New Gram-Positive Agents: the Next Generation of Oxazolidinones and Lipoglycopeptides

Mechanism of staphylococcal resistance to clinically relevant antibiotics

Staphylococcus aureus, a notorious pathogen with versatile virulence, poses a significant challenge to current antibiotic treatments due to its ability to develop resistance mechanisms against a variety of clinically relevant antibiotics. In this comprehensive review, we carefully dissect the resistance mechanisms employed by S. aureus against various antibiotics commonly used in clinical settings. The article navigates through intricate molecular pathways, elucidating the mechanisms by which S. aureus evades the therapeutic efficacy of antibiotics, such as β-lactams, vancomycin, daptomycin, linezolid, etc. Each antibiotic is scrutinised for its mechanism of action, impact on bacterial physiology, and the corresponding resistance strategies adopted by S. aureus. By synthesising the knowledge surrounding these resistance mechanisms, this review aims to serve as a comprehensive resource that provides a foundation for the development of innovative therapeutic strategies and alternative treatments for S. aureus infections. Understanding the evolving landscape of antibiotic resistance is imperative for devising effective countermeasures in the battle against this formidable pathogen.

Periprosthetic hip infection: Current concepts and the Wrightington experience

Total hip arthroplasty (THA) is a highly successful operation performed worldwide in increasing numbers for a wide range of indications. There has been a corresponding rise in the incidence of periprosthetic joint infection of the hip (PJIH), which is a devastating complication. There is a significant variation in the definition, diagnosis and management of PJIH largely due to a lack of high-level evidence. The current standard of practice is largely based on cohort studies from high-volume centres, consensus publications amongst subject experts, and national guidance. This review describes our philosophy and practical approach of managing PJIH at a regional tertiary high-volume joint replacement centre.

Use of oxazolidinones (linezolid or tedizolid) for the treatment of breast infections. A case series from a tertiary referral hospital

OBJECTIVES

Mastitis is mainly caused by Gram-positive bacteria and usually involves treatment with beta-lactam antibiotics and clindamycin. Oxazolidinones show good results in the treatment of skin and soft tissue infections (SSTIs) due to its pharmacokinetic characteristics. We aimed to describe clinical characteristics and outcomes of patients who received oxazolidinones for the treatment of SSTIs of the mammary tissue.

METHODS

Retrospective single-centre study of patients with a diagnosis of breast infection who received treatment with oxazolidinones as initial or salvage therapy between September 2016 and November 2022. Patients were identified through the pharmacy database. The primary outcome was clinical cure.

RESULTS

Twenty-nine patients received oxazolidinones: 27 received linezolid and 2 tedizolid. Median age was 41 years (IQR 31.0-56.5) and 28 patients were female. Ten patients (35%) had a history of breast cancer, while three (10%) had an immunosuppressive condition. Microbiological isolation was obtained in 24 individuals (83%). Predominant isolations were methicillin-resistant Staphylococcus aureus (8, 28%) and methicillin-susceptible S. aureus (7, 24%). Twenty-four patients (83%) received oxazolidinones as a salvage therapy, with a median duration of 14 days (IQR 10-17). Clinical cure was achieved in 24 patients (83%), while 4 relapsed after a median of 15 days (IQR 4-34). One was lost to follow-up. Three patients (10%) were taking selective serotonin reuptake inhibitors, and one of them concurrently received linezolid for 4 days with no adverse events recorded. Cytopenia during treatment was observed in 2/12 individuals. Oxazolidinones allowed hospital discharge in 11/13 hospitalized patients.

CONCLUSIONS

Oxazolidinones could be considered as an alternative for treating breast infections.

Oritavancin in vitro activity against Gram-positive organisms from European medical centers: a 10-year longitudinal overview from the SENTRY Antimicrobial Surveillance Program (2010-2019)

To assess oritavancin in vitro activity against clinically relevant Gram-positive pathogens in European (EU) hospitals, a total of 51,531 consecutive and unique clinical isolates collected in 2010-2019 were evaluated. All isolates were tested by CLSI broth microdilution methods. The key resistance phenotypes differed considerably between Eastern Europe (E-EU) and Western Europe (W-EU), respectively: methicillin-resistant (MR) Staphylococcus aureus 27.7%/22.9%; multidrug resistant (MDR) S. aureus, 19.7%/15.2%; MR coagulase-negative staphylococci, 77.3%/61.9%; vancomycin-resistant enterococci (E. faecium), 44.2%/20.9%; and MDR E. faecium, 63.8%/55.4%. There were no substantive differences in oritavancin minimum inhibitory concentration (MIC) values for the different species/organism groups over time or by EU region. Oritavancin inhibited 99.9% and 99.1% of all S. aureus and coagulase-negative staphylococci at 0.12 mg/L, respectively, and all isolates of E. faecalis and E. faecium at ≤0.5 mg/L. Oritavancin susceptibility rates against β-hemolytic and Viridans group streptococci isolates were 98.1% and 99.4%, respectively. Oritavancin had potent activity in vitro against this contemporary collection of European Gram-positive isolates from 2010 to 2019.

Periprosthetic joint infection: what next?

Periprosthetic joint infection (PJI) remains an extremely challenging complication. We have focused on this issue more over the last decade than previously, but there are still many unanswered questions. We now have a workable definition that everyone should align to, but we need to continue to focus on identifying the organisms involved. Surgical strategies are evolving and care is becoming more patient-centred. There are some good studies under way. There are, however, still numerous problems to resolve, and the challenge of PJI remains a major one for the orthopaedic community. This annotation provides some up-to-date thoughts about where we are, and the way forward. There is still scope for plenty of research in this area.

Cite this article: Bone Joint J 2022;104-B(11):1193–1195.

Antibiotic resistance in dermatology: The scope of the problem and strategies to address it

Antibiotic resistance is a growing health concern that has attracted increasing attention from clinicians and scientists in recent years. Although resistance is an inevitable consequence of bacterial evolution and natural selection, misuse and overuse of antibiotics play a significant role in its acceleration. Antibiotics are the mainstay of therapy for common dermatoses, including acne and rosacea, as well as for skin and soft tissue infections. Therefore, it is critical for dermatologists and physicians across all disciplines to identify, appropriately manage, and prevent cases of antibiotic resistance. This review explores dermatologic conditions in which the development of antibiotic resistance is a risk and discusses mechanisms underlying the development of resistance. We discuss disease-specific strategies for overcoming resistant strains and improving antimicrobial stewardship along with recent advances in the development of novel approaches to counter antibiotic resistance.

Genetics Behind the Glycosylation Patterns in the Biosynthesis of Dalbaheptides

Glycopeptide antibiotics are valuable natural metabolites endowed with different pharmacological properties, among them are dalbaheptides used to treat different infections caused by multidrug-resistant Gram-positive pathogens. Dalbaheptides are produced by soil-dwelling high G-C Gram-positive actinobacteria. Their biosynthetic pathways are encoded within large biosynthetic gene clusters. A non-ribosomally synthesized heptapeptide aglycone is the common scaffold for all dalbaheptides. Different enzymatic tailoring steps, including glycosylation, are further involved in decorating it. Glycosylation of dalbaheptides is a crucial step, conferring them specific biological activities. It is achieved by a plethora of glycosyltransferases, encoded within the corresponding biosynthetic gene clusters, able to install different sugar residues. These sugars might originate from the primary metabolism, or, alternatively, their biosynthesis might be encoded within the biosynthetic gene clusters. Already installed monosaccharides might be further enzymatically modified or work as substrates for additional glycosylation. In the current minireview, we cover recent updates concerning the genetics and enzymology behind the glycosylation of dalbaheptides, building a detailed and consecutive picture of this process and of its biological evolution. A thorough understanding of how glycosyltransferases function in dalbaheptide biosynthesis might open new ways to use them in chemo-enzymatic synthesis and/or in combinatorial biosynthesis for building novel glycosylated antibiotics.

Update on activity of dalbavancin and comparators against clinical isolates of Gram-positive pathogens from Europe and Russia (2017-2018), and on clonal distribution of MRSA

BACKGROUND

Gram-positive pathogens remain a major cause of healthcare- and community-associated infections. In particular, the dissemination of methicillin-resistant staphylococci, as methicillin-resistant S. aureus (MRSA) and vancomycin-resistant enterococci (VRE), have significantly reduced the therapeutic options, making the management of these infections even more challenging. Dalbavancin is a second-generation lipoglycopeptide approved for the treatment of moderate to severe acute bacterial skin and skin structure infections (ABSSSIs) caused by Gram-positive organisms, showing a bactericidal effect and a low propensity towards the selection of resistance over time.

AIM

This study aimed to evaluate the antimicrobial activity of dalbavancin and other comparators against recent clinical isolates of Gram-positive pathogens obtained from different sources and from several European countries, including countries of southern and eastern Europe and Russia, where resistance rates are typically high. This study also aimed to describe the clonal relationship of MRSA strains circulating in southern and eastern Europe and Russia.

RESULTS

A total of 1478 isolates were collected. Study results demonstrated the excellent and stable activity of dalbavancin against Gram-positive microorganisms, including MRSA. Interestingly, dalbavancin has retained unaltered MIC₅₀ and MIC₉₀ values over the years and seemed to have a low propensity in selecting resistance mechanisms.

CONCLUSIONS

Our data supported the potential efficacy of dalbavancin against Gram-positive bacteria and uncommon Gram-positive pathogens in patients with ABSSSIs. Of note, few CoNS isolates were resistant to dalbavancin and susceptible to vancomycin, pointing out the importance of testing the susceptibility to dalbavancin before its administration for CoNS infections.

Biomaterials and technologies in the management of periprosthetic infection after total hip arthroplasty: An updated review

Although total hip arthroplasty (THA) is considered one of the most efficacious procedures for managing various hip conditions, failures due to different mechanisms are still being reported. Periprosthetic joint infection (PJI) is one of the devastating causes of failure and revision of THA. PJI carries a burden on the patient, the surgeon, and the health-care system. The diagnosis and management of PJIs carry many morbidities and increased treatment costs. The development of PJI is multifactorial, including issues related to the patient’s general condition, the surgeon’s efficiency, surgical technique, and the implants used. Recent advances in the area of diagnosis and predicting PJI as well as introducing new technologies and biomaterials update for the prevention and treatment of PJI. Local implant coatings, advancement in the bearing surfaces technologies, and new technologies such as immunotherapy and bacteriophage therapy were introduced and suggested as contemporary PJI eradication solutions. In this review, we aimed at discussing some of the newly introduced materials and technologies for the sake of PJI control.

The classification of bacterial survival strategies in the presence of antimicrobials

The survival of bacteria under antibiotic therapy varies in nature and is based on the bacterial ability to employ a wide range of fundamentally different resistance mechanisms. This great diversity requires a disambiguation of the term 'resistance' and the development of a more precise classification of bacterial survival strategies during contact with antibiotics. The absence of a unified definition for the terms 'resistance', 'tolerance' and 'persistence' further aggravates the imperfections of the current classification system. This review suggests a number of original classification criteria that will take into account (1) the bacterial ability to replicate in the presence of antimicrobial agents, (2) existing evolutionary stability of a trait within a species, and (3) the presence or absence of specialized genes that determine the ability of a microorganism to decrease its own metabolism or switch it completely off. This review describes potential advantages of the suggested classification system, which include a better understanding of the relationship between bacterial survival in the presence of antibiotics and molecular mechanisms of cellular metabolism suppression, the opportunity to pinpoint targets to identify a true bacterial resistance profile. The true resistance profile in turn, could be used to develop effective diagnostic and antimicrobial therapy methods, while taking into consideration specific bacterial survival mechanisms.

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.

Engineered photo-chemical therapeutic nanocomposites provide effective antibiofilm and microbicidal activities against bacterial infections in porous devices

Today, prosthetic joint infection (PJI) is still a relatively rare but devastating complication following total hip and/or knee arthroplasty. The treatment of PJI is difficult due to a number of obstacles, such as microbial drug resistance, biofilm protection, and insufficient immune activity, which dramatically diminish the cure rate of PJI to <50%. To efficiently eradicate the bacteria hiding in the implant, photo-chemical joint antibacterial therapeutics based on indocyanine green (ICG) and rifampicin (RIF) co-loaded PLGA nanoparticles (IRPNPs) were developed in this study. The IRPNPs were first characterized as a spherical nanostructure with a size of 266 ± 18.2 nm and a surface charge of -28 ± 1.6 mV. In comparison with freely dissolved ICG, the IRPNPs may confer enhanced thermal stability to the encapsulated ICG and are able to provide a comparable hyperthermic effect and increased production of singlet oxygen under 808 nm near infrared (NIR) exposure with an intensity of 6 W cm-2. Based on the spectrophotometric analysis, the IRPNPs with ≥20-/3.52 μM ICG/RIF were able to provide remarkable antibiofilm and antimicrobial effects against bacteria in a porous silicon bead upon NIR exposure in vitro. Through the analysis of the microbial population index in an animal study, ≥70% Staphylococcus capitis subsp. urealyticus grown in a porous silicon bead in vivo can be successfully eliminated without organ damage or inflammatory lesions around the implant by using IRPNPs + NIR irradiation every 72 h for 9 days. The resulting bactericidal efficacy was approximately three-fold higher than that resulting from using an equal amount of free RIF alone. Taken together, we anticipate that IRPNP-mediated photochemotherapy can serve as a feasible antibacterial approach for PJI treatment in the clinic.

In vitro synergy of 5-nitrofurans, vancomycin and sodium deoxycholate against Gram-negative pathogens

Introduction

There is an urgent need for effective therapies against bacterial infections, especially those caused by antibiotic-resistant Gram-negative pathogens.

Hypothesis

Synergistic combinations of existing antimicrobials show promise due to their enhanced efficacies and reduced dosages which can mitigate adverse effects, and therefore can be used as potential antibacterial therapy.

Aim

In this study, we sought to characterize the in vitro interaction of 5-nitrofurans, vancomycin and sodium deoxycholate (NVD) against pathogenic bacteria.

Methodology

The synergy of the NVD combination was investigated in terms of growth inhibition and bacterial killing using checkerboard and time-kill assays, respectively.

Results

Using a three-dimensional checkerboard assay, we showed that 5-nitrofurans, sodium deoxycholate and vancomycin interact synergistically in the growth inhibition of 15 out of 20 Gram-negative strains tested, including clinically significant pathogens such as carbapenemase-producing Escherichia coli, Klebsiella pneumoniae and Acinetobacter baumannii, and interact indifferently against the Gram-positive strains tested. The time-kill assay further confirmed that the triple combination was bactericidal in a synergistic manner.

Conclusion

This study demonstrates the synergistic effect of 5-nitrofurans, sodium deoxycholate and vancomycin against Gram-negative pathogens and highlights the potential of the combination as a treatment for Gram-negative and Gram-positive infections.

Inhibition of mitochondrial translation overcomes venetoclax resistance in AML through activation of the integrated stress response

Venetoclax is a specific B cell lymphoma 2 (BCL-2) inhibitor with promising activity against acute myeloid leukemia (AML), but its clinical efficacy as a single agent or in combination with hypomethylating agents (HMAs), such as azacitidine, is hampered by intrinsic and acquired resistance. Here, we performed a genome-wide CRISPR knockout screen and found that inactivation of genes involved in mitochondrial translation restored sensitivity to venetoclax in resistant AML cells. Pharmacologic inhibition of mitochondrial protein synthesis with antibiotics that target the ribosome, including tedizolid and doxycycline, effectively overcame venetoclax resistance. Mechanistic studies showed that both tedizolid and venetoclax suppressed mitochondrial respiration, with the latter demonstrating inhibitory activity against complex I [nicotinamide adenine dinucleotide plus hydrogen (NADH) dehydrogenase] of the electron transport chain (ETC). The drugs cooperated to activate a heightened integrated stress response (ISR), which, in turn, suppressed glycolytic capacity, resulting in adenosine triphosphate (ATP) depletion and subsequent cell death. Combination treatment with tedizolid and venetoclax was superior to either agent alone in reducing leukemic burden in mice engrafted with treatment-resistant human AML. The addition of tedizolid to azacitidine and venetoclax further enhanced the killing of resistant AML cells in vitro and in vivo. Our findings demonstrate that inhibition of mitochondrial translation is an effective approach to overcoming venetoclax resistance and provide a rationale for combining tedizolid, azacitidine, and venetoclax as a triplet therapy for AML.

Characterization of a Lytic Bacteriophage vB_EfaS_PHB08 Harboring Endolysin Lys08 Against Enterococcus faecalis Biofilms

Enterococcus faecalis is an opportunistic pathogen that causes illnesses ranging from urinary tract infections to sepsis in humans and animals. However, the overuse of antibiotics has increased rates of drug resistance among E. faecalis isolates. Bacteriophages and their derivatives have recently been identified as good candidates for the treatment of drug-resistant bacterial infections. Here, we isolated a virulent E. faecalis phage, PHB08, using the double-layer plate method. The bioactivity of the phage was determined via one-step growth curve testing and bacterial killing assays, and whole-genome sequencing was performed using the Illumina HiSeq platform. In addition, protein expression and antibiofilm assays were performed to investigate the activity of the phage lysin. Results showed that PHB08 has a 55,244-bp linear double-stranded DNA genome encoding 91 putative coding sequences. PHB08 inhibited the growth of host strain EF3964 at 37 °C in tryptic soy broth (TSB) medium, while in vegetable models, PHB08 caused a 4.69-log decrease in viable E. faecalis cells after 24 h. Both PHB08 and its endolysin lys08 showed antibiofilm activity against E. faecalis biofilms, which was enhanced by Mn²⁺ ions. Thus, virulent phage PHB08 and endolysin lys08 may be good candidates for reducing and/or eradicating E. faecalis infections.

Characterization of Tn6349, a novel mosaic transposon carrying poxtA, cfr and other resistance determinants, inserted in the chromosome of an ST5-MRSA-II strain of clinical origin

OBJECTIVES

To characterize the genetic element carrying the poxtA oxazolidinone resistance gene found in the poxtA index strain Staphylococcus aureus AOUC-0915 isolated from a cystic fibrosis patient.

METHODS

The genetic context of poxtA was investigated by bioinformatics analysis of WGS data of strain AOUC-0915, followed by PCR and confirmatory Sanger sequencing for repetitive regions. Conjugation and electrotransformation experiments were carried out to assess horizontal transferability using S. aureus and Enterococcus faecalis recipients. Production of phage particles was evaluated by PCR using DNA preparations obtained after phage induction. Excision of the transposon carrying poxtA was evaluated by inverse PCR experiments for detection of circular intermediates.

RESULTS

poxtA was found to be associated with a 48 kb composite transposon of original structure, named Tn6349, inserted into a φN315-like prophage. The transposon was bounded by two IS1216 insertion sequences, carried several resistance genes [erm(B), cfr, poxtA and fexB] and exhibited a mosaic structure made by a derivative of plasmid pE35048-oc (previously described in an Enterococcus faecium clinical isolate) and Tn6657, a novel composite transposon carrying the poxtA and fexB genes. Excision ability of Tn6349 as a circular intermediate was demonstrated. Transferability of Tn6349 or modules thereof to S. aureus or E. faecalis by either conjugation or electrotransformation was not detected. Induction of the φN315-like prophage carrying Tn6349 was not observed.

CONCLUSIONS

This study describes the structure of Tn6349, a novel composite transposon carrying several resistance determinants to anti-ribosomal drugs, including cfr and poxtA, from an oxazolidinone-resistant MRSA strain. Analysis of Tn6349 revealed a modular structure that could favour the mobilization of its resistance determinants.

New developments and future challenges in prevention, diagnosis, and treatment of prosthetic joint infection

Prosthetic joint infection (PJI) is a devastating complication that results in substantial costs to society and patient morbidity. Advancements in our knowledge of this condition have focused on prevention, diagnosis, and treatment, in order to reduce rates of PJI and improve patient outcomes. Preventive measures such as optimization of patient comorbidities, and perioperative antibiotic usage are intensive areas of current clinical research to reduce the rate of PJI. Improved diagnostic tests such as synovial fluid (SF) α-defensin enzyme-linked immunosorbent assay, and nucleic acid-based tests for serum, SF, and tissue cultures, have improved diagnostic accuracy and organism identification. Increasing the diversity of available antibiotic therapy, immunotherapy, and alternative implant coatings remain promising treatments to improve infection eradication in the setting of PJI.

Radiosynthesis and Biodistribution of 18F-Linezolid in Mycobacterium tuberculosis-Infected Mice Using Positron Emission Tomography

Oxazolidinones are a novel class of antibacterials with excellent activity against resistant Gram-positive bacteria including strains causing multidrug-resistant tuberculosis (TB). Despite their excellent efficacy, optimal dosing strategies to limit their toxicities are still under development. Here, we developed a novel synthetic strategy for fluorine-18-radiolabeled oxazolidinones. As proof-of-concept, we performed whole-body ¹⁸F-linezolid positron emission tomography (PET) in a mouse model of pulmonary TB for noninvasive in situ measurements of time-activity curves in multiple compartments with subsequent confirmation by ex vivo tissue gamma counting. After intravenous injection, ¹⁸F-linezolid rapidly distributed to all organs with excellent penetration into Mycobacterium tuberculosis-infected lungs. Drug biodistribution studies with PET can provide unbiased, in situ drug measurements, which could boost efforts to optimize antibiotic dosing strategies.

Linezolid- and Vancomycin-resistant Enterococcus faecium in Solid Organ Transplant Recipients: Infection Control and Antimicrobial Stewardship Using Whole Genome Sequencing

BACKGROUND

Vancomycin-resistant enterococci are an important cause of healthcare-associated infections and are inherently resistant to many commonly used antibiotics. Linezolid is the only drug currently approved by the US Food and Drug Administration to treat vancomycin-resistant enterococci; however, resistance to this antibiotic appears to be increasing. Although outbreaks of linezolid- and vancomycin-resistant Enterococcus faecium (LR-VRE) in solid organ transplant recipients remain uncommon, they represent a major challenge for infection control and hospital epidemiology.

METHODS

We describe a cluster of 4 LR-VRE infections among a group of liver and multivisceral transplant recipients in a single intensive care unit. Failure of treatment with linezolid in 2 cases led to a review of standard clinical laboratory methods for susceptibility determination. Testing by alternative methods including whole genome sequencing (WGS) and a comprehensive outbreak investigation including sampling of staff members and surfaces was performed.

RESULTS

Review of laboratory testing methods revealed a limitation in the VITEK 2 system with regard to reporting resistance to linezolid. Linezolid resistance in all cases was confirmed by E-test method. The use of WGS identified a resistant subpopulation with the G2376C mutation in the 23S ribosomal RNA. Sampling of staff members' dominant hands as well as sampling of surfaces in the unit identified no contaminated sources for transmission.

CONCLUSIONS

This cluster of LR-VRE in transplant recipients highlights the possible shortcomings of standard microbiology laboratory methods and underscores the importance of WGS to identify resistance mechanisms that can inform patient care, as well as infection control and antibiotic stewardship measures.

Vancomycin-resistant Enterococcus in solid organ transplant recipients: Guidelines from the American Society of Transplantation Infectious Diseases Community of Practice

These updated guidelines from the Infectious Diseases Community of Practice of the American Society of Transplantation address vancomycin-resistant enterococci (VRE) infections in SOT candidates and recipients. VRE are an important cause of infection and have been named by the CDC as a serious public threat. Typically, a commensal of the gastrointestinal tract, VRE may become pathogenic after abdominal organ manipulation like transplantation. This guideline reviews the microbiology, antimicrobial resistance mechanisms, epidemiology, and clinical manifestations of VRE infection in the context of solid organ transplantation. Treatment regimens including combination therapies and novel investigational agents are also reviewed. Finally, an updated appraisal of infection control measures relevant to VRE infection and colonization is presented.

Structural basis of translation inhibition by cadazolid, a novel quinoxolidinone antibiotic

Oxazolidinones are synthetic antibiotics used for treatment of infections caused by Gram-positive bacteria. They target the bacterial protein synthesis machinery by binding to the peptidyl transferase centre (PTC) of the ribosome and interfering with the peptidyl transferase reaction. Cadazolid is the first member of quinoxolidinone antibiotics, which are characterized by combining the pharmacophores of oxazolidinones and fluoroquinolones, and it is evaluated for treatment of Clostridium difficile gastrointestinal infections that frequently occur in hospitalized patients. In vitro protein synthesis inhibition by cadazolid was shown in Escherichia coli and Staphylococcus aureus, including an isolate resistant against linezolid, the prototypical oxazolidinone antibiotic. To better understand the mechanism of inhibition, we determined a 3.0 Å cryo-electron microscopy structure of cadazolid bound to the E. coli ribosome in complex with mRNA and initiator tRNA. Here we show that cadazolid binds with its oxazolidinone moiety in a binding pocket in close vicinity of the PTC as observed previously for linezolid, and that it extends its unique fluoroquinolone moiety towards the A-site of the PTC. In this position, the drug inhibits protein synthesis by interfering with the binding of tRNA to the A-site, suggesting that its chemical features also can enable the inhibition of linezolid-resistant strains.

New Innovations in the Treatment of PJI and Biofilms-Clinical and Preclinical Topics

PURPOSE OF REVIEW

Periprosthetic joint infection (PJI) is a devastating complication after total joint replacement. A main source for antibiotic tolerance and treatment failure is bacterial production of biofilm-a resilient barrier against antibiotics, immune system, and mechanical debridement. The purpose of this review is to explore some novel approaches to treat PJI and biofilm-related infections.

RECENT FINDINGS

Innovative treatment strategies of bacterial and biofilm infections revolve around (a) augmenting current therapies, such as improving the delivery and efficiency of conventional antibiotics and enhancing the efficacy of antiseptics and (b) administrating completely new therapeutic modalities, such as using immunotherapy, nanoparticles, lytic bacteriophages, photodynamic therapy, novel antibiotics, and antimicrobial peptides. Several promising treatment strategies for PJI are available to be tested further. The next requirement for most of the novel treatments is reproducing their effects in clinically representative animal models of PJI against clinical isolates of relevant bacteria.

Old and new glycopeptide antibiotics: From product to gene and back in the post-genomic era

Glycopeptide antibiotics are drugs of last resort for treating severe infections caused by multi-drug resistant Gram-positive pathogens. First-generation glycopeptides (vancomycin and teicoplanin) are produced by soil-dwelling actinomycetes. Second-generation glycopeptides (dalbavancin, oritavancin, and telavancin) are semi-synthetic derivatives of the progenitor natural products. Herein, we cover past and present biotechnological approaches for searching for and producing old and new glycopeptide antibiotics. We review the strategies adopted to increase microbial production (from classical strain improvement to rational genetic engineering), and the recent progress in genome mining, chemoenzymatic derivatization, and combinatorial biosynthesis for expanding glycopeptide chemical diversity and tackling the never-ceasing evolution of antibiotic resistance.

Oritavancin in vitro activity against gram-positive organisms from European and United States medical centers: results from the SENTRY Antimicrobial Surveillance Program for 2010-2014

The in vitro activity of oritavancin was assessed against 44,715 gram-positive pathogens causing infections in European and United States (US) hospitals (2010-2014). There were no substantive differences (>±2-fold dilution) in oritavancin MIC₅₀ or MIC₉₀ values for different species/organism groups over time or by region. Oritavancin (99.9% susceptible) showed modal MIC, MIC₅₀, and MIC₉₀ results of 0.03, 0.03, and 0.06-0.12 mg/L when tested against Staphylococcus aureus, regardless of methicillin susceptibility, year, or region. Coagulase-negative staphylococci from the US and Europe demonstrated equal MIC₅₀ values for oritavancin (MIC₅₀, 0.03 mg/L). Oritavancin inhibited 99.9% of Enterococcus faecalis and all E. faecium at ≤0.5 mg/L, including vancomycin-resistant isolates. Oritavancin exhibited MIC₅₀ results of 0.03 and ≤0.008 mg/L when tested against β-hemolytic and viridans group streptococci isolates, respectively, regardless of geographical region. Oritavancin maintained potent activity in vitro against this contemporary collection of European and US gram-positive isolates over 5 years (2010-2014).

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.

New Antimicrobial Agents for the Treatment of Staphylococcal Infections in Children

Several new antimicrobial agents-daptomycin, ceftaroline, telavancin, dalbavancin, and-tedizolid have been approved for the treatment of staphylococcal infections, including methicillin-resistant Staphylococcus aureus (MRSA), in adults. Ceftaroline and daptomycin have been approved by the US Food and Drug Administration for use in children. Ceftaroline, a beta-lactam antibiotic with activity against MRSA, has been approved for treatment of community-acquired bacterial pneumonia and complicated skin and skin structure infections. Daptomycin has been approved for treatment of complicated skin and skin structure infections. In this article, we review the pharmacokinetics and pharmacodynamics of these antibiotics and available data on use in children.

Multidrug-resistant Enterobacteriaceae, Pseudomonas aeruginosa, and vancomycin-resistant Enterococcus: Three major threats to hematopoietic stem cell transplant recipients

Hematopoietic stem cell transplant (HSCT) recipients are uniquely threatened by the emergence of multidrug-resistant (MDR) bacteria because these patients rely on immediate active antimicrobial therapy to combat bacterial infections. This review describes the epidemiology and treatment considerations for three challenging MDR bacterial pathogens in HSCT recipients: MDR Enterobacteriaceae, including extended-spectrum β-lactamase (ESBL)-producing and carbapenem-resistant Enterobacteriaceae (CRE), Pseudomonas aeruginosa, and vancomycin-resistant Enterococcus (VRE). These bacteria are common causes of infection in this population and bacteremias caused by these organisms are associated with high mortality rates. Carbapenems remain the treatments of choice for serious infections due to ESBL-producing Enterobacteriaceae in HSCT recipients. Administration of β-lactam agents as an extended infusion is associated with improved outcomes in patients with severe infections caused by P. aeruginosa. Older agents used for the treatment of CRE and MDR P. aeruginosa infections, such as polymyxins and aminoglycosides, have major limitations. Newer agents, such as ceftazidime-avibactam and ceftolozane-tazobactam have great potential for the treatment of Klebsiella pneumoniae carbapemenase-producing CRE and MDR P. aeruginosa, respectively, but more pre-clinical and clinical data are needed to better evaluate their efficacy. Daptomycin dosages ≥8 mg/kg/day are recommended to treat VRE infections in this population, particularly in the setting of increasing daptomycin resistance. Strategies to prevent these infections include strict adherence to recommended infection control practices and multidisciplinary antimicrobial stewardship. Last, gastrointestinal screening to guide empirical therapy and the use of polymerase chain reaction-based rapid diagnostics may decrease the time to administration of appropriate therapy for these infections, thereby leading to improved outcomes.

Purified citritin in combination with vancomycin inhibits VRE in vitro and in vivo

Gram-positive pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium (VRE) have been frequently associated with bacterial resistance mechanisms. These mechanisms, in turn, restrict a range of therapeutic opportunities for the treatment of infections caused by these micro-organisms. Faced with this problem, the present study aims to isolate and characterize molecules with antimicrobial activity derived from the fungus Penicillium citrinum isolated from Cerrado soil. Furthermore, we also tested possible antibacterial potential alone and in combination with commercial antimicrobial agents. In this context, citrinin was isolated and characterized by nuclear magnetic resonance and electrospray ionization. Functional analyses showed MIC of 128 µg ml^-1 against S. aureus ATCC 25923, E. faecalis ATCC 29212 and a clinical isolate of vancomycin-resistant E. faecium (VRE01). However, for a clinical strain of methicillin-resistant S. aureus (MRSA01), the MIC was 256 µg ml^-1. In order to avoid such high concentrations and reduce the collateral effects, additive effects were evidenced by combining citrinin with cefoxitin against MRSA01 (FIC index=0.5) and also citrinin with vancomycin toward VRE01 (FIC index=0.5). In vivo studies with BALB/c-tipe mice (MRSA assay) demonstrated a clinical ineffectiveness of cefoxitin associated with citrinin (9.8 mg kg^-1 of cefoxitin +0.2 mg kg^-1 of citrinin), with this combination being inefficient to increase animal survival. However, the combination used in the treatment of VRE (23.5 mg kg^-1 of citrinin +1.5 mg kg^-1 of vancomycin) sepsis model was extremely promising, leading to an animal survival rate of 80 percent. In summary, our data show, for the first time, the possible successful use of citrinin associated with vancomycin for pathogenic bacteria control.

Management of multidrug resistant Gram-negative bacilli infections in solid organ transplant recipients: SET/GESITRA-SEIMC/REIPI recommendations

Solid organ transplant (SOT) recipients are especially at risk of developing infections by multidrug resistant (MDR) Gram-negative bacilli (GNB), as they are frequently exposed to antibiotics and the healthcare setting, and are regulary subject to invasive procedures. Nevertheless, no recommendations concerning prevention and treatment are available. A panel of experts revised the available evidence; this document summarizes their recommendations: (1) it is important to characterize the isolate's phenotypic and genotypic resistance profile; (2) overall, donor colonization should not constitute a contraindication to transplantation, although active infected kidney and lung grafts should be avoided; (3) recipient colonization is associated with an increased risk of infection, but is not a contraindication to transplantation; (4) different surgical prophylaxis regimens are not recommended for patients colonized with carbapenem-resistant GNB; (5) timely detection of carriers, contact isolation precautions, hand hygiene compliance and antibiotic control policies are important preventive measures; (6) there is not sufficient data to recommend intestinal decolonization; (7) colonized lung transplant recipients could benefit from prophylactic inhaled antibiotics, specially for Pseudomonas aeruginosa; (8) colonized SOT recipients should receive an empirical treatment which includes active antibiotics, and directed therapy should be adjusted according to susceptibility study results and the severity of the infection.

Diagnosis and management of skin and soft-tissue infections (SSTI). A literature review and consensus statement: an update

Skin and soft-tissue infections (SSTIs) are among the most common bacterial infections, posing considerable diagnostic and therapeutic challenges. Fourteen members of the Italian Society of Infectious Diseases, after a careful review of the most recent literature using Medline database and their own clinical experience, updated a previous paper published in 2011 by preparing a draught manuscript of the statements. The manuscript was successively reviewed by all members and ultimately re-formulated the present manuscript during a full day consensus meeting. The microbiological and clinical aspects together with diagnostic features were considered for necrotizing and not necrotizing SSTIs in the light of the most recent guidelines and evidences published in the last five years. The antimicrobial therapy was considered as well - both empirical and targeted to methicillin-resistant Staphylococcus aureus and/or other pathogens, also taking into account the epidemiological and bacterial resistance data and the availability of new antibacterial agents.

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.

Global Emergence and Dissemination of Enterococci as Nosocomial Pathogens: Attack of the Clones?

Enterococci are Gram-positive bacteria that are found in plants, soil and as commensals of the gastrointestinal tract of humans, mammals, and insects. Despite their commensal nature, they have also become globally important nosocomial pathogens. Within the genus Enterococcus, Enterococcus faecium, and Enterococcus faecalis are clinically most relevant. In this review, we will discuss how E. faecium and E. faecalis have evolved to become a globally disseminated nosocomial pathogen. E. faecium has a defined sub-population that is associated with hospitalized patients and is rarely encountered in community settings. These hospital-associated clones are characterized by the acquisition of adaptive genetic elements, including genes involved in metabolism, biofilm formation, and antibiotic resistance. In contrast to E. faecium, clones of E. faecalis isolated from hospitalized patients, including strains causing clinical infections, are not exclusively found in hospitals but are also present in healthy individuals and animals. This observation suggests that the division between commensals and hospital-adapted lineages is less clear for E. faecalis than for E. faecium. In addition, genes that are reported to be associated with virulence of E. faecalis are often not unique to clinical isolates, but are also found in strains that originate from commensal niches. As a reflection of more ancient association of E. faecalis with different hosts, these determinants Thus, they may not represent genuine virulence genes but may act as host-adaptive functions that are useful in a variety of intestinal environments. The scope of the review is to summarize recent trends in the emergence of antibiotic resistance and explore recent developments in the molecular epidemiology, population structure and mechanisms of adaptation of E. faecium and E. faecalis.

In vitro activity of dalbavancin against biofilms of staphylococci isolated from prosthetic joint infections

The in vitro activity of dalbavancin was tested against biofilms of 171 staphylococci associated with prosthetic joint infection. Dalbavancin minimum biofilm bactericidal concentration (MBBC) values were: MBBC50 for Staphylococcus aureus and Staphylococcus epidermidis, 1μg/mL; MBBC90 for S. aureus, 2μg/mL; MBBC90 for S. epidermidis, 4μg/mL.