Tedizolid for the management of human infections: in vitro characteristics

Incidence of serotonin syndrome in patients receiving tedizolid and concomitant serotonergic agents

This study investigated the real-world incidence rate of serotonin syndrome in patients receiving tedizolid and concomitant serotonergic agents. A retrospective cohort of 479 adult patients was assessed between January 2015 and July 2023. Overall, a rare rate of 0.4% (2/479) of possible serotonin syndrome with tedizolid was identified. Given that concomitant serotonergic agents were commonly used, further study is warranted to determine causality.

Staph wars: the antibiotic pipeline strikes back

Antibiotic chemotherapy is widely regarded as one of the most significant medical advancements in history. However, the continued misuse of antibiotics has contributed to the rapid rise of antimicrobial resistance (AMR) globally. Staphylococcus aureus, a major human pathogen, has become synonymous with multidrug resistance and is a leading antimicrobial-resistant pathogen causing significant morbidity and mortality worldwide. This review focuses on (1) the targets of current anti-staphylococcal antibiotics and the specific mechanisms that confirm resistance; (2) an in-depth analysis of recently licensed antibiotics approved for the treatment of S. aureus infections; and (3) an examination of the pre-clinical pipeline of anti-staphylococcal compounds. In addition, we examine the molecular mechanism of action of novel antimicrobials and derivatives of existing classes of antibiotics, collate data on the emergence of resistance to new compounds and provide an overview of key data from clinical trials evaluating anti-staphylococcal compounds. We present several successful cases in the development of alternative forms of existing antibiotics that have activity against multidrug-resistant S. aureus. Pre-clinical antimicrobials show promise, but more focus and funding are required to develop novel classes of compounds that can curtail the spread of and sustainably control antimicrobial-resistant S. aureus infections.

Real-World Use of Tedizolid Phosphate for 28 Days or More: A Case Series Describing Tolerability and Clinical Success

Tedizolid has activity against Gram-positive pathogens as well as Mycobacterium spp and Nocardia spp. Real-world evidence supporting long-term tolerability and clinical success of tedizolid is lacking. Prolonged tedizolid therapy (median, 188 days; interquartile range, 62-493 days) appeared to be well tolerated in 37 patients (8.1% experienced adverse effect leading to discontinuation). Clinical success was 81.3% in those evaluated.

Alternatives to Fight Vancomycin-Resistant Staphylococci and Enterococci

Gram positive pathogens are a significant cause of healthcare-associated infections, with Staphylococci and Enterococci being the most prevalent ones. Vancomycin, a last resort glycopeptide, is used to fight these bacteria but the emergence of resistance against this drug leaves some patients with few therapeutic options. To counter this issue, new generations of antibiotics have been developed but resistance has already been reported. In this article, we review the strategies in place or in development to counter vancomycin-resistant pathogens. First, an overview of traditional antimicrobials already on the market or in the preclinical or clinical pipeline used individually or in combination is summarized. The second part focuses on the non-traditional antimicrobials, such as antimicrobial peptides, bacteriophages and nanoparticles. The conclusion is that there is hitherto no substitute equivalent to vancomycin. However, promising strategies based on drugs with multiple mechanisms of action and treatments based on bacteriophages possibly combined with conventional antibiotics are hoped to provide treatment options for vancomycin-resistant Gram-positive pathogens.

A mean-field approach for modeling the propagation of perturbations in biochemical reaction networks

Often, the time evolution of a biochemical reaction network is crucial for determining the effects of combining multiple pharmaceuticals. Here we illustrate a mathematical framework for modeling the dominant temporal behaviour of a complicated molecular pathway or biochemical reaction network in response to an arbitrary perturbation, such as resulting from the administration of a therapeutic agent. The method enables the determination of the temporal evolution of a target protein as the perturbation propagates through its regulatory network. The mathematical approach is particularly useful when the experimental data that is available for characterizing or parameterizing the regulatory network is limited or incomplete. To illustrate the method, we consider the examples of the regulatory networks for the target proteins c-Myc and Chop, which play an important role in venetoclax resistance in acute myeloid leukemia. First we show how the networks that regulate each target protein can be reduced to a mean-field model by identifying the distinct effects that groups of proteins in the regulatory network have on the target protein. Then we show how limited protein-level data can be used to further simplify the mean-field model to pinpoint the dominant effects of the network perturbation on the target protein. This enables a further reduction in the number of parameters in the model. The result is an ordinary differential equation model that captures the temporal evolution of the expression of a target protein when one or more proteins in its regulatory network have been perturbed. Finally, we show how the dominant effects predicted by the mathematical model agree with RNA sequencing data for the regulatory proteins comprising the molecular network, despite the model not having a priori knowledge of this data. Thus, while the approach gives a simplified model for the expression of the target protein, it allows for the interpretation of the effects of the perturbation on the regulatory network itself. This method can be easily extended to sets of target proteins to model components of a larger systems biology model, and provides an approach for partially integrating RNA sequencing data and protein expression data. Moreover, it is a general approach that can be used to study drug effects on specific protein(s) in any disease or condition.

Tedizolid activity against a multicentre worldwide collection of Staphylococcus aureus and Streptococcus pneumoniae recovered from patients with pneumonia (2017-2019)

OBJECTIVES

The antimicrobial activity of tedizolid and comparators was evaluated against a large worldwide collection of Staphylococcus aureus and Streptococcus pneumoniae isolates recovered from patients with pneumonia.

METHODS

Clinical isolates were collected from patients in 96 medical centres in the Asia-Pacific region, Europe, Latin America and the USA between 2017 and 2019, and tested for susceptibility by reference broth microdilution.

RESULTS

The most active agents against S. aureus (n = 4667) were tedizolid (100.0% susceptible), linezolid (100.0% susceptible), ceftaroline (96.2% susceptible) and vancomycin (100.0% susceptible), but only tedizolid, linezolid and vancomycin retained activity against >95% of meticillin-resistant S. aureus isolates from all regions. In general, linezolid, ceftriaxone, ceftaroline, levofloxacin, penicillin and vancomycin showed susceptibility rates >95% against S. pneumoniae (n = 3008). However, only linezolid, ceftaroline, levofloxacin and vancomycin remained active (>95% susceptibility) against isolates displaying penicillin-non-susceptible or multidrug-resistant phenotypes. Penicillin-non-susceptible S. pneumoniae isolates were recovered less frequently from patients aged <5 years compared with other age groups.

CONCLUSION

The in-vitro data presented here confirm the high potency of tedizolid against S. aureus and S. pneumoniae causing pneumonia worldwide. There is a need for further clinical evaluations of tedizolid for treating pneumonia caused by these pathogens.

Tedizolid is a promising antimicrobial option for the treatment of Staphylococcus aureus infections in cystic fibrosis patients

BACKGROUND

Tedizolid is a protein synthesis inhibitor in clinical use for the treatment of Gram-positive infections. Pulmonary MRSA infections are a growing problem in patients with cystic fibrosis (CF) and the efficacy of tedizolid-based therapy in CF pulmonary infections is unknown.

OBJECTIVES

To evaluate the in vitro and in vivo activity of tedizolid and predict the likelihood of tedizolid resistance selection in CF-background Staphylococcus aureus strains.

METHODS

A collection of 330 S. aureus strains (from adult and paediatric patients), either of normal or small colony variant (SCV) phenotypes, gathered at three CF centres in the USA was used. Tedizolid activity was assessed by broth microdilution, Etest and time-kill analysis. In vivo tedizolid efficacy was tested in a murine pneumonia model. Tedizolid in vitro mutants were obtained by 40 days of exposure and progressive passages. Whole genome sequencing of clinical S. aureus strains with reduced susceptibility to tedizolid was performed.

RESULTS

MRSA strain MIC90s were tedizolid 0.12-0.25 mg/L and linezolid 1-2 mg/L; for MSSA strains, MIC90s were tedizolid 0.12 mg/L and linezolid 1-2 mg/L. Two strains, WIS 441 and Seattle 106, with tedizolid MICs of 2 mg/L and 1 mg/L, respectively, had MICs above the FDA tedizolid breakpoint (0.5 mg/L). Tedizolid at free serum concentrations exhibited a bacteriostatic effect. Mean bacterial burdens in lungs (log10 cfu/g) for WIS 423-infected mice were: control, 11.2±0.5; tedizolid-treated (10 mg/kg), 3.40±1.87; linezolid-treated (40 mg/kg), 4.51±2.1; and vancomycin-treated (30 mg/kg), 5.21±1.93. For WIS 441-infected mice the (log10 cfu/g) values were: control, 9.66±0.8; tedizolid-treated, 3.18±1.35; linezolid-treated 5.94±2.19; and vancomycin-treated, 4.35±1.7.

CONCLUSIONS

These results suggest that tedizolid represents a promising therapeutic option for the treatment of CF-associated MRSA/MSSA infections, having potent in vivo activity and low resistance potential.

Chemotherapeutic Strategies for Combating Staphylococcus aureus Infections

Staphylococcus aureus is a prominent human pathogen that causes nosocomial and community acquired infections. The accelerating emergence and prevalence of staphylococcal infections have grotesque health consequences which are mostly due to its anomalous capability to acquire drug resistance and scarcity of novel classes of antibacterials. Many combating therapies are centered on primary targets of S. aureus which are cell envelope, ribosomes and nucleic acids. This review describes various chemotherapeutic strategies for combating S. aureus infections which includes monotherapy, combination drug therapy, phage endolysin therapy, lysostaphins and antibacterial drones. Monotherapy has dwindled in due course of time but combination therapy, endolysin therapy, lysostaphin and antibacterial drones are emerging alternatives which efficiently conquer the shortcomings of monotherapy. Combinations of more than one antibiotic agents or combination of adjuvant with antibiotics provide a synergistic approach to combat infections causing pathogenic strains. Phage endolysin therapy and lysostaphin are also presents as possible alternatives to conventional antibiotic therapies. Antibacterial Drones goes a step further by specifically targeting the virulence genes in bacteria giving them a certain advantage over existing antibacterial strategies. But the challenge remains on the better understanding of these strategies for executing and implementing them in health sector. In this day and age, most of the S. aureus strains are resistant to ample number of antibiotics, so there is an urgent need to overcome such multidrug resistant strains for the welfare of our community.

UPLC-MS/MS assay of Tedizolid in rabbit aqueous humor: Application to ocular pharmacokinetic study

Tedizolid phosphate (TZP) a prodrug of Tedizolid (TDZ) is a novel oxazolidinone antibiotic, used for the treatment of acute bacterial skin, skin structure infections and other serious gram positive and MRSA infections. In the present study, a sensitive UPLC-MS/MS analytical method was developed and validated for the quantification of TDZ in rabbit's aqueous humor (AqH) by using linezolid as internal standard (IS). Both TDZ and IS were separated on an Acquity™ HILIC column using an isocratic mobile phase comprising of acetonitrile: 20 mM ammonium acetate (85:15, v/v), eluted at 0.3mLmin^-1 flow rate with total run time of 3 min. The AqH samples were processed by protein precipitation method by using acetonitrile as precipitating agent. TDZ and IS were detected in positive mode using electrospray ionization source. The precursor to product ion transitions at m/z 371.15 to 343.17 for TDZ and m/z 338.18 to 296.22 for IS were used for the quantification in multiple reaction monitoring mode. The calibration curve was linear in the concentration range of 4.98-1000ngmL^-1 and the lower limit of detection was 1.97ngmL^-1 only. The method was validated following US-FDA-guidelines and the results of validation parameter were found within the set limits. The developed UPLC-MS/MS method was fast, sensitive and reliable for the quantification of TDZ in the rabbit AqH and was successfully employed for ocular pharmacokinetic study of TDZ in AqH after topical ocular application of TZP-containing formulations in rabbit eyes.

Tedizolid (torezolid) for the treatment of complicated skin and skin structure infections

INTRODUCTION

Acute bacterial skin and skin structure infections (ABSSSI) are among the most frequent infectious diseases. Recently, several new antibiotics with activity against MRSA have been approved. Tedizolid, a second-generation oxazolidinone approved for ABSSSI offers theoretical advantages over first-generation oxazolidinones.

AREAS COVERED

A comprehensive online search of Medline, ClinicalTrials.gov, and conference presentations was made, selecting articles between January 2000 and April 2020. In this review, the authors discuss the chemical and microbiological properties of tedizolid, summarize its efficacy, safety, and potential role in the treatment of ABSSSI as well as the potential for future indications.

EXPERT OPINION

Tedizolid has proven to be non-inferior compared to linezolid for the treatment of ABSSSI in two registrational phase III clinical trials, being well tolerated. Tedizolid exhibits antibacterial activity against the most important ABSSSI pathogens (including multidrug-resistant strains of MRSA), as well as mycobacteria and Nocardia. It appears to have a safe profile, including decreased myelotoxicity and no significant drug interactions. Preliminary studies with longer duration of therapy seem to confirm these potential benefits. Overall, tedizolid expands the newly acquired armamentarium to treat ABSSSI. The role of tedizolid for other indications is under investigation and has yet to be determined.

Transferable Resistance Gene optrA in Enterococcus faecalis from Swine in Brazil

OptrA is an ATP-binding cassette (ABC)-F protein that confers resistance to oxazolidinones and phenicols and can be either plasmid-encoded or chromosomally encoded. Here, we isolated 13 Enterococcus faecalis strains possessing a linezolid MIC of ≥4 mg/liter from nursery pigs in swine herds located across Brazil. Genome sequence comparison showed that these strains possess optrA in different genetic contexts occurring in 5 different E. faecalis sequence type backgrounds. The optrA gene invariably occurred in association with an araC regulator and a gene encoding a hypothetical protein. In some contexts, this genetic island was able to excise and form a covalently closed circle within the cell; this circle appeared to occur in high abundance and to be transmissible by coresident plasmids.

Current role of oxazolidinones and lipoglycopeptides in skin and soft tissue infections

PURPOSE OF REVIEW

An increase of skin and soft tissue infections involving Staphylococcus aureus has been reported in community and hospital settings. Methicillin resistance in S. aureus is associated with treatment failure and increased mortality. Recently, new antimicrobials with enhanced activity against methicillin-resistant Staph. aureus have been approved for the treatment of skin and soft tissue infections. Among these, novel oxazolidinones and lipoglycopeptides represent options with favorable pharmacokinetic characteristics and safety profiles.

RECENT FINDINGS

Newly approved compounds include tedizolid, characterized by the availability of both oral and intravenous formulation and once daily administration and dalbavancin, a long-acting antimicrobial allowing for weekly administration. These new molecules present advantages, such as enhanced activity against multidrug-resistant Gram-positive bacteria and favorable safety profiles.

SUMMARY

We have reviewed the pharmacokinetic characteristics and the implications for use in skin and soft tissue infections of tedizolid and dalbavancin. Advantages associated with the use of these compounds include the possibility for early patient discharge, reduced hospital length of stay, and outpatient treatment, with potential impact on morbidity, mortality, and overall health-care costs.

Defect-engineering a metal–organic framework for CO2 fixation in the synthesis of bioactive oxazolidinones

Three-component, solvent-free cycloaddition of epoxides with aromatic amines and CO₂.

Analysis of combined resistance to oxazolidinones and phenicols among bacteria from dogs fed with raw meat/vegetables and the respective food items

The gene optrA is the first gene that confers resistance to the oxazolidinone tedizolid, a last resort antimicrobial agent in human medicine. In this study we investigated the presence of optrA and the multi-resistance genes poxtA and cfr in enterococci and staphylococci from (i) pet animals known to be fed raw meat and vegetables and (ii) the respective food items. We examined 341 bacterial isolates from cats and dogs, 195 bacterial isolates from supermarket food items and only one E. faecium collected from industrial food in Beijing during 2016. Thirty-five (6.5%) of the 537 isolates, including 31/376 (8.2%) enterococci and 4/161 (2.5%) staphylococci, were positive for optrA, while all isolates were negative for poxtA and cfr. S1-nuclease pulsed-field gel electrophoresis (PFGE) and Southern blotting confirmed that optrA was located in the chromosomal DNA of 19 isolates and on a plasmid in the remaining 16 isolates. Whole genome sequencing revealed several different genetic environments of optrA in plasmid- or chromosome-borne optrA genes. PFGE, multilocus sequence typing (MLST) and/or SNP analysis demonstrated that the optrA-carrying Staphylococcus and Enterococcus isolates were genetically heterogeneous. However, in single cases, groups of related isolates were identified which might suggest a transfer of closely related optrA-positive E. faecalis isolates between food items and dogs.

Effect of tedizolid on clinical Enterococcus isolates: in vitro activity, distribution of virulence factor, resistance genes and multilocus sequence typing

Enterococcal infections have become one of the most challenging nosocomial problems. Tedizolid, the second oxazolidinone, is 4-fold to 8-fold more potent in vivo and in vitro than linezolid against enterococci. However, the characteristics of tedizolid related to enterococci isolates in China remain elusive. The aim of this study was to evaluate in vitro activity of tedizolid against enterococcal isolates from patients with infections at a teaching hospital in China and to investigate the correlations between in vitro tedizolid activity against enterococci and the distribution of multilocus sequence types (MLST), resistance genes and virulence factors. A total of 289 non-duplicate Enterococcus faecalis strains and 68 E. faecium strains were isolated. Tedizolid inhibited 95.24% of all enterococcal isolates with an MIC ≤ 0.5μg/ml. Seventeen E. faecalis strains had an MIC > 0.5 μg/ml, and all E. faecium were inhibited at MIC ≤ 0.5 μg/ml. The proportion of tedizolid non-susceptible E. faecalis strains with optrA genes was higher than that among tedizolid-susceptible strains. Tedizolid exhibited good in vitro activity against all E. faecium strains, including multidrug-resistant E. faecium carrying tet(M), tet(L), tet(U),erm(A), erm(B) and erm(C) genes. In summary, tedizolid has an advantage (higher sensitivity rate) compared to linezolid among enterococci, except for isolates expressing the plasmid-encoded optrA gene.

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.

Tedizolid in vitro activity against Gram-positive clinical isolates causing bone and joint infections in hospitals in the USA and Europe (2014–17)

Background

Despite the advances in current healthcare, bone and joint infections (BJIs) are a major clinical challenge that frequently involve prolonged systemic antibiotic use. Healthcare providers consider tedizolid an attractive candidate for therapy in adults and children with BJI.

Objectives

We tested tedizolid against a US and European collection of Gram-positive BJI isolates (n = 797) consecutively collected from 2014 to 2017.

Methods

Organisms were tested by broth microdilution susceptibility methods following current CLSI guidelines and interpreted by both CLSI and EUCAST breakpoint criteria.

Results

Staphylococcus aureus (59.3%; 58.6% in the USA and 60.4% in Europe) was the most common pathogen with a 29.6% MRSA rate and tedizolid MIC50/90 of 0.12/0.25 mg/L (100% susceptible). CoNS (15.0% of BJI in adults and <5% in children) had tedizolid MIC50/90 values of 0.12/0.12 mg/L (99.1% susceptible). Tedizolid exhibited MIC50/90 values of 0.12/0.25 mg/L for all streptococci and enterococci. Overall, high susceptibility rates (>95%) for vancomycin, daptomycin and linezolid were observed and, based on MIC90 values, tedizolid (MIC90 0.12–0.25 mg/L) was 4- to 8-fold more potent than linezolid (MIC90 0.5–2  mg/L) against this collection of Gram-positive pathogens causing BJI.

Conclusions

This study showed that tedizolid had potent in vitro activity against contemporary Gram-positive cocci causing BJI in adults and children in US and European hospitals.

Subinhibitory concentrations of tedizolid potently inhibit extracellular toxin production by methicillin-sensitive and methicillin-resistant Staphylococcus aureus

PURPOSE

Potent extracellular toxins including alpha-haemolysin, Panton-Valentine leukocidin (PVL) and toxic-shock syndrome toxin 1 (TSST-1) significantly contribute to Staphylococcus aureus pathogenesis, thus, toxin suppression is a primary focus in treatment of staphylococcal disease. S. aureus maintains complex strategies to regulate toxin expression and previous data have demonstrated that subinhibitory concentrations of beta-lactam antibiotics can adversely increase S. aureus exotoxin production. The current study evaluates the effects of subinhibitory concentrations of tedizolid, a second-generation oxazolidinone derivative, on expression of staphylococcal exotoxins in both methicillin-resistant and methicillin-sensitive S. aureus.

METHODOLOGY

S. aureus exotoxin expression levels were compared at 12 and 24 h following treatment with tedizolid, linezolid, nafcillin or vehicle control.

RESULTS

Our findings show that the level of antibiotic required to alter toxin production was strain-dependent and corresponds with the quantity of toxin produced, but both tedizolid and linezolid could effectively reduce expression of alpha-haemolysin, PVL and TSST-1 toxin at subinhibitory concentrations. In contrast, nafcillin showed less attenuation and, in some S. aureus strains, led to an increase in toxin expression. Tedizolid consistently inhibited toxin production at a lower overall drug concentration than comparator agents.

CONCLUSION

Together, our data support that tedizolid has the potential to improve outcomes of infection due to its superior ability to inhibit S. aureus growth and attenuate exotoxin production.

Mechanisms of antimicrobial resistance among hospital-associated pathogens

INTRODUCTION

The introduction of antibiotics revolutionized medicine in the 20th-century permitting the treatment of once incurable infections. Widespread use of antibiotics, however, has led to the development of resistant organisms, particularly in the healthcare setting. Today, the clinician is often faced with pathogens carrying a cadre of resistance determinants that severely limit therapeutic options. The genetic plasticity of microbes allows them to adapt to stressors via genetic mutations, acquisition or sharing of genetic material and modulation of genetic expression leading to resistance to virtually any antimicrobial used in clinical practice. Areas covered: This is a comprehensive review that outlines major mechanisms of resistance in the most common hospital-associated pathogens including bacteria and fungi. Expert commentary: Understanding the genetic and biochemical mechanisms of such antimicrobial adaptation is crucial to tackling the rapid spread of resistance, can expose unconventional therapeutic targets to combat multidrug resistant pathogens and lead to more accurate prediction of antimicrobial susceptibility using rapid molecular diagnostics. Clinicians making treatment decisions based on the molecular basis of resistance may design therapeutic strategies that include de-escalation of broad spectrum antimicrobial usage, more focused therapies or combination therapies. These strategies are likely to improve patient outcomes and decrease the risk of resistance in hospital settings.

Current and future treatment options for community-associated MRSA infection

INTRODUCTION

Community-associated MRSA (CA-MRSA) represents a global epidemic which beautifully encapsulates the fascinating ability of bacterial organisms to adapt quickly on an evolutionary basis to the extreme selective pressure of antibiotic exposure. In stark contrast to Healthcare-associated MRSA (HA-MRSA), it has become apparent that CA-MRSA is less straight forward of a challenge in terms of controlling its transmission, and has forced clinicians to adjust empiric management of clinical syndromes such as skin and soft tissue infection (SSTI) as well as pneumonia.

AREAS COVERED

This review details the history and epidemiology of CA-MRSA, while covering both current and future treatment options that are and may be available to clinicians. The authors reviewed both historic and more recent literature on this ever-evolving topic.

EXPERT OPINION

While development of new anti-MRSA agents should be encouraged, the importance of antimicrobial stewardship in the battle to stay ahead of the curve with regards to the ongoing control of the MRSA epidemic should be emphasised.

Binding and Action of Amino Acid Analogs of Chloramphenicol upon the Bacterial Ribosome

Antibiotic chloramphenicol (CHL) binds with a moderate affinity at the peptidyl transferase center of the bacterial ribosome and inhibits peptide bond formation. As an approach for modifying and potentially improving properties of this inhibitor, we explored ribosome binding and inhibitory activity of a number of amino acid analogs of CHL. The L-histidyl analog binds to the ribosome with the affinity exceeding that of CHL by 10 fold. Several of the newly synthesized analogs were able to inhibit protein synthesis and exhibited the mode of action that was distinct from the action of CHL. However, the inhibitory properties of the semi-synthetic CHL analogs did not correlate with their affinity and in general, the amino acid analogs of CHL were less active inhibitors of translation in comparison with the original antibiotic. The X-ray crystal structures of the Thermus thermophilus 70S ribosome in complex with three semi-synthetic analogs showed that CHL derivatives bind at the peptidyl transferase center, where the aminoacyl moiety of the tested compounds established idiosyncratic interactions with rRNA. Although still fairly inefficient inhibitors of translation, the synthesized compounds represent promising chemical scaffolds that target the peptidyl transferase center of the ribosome and potentially are suitable for further exploration.

Antibiotic resistance in Staphylococcus aureus. Current status and future prospects

The major targets for antibiotics in staphylococci are (i) the cell envelope, (ii) the ribosome and (iii) nucleic acids. Several novel targets emerged from recent targeted drug discovery programmes including the ClpP protease and FtsZ from the cell division machinery. Resistance can either develop by horizontal transfer of resistance determinants encoded by mobile genetic elements viz plasmids, transposons and the staphylococcal cassette chromosome or by mutations in chromosomal genes. Horizontally acquired resistance can occur by one of the following mechanisms: (i) enzymatic drug modification and inactivation, (ii) enzymatic modification of the drug binding site, (iii) drug efflux, (iv) bypass mechanisms involving acquisition of a novel drug-resistant target, (v) displacement of the drug to protect the target. Acquisition of resistance by mutation can result from (i) alteration of the drug target that prevents the inhibitor from binding, (ii) derepression of chromosomally encoded multidrug resistance efflux pumps and (iii) multiple stepwise mutations that alter the structure and composition of the cell wall and/or membrane to reduce drug access to its target. This review focuses on development of resistance to currently used antibiotics and examines future prospects for new antibiotics and informed use of drug combinations.

A metal–metalloporphyrin framework based on an octatopic porphyrin ligand for chemical fixation of CO2with aziridines

A new porous metal–metalloporphyrin framework, MMPF-10, was synthesized for CO₂cycloaddition with aziridines.

In Vitro Susceptibility Testing of Tedizolid against Isolates of Nocardia

There is a paucity of efficacious antimicrobials (especially oral) against clinically relevant species of Nocardia To date, all species of Nocardia have been susceptible to linezolid, the first commercially available oxazolidinone. Tedizolid is a new oxazolidinone with previously reported improved in vitro and in vivo (intracellular) potency against multidrug-resistant strains of Mycobacterium sp. and Nocardia brasiliensis Using the current Clinical and Laboratory Standards Institute-recommended broth microdilution method, 101 isolates of Nocardia spp., including 29 Nocardia cyriacigeorgica, 17 Nocardia farcinica, 13 Nocardia nova complex, 21 Nocardia brasiliensis, 5 Nocardia pseudobrasiliensis, and 5 Nocardia wallacei isolates and 11 isolates of less common species, were tested for susceptibility to tedizolid and linezolid. For the most common clinically significant species of Nocardia, tedizolid MIC₅₀ values were 0.25 μg/ml for N. nova complex, N. brasiliensis, N. pseudobrasiliensis, and N. wallacei, compared to linezolid MIC₅₀ values of 1, 2, 0.5, and 1 μg/ml, respectively. Tedizolid and linezolid MIC₉₀ values were 2 μg/ml for N. nova complex and N. brasiliensis Tedizolid MIC₅₀ and MIC₉₀ values for both N. cyriacigeorgica and N. farcinica were 0.5 μg/ml and 1 μg/ml, respectively, compared to linezolid MIC₅₀ and MIC₉₀ values of 2 and 4 μg/ml, respectively. Based on MIC₉₀ values, this study showed that tedizolid was 2- to 3-fold more active than linezolid in vitro against most common species of Nocardia, with the exception of the N. nova complex and N. brasiliensis, for which values were the same. These results may warrant evaluation of tedizolid as a potential treatment option for Nocardia infections.

Determination of Tedizolid susceptibility interpretive criteria for gram-positive pathogens according to clinical and laboratory standards institute guidelines

For effective antibacterial therapy, physicians require qualitative test results using susceptibility breakpoints provided by clinical microbiology laboratories. This article summarizes the key components used to establish the Clinical Laboratory Standards Institute (CLSI) breakpoints for tedizolid. First, in vitro studies using recent surveillance and clinical trial isolates ascertained minimal inhibitory concentration (MIC) distributions against pertinent organisms, including staphylococci, streptococci, and enterococci. Studies in animal models of infection determined rates of antibacterial efficacy and survival following administration of tedizolid phosphate at doses equivalent to those in humans. Pharmacokinetic and pharmacodynamic analyses examined the relationship between plasma concentrations and MICs against the target organism. Finally, clinical trials assessed clinical and microbiologic outcomes by MIC. All these data were evaluated and combined to obtain the ratified CLSI susceptibility criteria for tedizolid of ≤0.5μg/mL for Staphylococcus aureus, Streptococcus pyogenes, Streptococcus agalactiae, and Enterococcus faecalis and ≤0.25μg/mL for Streptococcus anginosus group.

Mechanisms of Antibiotic Resistance

Emergence of resistance among the most important bacterial pathogens is recognized as a major public health threat affecting humans worldwide. Multidrug-resistant organisms have not only emerged in the hospital environment but are now often identified in community settings, suggesting that reservoirs of antibiotic-resistant bacteria are present outside the hospital. The bacterial response to the antibiotic "attack" is the prime example of bacterial adaptation and the pinnacle of evolution. "Survival of the fittest" is a consequence of an immense genetic plasticity of bacterial pathogens that trigger specific responses that result in mutational adaptations, acquisition of genetic material, or alteration of gene expression producing resistance to virtually all antibiotics currently available in clinical practice. Therefore, understanding the biochemical and genetic basis of resistance is of paramount importance to design strategies to curtail the emergence and spread of resistance and to devise innovative therapeutic approaches against multidrug-resistant organisms. In this chapter, we will describe in detail the major mechanisms of antibiotic resistance encountered in clinical practice, providing specific examples in relevant bacterial pathogens.

In Vitro Susceptibility Testing of Tedizolid against Nontuberculous Mycobacteria

Tedizolid is a new oxazolidinone with improved in vitro and intracellular potency against Mycobacterium tuberculosis, including multidrug-resistant strains, and some species of nontuberculous mycobacteria (NTM) compared with that of linezolid. Using the current Clinical and Laboratory Standards Institute (CLSI)-recommended method of broth microdilution, susceptibility testing of 170 isolates of rapidly growing mycobacteria showed equivalent or lower (1- to 8-fold) MIC₅₀ and/or MIC₉₀ values for tedizolid compared with that for linezolid. The tedizolid MIC₉₀ values for 81 isolates of M. abscessus subsp. abscessus and 12 isolates of M. abscessus subsp. massiliense were 8 μg/ml and 4 μg/ml, respectively, compared with linezolid MIC₉₀ values of 32 μg/ml for both. The MIC₉₀ values for 20 isolates of M. fortuitum were 2 μg/ml for tedizolid and 4 μg/ml for linezolid. Twenty-two isolates of M. chelonae had tedizolid and linezolid MIC₉₀s of 2 μg/ml and 16 μg/ml, respectively. One hundred forty-two slowly growing NTM, including 7/7 M. marinum, 7/7 M. kansasii, and 7/11 of other less commonly isolated species, had tedizolid MICs of ≤1 μg/ml and linezolid MICs of ≤4 μg/ml. One hundred isolates of Mycobacterium avium complex and eight M. simiae isolates had tedizolid MIC₅₀s of 8 μg/ml and linezolid MIC₅₀s 32 and 64 μg/ml, respectively. Nine M. arupense isolates had MIC₅₀s of 4 μg/ml and 16 μg/ml for tedizolid and linezolid, respectively. These findings demonstrate a greater in vitro potency of tedizolid than linezolid against NTM and suggest that an evaluation of tedizolid as a potential treatment agent for infections caused by selected NTM is warranted.

Pharmacokinetic drug evaluation of tedizolid for the treatment of skin infections

INTRODUCTION

Tedizolid is indicated for the treatment of acute bacterial skin and skin structure infections (ABSSSI). Although tedizolid shares many similar properties with linezolid, another oxazolidinone used to treat ABSSSI, the two antibiotics have several key differences. Areas covered: This review provides a detailed summary of the overall pharmacodynamics, pharmacokinetics, clinical efficacy, and safety of tedizolid for the treatment of ABSSSI. Expert opinion: Compared to other antibiotics used for ABSSSI, tedizolid has several advantages. Tedizolid has a long half-life, allowing for once daily dosing. Tedizolid also has broad spectrum of activity against Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus, Coagulase-negative Staphylococci, and Enterococci - including isolates demonstrating resistance to linezolid. It is available in both oral and intravenous formulations, and, has outstanding oral bioavailability, allowing for oral-step down therapy. There is also some evidence that, tedizolid has fewer significant interactions with serotonin reuptake inhibitors or monoamine oxidase inhibitors than linezolid. Finally, thrombocytopenia may occur less often with tedizolid than linezolid. However, these benefits must be weighed against the financial cost of tedizolid and the availability of alternative antibiotic choices.

Activity of Tedizolid in Methicillin-Resistant Staphylococcus epidermidis Experimental Foreign Body-Associated Osteomyelitis

We developed a rat model of methicillin-resistant Staphylococcus epidermidis (MRSE) foreign body-associated osteomyelitis and used it to compare tedizolid alone and in combination with rifampin against rifampin alone, vancomycin plus rifampin, and vancomycin alone. A clinical strain of MRSE was inoculated into the proximal tibia, and a stainless steel wire with a precolonized MRSE biofilm was implanted. Following a 1-week infection period, 92 rats received either no treatment (n = 17) or 14 days of intraperitoneal tedizolid (n = 15), tedizolid plus rifampin (n = 15), rifampin (n = 15), vancomycin plus rifampin (n = 15), or vancomycin (n = 15). Quantitative bone and wire cultures were performed after treatment completion and also 1 week after infection in a separate group of five rats. The median quantity of staphylococci in bone after the 1-week infection period was 4.89 log₁₀ CFU/g bone (interquartile range, 3.83 to 5.33 log₁₀ CFU/g bone); staphylococci were recovered from all associated wires. A median quantity of staphylococci of 3.70 log₁₀ CFU/g bone was detected in bones of untreated control rats after 3 weeks. Quantities of staphylococci in bones of all treatment groups except the group receiving vancomycin alone (2.78 log₁₀ CFU/g) were significantly lower than those for untreated controls, with no staphylococci being detected in the groups receiving rifampin monotherapy, tedizolid-plus-rifampin combination therapy, and vancomycin-plus-rifampin combination therapy. Quantities of staphylococci on wires from all treatment groups that included rifampin were significantly lower than those for untreated controls. No resistance to rifampin, tedizolid, or vancomycin was detected. Tedizolid combined with rifampin was active in a rat model of MRSE foreign body-associated osteomyelitis.

Comparative In Vivo Efficacies of Tedizolid in Neutropenic versus Immunocompetent Murine Streptococcus pneumoniae Lung Infection Models

Given that tedizolid exhibits substantial lung penetration, we hypothesize that it could achieve good efficacy against Streptococcus pneumoniae lung infections. We evaluated the pharmacodynamics of tedizolid for treatment of S. pneumoniae lung infections and compared the efficacies of tedizolid human-simulated epithelial lining fluid (ELF) exposures in immunocompetent and neutropenic murine lung infection models. ICR mice were rendered neutropenic via intraperitoneal cyclophosphamide injections and then inoculated intranasally with S. pneumoniae suspensions. Immunocompetent CBA/J mice were inoculated similarly. Single daily tedizolid doses were administered 4 h postinoculation (termed 0 h). Changes in log₁₀ CFU at 24 h compared with 0-h controls were estimated. Ratios of area under the free-drug concentration-time curve to MIC (fAUC_0-24/MIC) required to achieve various efficacy endpoints against each isolate were estimated using the Hill equation. Tedizolid doses in neutropenic and immunocompetent mice that mimic the human-simulated ELF exposure were examined. Stasis, 1-log reduction, and 2-log reduction were achieved at fAUC_0-24/MIC of 8.96, 24.62, and 48.34, respectively, in immunocompetent mice and 19.21, 48.29, and 103.95, respectively, in neutropenic mice. Tedizolid at 40 mg/kg of body weight/day and 55 mg/kg/day in immunocompetent and neutropenic mice, respectively, resulted in ELF AUC_0-24 comparable to that achieved in humans following a 200-mg once-daily clinical dose. These human-simulated ELF exposures were adequate to attain >2-log reduction in bacterial burden at 24 h in 3 out of 4 isolates in both models and 1.58- and 0.74-log reductions with the fourth isolate in immunocompetent and neutropenic mice, respectively. Tedizolid showed potent in vivo efficacy against S. pneumoniae in both immunocompetent and neutropenic lung infection models, which support its consideration for S. pneumoniae lung infections.

Critical role of tedizolid in the treatment of acute bacterial skin and skin structure infections

Tedizolid phosphate has high activity against the Gram-positive microorganisms mainly involved in acute bacterial skin and skin structure infections, such as strains of Staphylococcus aureus (including methicillin-resistant S. aureus strains and methicillin-sensitive S. aureus strains), Streptococcus pyogenes, Streptococcus agalactiae, the Streptococcus anginosus group, and Enterococcus faecalis, including those with some mechanism of resistance limiting the use of linezolid. The area under the curve for time 0-24 hours/minimum inhibitory concentration (MIC) pharmacodynamic ratio has shown the best correlation with the efficacy of tedizolid, versus the time above MIC ratio and the maximum drug concentration/minimum inhibitory concentration ratio. Administration of this antibiotic for 6 days has shown its noninferiority versus administration of linezolid for 10 days in patients with skin and skin structure infections enrolled in two Phase III studies (ESTABLISH-1 and ESTABLISH-2). Tedizolid's more favorable safety profile and dosage regimen, which allow once-daily administration, versus linezolid, position it as a good therapeutic alternative. However, whether or not the greater economic cost associated with this antibiotic is offset by its shorter treatment duration and possibility of oral administration in routine clinical practice has yet to be clarified.

Linezolid: a promising option in the treatment of Gram-positives

Linezolid, an oxazolidinone antimicrobial agent that acts by inhibiting protein synthesis in a unique fashion, is used in the treatment of community-acquired pneumonia, skin and soft-tissue infections and other infections caused by Gram-positive bacteria including VRE and methicillin-resistant staphylococci. Currently, linezolid resistance among these pathogens remains low, commonly <1.0%, although the prevalence of antibiotic resistance is increasing in many countries. Therefore, the development of resistance by clinical isolates should prompt increased attention of clinical laboratories to routinely perform linezolid susceptibility testing for this important agent and should be taken into account when considering its therapeutic use. Considering the importance of linezolid in the treatment of infections caused by Gram-positive bacteria, this review was undertaken to optimize the clinical use of this antibiotic.

New agents approved for treatment of acute staphylococcal skin infections

Vancomycin has been a predominant treatment for methicillin-resistant Staphylococcus aureus (MRSA) infections for decades. However, growing reservations about its efficacy led to an urgent need for new antibiotics effective against MRSA and other drug-resistant Staphylococcus aureus strains. This review covers three new anti-MRSA antibiotics that have been recently approved by the FDA: dalbavancin, oritavancin, and tedizolid. The mechanism of action, indications, antibacterial activity profile, microbial resistance, pharmacokinetics, clinical efficacy, adverse effects, interactions as well as available formulations and administration of each of these new antibiotics are described. Dalbavancin is a once-a-week, two-dose, long-acting intravenous bactericidal lipoglycopeptide antibiotic. Oritavancin, a lipoglycopeptide with bactericidal activity, was developed as a single-dose intravenous treatment for acute bacterial skin and skin-structure infections (ABSSSI), which offers simplifying treatment of infections. Tedizolid is an oxazolidinone-class bacteriostatic once-daily agent, available for intravenous as well as oral use. Increased ability to overcome bacterial resistance is the main therapeutic advantage of the novel agents over existing antibiotics.

Resistance to Non-glycopeptide Agents in Serious Staphylococcus aureus Infections

The role of vancomycin in the treatment of serious Staphylococcus aureus infections, both methicillin-susceptible and methicillin-resistant, is becoming increasingly ineffective due to increasing MIC and failure. The development of reduced vancomycin susceptibility by S. aureus to glycopeptides highlights the need for clinicians to reexamine the roles of non-glycopeptide therapy. As the use of these alternative non-glycopeptides antimicrobials increases, it will become pertinent to monitor the rates of resistance. Large surveillance programs have provided data for resistance against S. aureus for the non-glycopeptides (daptomycin, ceftaroline, tigecycline, linezolid, and tedizolid). The current published literatures suggest that worldwide resistance rates to these non-glycopeptides for serious MRSA infections are still low. Implementation of antimicrobial stewardship programs will be crucial in prevention of resistance of these antimicrobials against S. aureus.

Activity of Tedizolid in Methicillin-Resistant Staphylococcus aureus Experimental Foreign Body-Associated Osteomyelitis

We compared tedizolid alone and tedizolid with rifampin to rifampin and vancomycin plus rifampin in a rat model of methicillin-resistant Staphylococcus aureus (MRSA) foreign body-associated osteomyelitis. The study strain was a prosthetic joint infection-associated isolate. Steady-state pharmacokinetics for intraperitoneal administration of tedizolid, vancomycin, and rifampin were determined in uninfected rats. MRSA was inoculated into the proximal tibia, and a wire was implanted. Four weeks later, the rats were treated intraperitoneally for 21 days with tedizolid (n = 14), tedizolid plus rifampin (n = 11), rifampin (n = 16), or vancomycin plus rifampin (n = 13). Seventeen rats received no treatment. After treatment, quantitative bone cultures were performed. Blood was obtained for determination of drug trough concentrations in the tedizolid and tedizolid plus rifampin groups. The mean peak plasma concentration and mean area under the concentration-time curve from time zero to 24 h for tedizolid were 12 μg/ml and 60 μg · h/ml, respectively. The bacterial loads in all treatment groups were significantly lower than those in the control group; those in the tedizolid- plus rifampin-treated animals were not significantly different from those in the vancomycin- plus rifampin-treated animals. The range of mean plasma trough concentrations in the tedizolid group was 0.44 to 0.73 μg/ml. Although neither tedizolid nor vancomycin resistance was detected in isolates recovered from bones, rifampin resistance was detected in 10 animals (63%) in the rifampin group, 8 animals (73%) in the tedizolid plus rifampin group, and a single animal (8%) in the vancomycin plus rifampin group. Tedizolid alone or tedizolid combined with rifampin was active in a rat model of MRSA foreign body-associated osteomyelitis. The emergence of rifampin resistance was noted in animals receiving tedizolid plus rifampin.

Prevalence and Abundance of Florfenicol and Linezolid Resistance Genes in Soils Adjacent to Swine Feedlots

Florfenicol is extensively used in livestock to prevent or cure bacterial infections. However, it is not known whether the administration of florfenicol has resulted in the emergence and dissemination of florfenicol resistance genes (FRGs, including fexA, fexB, cfr, optrA, floR, and pexA) in microbial populations in surrounding farm environments. Here we collected soil samples for the detection of FRGs and the residue of florfenicol from six swine farms with the record of florfenicol usage. Quantitative polymerase chain reaction and metagenomic sequencing revealed a significantly higher relative abundance of FRGs in the soils adjacent to the three swine farms where florfenicol was heavily used compared with the other sites. Meanwhile, the detectable levels of florfenicol were also identified in soils from two of these three farms using ultra-performance liquid chromatography tandem mass spectrometry. It appears that amount of florfenicol used on swine farms and the spreading of soils with swine waste could promote the prevalence and abundance of FRGs, including the linezolid resistance genes cfr and optrA, in adjacent soils, and agricultural application of swine manure with florfenicol may have caused a residual level of florfenicol in the soils.

Activities of Tedizolid and Linezolid Determined by the Reference Broth Microdilution Method against 3,032 Gram-Positive Bacterial Isolates Collected in Asia-Pacific, Eastern Europe, and Latin American Countries in 2014

Tedizolid and linezolid in vitro activities against 3,032 Gram-positive pathogens collected in Asia-Pacific, Eastern European, and Latin American medical centers during 2014 were assessed. The isolates were tested for susceptibility by the current reference broth microdilution methods. Due to concern over the effect of MIC endpoint criteria on the results of testing the oxazolidinones tedizolid and linezolid, MIC endpoint values were read by two methods: (i) reading the MIC at the first well where the trailing began without regard for pinpoint trailing, according to CLSI M07-A10 and M100-S26 document instructions for reading linezolid (i.e., 80% inhibition of growth; these reads were designated tedizolid 80 and linezolid 80), and (ii) at 100% inhibition of growth (designated tedizolid 100 and linezolid 100). All Staphylococcus aureus, Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus anginosus group, and Enterococcus faecalis isolates were inhibited at tedizolid 80 and 100 MIC values of 0.25 and 0.5, 0.25 and 0.25, 0.25 and 0.5, 0.12 and 0.25, and 0.5 and 1 μg/ml, respectively. Generally, MIC50 and MIC90 results for tedizolid 80 and linezolid 80 were one doubling dilution lower than those read at 100% inhibition. Tedizolid was 4- to 8-fold more potent than linezolid against all the isolates tested regardless of the MIC endpoint criterion used. Despite the differences in potency, >99.9% of isolates tested in this survey were susceptible to both linezolid and tedizolid using CLSI and EUCAST interpretive criteria. In conclusion, tedizolid demonstrated greater in vitro potency than linezolid against Gram-positive pathogens isolated from patients in medical centers across the Asia-Pacific region, Eastern Europe, and Latin America.