Glycopeptides: Update on an old successful antibiotic class

Rapid detection of major enterotoxin genes and antibiotic resistance of Staphylococcus aureus isolated from raw milk in the Yazd province, Iran

INTRODUCTION

Raw milk is a nutrient-rich food, but it may harbour harmful bacteria, such as enterotoxigenic Staphylococcus aureus (S. aureus), which can cause staphylococcal food poisoning. Antibiotic resistance of S. aureus in raw milk can increase the risk of such infections, particularly among susceptible individuals.

OBJECTIVE

This study aimed to investigate the prevalence of enterotoxin genes a, d, g, i and j and the antibiotic resistance of S. aureus isolated from raw milk samples.

METHODS

During a 6-month sampling period, 60 raw milk specimens were obtained from diverse locations in Yazd province, Iran. Antibiogram profiling was conducted via the disc diffusion method. In addition, staphylococcal enterotoxin (SE) genes a, d, g, i, and j were detected through real-time PCR analysis.

RESULTS

Bacteriological assays confirmed the presence of S. aureus in 11 samples (18.3%). All isolates demonstrated 100% resistance to penicillin G but exhibited sensitivity to vancomycin, while resistance to other antibiotics ranged from 36.4% to 45.5%. The prevalence of enterotoxin genes in these strains showed variable distribution, with sea being the predominant SE (45.5%), followed by sed (36.4%), seg (18.2), sej and sei (9.1% each).

CONCLUSIONS

This study discovered the presence of multiple enterotoxins in S. aureus strains obtained from raw milk samples. These strains also demonstrated resistance to a variety of antibiotics. Since enterotoxigenic S. aureus is known to cause human food poisoning, monitoring food hygiene practices, especially during raw milk production, is critical.

New Perspectives on Old and New Therapies of Staphylococcal Skin Infections: The Role of Biofilm Targeting in Wound Healing

Among the most common complications of both chronic wound and surgical sites are staphylococcal skin infections, which slow down the wound healing process due to various virulence factors, including the ability to produce biofilms. Furthermore, staphylococcal skin infections are often caused by methicillin-resistant Staphylococcus aureus (MRSA) and become a therapeutic challenge. The aim of this narrative review is to collect the latest evidence on old and new anti-staphylococcal therapies, assessing their anti-biofilm properties and their effect on skin wound healing. We considered antibiotics, quorum sensing inhibitors, antimicrobial peptides, topical dressings, and antimicrobial photo-dynamic therapy. According to our review of the literature, targeting of biofilm is an important therapeutic choice in acute and chronic infected skin wounds both to overcome antibiotic resistance and to achieve better wound healing.

Chemically modified and conjugated antimicrobial peptides against superbugs

Antimicrobial resistance (AMR) is one of the greatest threats to human health that, by 2050, will lead to more deaths from bacterial infections than cancer. New antimicrobial agents, both broad-spectrum and selective, that do not induce AMR are urgently required. Antimicrobial peptides (AMPs) are a novel class of alternatives that possess potent activity against a wide range of Gram-negative and positive bacteria with little or no capacity to induce AMR. This has stimulated substantial chemical development of novel peptide-based antibiotics possessing improved therapeutic index. This review summarises recent synthetic efforts and their impact on analogue design as well as their various applications in AMP development. It includes modifications that have been reported to enhance antimicrobial activity including lipidation, glycosylation and multimerization through to the broad application of novel bio-orthogonal chemistry, as well as perspectives on the direction of future research. The subject area is primarily the development of next-generation antimicrobial agents through selective, rational chemical modification of AMPs. The review further serves as a guide toward the most promising directions in this field to stimulate broad scientific attention, and will lead to new, effective and selective solutions for the several biomedical challenges to which antimicrobial peptidomimetics are being applied.

Comparison of breakthrough Gram-positive cocci infection during vancomycin vs teicoplanin therapy in patients receiving haematopoietic stem cell transplantation

WHAT IS KNOWN AND OBJECTIVE

Our previous report indicated that teicoplanin (TEIC) caused fewer adverse effects than vancomycin (VCM) in patients with febrile neutropenia (FN) receiving haematopoietic stem cell transplantation (HSCT). However, we observed breakthrough methicillin-resistant-Staphylococcus haemolyticus (MR-S haemolyticus) infection during TEIC therapy in these patients. In this study, we sought to compare the incidence of breakthrough Gram-positive cocci (GPC) infection during VCM and TEIC therapy in this population.

METHODS

A single-centre, retrospective cohort study was conducted. Patients who had received HSCT and were administered VCM (n = 19) or TEIC (n = 38) for FN from 1 September 2011 to 31 August 2019 were enrolled. We compared the incidence of breakthrough GPC infection between the VCM and TEIC groups.

RESULTS

Breakthrough GPC infection during glycopeptide therapy in febrile neutropenic patients received HSCT was observed in three patients (7.9%) in the TEIC group but in none of patients (0%) in the VCM group. MR-S haemolyticus with low glycopeptide susceptibility (TEIC MIC = 2-8 μg/mL, VCM MIC = 2-4 μg/mL) was isolated from blood cultures in all patients with breakthrough GPC infections. All breakthrough infections were cured by changing from TEIC to daptomycin (DAP).

WHAT IS NEW AND CONCLUSION

The incidence of breakthrough GPC infection during glycopeptide therapy in febrile neutropenic HSCT patients was higher in the TEIC group than in the VCM group. MR-S haemolyticus with low glycopeptide susceptibility was isolated from all patients with breakthrough GPC infection and successfully treated with DAP.

Comparative efficacy and safety of vancomycin versus teicoplanin in febrile neutropenic patients receiving hematopoietic stem cell transplantation

WHAT IS KNOWN AND OBJECTIVE

Patients who receive hematopoietic stem cell transplantation (HSCT) are usually administered a calcineurin inhibitor. Because vancomycin is associated with an increased incidence of nephrotoxicity, neutropenic patients receiving HSCT are considered a high-risk population for nephrotoxicity with vancomycin. We retrospectively compared the efficacy and safety of vancomycin and teicoplanin in febrile neutropenic patients receiving HSCT.

METHODS

A single-centre, retrospective cohort study was conducted at the 614-bed Gifu University Hospital in Japan. Patients who received HSCT and were administered vancomycin or teicoplanin by injection for febrile neutropenia from 1 January 2012 to 31 August 2017 were enrolled. Time to attain an effective trough concentration, clinical efficacy and adverse events were compared between the two groups.

RESULTS

Time to attain an effective trough concentration of over 10 μg/mL tended to be shorter in the teicoplanin group than in the vancomycin group (median 3, 95% confidence interval [CI] 2.4-3.6 days vs median 6, 95% CI 1.5-10.5 days; hazard ratio [HR] 0.4, 95% CI 0.15-1.06; P = .066). The rate of clinical failure was lower in the teicoplanin group than in the vancomycin group (18.8% vs 53.8%, P = .113). In addition, the overall incidence of nephrotoxicity was significantly lower in the teicoplanin group (0% vs 46.2%, P = .004).

WHAT IS NEW AND CONCLUSION

Our findings suggest that administration of teicoplanin may lead to early attainment of the effective concentration with a lower rate of clinical failure and incidence of nephrotoxicity compared to vancomycin in febrile neutropenic patients receiving HSCT.

Thermosensitive hybrid hydrogels for the controlled release of bioactive vancomycin in the treatment of orthopaedic implant infections

The purpose of this work was the development of antibacterial delivery systems for vancomycin, with potential application in the prevention or treatment of orthopedic implant infections. Previous studies have shown tandem thermal gelling and Michael addition cross-linking of hydrogels based on methacrylate, acrylate or vinylsulfone triblock copolymers of PEG-p(HPMAm-lac_1-2) and thiolated hyaluronic acid. In this work we exploited these α-β unsaturated derivatives of PEG-p(HPMAm-lac_1-2) triblock copolymers and used them in combination with thiolated hyaluronic acid as controlled delivery systems for vancomycin. It was found that the antibiotic was sustainably released from the hydrogel networks for at least 5 days with release kinetics depending on diffusion and dissociation of the positively charged vancomycin from the negatively charged hyaluronic acid. The release of vancomycin could be tailored mainly by HA-SH solid content and degree of thiolation. The developed hydrogels were demonstrate efficacious in preserving the structural and functional integrity of the encapsulated drug by physical immobilization within the gel network and ionic interaction with hyaluronic acid, thereby preventing vancomycin deamidation processes. Furthermore, the antimicrobial activity of vancomycin loaded hydrogels was assessed, demonstrating retention of inhibitory activity towards Staphylococcus aureus during formulation and release, with slightly increased activity of vancomycin encapsulated in hydrogels of higher HA-SH content as compared to controls.

Role of Daptomycin on Burn Wound Healing in an Animal Methicillin-Resistant Staphylococcus aureus Infection Model

Prolonged hospitalization and antibiotic therapy are risk factors for the development of methicillin-resistant Staphylococcus aureus (MRSA) infections in thermal burn patients. We used a rat model to study the in vivo efficacy of daptomycin in the treatment of burn wound infections by S. aureus, and we evaluated the wound healing process through morphological and immunohistochemical analysis. A copper bar heated in boiling water was applied on a paraspinal site of each rat, resulting in two full-thickness burns. A small gauze was placed over each burn and inoculated with 5 × 10⁷ CFU of S. aureus ATCC 43300. The study included two uninfected control groups with and without daptomycin treatment, an infected control group that did not receive any treatment, and two infected groups treated, respectively, with intraperitoneal daptomycin and teicoplanin. The main outcome measures were quantitative culture, histological evaluation of tissue repair, and immunohistochemical expression of wound healing markers: epidermal growth factor receptor (EGFR) and fibroblast growth factor 2 (FGF-2). The highest inhibition of infection was achieved in the group that received daptomycin, which reduced the bacterial load from 10⁷ CFU/ml to about 10³ CFU/g (P < 0.01). The groups treated with daptomycin showed better overall healing with epithelialization and significantly higher collagen scores than the other groups, and these findings were also confirmed by immunohistochemical data. In conclusion, our results support the hypothesis that daptomycin is an important modulator of wound repair by possibly reducing hypertrophic burn scar formation.

A Fluorescent Probe for Detecting Mycobacterium tuberculosis and Identifying Genes Critical for Cell Entry

The conventional method for quantitating Mycobacterium tuberculosis (Mtb) in vitro and in vivo relies on bacterial colony forming unit (CFU) enumeration on agar plates. Due to the slow growth rate of Mtb, it takes 3-6 weeks to observe visible colonies on agar plates. Imaging technologies that are capable of quickly quantitating both active and dormant tubercle bacilli in vitro and in vivo would accelerate research toward the development of anti-TB chemotherapies and vaccines. We have developed a fluorescent probe that can directly label the Mtb cell wall components. The fluorescent probe, designated as DLF-1, has a strong affinity to the D-Ala-D-Ala unit of the late peptidoglycan intermediates in the bacterial cell wall. We demonstrate that DLF-1 is capable of detecting Mtb in both the actively replicating and dormant states in vitro at 100 nM without inhibiting bacterial growth. The DLF-1 fluorescence signal correlated well with CFU of the labeled bacteria (R² = 1 and 0.99 for actively replicating and dormant Mtb, respectively). DLF-1 can also quantitate labeled Mtb inside of cells. The utility of DLF-1 probe to quantitate Mtb was successfully applied to identify genes critical for cell invasion. In conclusion, this novel near infrared imaging probe provides a powerful new tool for enumerating Mtb with potential future use in bacterial virulence study.

Role of the Gram-Negative Envelope Stress Response in the Presence of Antimicrobial Agents

Bacterial survival necessitates endurance of many types of antimicrobial compound. Many Gram-negative envelope stress responses, which must contend with an outer membrane and a dense periplasm containing the cell wall, have been associated with the status of protein folding, membrane homeostasis, and physiological functions such as efflux and the proton motive force (PMF). In this review, we discuss evidence that indicates an emerging role for Gram-negative envelope stress responses in enduring exposure to diverse antimicrobial substances, focusing on recent studies of the γ-proteobacterial Cpx envelope stress response.

No Outbreak of Vancomycin and Linezolid Resistance in Staphylococcal Pneumonia over a 10-Year Period

BACKGROUND

Staphylococci can cause wound infections and community- and nosocomial-acquired pneumonia, among a range of illnesses. Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) have been rapidly increasing as a cause of infections worldwide in recent decades. Numerous reports indicate that S. aureus and MRSA are becoming resistant to many antibiotics, which makes them very dangerous. Therefore, this study retrospectively investigated the resistance to antimicrobial agents in all hospitalized patients suffering from community- or nosocomial-acquired pneumonia due to S. aureus and MRSA.

METHODS

Information from the study groups suffering from either community- or nosocomial-acquired pneumonia caused by S. aureus or MRSA was gathered by searching records from 2004 to 2014 at the HELIOS Clinic Wuppertal, Witten/Herdecke University, Germany. The findings of antibiotic resistance were analyzed after the evaluation of susceptibility testing for S. aureus and MRSA.

RESULTS

Total of 147 patients (63.9%, 95% CI 57.5%-69.8%), mean age 67.9 ± 18.5 years, with pneumonia triggered by S. aureus, and 83 patients (36.1%, 95% CI 30.2%-42.5%), mean age 72.3 ± 13.8 years, with pneumonia due to MRSA. S. aureus and MRSA developed no resistance to vancomycin (P = 0.019 vs. < 0.0001, respectively) or linezolid (P = 0.342 vs. < 0.0001, respectively). MRSA (95.3%) and S. aureus (56.3%) showed a high resistance to penicillin. MRSA (87.7%) was also found to have a high antibiotic resistance against ß-lactam antibiotics, compared to S. aureus (9.6%). Furthermore, MRSA compared to S. aureus, respectively, had increased antibiotic resistance to ciprofloxacin (90.1% vs. 17.0%), cefazolin (89.7% vs. 10.2%), cefuroxime (89.0% vs. 9.1%), levofloxacin (88.2% vs. 18.4%), clindamycin (78.0% vs. 14.7%), and erythromycin (76.5% vs. 20.8%).

CONCLUSION

No development of resistance was found to vancomycin and linezolid in patients with pneumonia caused by S. aureus and MRSA.

Structural variations of the cell wall precursor lipid II and their influence on binding and activity of the lipoglycopeptide antibiotic oritavancin

Oritavancin is a semisynthetic derivative of the glycopeptide antibiotic chloroeremomycin with activity against Gram-positive pathogens, including vancomycin-resistant staphylococci and enterococci. Compared to vancomycin, oritavancin is characterized by the presence of two additional residues, a hydrophobic 4'-chlorobiphenyl methyl moiety and a 4-epi-vancosamine substituent, which is also present in chloroeremomycin. Here, we show that oritavancin and its des-N-methylleucyl variant (des-oritavancin) effectively inhibit lipid I- and lipid II-consuming peptidoglycan biosynthesis reactions in vitro. In contrast to that for vancomycin, the binding affinity of oritavancin to the cell wall precursor lipid II appears to involve, in addition to the D-Ala-D-Ala terminus, other species-specific binding sites of the lipid II molecule, i.e., the crossbridge and D-isoglutamine in position 2 of the lipid II stem peptide, both characteristic for a number of Gram-positive pathogens, including staphylococci and enterococci. Using purified lipid II and modified lipid II variants, we studied the impact of these modifications on the binding of oritavancin and compared it to those of vancomycin, chloroeremomycin, and des-oritavancin. Analysis of the binding parameters revealed that additional intramolecular interactions of oritavancin with the peptidoglycan precursor appear to compensate for the loss of a crucial hydrogen bond in vancomycin-resistant strains, resulting in enhanced binding affinity. Augmenting previous findings, we show that amidation of the lipid II stem peptide predominantly accounts for the increased binding of oritavancin to the modified intermediates ending in D-Ala-D-Lac. Corroborating our conclusions, we further provide biochemical evidence for the phenomenon of the antagonistic effects of mecA and vanA resistance determinants in Staphylococcus aureus, thus partially explaining the low frequency of methicillin-resistant S. aureus (MRSA) acquiring high-level vancomycin resistance.

Antibiotics and bacterial resistance in the 21st century

Dangerous, antibiotic resistant bacteria have been observed with increasing frequency over the past several decades. In this review the factors that have been linked to this phenomenon are addressed. Profiles of bacterial species that are deemed to be particularly concerning at the present time are illustrated. Factors including economic impact, intrinsic and acquired drug resistance, morbidity and mortality rates, and means of infection are taken into account. Synchronously with the waxing of bacterial resistance there has been waning antibiotic development. The approaches that scientists are employing in the pursuit of new antibacterial agents are briefly described. The standings of established antibiotic classes as well as potentially emerging classes are assessed with an emphasis on molecules that have been clinically approved or are in advanced stages of development. Historical perspectives, mechanisms of action and resistance, spectrum of activity, and preeminent members of each class are discussed.

Resistance to antibiotics targeted to the bacterial cell wall

Peptidoglycan is the main component of the bacterial cell wall. It is a complex, three-dimensional mesh that surrounds the entire cell and is composed of strands of alternating glycan units crosslinked by short peptides. Its biosynthetic machinery has been, for the past five decades, a preferred target for the discovery of antibacterials. Synthesis of the peptidoglycan occurs sequentially within three cellular compartments (cytoplasm, membrane, and periplasm), and inhibitors of proteins that catalyze each stage have been identified, although not all are applicable for clinical use. A number of these antimicrobials, however, have been rendered inactive by resistance mechanisms. The employment of structural biology techniques has been instrumental in the understanding of such processes, as well as the development of strategies to overcome them. This review provides an overview of resistance mechanisms developed toward antibiotics that target bacterial cell wall precursors and its biosynthetic machinery. Strategies toward the development of novel inhibitors that could overcome resistance are also discussed.

Dalbavancin, a long-acting lipoglycopeptide for the treatment of multidrug-resistant Gram-positive bacteria

Dalbavancin is a new lipoglycopeptide antibiotic in late-stage clinical development as a once-weekly treatment for serious infections including skin and skin structure infections. Its in vitro potency is greater than that of vancomycin, with a MIC(90) of 0.06 mg/l for Staphylococcus aureus and coagulase-negative staphylococci (irrespective of oxacillin susceptibility), 0.06-0.12 mg/l for vancomycin-susceptible Enterococcus spp. and 0.003 mg/l or less for Streptococcus pneumoniae or beta-hemolytic streptococci. Dalbavancin has dual routes of elimination. The results of Phase II/III studies show clinical efficiency in complicated skin and skin structure infection. During clinical trials, dalbavancin was as effective as linezolid or vancomycin in the treatment of patients with complicated skin and skin structure infection, including those with methicillin-resistant S. aureus. An additional Phase II study demonstrated efficacy in catheter-related bacteremia. Other preliminary in vitro and in vivo data have identified putative interest of dalbavancin in endocarditis, osteitis, diabetic foot, respiratory tract or joint infection.

Treatment options for multidrug-resistant bacteria

As a consequence of antibiotic overuse and misuse, nosocomial infections caused by multidrug-resistant bacteria represent a physician's nightmare throughout the world. No newer antimicrobials active against Pseudomonas aeruginosa, the main multidrug-resistant nosocomial pathogen, are available or under investigation. The only exceptions are linezolid, some newer glycopeptides (dalbavancin, oritavancin and telavancin) and daptomycin (a lipopeptide), which are active against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) strains, as well as tigecycline, a potent in vitro glycylcycline against MRSA, VRE, Acinetobacter baumannii and entended-spectrum beta-lactamase (ESBL)+ Enterobacteriaceae. Colistin, an antibiotic of the 1950s has been rediscovered by intensive care unit physicians for use against ESBL+ Enterobacteriaceae, as well as against multidrug-resistant P. aeruginosa and A. baumannii isolates. Although success rates with colistin range between 50 and 73%, almost all studies are retrospective. Immunostimulation efforts against S. aureus are still under development. As antibiotic research and development stagnate, rational policies for prescribing existing antibiotics plus strict infection control are the current mainstay efforts for preventing and combating multidrug-resistant bacterial infections.

IB-367 pre-treatment improves the in vivo efficacy of teicoplanin and daptomycin in an animal model of wounds infected with meticillin-resistant Staphylococcus aureus

Antimicrobial peptides are known as immunomodulators and antibiotic enhancers. We report that administration of an antimicrobial peptide, IB-367, was efficacious in increasing the antimicrobial activity of daptomycin and teicoplanin in a mouse model of wound infection caused by meticillin-resistant Staphylococcus aureus (MRSA). Mice were assigned to seven groups: an IB-367 pre-treated group with no antibiotics given after challenge, two IB-367 pre-treated groups plus daptomycin or teicoplanin given after challenge, two groups treated with daptomycin or teicoplanin only after challenge, and two control groups without infection or that did not receive any treatment. The main outcome measures were quantitative bacterial culture and analysis of natural killer (NK) cytotoxicity and leukocyte phenotype. The wound, established through the panniculus carnosus muscle of mice, was infected by MRSA. Bacterial cultures of mice receiving antibiotics alone showed a −2 log decrease, whilst those for IB-367 plus daptomycin or teicoplanin showed a −4 log decrease. IB-367 plus daptomycin showed the highest efficacy. The higher antimicrobial effect exerted by IB-367 was associated with increased levels of NK cytotoxicity but not of NK cell number. IB-367 increased the number of both CD11b and Gr-1 cells 3 days after MRSA challenge, whereas both of these leukocyte populations were reduced at 10 days after challenge. Our data suggest that a combination of IB-367 with antibiotic exerts a therapeutic effect and may be useful for the management of staphylococcal wounds.

Unmodified gold nanoparticles as a simple colorimetric probe for ramoplanin detection

In this paper unmodified gold nanoparticles (AuNPs) were used as a sensing element to detect ramoplamin. Detection relies on the fact that the dispersed AuNPs solution is red due to the intense surface plasmon absorption band at 530 nm whereas the AuNPs solution in the presence of ramoplanin is blue. Upon aggregation, there is a significant change in absorbance intensity at 620 nm. Based on the aggregation of AuNPs induced by ramoplanin, a simple colorimetric method was developed for determining the of ramoplanin concentration. Experimental conditions influencing the analytical performance such as particle size, amount of AuNPs, incubation time and pH were evaluated. Under the optimized experimental conditions, this method could detect ramoplanin in a linear range from 0.30 to 1.30 ppm with a detection limit of 0.01 ppm and exhibited good reproducibility, selectivity and recovery. Analysis time of this assay was only 2 min. To investigate its potential applicability, this assay was successfully applied for the determination of ramoplanin in urine samples without costly instruments.

Asymmetric catalysis at a distance: catalytic, site-selective phosphorylation of teicoplanin

We report three distinct, peptide-based catalysts that enable site-selective phosphorylation of three distinct hydroxyl groups within the complex glycopeptide antibiotic teicoplanin A2-2. Two of the catalysts are based on a design that capitalizes on a catalyst-substrate interaction that mimics the biological mechanism of action for teicoplanin. These catalysts are based on a DXaa-DXaa peptide motif that is known to target the teicoplanin structure in a specific manner. The third was identified through evaluation of a set of catalysts that had been developed for historically distinct projects. Each catalyst contains additional functionality designed to dispose a catalytic moiety (a nucleophilic alkylimidazole) at a different region of the glycopeptide structure. A combination of mass spectrometry and 2D-NMR spectroscopy allowed structural assignment of the distinct phosphorylated teicoplanin derivatives. Mechanistic studies are also reported that support the hypotheses that led to the discovery of the catalysts. In this manner, small molecule catalysts have been achieved that allow rational, catalytic control over reactions at sites that are separated by 11.6, 16.5, and nearly 17.7 Å, based on the X-ray crystal structure of teicoplanin A2-2. Finally, we report the biological activity of the new phosphorylated teicoplanin analogs and compare the results to the natural product itself.

Advances in MRSA drug discovery: where are we and where do we need to be?

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) have been on the increase during the past decade, due to the steady growth of the elderly and immunocompromised patients, and the emergence of multidrug-resistant (MDR) bacterial strains. Although there are a limited number of anti-MRSA drugs available, a number of different combination antimicrobial drug regimens have been used to treat serious MRSA infections. Thus, the addition of several new antistaphylococcal drugs into clinical practice should broaden clinician's therapeutic options. As MRSA is one of the most common and problematic bacteria associated with increasing antimicrobial resistance, continuous efforts for the discovery of lead compounds as well as development of alternative therapies and faster diagnostics are required.

AREAS COVERED

This article summarizes the FDA-approved drugs to treat MRSA infections, the drugs in clinical trials, and the drug leads for MRSA and related Gram-positive bacterial infections. In addition, the article discusses the mode of action of antistaphylococcal molecules and the resistant mechanisms of some molecules.

EXPERT OPINION

The number of pipeline drugs presently undergoing clinical trials is not particularly encouraging. There are limited and rather expensive therapeutic options for MRSA infections in the critically ill. Further research efforts are required for effective phage therapy on MRSA infections in clinical use, which seem to be attractive therapeutic options for the future.

Phylogeny-driven target selection for large-scale genome-sequencing (and other) projects

Despite the steadily decreasing costs of genome sequencing, prioritizing organisms for sequencing remains important in large-scale projects. Phylogeny-based selection is of interest to identify those organisms whose genomes can be expected to differ most from those that have already been sequenced. Here, we describe a method that infers a phylogenetic scoring independent of which set of organisms has previously been targeted, which is computationally simple and easy to apply in practice. The scoring itself, as well as pre- and post-processing of the data, is illustrated using two real-world examples in which the method has already been applied for selecting targets for genome sequencing. These projects are the JGI CSP Genomic Encyclopedia of Bacteria and Archaea phase I, targeting 1,000 type strains, and, on a smaller-scale, the phylogenomics of the Roseobacter clade. Potential artifacts of the method are discussed and compared to a selection approach based on the taxonomic classification.

Update on carbohydrate-containing antibacterial agents

BACKGROUND

Since the first known use of antibiotics > 2,500 years ago, a research field with immense importance for the welfare of mankind has been developed. After a decrease in interest in this topic by the end of the 20th century the occurrence of (poly-)resistant strains of bacteria induced a revival of antibiotics research. Health systems have been seeking viable and reliable solutions to this dangerous and expansive threat.

OBJECTIVE

This review will focus on carbohydrate-containing antibiotics and will give an outline of recently published novel isolated, semisynthetic as well as synthetic structures, their mechanism of action, if known, and the strategies for the design of compounds with potential by improved antibacterial properties.

METHODS

The literature between 2000 and 2008 was screened with main focus on recent examples of novel structures and strategies for the lead finding of exclusively antibacterial agents.

RESULTS/CONCLUSION

With the explanation of the role of the carbohydrate moieties in the respective antibacterial agents together with better synthetic strategies in carbohydrate chemistry as well as improvements in assay development for high throughput screening methods, carbohydrate-containing antibiotics can be used for the finding of potential drug leads that contribute to the fight against infections and diseases caused by (resistant) bacterial pathogens.

Viable screening targets related to the bacterial cell wall

The synthesis of the bacterial peptidoglycan has been recognized for over 50 years as fertile ground for antibacterial discovery. Initially, empirical screening of natural products for inhibition of bacterial growth detected many chemical classes of antibiotics whose specific mechanisms of action were eventually dissected and defined. Of the nontoxic antibiotics discovered, most were found to be inhibitors of either protein synthesis or cell wall synthesis, which led to more directed screening for inhibitors of these pathways. Directed screening and design programs for cell wall inhibitors have been undertaken since the 1960s. In that time it has become clear that, while certain steps and intermediates have yielded selective inhibitors and are established targets, other potential targets have not yielded inhibitors whose antibacterial activity is proven to be solely due to that inhibition. Why has this search been so problematic? Are the established targets still worth pursuing? This review will attempt to answer these and other questions and evaluate the viability of targets related to peptidoglycan synthesis.

Synthesis of fluorescent ristocetin aglycon derivatives with remarkable antibacterial and antiviral activities

Isoindole and benzoisoindole derivatives of ristocetin aglycon have been prepared by reaction with o-phthalaldehyde or naphthalene-2,3-dialdehyde and various thiols. The new compounds exhibited potent antibacterial and anti-influenza virus activity. The cluster forming and fluorescent properties of the aglycon derivatives were also studied.

Antibiotic-resistance Staphylococcus aureus isolated from cow's milk in the Hawassa area, South Ethiopia

BACKGROUND

Quarter milk samples from cows were examined to determine the prevalence of Staphylococcus aureus (SA) and different antibiotic resistant pattern were determined in a cross-sectional study design.

OBJECTIVE

The objective of this study was to isolate Staphylococcus aureus from samples of cow's milk obtained from Hawassa area and to determine their antibiotic susceptibility patterns.

METHOD

A total of 160 milk (CCP1-CCP5) samples were collected and screened for the presence of S. aureus. Gram staining, oxidase, catalase, DNase, haemolysis and coagulase tests were employed for bacterial identification.

RESULTS

All the samples were contaminated with S. aureus. A total of 78 S. aureus isolates were obtained during this study. The levels of contamination with S. aureus were higher in milk obtained from CCP1, CCP2, CCP3, CCP4 and CCP5 at Hawassa area farms (18.0%, 25.6%, 27.0%, 21.8% and 7.7%) respectively. A large percentage of the S. aureus isolates (25.6% and 27.0%) were from CCP2 and CCP3. All strains were resistant to Penicillin G (PG) (10 μg), Ampicillin (AP) (10 μg), Amoxicillin-Clavulanic acid (AC) (30 μg), Ciprofloxacin (CIP) (5 μg), Erythromycin (E) (15 μg), Ceftriaxone (CRO) (30 μg), Trimethoprime-Sulfamethoxazole (TMP-SMZ) (25 μg) Oxacillin (Ox) (1 μg) and Vancomycin (V) (30 μg), 67.9%, 70.9%, 30.9%, 0%, 32.1%, 23.1%, 7.7%, 60.3% and 38.5% respectively.

CONCLUSION

The proportion of isolates resistant to CIP, TMP-SMZ, CRO, AC, E and V were low compared to AP, PG and Ox. S. aureus is normally resident in humans; therefore, the S. aureus present in the cow's milk may have resulted from transmission between the two species, emphasizing the need to improve sanitary conditions in the milking environment.

Recent advances in the synthesis of new glycopeptide antibiotics

The vancomycin family of glycopeptide antibiotics has been inspiring research in the field of synthetic chemistry since the 1980s. Recent studies have moved away from the focus of total synthesis into new territory: the design and evaluation of novel compounds based on the natural products which exhibit improved antibacterial activity. Modern approaches to drug synthesis draw together investigations into the nature of the binding environment, and innovative synthetic methodologies which provide solutions to the challenging structural features and stereochemistry associated with this intriguing class of compounds. New analogues, derivatives and dimers of the natural products, as well as recent successes in the total synthesis of the complestatins are described in this tutorial review, covering literature from the last decade.

Update on the appropriate use of linezolid in clinical practice

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

Effectiveness of antimicrobial photodynamic therapy with a single treatment of RLP068/Cl in an experimental model of Staphylococcus aureus wound infection

BACKGROUND

Chronic leg ulceration is a common health problem. It is well known that a clinically relevant bacterial load in chronic cutaneous wounds interferes significantly with the normal process of healing. Staphylococcus aureus is the most important representative of the staphylococcal group which causes clinically relevant infections within immunocompetent patients.

OBJECTIVES

To investigate the efficacy of a single treatment of antimicrobial photodynamic therapy (APDT) with RLP068/Cl in a mouse model of a surgical wound infection induced with a methicillin-resistant strain of S. aureus (MRSA).

METHODS

Wounds, established through the panniculus carnosus of BALB/c and CD1 mice, were inoculated with 5 x 10(7) c.f.u. of MRSA. Mice were randomized into four groups respectively receiving no treatment, APDT with placebo, APDT with a new phthalocyanine derivative (RLP068/Cl) and intraperitoneal teicoplanin.

RESULTS

On day 2 from infection, a strong reduction of bacterial counts (≈ 3 logs) was observed in mice treated with RLP068/Cl in comparison with infected untreated mice. On day 9 from infection, a comparable and significant (≈ 2 logs) reduction of bacterial counts was found in mice treated with RLP068/Cl or with teicoplanin. At this time, histological examinations revealed that wounds treated with RLP068/Cl showed a complete re-epithelialization with a continuous epithelial lining.

CONCLUSIONS

The results of the in vivo study demonstrated that APDT with RLP068/Cl may be useful in the management of chronic infected wounds, accelerating the repair process through a significant bacterial inhibition.

Tailoring enzyme-rich environmental DNA clones: a source of enzymes for generating libraries of unnatural natural products

A detailed bioinformatics analysis of six glycopeptide biosynthetic gene clusters isolated from soil environmental DNA (eDNA) megalibraries indicates that a subset of these gene clusters contains collections of tailoring enzymes that are predicted to result in the production of new glycopeptide congeners. In particular, sulfotransferases appear in eDNA-derived gene clusters at a much higher frequency than would be predicted from the characterization of glycopeptides from cultured Actinomycetes . Enzymes found on tailoring-enzyme-rich eDNA clones associated with these six gene clusters were used to produce a series of new sulfated glycopeptide derivatives in both in vitro and in vivo derivatization studies. The derivatization of known natural products with eDNA-derived tailoring enzymes is likely to be a broadly applicable strategy for generating libraries of new natural product variants.

Vancomycin analogs: Seeking improved binding of d-Ala-d-Ala and d-Ala-d-Lac peptides by side-chain and backbone modifications

In order to seek vancomycin analogs with improved performance against VanA and VanB resistant bacterial strains, extensive computational investigations have been performed to examine the effects of side-chain and backbone modifications. Changes in binding affinities for tripeptide cell-wall precursor mimics, Ac(2)-l-Lys-d-Ala-d-Ala (3) and Ac(2)-l-Lys-d-Ala-d-Lac (4), with vancomycin analogs were computed with Monte Carlo/free energy perturbation (MC/FEP) calculations. Replacements of the 3-hydroxyl group in residue 7 with small alkyl or alkoxy groups, which improve contacts with the methyl side chain of the ligands'd-Ala residue, are predicted to be the most promising to enhance binding for both ligands. The previously reported amine backbone modification as in 5 is shown to complement the hydrophobic modifications for binding monoacetylated tripeptides. In addition, replacement of the hydroxyl groups in residues 5 and 7 by fluorine is computed to have negligible impact on binding the tripeptides, though it may be pharmacologically advantageous.

Comparative efficacy and safety of vancomycin versus teicoplanin: systematic review and meta-analysis

Vancomycin and teicoplanin are the glycopeptides currently in use for the treatment of infections caused by invasive beta-lactam-resistant gram-positive organisms. We conducted a systematic review and meta-analysis of randomized controlled trials that have compared vancomycin and teicoplanin administered systemically for the treatment of suspected or proven infections. A comprehensive search of trials without year, language, or publication status restrictions was performed. The primary outcome was all-cause mortality. Two reviewers independently extracted the data. Risk ratios (RRs) with 95% confidence intervals (CIs) were pooled by using the fixed-effect model (RRs of >1 favor vancomycin). Twenty-four trials were included. All-cause mortality was similar overall (RR, 0.95; 95% CI, 0.74 to 1.21), and there was no significant heterogeneity. In trials that used adequate allocation concealment, the results favored teicoplanin (RR, 0.82; 95% CI, 0.63 to 1.06), while in trials with unknown methods or inadequate concealment, the results favored vancomycin (RR, 3.61; 95% CI, 1.27 to 10.30). The latter trials might have recruited more severely ill patients. No other variable affected the RRs for mortality, including the assessment of glycopeptides administered empirically or for proven infections, neutropenia, the participant's age, and drug dosing. There were no significant differences between teicoplanin and vancomycin with regard to clinical failure (RR, 0.92; 95% CI, 0.81 to 1.05), microbiological failure (RR, 1.24; 95% CI, 0.93 to 1.65), and other efficacy outcomes. Lower RRs (in favor of teicoplanin) for clinical failure were observed with a lower risk of bias and when treatment was initiated for infections caused by gram-positive organisms rather than empirically. Total adverse events (RR, 0.61; 95% CI, 0.50 to 0.74), nephrotoxicity (RR, 0.44; 95% CI, 0.32 to 0.61), and red man syndrome were significantly less frequent with teicoplanin. Teicoplanin is not inferior to vancomycin with regard to efficacy and is associated with a lower adverse event rate than vancomycin.

Vancomycin resistance: are there better glycopeptides coming?

The appearance and dissemination of vancomycin resistance among clinically important Gram-positive bacteria was an important watershed in antimicrobial resistance trends that drastically narrows therapeutic options, particularly among the enterococci. Clinical resistance despite apparent susceptibility has also become an increasingly recognized issue with vancomycin treatment of methicillin-resistant Staphylococcus aureus pneumonia and endocarditis, which may be, in part, due to vancomycin-heteroresistant strains. The newly developed glycopeptides telavancin, dalbavancin and oritavancin have superior in vitro activity, enhanced bactericidality and unique pharmacokinetic properties compared with vancomycin and teicoplanin. Current clinical trial data show noninferiority to vancomycin or standard-of-care antistaphylococcal therapy for complicated skin-skin structure infections, and acceptable safety profiles. Although promising, whether or not these new compounds are clinically efficacious for the true therapeutic deficits created by in vitro and clinical vancomycin resistance is yet to be determined.

Anti-influenza virus activity and structure-activity relationship of aglycoristocetin derivatives with cyclobutenedione carrying hydrophobic chains

Previous studies have demonstrated that glycopeptide compounds carrying hydrophobic substituents can have favorable pharmacological (i.e. antibacterial and antiviral) properties. We here report on the in vitro anti-influenza virus activity of aglycoristocetin derivatives containing hydrophobic side chain-substituted cyclobutenedione. The lead compound 8e displayed an antivirally effective concentration of 0.4 μM, which was consistent amongst influenza A/H1N1, A/H3N2 and B viruses, and a selectivity index ≥50. Structural analogues derived from aglycovancomycin were found to be inactive. The hydrophobic side chain was shown to be an important determinant of activity. The narrow structure–activity relationship and broad activity against several human influenza viruses suggest a highly conserved interaction site, which is presumably related to the influenza virus entry process. Compound 8e proved to be inactive against several unrelated RNA and DNA viruses, except for varicella-zoster virus, against which a favorable activity was noted.

Current and novel antibiotics against resistant Gram-positive bacteria

The challenge posed by resistance among Gram-positive bacteria, epitomized by methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE) and vancomycin-intermediate and -resistant S. aureus (VISA and VRSA) is being met by a new generation of antimicrobials. This review focuses on the new β-lactams with activity against MRSA (ceftobiprole and ceftaroline) and on the new glycopeptides (oritavancin, dalbavancin, and telavancin). It will also consider the role of vancomycin in an era of existing alternatives such as linezolid, daptomycin and tigecycline. Finally, compounds in early development are described, such as iclaprim, friulimicin, and retapamulin, among others.

Ideal microbiological and pharmacological characteristics of a quality antimicrobial agent: comparing original and generic molecules

This article critically evaluates the main in vitro and in vivo studies published which compare generic with the original molecules, both those administered orally and parenterally. The authors indicate that caution should be used in assuming bioequivalence of the generic drug with its clinical efficacy in clinical practice. In fact, mild differences in the content of the active ingredient, less relevant in healthy volunteers, may have an impact in the actual population, which is heterogeneous for age, sex, weight, concomitant risk factors and severity of the underlying disease, as in critically ill patients, with consequences for the patient and ecosystem. Nowadays the requirements for authorization to commercialize a generic antimicrobial agent are focused on demonstration of bioequivalence to the original molecule, with a range variability of +/-20%. However this kind of trial is not sufficient to predict the actual profile in clinical practice, particularly in critically ill patients. Thus while generics can represent an opportunity for physicians, patients and healthcare systems the regulatory procedures do not seem exhaustive, and it is probably necessary to define an ad hoc technical standard of quality before their commercialization and to perform adequate clinical trials regarding efficacy and safety of the "equivalent molecule", especially for drugs used in critically ill patients.

Natural products to drugs: natural product-derived compounds in clinical trials

Natural product and natural product-derived compounds that are being evaluated in clinical trials or are in registration (as at 31st December 2007) have been reviewed, as well as natural product-derived compounds for which clinical trials have been halted or discontinued since 2005. Also discussed are natural product-derived drugs launched since 2005, new natural product templates and late-stage development candidates.

RNAIII-inhibiting peptide enhances healing of wounds infected with methicillin-resistant Staphylococcus aureus

Quorum sensing is a mechanism through which a bacterial population receives input from neighboring cells and elicits an appropriate response to enable survival within the host. Inhibiting quorum sensing by RNAIII-inhibiting peptide (RIP) has been demonstrated as a very effective mode of prevention and therapy for device-associated staphylococcal infections and was tested here for healing of wounds that are otherwise resistant to conventional antibiotics. Wounds, established through the panniculus carnosus of BALB/c mice, were inoculated with 5 x 10(7) CFU of methicillin-resistant Staphylococcus aureus. Mice were treated with Allevyn, RIP-soaked Allevyn (containing 20 microg RIP), daily intraperitoneal teicoplanin (7 mg/kg of body weight), Allevyn and teicoplanin, and RIP-soaked Allevyn and daily intraperitoneal teicoplanin. The main outcome measures were quantitative bacterial culture and histological examination with assessment of microvessel density and of vascular endothelial growth factor (VEGF) expression in tissue sections. Treatment with RIP-soaked Allevyn together with teicoplanin injection greatly reduced the bacterial load to 13 CFU/g (control untreated animals had 10(8) CFU/g bacteria). All other treatments were also significantly effective but only reduced the bacterial load to about 10(3) CFU/ml. Histological examination indicated that only treatment with RIP-soaked Allevyn with teicoplanin injection restored epithelial, granulation, and collagen scores, as well as microvessel density and VEGF expression, to the levels found with uninfected mice. In conclusion, we observed that RIP may be useful for the management of infected wounds and that it could represent an exciting and future alternative to the conventional antibiotics, at present considered the gold-standard treatments for methicillin-resistant S. aureus infections.

Temporin A is effective in MRSA-infected wounds through bactericidal activity and acceleration of wound repair in a murine model

We investigated the effect of topical temporin A in the management of methicillin-resistant strain of Staphylococcus aureus (MRSA)-infected experimental surgical wounds in mice. The wound, cut through the panniculus carnosus of BALB/c mice, was inoculated with 5x10(7) colony-forming units of MRSA. Mice were treated with Allevyn, temporin A-soaked Allevyn, Allevyn and daily intraperitoneal teicoplanin (7mg/kg), temporin A-soaked Allevyn and daily intraperitoneal teicoplanin. Main outcome measurements were: quantitative bacterial culture, histological examination with assessment of micro-vessel density and of vascular endothelial growth factor (VEGF) expression in tissue sections, and VEGF plasma levels alike. Treatment with temporin-A associated with teicoplanin injection significantly reduced bacterial load to 0.85 x 10(1)+/-0.1 x 10(1)CFU/ml. Histological examination showed that infected mice receiving temporin A-soaked Allevyn (with or without teicoplanin) had a higher degree of granulation tissue formation and collagen deposition compared to the other treated groups. A significant increase in serum VEGF expression was observed in mice receiving temporin A topically and temporin A topically associated with intraperitoneal teicoplanin. In conclusion our results demonstrated that temporin A is effective in the management of infected wounds, by a significant bacterial growth inhibition and acceleration of wound repair process.