavancin, rifampin, and gentamicin were tested against 20 MRSE isolates recovered from prosthetic joint infection (PJI). Time-kill studies were used to evaluate the activities of the three antimicrobial agents individually vs. combinations of oritavancin with rifampin or gentamicin against MRSE biofilms formed on Teflon coupons. At 24 h, the combination of oritavancin and rifampin resulted in a significant (P≤0.001) reduction in biofilm density compared with either antimicrobial alone for 85% (17/20) of isolates. Oritavancin combined with gentamicin showed a significant (P≤0.001) reduction in biofilm density compared with either antimicrobial alone against 55% (11/20) of isolates at 24 h. Synergy (defined as a ≥2 log₁₀ cfu/cm² decrease at 24 h for the antimicrobial combination compared with the most active single antimicrobial) was observed against 65% (13/20) of the isolates for oritavancin in combination with rifampin and 35% (7/20) of the isolates for oritavancin in combination with gentamicin. Oritavancin in combination with rifampin or gentamicin demonstrated bactericidal activity (defined as a ≥3 log₁₀ cfu/cm² reduction at 24 h from the starting biofilm bacterial density) for 85% (17/20) and 80% (16/20) isolates, respectively. Our study suggests that oritavancin and rifampin combination therapy may be an option for antimicrobial management of PJIs caused by MRSE.

Detection and Investigation of Eagle Effect Resistance to Vancomycin in Clostridium difficile With an ATP-Bioluminescence Assay

Vancomycin was bactericidal against Clostridium difficile at eightfold the minimum inhibitory concentration (MIC) using a traditional minimum bactericidal concentration (MBC) assay. However, at higher concentrations up to 64 × MIC, vancomycin displayed a paradoxical “more-drug-kills-less” Eagle effect against C. difficile. To overcome challenges associated with performing the labor-intensive agar-based MBC method under anaerobic growth conditions, we investigated an alternative more convenient ATP-bioluminescence assay to assess the Eagle effect in C. difficile. The commercial BacTiter-Glo^TM assay is a homogenous method to determine bacterial viability based on quantification of bacterial ATP as a marker for metabolic activity. The ATP-bioluminescence assay was advantageous over the traditional MBC-type assay in detecting the Eagle effect because it reduced assay time and was simple to perform; measurement of viability could be performed in less than 10 min outside of the anaerobic chamber. Using this method, we found C. difficile survived clinically relevant, high concentrations of vancomycin (up to 2048 μg/mL). In contrast, C. difficile did not survive high concentrations of metronidazole or fidaxomicin. The Eagle effect was also detected for telavancin, but not for teicoplanin, dalbavancin, oritavancin, or ramoplanin. All four pathogenic strains of C. difficile tested consistently displayed Eagle effect resistance to vancomycin, but not metronidazole or fidaxomicin. These results suggest that Eagle effect resistance to vancomycin in C. difficile could be more prevalent than previously appreciated, with potential clinical implications. The ATP-Bioluminescence assay can thus be used as an alternative to the agar-based MBC assay to characterize the Eagle effect against a variety of antibiotics, at a wide-range of concentrations, with much greater throughput. This may facilitate improved understanding of Eagle effect resistance and promote further research to understand potential clinical relevance.

Pharmacological Basis of CD101 Efficacy: Exposure Shape Matters

CD101 is a novel echinocandin with concentration-dependent fungicidal activity in vitro and a long half-life (∼133 h in humans, ∼70 to 80 h in mice). Given these characteristics, it is likely that the shape of the CD101 exposure (i.e., the time course of CD101 concentrations) influences efficacy. To test this hypothesis, doses which produce the same total area under the concentration-time curve (AUC) were administered to groups of neutropenic ICR mice infected with Candida albicans R303 using three different schedules. A total CD101 dose of 2 mg/kg was administered as a single intravenous (i.v.) dose or in equal divided doses of either 1 mg/kg twice weekly or 0.29 mg/kg/day over 7 days. The studies were performed using a murine disseminated candidiasis model. Animals were euthanized at 168 h following the start of treatment. Fungi grew well in the no-treatment control group and showed variable changes in fungal density in the treatment groups. When the CD101 AUC from 0 to 168 h (AUC_0–168) was administered as a single dose, a >2 log₁₀ CFU reduction from the baseline at 168 h was observed. When twice-weekly and daily regimens with similar AUC values were administered, net fungal stasis and a >1 log₁₀ CFU increase from the baseline were observed, respectively. These data support the hypothesis that the shape of the CD101 AUC influences efficacy. Thus, CD101 administered once per week demonstrated a greater degree of fungal killing than the same dose divided into twice-weekly or daily regimens.

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.

Antibiotic Classification and Indication Review for the Infusion Nurse

Outpatient parenteral antimicrobial therapy (OPAT) has become an increasingly common practice for the treatment of infections. The infusion nurse plays a vital role in administering, monitoring, and educating patients about parenteral antibiotics, while bridging communication between the patient and OPAT team. It is important for the infusion nurse to know common indications, adverse effects, monitoring parameters, and the mechanism of action for antibiotics used in OPAT to provide optimal patient care. This review includes those antibiotics, which are frequently administered or recently approved with a high likelihood of being used in OPAT.

Surface mediated cooperative interactions of drugs enhance mechanical forces for antibiotic action

The alarming increase of pathogenic bacteria that are resistant to multiple antibiotics is now recognized as a major health issue fuelling demand for new drugs. Bacterial resistance is often caused by molecular changes at the bacterial surface, which alter the nature of specific drug-target interactions. Here, we identify a novel mechanism by which drug-target interactions in resistant bacteria can be enhanced. We examined the surface forces generated by four antibiotics; vancomycin, ristomycin, chloroeremomycin and oritavancin against drug-susceptible and drug-resistant targets on a cantilever and demonstrated significant differences in mechanical response when drug-resistant targets are challenged with different antibiotics although no significant differences were observed when using susceptible targets. Remarkably, the binding affinity for oritavancin against drug-resistant targets (70 nM) was found to be 11,000 times stronger than for vancomycin (800 μM), a powerful antibiotic used as the last resort treatment for streptococcal and staphylococcal bacteria including methicillin-resistant Staphylococcus aureus (MRSA). Using an exactly solvable model, which takes into account the solvent and membrane effects, we demonstrate that drug-target interactions are strengthened by pronounced polyvalent interactions catalyzed by the surface itself. These findings further enhance our understanding of antibiotic mode of action and will enable development of more effective therapies.

Oritavancin: a review in acute bacterial skin and skin structure infections

Oritavancin (Orbactiv(®)) is a new generation lipoglycopeptide approved for use in adult patients with acute bacterial skin and skin structure infections (ABSSSI). It is administered as a single 1200 mg intravenous infusion over 3 h. In phase 3 trials in adult patients with ABSSSI, oritavancin was noninferior to vancomycin in terms of a composite outcome (cessation of spreading or reduction in the size of the baseline lesion, absence of fever and no rescue antibacterials required; primary endpoint) assessed at an US FDA-recommended early timepoint of 48-72 h after initiation of treatment. Oritavancin was also noninferior to vancomycin in terms of a ≥20 % reduction in the baseline lesion size at the early timepoint and clinical cure rate 7-14 days after the end of treatment. Oritavancin was generally well tolerated in the phase 3 trials, with most treatment-emergent adverse reactions being mild in severity. The most common adverse events occurring in oritavancin recipients were nausea, headache, vomiting, limb and subcutaneous abscesses, and diarrhoea. Oritavancin offers a number of potential advantages, including a convenient single dose treatment that may shorten or eliminate hospital stays, a reduction in healthcare resource utilization and cost, no need for dosage adjustment in patients with mild to moderate hepatic or renal impairment, no need for therapeutic drug monitoring, and elimination of compliance concerns. Therefore, oritavancin is a useful treatment option for adults with ABSSSI.

Dalbavancin and Oritavancin: An Innovative Approach to the Treatment of Gram-Positive Infections

Health care-associated infections, especially those caused by multidrug-resistant gram-positive organisms, such as methicillin-resistant Staphylococcus aureus (MRSA), are a growing public health threat. In 2014, the U.S. Food and Drug Administration approved two new lipoglycopeptides, oritavancin and dalbavancin, for the treatment of acute bacterial skin and skin structure infections. The rationale for the development of these antimicrobials was partly to aid in the battle against vancomycin resistance in both Staphylococcus and Enterococcus. Considered a subclass of the glycopeptide antibiotics, the new lipoglycopeptides have similar mechanisms of action of binding to the carboxyl terminal d-alanyl-d-alanine residue of the growing peptide chains but differ from their parent glycopeptides by the addition of lipophilic tails. This addition allows for these agents to have prolonged half-lives, giving them unique dosing profiles. In addition, by concentrating at the site of action, they have increased potency against MRSA compared with vancomycin, the current mainstay of therapy. In this review, we focus on comparing and contrasting these two new agents with regard to their pharmacology, mechanisms of action, spectrum of activity, safety profiles, dosage and administration, and drug and laboratory interactions, and we review the clinical trials evaluating their use.

Targeting bactoprenol-coupled cell envelope precursors

Targeting the bactoprenol-coupled cell wall precursor lipid II is a validated antibacterial strategy. In this review, selected prototype lipid II-binding antibiotics of different chemical classes are discussed. Although these compounds attack the same molecular target, they trigger nuanced and diverse cellular effects. Consequently, the mechanisms of antibacterial resistance and the likelihood of resistance development may vary substantially.

Oritavancin: a long-acting antibacterial lipoglycopeptide

Oritavancin is a new lipoglycopeptide antibacterial agent with an exceptionally long terminal half-life and a rapid bactericidal effect. Multiple mechanisms of action lead to a broad activity against Gram-positive bacteria, such as staphylococci, streptococci and enterococci, including methicillin-resistant Staphylococcus aureus. Its long terminal half-life allows for single-dose treatment of acute bacterial skin and skin structure infections. Oritavancin was found to be safe and effective in treating acute bacterial skin and skin structure infections in adults and it is currently approved in the USA and in Europe for this indication. Unfortunately, data for other indications are lacking. Here, we review chemistry, microbiology, pharmacology, efficacy and tolerability of oritavancin.

Oritavancin Combinations with β-Lactams against Multidrug-Resistant Staphylococcus aureus and Vancomycin-Resistant Enterococci

Oritavancin possesses activity against vancomycin-resistant enterococci (VRE) and methicillin-resistantStaphylococcus aureus(MRSA).In vitrodata suggest synergy between beta-lactams (BLs) and vancomycin or daptomycin, agents similar to oritavancin. We evaluated the activities of BLs combined with oritavancin against MRSA and VRE. Oritavancin MICs were determined for 30 strains, 5 each of MRSA, daptomycin-nonsusceptible (DNS) MRSA, vancomycin-intermediate MRSA (VISA), heteroresistant VISA (hVISA), vancomycin-resistantEnterococcus faecalis, and vancomycin-resistantEnterococcus faecium Oritavancin MICs were determined in the presence of subinhibitory concentrations of BLs. Oritavancin combined with ceftaroline, cefazolin, or nafcillin was evaluated for lethal synergy against MRSA, and oritavancin combined with ceftaroline, ampicillin, or ertapenem was evaluated for lethal synergy against VRE in 24-h time-kill assays. Oritavancin at 0.5× the MIC was combined with BLs at 0.5× the MIC or the biological free peak concentration, whichever one was lower. Synergy was defined as a ≥2-log10-CFU/ml difference between the killing achieved with the combination and that achieved with the most active single agent at 24 h. Oritavancin MICs were ≤0.125 μg/ml for all MRSA isolates except three VISA isolates with MICs of 0.25 μg/ml. Oritavancin MICs for VRE ranged from 0.03 to 0.125 μg/ml. Oritavancin in combination with ceftaroline was synergistic against all MRSA phenotypes and statistically superior to all other combinations against DNS MRSA, hVISA, and MRSA isolates (P< 0.02). Oritavancin in combination with cefazolin and oritavancin in combination with nafcillin were also synergistic against all MRSA strains. Synergy between oritavancin and all BLs was revealed against VRE strain 8019, while synergy between oritavancin and ampicillin or ertapenem but not ceftaroline was demonstrated against VRE strain R7164. The data support the potential use of oritavancin in combination with BLs, especially oritavancin in combination with ceftaroline, for the treatment of infections caused by MRSA. The data from the present study are not as strong for oritavancin in combination with BLs for VRE. Further study of both MRSA and VRE in more complex models is warranted.

Oritavancin: A New Lipoglycopeptide Antibiotic in the Treatment of Gram-Positive Infections

Resistance among Gram-positive organisms has been steadily increasing over the last several years; however, the development of new antibiotics to treat infections caused from these organisms has fallen short of the emergent need. Specifically, resistance among Staphylococcus aureus and Enterococcus spp. to essential antibiotics is considered a major problem. Oritavancin is a semisynthetic lipoglycopeptide antibiotic that was recently approved for the treatment of acute bacterial skin and skin structure infections (ABSSSI). While structurally related to vancomycin, oritavancin also possesses unique mechanisms of action that greatly enhance its antimicrobial potency against multi-drug resistant pathogens including both VanA- and VanB-mediated vancomycin-resistant enterococci. Owing to the addition of the highly hydrophobic tail group, oritavancin possesses a prolonged half-life ranging from 200-300 h. Although oritavancin is only currently Food and Drug Administration approved for ABSSSI, this agent may eventually play a role in additional indications where new innovative therapy is needed including bacteremia and deep-seeded, Gram-positive infections such as infective endocarditis or osteomyelitis. This review will focus on oritavancin's spectrum of activity, mechanisms of action and resistance, pharmacokinetic and pharmacodynamic properties, and the completed and ongoing clinical studies evaluating its use.

Glabridin-chalcone hybrid molecules: drug resistance reversal agent against clinical isolates of methicillin-resistant Staphylococcus aureus

16 folds reduction in MICs with norfloxacin against various clinical isolates of MRSA (FICI range from 0.312–0.375).

Synergistic effect of (+)-pinitol from Saraca asoca with β-lactam antibiotics and studies on the in silico possible mechanism

Saraca asoca bark has been used in the Ayurvedic system of medicine for female urino-genital disorders. We have recently reported the isolation and characterization of several compounds as markers to develop HPLC profiling of its methanol and aqueous methanol extracts. Now, a HPLC-PDA inactive compound, (+)-pinitol has been isolated and characterized from the bark of this medicinally important tree. Pinitol is a well known bioactive compound for a variety of biological activities, including hypoglycemic and anti-inflammatory activities. A process for the isolation of relatively good concentration of (+)-pinitol from S. asoca bark has been developed and its in vitro anti TNF-α and anti-inflammatory activities against carragenan-induced edema confirmed. While conducting experiments on the possible agonistic activity, it was found that (+)-pinitol showed up to eight fold reduction in the doses of β-lactam antibiotics. The mechanism of its agonistic activity was studied by docking experiments which showed that different conformations of (+)-pinitol and antibiotics were actually in the same binding site with no significant change in the binding energy. These docking simulations, thus predict the possible binding mode of studied compounds and probable reason behind the synergistic effect of (+)-pinitol along with β-lactam antibiotics.

Prolonged Use of Oritavancin for Vancomycin-Resistant Enterococcus faecium Prosthetic Valve Endocarditis

Oritavancin is a novel lipoglycopeptide with activity against Gram-positive organisms including streptococci, methicillin-resistant Staphylococcus aureus, vancomycin-resistant S aureus (VRSA), and vancomycin-resistant enterococci (VRE) [1-3]. The US Food and Drug Administration approved oritavancin as a single intravenous dose of 1200 mg for the treatment of acute bacterial skin and skin structure infections on the basis of 2 clinical trials demonstrating noninferiority compared with vancomycin [4, 5]. There are limited options for treatment of serious VRE infections. Monotherapy with daptomycin or tigecycline or linezolid may be sufficient in some cases, but combination therapy is often indicated for severe or complicated infections such as endocarditis. Several antibiotic combinations have been used in isolated case reports with some efficacy, including the following: high-dose ampicillin with an aminoglycoside [6], ampicillin with ceftriaxone or imipenem [7, 8], high-dose daptomycin with ampicillin and gentamicin [9] or with gentamicin and rifampin [10], daptomycin with tigecycline [11, 12], quinupristin-dalfopristin with high-dose ampicillin [13] or doxycycline and rifampin [14], and linezolid with tigecycline [15]. The limited efficacy, limited susceptibility, and extensive toxicities with many of these agents and combinations present barriers to effective treatment. Additional treatment options for VRE endocarditis would be valuable. Although oritavancin has been shown to have in vitro activity against some isolates of VRE, clinical data are lacking. We describe the first use of a prolonged course of oritavancin in the treatment of a serious VRE infection, prosthetic valve endocarditis.

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.

Optimizing therapy for vancomycin-resistant enterococcal bacteremia in children

PURPOSE OF REVIEW

Uncertainties exist regarding the optimal treatment for vancomycin-resistant enterococcal (VRE) bloodstream infections, particularly in settings in which ampicillin cannot be used.

RECENT FINDINGS

Quinupristin-dalfopristin, linezolid, and daptomycin, all approved between 1999 and 2003, represent the mainstays of therapy for VRE bacteremia, although only linezolid has been specifically approved by the United States Food and Drug Administration for this indication. The main objective of this review is to compare the relative efficacies, dosing strategies, and side-effect profiles of quinupristin-dalfopristin, linezolid, and daptomycin for VRE bacteremia in the pediatric population. A brief description of recently approved broad-spectrum Gram-positive agents that may have a role in the management of VRE bacteremia in upcoming years is also provided.

SUMMARY

Linezolid, despite its bacteriostatic activity against VRE, may be the most versatile of the available drugs. It has activity against both Enterococcus faecalis and E. faecium, can be administered orally, and resistance appears to be less of a concern with linezolid compared with the other agents. Additionally, the results of two recent meta-analyses demonstrate more favorable outcomes with linezolid compared with daptomycin for the treatment of VRE bacteremia. The clinical pharmacokinetics of linezolid have been well described in children. The most notable concern with linezolid, however, is toxicities associated with prolonged use. Until more prospective data are available, we favor linezolid as first-line therapy for the treatment of VRE bacteremia in children.