Macrolide antibiotics inhibit 50S ribosomal subunit assembly in Bacillus subtilis and Staphylococcus aureus

Clarithromycin Suppresses Apple Proliferation Phytoplasma in Explant Cultures

Apple proliferation, caused by 'Candidatus Phytoplasma mali', is one of the most important economic threats in the field of apple production. Especially at a young age, infected trees can be affected by excessive bud proliferation and general decline. The fruit quality is also significantly reduced by this disease. To investigate treatment options, we applied a clarithromycin chemotherapy to infected in vitro cultures of 'Golden Delicious'. With increasing concentrations of clarithromycin in the media, the phytoplasma load decreased rapidly after one month of treatment, but phytotoxicity led to a pronounced mortality at 40 mg/L, which was the highest dose used in our experiment. Out of 45 initial explants, we obtained one negative mericlone and two mericlones with a concentration of phytoplasma DNA at the detection limit of PCR. The culture propagated from the mericlone that tested negative remained phytoplasma-free after 18 months of subculturing. Our results suggest the applicability of macrolide antibiotics against phytoplasma infections in vitro; however, it might be challenging to find the threshold zone where the concentration is sufficient for pathogen elimination, but not lethal for the plant material of different cultivars.

Azithromycin inhibits glioblastoma angiogenesis in mice via inducing mitochondrial dysfunction and oxidative stress

The poor outcomes in glioblastoma (GBM) necessitate new treatments. As GBM is highly vascularized and its growth is largely dependent on angiogenesis, angiogenesis inhibitors have been hotly evaluated in clinical trials for GBM treatment for the last decade. In line with these efforts, our work reveals that azithromycin, a clinically available antibiotic, is a novel angiogenesis inhibitor. Azithromycin inhibits vessel structure formation on Matrigel of GBM-derived endothelial cell (ECs) and other types of ECs. Time course analysis shows that azithromycin interferes with the early stage of angiogenesis. Azithromycin also inhibits GBM-derived EC adhesion, growth and survival but not migration. The transgenic zebrafish Tg (fli1a: EGFP) model clearly shows that azithromycin inhibits angiogenesis in vivo. Of note, azithromycin at non-toxic dose inhibits GBM growth in mice and increases overall survival, and furthermore, this is associated with angiogenesis inhibition. Mechanism studies show that azithromycin decreases mitochondrial respiration by suppressing the activity of multiple complexes, leading to ATP reduction, oxidative stress and damage. In addition, oxidative stress induced by azithromycin is through thiol redox-mediated pathways. Our work demonstrates the anti-angiogenic activity of azithromycin via inducing mitochondrial dysfunction and oxidative stress. Our pre-clinical evidence provides a rationale for initiating clinical trials using azithromycin in combination with standard-of-care drugs for GBM patients.

Antibiotics and Bacterial Resistance-A Short Story of an Endless Arms Race

Despite the undisputed development of medicine, antibiotics still serve as first-choice drugs for patients with infectious disorders. The widespread use of antibiotics results from a wide spectrum of their actions encompassing mechanisms responsible for: the inhibition of bacterial cell wall biosynthesis, the disruption of cell membrane integrity, the suppression of nucleic acids and/or proteins synthesis, as well as disturbances of metabolic processes. However, the widespread availability of antibiotics, accompanied by their overprescription, acts as a double-edged sword, since the overuse and/or misuse of antibiotics leads to a growing number of multidrug-resistant microbes. This, in turn, has recently emerged as a global public health challenge facing both clinicians and their patients. In addition to intrinsic resistance, bacteria can acquire resistance to particular antimicrobial agents through the transfer of genetic material conferring resistance. Amongst the most common bacterial resistance strategies are: drug target site changes, increased cell wall permeability to antibiotics, antibiotic inactivation, and efflux pumps. A better understanding of the interplay between the mechanisms of antibiotic actions and bacterial defense strategies against particular antimicrobial agents is crucial for developing new drugs or drug combinations. Herein, we provide a brief overview of the current nanomedicine-based strategies that aim to improve the efficacy of antibiotics.

Highly sensitive electrochemical sensor based on carbon paste electrode modified with graphene nanoribbon-CoFe2O4@NiO and ionic liquid for azithromycin antibiotic monitoring in biological and pharmaceutical samples

In this report, Azithromycin (Azi) antibiotic was measured by carbon paste electrode (CPE) improved by graphene nanoribbon-CoFe2O4@NiO nanocomposite and 1-hexyl-3 methylimidazolium hexafluorophosphate (HMIM PF6) as an ionic liquid binder. The electrochemical behavior of Azi on the graphene nanoribbon-CoFe2O4@NiO/HMIM PF6/CPE is investigated by voltammetric methods, and the results showed that the modifiers improve the conductivity and electrochemical activity of the CPE. According to obtained data, the electrochemical behavior of Azi is related to pH. under optimum conditions, the sensor has linear ranges from 10 µM to 2 mM with a LOD of 0.66 µM. The effect of scan rate and chronoamperometry were studied, which showed that the Azi electro-oxidation is diffusion controlled with the diffusion coefficient of 9.22 × 10-6 cm2/s. The reproducibility (3.15%), repeatability (2.5%), selectivity, and stability (for 30 days) tests were investigated, which results were acceptable. The actual sample analysis confirmed that the proposed sensor is an appropriate electrochemical tool for Azi determination in urine and Azi capsule.

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

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

Antimicrobial evaluation of the Cynara cardunculus extract in Helicobacter pylori cells using mid-infrared spectroscopy and chemometric methods

AIMS

The treatment effectiveness of gastric diseases caused by the bacteria Helicobacter pylori is failing due to high resistance to some antibiotics. Consequently, it is urgent to develop an accurate methodology to screen new antimicrobial agents.

METHODS AND RESULTS

A preliminary assay, using both therapeutic-based antibiotics (clarithromycin and metronidazole), was conducted to optimize experimental conditions in terms of the sensibility of the Fourier Transform Mid-Infrared spectroscopy (MIR-FTIR) associated with chemometric methods. Principal component analysis was applied to understand how the Cynara extract concentration acts differentially against H. pylori bacteria. The partial least squares model, characterized by R² = 0.98, and root mean square error cross-validation, 0.011, was developed for the spectral regions (3600 - 2500 cm^-1 , and 2000 - 698 cm^-1 ).

CONCLUSIONS

MIR-FTIR spectroscopy associated with chemometric methods can be considered a suitable approach to discover and analyze the promissory antimicrobial agents based on the biomolecular changes observed according to the Cynara extract.

SIGNIFICANCE AND IMPACT OF THE STUDY

MIR-FTIR spectroscopy and chemometric methods allowed to register the biomolecular changes due to the potential antimicrobial drugs at reduced concentrations comparatively to the conventional assay based on an agar-dilution method, being considered a useful approach to develop a platform to discover new bioactive molecules, allowing to reduce time and costs related to the exploratory step.

Mutation of TonB-Dependent Receptor Encoding Gene MCR_0492 Potentially Associates with Macrolides Resistance in Moraxella catarrhalis Isolates

Introduction

Moraxella catarrhalis, which is an opportunistic pathogen and is one of the three major pathogens of community-acquired pneumonia, causes a variety of infections in clinic. In recent years, the isolation rate of Moraxella catarrhalis has gradually increased. In China, due to the clinical empirical use of antibiotics, the resistance rate of Moraxella catarrhalis isolated from children to β-lactam antibiotics has reached 99%. The non-susceptible rate of Moraxella catarrhalis to macrolide antibiotics has also increased significantly.

Methods

Two isolates of Moraxella catarrhalis (R17123922_R and R18013231_R) were isolated from in-patients and were confirmed to be resistant to macrolide antibiotics using the standard disk diffusion and broth microdilution method recommended by CLSI. Whole-genome sequencing (WGS) analysis was performed in these two resistant strains.

Results

A total of 696 SNVs (single nucleotide variations), and 79 indels (Insertion and Deletion) were found in R17123922_R and R18013231_R. These SNVs and indels were distributed evenly in the genome, and no centralized distribution occurred. Moreover, two isolates did not harbor any previously reported mutations in the 23S rRNA and ribosomal proteins.

Conclusion

A novel indel in the MCR_0492 gene encoding TonB-dependent receptor protein was identified, and we speculated that TonB-dependent protein receptor may play an important role in macrolide resistance of Moraxella catarrhalis.

Unprecedented Epimerization of an Azithromycin Analogue: Synthesis, Structure and Biological Activity of 2'-Dehydroxy-5″-Epi-Azithromycin

Certain macrolide antibiotics, azithromycin included, possess anti-inflammatory properties that are considered fundamental for their efficacy in the treatment of chronic inflammatory diseases, such as diffuse pan-bronchiolitis and cystic fibrosis. In this study, we disclose a novel azithromycin analog obtained via Barton-McCombie oxidation during which an unprecedented epimerization on the cladinose sugar occurs. Its structure was thoroughly investigated using NMR spectroscopy and compared to the natural epimer, revealing how the change in configuration of one single stereocenter (out of 16) profoundly diminished the antimicrobial activity through spatial manipulation of ribosome binding epitopes. At the same time, the anti-inflammatory properties of parent macrolide were retained, as demonstrated by inhibition of LPS- and cigarette-smoke-induced pulmonary inflammation. Not surprisingly, the compound has promising developable properties including good oral bioavailability and a half-life that supports once-daily dosing. This novel anti-inflammatory candidate has significant potential to fill the gap in existing anti-inflammatory agents and broaden treatment possibilities.

Bacterial Targets of Antibiotics in Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most prevalent bacterial pathogens and continues to be a leading cause of morbidity and mortality worldwide. MRSA is a commensal bacterium in humans and is transmitted in both community and healthcare settings. Successful treatment remains a challenge, and a search for new targets of antibiotics is required to ensure that MRSA infections can be effectively treated in the future. Most antibiotics in clinical use selectively target one or more biochemical processes essential for S. aureus viability, e.g., cell wall synthesis, protein synthesis (translation), DNA replication, RNA synthesis (transcription), or metabolic processes, such as folic acid synthesis. In this review, we briefly describe the mechanism of action of antibiotics from different classes and discuss insights into the well-established primary targets in S. aureus. Further, several components of bacterial cellular processes, such as teichoic acid, aminoacyl-tRNA synthetases, the lipid II cycle, auxiliary factors of β-lactam resistance, two-component systems, and the accessory gene regulator quorum sensing system, are discussed as promising targets for novel antibiotics. A greater molecular understanding of the bacterial targets of antibiotics has the potential to reveal novel therapeutic strategies or identify agents against antibiotic-resistant pathogens.

Antibiotics targeting bacterial ribosomal subunit biogenesis

This article describes 20 years of research that investigated a second novel target for ribosomal antibiotics, the biogenesis of the two subunits. Over that period, we have examined the effect of 52 different antibiotics on ribosomal subunit formation in six different microorganisms. Most of the antimicrobials we have studied are specific, preventing the formation of only the subunit to which they bind. A few interesting exceptions have also been observed. Forty-one research publications and a book chapter have resulted from this investigation. This review will describe the methodology we used and the fit of our results to a hypothetical model. The model predicts that inhibition of subunit assembly and translation are equivalent targets for most of the antibiotics we have investigated.

Comparison of in vitro synergistic effect between clarithromycin or azithromycin in combination with amikacin against Mycobacterium intracellulare

OBJECTIVES

This study compared the in vitro synergistic effect between clarithromycin or azithromycin in combination with amikacin against Mycobacterium intracellulare.

METHODS

In vitro antimicrobial susceptibility of M. intracellulare isolates was determined by the broth microdilution method in cation-adjusted Mueller-Hinton broth. The fractional inhibitory concentration index (FICI) was also calculated to assess synergy between the antimicrobial agents.

RESULTS

A total of 32 respiratory M. intracellulare isolates were included in the study. Clarithromycin was the most potent agent against M. intracellulare, with MIC₅₀ and MIC₉₀ values (minimum inhibitory concentration required to inhibit 50% and 90% of the isolates, respectively) of 0.5μg/mL and 8μg/mL, respectively. Azithromycin and amikacin also showed moderate activity against M. intracellulare, with MIC₉₀ values of 16μg/mL and 4μg/mL, respectively. The percentage of resistant strains among the 32 M. intracellulare isolates was 3.1% for clarithromycin, 9.3% for amikacin and 12.5% for azithromycin. The presence of amikacin had no effect on the MIC₅₀ of clarithromycin, whereas the presence of amikacin resulted in a two-fold increase in the MIC₅₀ of azithromycin. In addition, antagonism for the clarithromycin-amikacin combination was noted in 5 (15.6%) of the 32 M. intracellulare isolates, which was significantly lower than for the azithromycin-amikacin combination (14/32; 43.8%) (P = 0.042).

CONCLUSION

These data demonstrated that clarithromycin displayed more potent in vitro activity against M. intracellulare isolates than azithromycin. In addition, the antagonistic effect between azithromycin and amikacin was more frequent in M. intracellular isolates than that between clarithromycin and amikacin.

Viral-Bacterial Co-infections in the Cystic Fibrosis Respiratory Tract

A majority of the morbidity and mortality associated with the genetic disease Cystic Fibrosis (CF) is due to lung disease resulting from chronic respiratory infections. The CF airways become chronically colonized with bacteria in childhood, and over time commensal lung microbes are displaced by bacterial pathogens, leading to a decrease in microbial diversity that correlates with declining patient health. Infection with the pathogen Pseudomonas aeruginosa is a major predictor of morbidity and mortality in CF, with CF individuals often becoming chronically colonized with P. aeruginosa in early adulthood and thereafter having an increased risk of hospitalization. Progression of CF respiratory disease is also influenced by infection with respiratory viruses. Children and adults with CF experience frequent respiratory viral infections with respiratory syncytial virus (RSV), rhinovirus, influenza, parainfluenza, and adenovirus, with RSV and influenza infection linked to the greatest decreases in lung function. Along with directly causing severe respiratory symptoms in CF populations, the impact of respiratory virus infections may be more far-reaching, indirectly promoting bacterial persistence and pathogenesis in the CF respiratory tract. Acquisition of P. aeruginosa in CF patients correlates with seasonal respiratory virus infections, and CF patients colonized with P. aeruginosa experience increased severe exacerbations and declines in lung function during respiratory viral co-infection. In light of such observations, efforts to better understand the impact of viral-bacterial co-infections in the CF airways have been a focus of clinical and basic research in recent years. This review summarizes what has been learned about the interactions between viruses and bacteria in the CF upper and lower respiratory tract and how co-infections impact the health of individuals with CF.

Azithromycin effectively inhibits tumor angiogenesis by suppressing vascular endothelial growth factor receptor 2-mediated signaling pathways in lung cancer

Tumor angiogenesis is essential during lung cancer development and targeting angiogenesis may possess a potential therapeutic value. The present study demonstrates that azithromycin, a Food and Drug Administration-approved antibiotic drug, is a novel tumor angiogenesis inhibitor. Azithromycin inhibits capillary network formation of human lung tumor associated-endothelial cells (HLT-ECs) in vitro and in vivo. It significantly inhibits HLT-EC adhesion and vascular endothelial growth factor (VEGF)-induced proliferation of HLT-ECs in a dose-dependent manner without affecting migration. In addition, azithromycin induces apoptosis of HLT-ECs even in the presence of VEGF. Notably, azithromycin inhibits proliferation and induces apoptosis in multiple lung cancer cell lines to a significantly reduced extent compared with in HLT-ECs, suggesting that HLT-ECs are more susceptible to azithromycin treatment. In a lung tumor xenograft model, azithromycin significantly inhibits tumor growth and its anti-tumor activities are achieved by suppressing angiogenesis. Notably, the inhibitory effects of azithromycin on angiogenesis are associated with its ability to suppress VEGF-induced activation of VEGF receptor 2 (VEGFR2), phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt), focal adhesion kinase, and disruption of focal adhesion assembly and actin stress fiber formation in HLT-ECs. The present study identifies that azithromycin targets VEGFR2-mediated focal adhesion and PI3K/Akt signaling pathways in HLT-ECs, leading to the suppression of angiogenesis and lung tumor growth.

Evaluation of macrolides for possible use against multidrug-resistant Mycobacterium tuberculosis

Multidrug-resistant tuberculosis (MDR-TB) is a major global health problem. The loss of susceptibility to an increasing number of drugs behoves us to consider the evaluation of non-traditional anti-tuberculosis drugs.

Clarithromycin, a macrolide antibiotic, is defined as a group 5 anti-tuberculosis drug by the World Health Organization; however, its role or efficacy in the treatment of MDR-TB is unclear. A systematic review of the literature was conducted to summarise the evidence for the activity of macrolides against MDR-TB, by evaluating in vitro, in vivo and clinical studies. PubMed and Embase were searched for English language articles up to May 2014.

Even though high minimum inhibitory concentration values are usually found, suggesting low activity against Mycobacterium tuberculosis, the potential benefits of macrolides are their accumulation in the relevant compartments and cells in the lungs, their immunomodulatory effects and their synergistic activity with other anti-TB drugs.

A future perspective may be use of more potent macrolide analogues to enhance the activity of the treatment regimen.

Effect of azithromycin on the LPS-induced production and secretion of phospholipase A2 in lung cells

Azithromycin is a member of macrolides, utilized in the treatment of infections. Independently, these antibiotics also possess anti-inflammatory and immunomodulatory properties. Phospholipase A2 isotypes, which are implicated in the pathophysiology of inflammatory lung disorders, are produced by alveolar macrophages and other lung cells during inflammatory response and can promote lung injury by destructing lung surfactant. The aim of the study was to investigate whether in lung cells azithromycin can inhibit secretory and cytosolic phospholipases A2, (sPLA2) and (cPLA2), respectively, which are induced by an inflammatory trigger. In this respect, we studied the lipopolysaccharide (LPS)-mediated production or secretion of sPLA2 and cPLA2 from A549 cells, a cancer bronchial epithelial cell line, and alveolar macrophages, isolated from bronchoalveolar lavage fluid of ARDS and control patients without cardiopulmonary disease or sepsis. Pre-treatment of cells with azithromycin caused a dose-dependent decrease in the LPS-induced sPLA2-IIA levels in A549 cells. This inhibition was rather due to reduced PLA2G2A mRNA expression and secretion of sPLA2-IIA protein levels, as observed by western blotting and indirect immunofluorescence by confocal microscopy, respectively, than to the inhibition of the enzymic activity per se. On the contrary, azithromycin had no effect on the LPS-induced production or secretion of sPLA2-IIA from alveolar macrophages. The levels of LPS-induced c-PLA2 were not significantly affected by azithromycin in either cell type. We conclude that azithromycin exerts anti-inflammatory properties on lung epithelial cells through the inhibition of both the expression and secretion of LPS-induced sPLA2-IIA, while it does not affect alveolar macrophages.

Quantitative proteomic analysis of ribosome assembly and turnover in vivo

Although high-resolution structures of the ribosome have been solved in a series of functional states, relatively little is known about how the ribosome assembles, particularly in vivo. Here, a general method is presented for studying the dynamics of ribosome assembly and ribosomal assembly intermediates. Since significant quantities of assembly intermediates are not present under normal growth conditions, the antibiotic neomycin is used to perturb wild-type Escherichia coli. Treatment of E. coli with the antibiotic neomycin results in the accumulation of a continuum of assembly intermediates for both the 30S and 50S subunits. The protein composition and the protein stoichiometry of these intermediates were determined by quantitative mass spectrometry using purified unlabeled and (15)N-labeled wild-type ribosomes as external standards. The intermediates throughout the continuum are heterogeneous and are largely depleted of late-binding proteins. Pulse-labeling with (15)N-labeled medium time-stamps the ribosomal proteins based on their time of synthesis. The assembly intermediates contain both newly synthesized proteins and proteins that originated in previously synthesized intact subunits. This observation requires either a significant amount of ribosome degradation or the exchange or reuse of ribosomal proteins. These specific methods can be applied to any system where ribosomal assembly intermediates accumulate, including strains with deletions or mutations of assembly factors. This general approach can be applied to study the dynamics of assembly and turnover of other macromolecular complexes that can be isolated from cells.

YsxC, an essential protein in Staphylococcus aureus crucial for ribosome assembly/stability

Background

Bacterial growth and division requires a core set of essential proteins, several of which are still of unknown function. They are also attractive targets for the development of new antibiotics. YsxC is a member of a family of GTPases highly conserved across eubacteria with a possible ribosome associated function.

Results

Here, we demonstrate by the creation of a conditional lethal mutant that ysxC is apparently essential for growth in S. aureus. To begin to elucidate YsxC function, a translational fusion of YsxC to the CBP-ProteinA tag in the staphylococcal chromosome was made, enabling Tandem Affinity Purification (TAP) of YsxC-interacting partners. These included the ribosomal proteins S2, S10 and L17, as well as the ^β' subunit of the RNA polymerase. YsxC was then shown to copurify with ribosomes as an accessory protein specifically localizing to the 50 S subunit. YsxC depletion led to a decrease in the presence of mature ribosomes, indicating a role in ribosome assembly and/or stability in S. aureus.

Conclusions

In this study we demonstrate that YsxC of S. aureus localizes to the ribosomes, is crucial for ribosomal stability and is apparently essential for the life of S. aureus.

Erythromycin resistance by L4/L22 mutations and resistance masking by drug efflux pump deficiency

We characterized the effects of classical erythromycin resistance mutations in ribosomal proteins L4 and L22 of the large ribosomal subunit on the kinetics of erythromycin binding. Our data are consistent with a mechanism in which the macrolide erythromycin enters and exits the ribosome through the nascent peptide exit tunnel, and suggest that these mutations both impair passive transport through the tunnel and distort the erythromycin-binding site. The growth-inhibitory action of erythromycin was characterized for bacterial populations with wild-type and L22-mutated ribosomes in drug efflux pump deficient and proficient backgrounds. The L22 mutation conferred reduced erythromycin susceptibility in the drug efflux pump proficient, but not deficient, background. This 'masking' of drug resistance by pump deficiency was reproduced by modelling with input data from our biochemical experiments. We discuss the general principles behind the phenomenon of drug resistance 'masking', and highlight its potential importance for slowing down the evolution of drug resistance among pathogens.

Erythromycin- and chloramphenicol-induced ribosomal assembly defects are secondary effects of protein synthesis inhibition

Several protein synthesis inhibitors are known to inhibit ribosome assembly. This may be a consequence of direct binding of the antibiotic to ribosome precursor particles, or it could result indirectly from loss of coordination in the production of ribosomal components due to the inhibition of protein synthesis. Here we demonstrate that erythromycin and chloramphenicol, inhibitors of the large ribosomal subunit, affect the assembly of both the large and small subunits. Expression of a small erythromycin resistance peptide acting in cis on mature ribosomes relieves the erythromycin-mediated assembly defect for both subunits. Erythromycin treatment of bacteria expressing a mixture of erythromycin-sensitive and -resistant ribosomes produced comparable effects on subunit assembly. These results argue in favor of the view that erythromycin and chloramphenicol affect the assembly of the large ribosomal subunit indirectly.

Macrolide myths

In spite of decades of research, our knowledge of the mode of interaction of macrolide antibiotics with their ribosomal target and of the mechanism of action of these drugs remain fragmentary. Experimental facts obtained over the past several years question some of the concepts that were viewed as a 'common knowledge'. This review focuses on certain aspects of binding and action of macrolides that may need re-evaluation in view of the new findings.

Three methods to assay inhibitors of ribosomal subunit assembly

The inhibition of bacterial ribosomal subunit formation is a novel target for translational inhibitors. Inhibition of subunit biogenesis has been shown to be equivalent to the inhibition of protein biosynthesis for many antibiotics. This chapter describes three methods for examining the inhibition of subunit formation in growing bacterial cells. The first method permits the determination of the IC50 value for inhibition of assembly and protein synthesis. The second is a pulse and chase labeling procedure to measure the kinetics of subunit formation. The third procedure allows an examination of ribosome reformation after antibiotic removal as a part of the post-antibiotic effect. Together these procedures give a description of the relative inhibitory effects of an antibiotic on translation and subunit formation.

Novel mutations in ribosomal proteins L4 and L22 that confer erythromycin resistance in Escherichia coli

L4 and L22, proteins of the large ribosomal subunit, contain globular surface domains and elongated ‘tentacles’ that reach into the core of the large subunit to form part of the lining of the peptide exit tunnel. Mutations in the tentacles of L4 and L22 confer macrolide resistance in a variety of pathogenic and non-pathogenic bacteria. In Escherichia coli, a Lys-to-Glu mutation in L4 and a three-amino-acid deletion in the L22 had been reported. To learn more about the roles of the tentacles in ribosome assembly and function, we isolated additional erythromycin-resistant E. coli mutants. Eight new mutations mapped in L4, all within the tentacle. Two new mutations were identified in L22; one mapped outside the tentacle. Insertion mutations were found in both genes. All of the mutants grew slower than the parent, and they all showed reduced in vivo rates of peptide-chain elongation and increased levels of precursor 23S rRNA. Large insertions in L4 and L22 resulted in very slow growth and accumulation of abnormal ribosomal subunits. Our results highlight the important role of L4 and L22 in ribosome function and assembly, and indicate that a variety of changes in these proteins can mediate macrolide resistance.

Hygromycin B inhibition of protein synthesis and ribosome biogenesis in Escherichia coli

The aminoglycoside antibiotic hygromycin B was examined in Escherichia coli cells for inhibitory effects on translation and ribosomal-subunit formation. Pulse-chase labeling experiments were performed, which verified lower rates of ribosomal-subunit synthesis in drug-treated cells. Hygromycin B exhibited a concentration-dependent inhibitory effect on viable-cell numbers, growth rate, protein synthesis, and 30S and 50S subunit formation. Unlike other aminoglycosides, hygromycin B was a more effective inhibitor of translation than of ribosomal-subunit formation in E. coli. Examination of total RNA from treated cells showed an increase in RNA corresponding to a precursor to the 16S rRNA, while mature 16S rRNA decreased. Northern hybridization to rRNA in cells treated with hygromycin B showed that RNase II- and RNase III-deficient strains of E. coli accumulated 16S rRNA fragments upon treatment with the drug. The results indicate that hygromycin B targets protein synthesis and 30S ribosomal-subunit assembly.

Novel treatment options for infectious exacerbations

Herein, we detail characteristics shared between two common therapeutic approaches, macrolide antibiotic therapy and systemic corticosteroids, in an attempt to propose an alternative treatment paradigm.

New research in macrolides and ketolides since 1997

Macrolide and ketolide antibacterials remain a very dynamically active group. To overcome erythromycin A resistance within Gram-positive cocci and bacteria, novel compounds have been semi-synthesised, such as ketolides and C-4'' carbamate erythromycylamine derivatives. The continual efforts of those studying macrolides have led to molecular level investigations into the mechanism of action of these antibacterials. Among all novel derivatives, only telithromycin and AB-773 are currently under development. No real novel developments have been seen with the 15- and 16-membered ring macrolides, however, research is also continuing in this area. This review is an update of our knowledge in the field of macrolides.

A guide to selection and appropriate use of macrolides in skin infections

Dermatologists must be aware of the adverse effects of antimicrobial agents as well as various drug interactions that may influence the choice of drug as well as specific drug schedules. The development of modern antibacterials has improved the treatment of cutaneous bacterial infections. Macrolide antibacterials continue to be an important therapeutic class of drugs with established efficacy in a variety of skin infections. All macrolides inhibit protein synthesis by reversibly binding to the 23S ribosomal RNA in the 50S-subunit. Erythromycin, the prototype of macrolide antibacterials, was isolated from the metabolic products of a strain of Streptomyces erytherus in 1952. Originally, erythromycin was introduced as an alternative to penicillin because of its activity against the Gram-positive organisms. Numerous studies have demonstrated the efficacy and safety of erythromycin for various infectious diseases. Unfortunately, erythromycin is associated with a number of drawbacks including a narrow spectrum of activity, unfavorable pharmacokinetic properties, poor gastrointestinal tolerability, and a significant number of drug-drug interactions. Newer macrolides have been developed to address these limitations. The pharmacokinetics of azithromycin and clarithromycin allow for shorter dosing schedules because of prolonged tissue levels. The efficacy of azithromycin for the treatment of skin and soft tissue infections in adults and children is well established. The unique pharmakinetics of azithromycin makes it a suitable agent for the treatment of acne. Clarithromycin represents a clear advance in the macrolide management of patients with leprosy and skin infections with atypical mycobacteria. Dirithromycin and roxithromycin display no clinical or bacteriological adcantage over erythromycin despite a superior pharmacokinetic profile. An area of concern is the increasing macrolide resistance that is being reported with some of the common pathogens which may limit the clinical usefulness of this class of antimicrobial agents in future.

Review of macrolides and ketolides: focus on respiratory tract infections

The first macrolide, erythromycin A, demonstrated broad-spectrum antimicrobial activity and was used primarily for respiratory and skin and soft tissue infections. Newer 14-, 15- and 16-membered ring macrolides such as clarithromycin and the azalide, azithromycin, have been developed to address the limitations of erythromycin. The main structural component of the macrolides is a large lactone ring that varies in size from 12 to 16 atoms. A new group of 14-membered macrolides known as the ketolides have recently been developed which have a 3-keto in place of the L-cladinose moiety. Macrolides reversibly bind to the 23S rRNA and thus, inhibit protein synthesis by blocking elongation. The ketolides have also been reported to bind to 23S rRNA and their mechanism of action is similar to that of macrolides. Macrolide resistance mechanisms include target site alteration, alteration in antibiotic transport and modification of the antibiotic. The macrolides and ketolides exhibit good activity against gram-positive aerobes and some gram-negative aerobes. Ketolides have excellent activity versus macrolide-resistant Streptococcus spp. Including mefA and ermB producing Streptococcus pneumoniae. The newer macrolides, such as azithromycin and clarithromycin, and the ketolides exhibit greater activity against Haemophilus influenzae than erythromycin. The bioavailability of macrolides ranges from 25 to 85%, with corresponding serum concentrations ranging from 0.4 to 12 mg/L and area under the concentration-time curves from 3 to 115 mg/L x h. Half-lives range from short for erythromycin to medium for clarithromycin, roxithromycin and ketolides, to very long for dirithromycin and azithromycin. All of these agents display large volumes of distribution with excellent uptake into respiratory tissues and fluids relative to serum. The majority of the agents are hepatically metabolised and excretion in the urine is limited, with the exception of clarithromycin. Clinical trials involving the macrolides are available for various respiratory infections. In general, macrolides are the preferred treatment for community-acquired pneumonia and alternative treatment for other respiratory infections. These agents are frequently used in patients with penicillin allergies. The macrolides are well-tolerated agents. Macrolides are divided into 3 groups for likely occurrence of drug-drug interactions: group 1 (e.g. erythromycin) are frequently involved, group 2 (e.g. clarithromycin, roxithromycin) are less commonly involved, whereas drug interactions have not been described for group 3 (e.g. azithromycin, dirithromycin). Few pharmacoeconomic studies involving macrolides are presently available. The ketolides are being developed in an attempt to address the increasingly prevalent problems of macrolide-resistant and multiresistant organisms.

Erythromycin inhibition of 50S ribosomal subunit formation in Escherichia coli cells

The effects of erythromycin on the formation of ribosomal subunits were examined in wild-type Escherichia coli cells and in an RNase E mutant strain. Pulse-chase labelling kinetics revealed a reduced rate of 50S subunit formation in both strains compared with 30S synthesis, which was unaffected by the antibiotic. Growth of cells in the presence of [14C]-erythromycin showed drug binding to 50S particles and to a 50S subunit precursor sedimenting at about 30S in sucrose gradients. Antibiotic binding to the precursor correlated with the decline in 50S formation in both strains. Erythromycin binding to the precursor showed the same 1:1 stoichiometry as binding to the 50S particle. Gel electrophoresis of rRNA from antibiotic-treated organisms revealed the presence of both 23S and 5S rRNAs in the 30S region of sucrose gradients. Hybridization with a 23S rRNA-specific probe confirmed the presence of this species of rRNA in the precursor. Eighteen 50S ribosomal proteins were associated with the precursor particle. A model is presented to account for erythromycin inhibition of 50S formation.

Evernimicin (SCH27899) inhibits both translation and 50S ribosomal subunit formation in Staphylococcus aureus cells

The effects of the everninomicin antibiotic evernimicin (SCH27899) on growing Staphylococcus aureus cells were investigated. Cellular growth rates and viable cell numbers decreased with increasing antibiotic concentrations. The rate of protein synthesis, measured as (35)S-amino acid incorporation, declined in parallel with the growth rate. Significantly, the formation of the 50S ribosomal subunit was inhibited in a dose-dependent fashion as well. 30S ribosomal subunit synthesis was not affected over the same concentration range. Evernimicin did not stimulate the breakdown of mature ribosomal subunits. Pulse-chase labeling experiments revealed a reduced rate of 50S subunit formation in drug-treated cells. Two erythromycin-resistant strains of S. aureus that carried the ermC gene were as sensitive as wild-type cells to antibiotic inhibition. In addition, two methicillin-resistant S. aureus organisms, one sensitive to erythromycin and one resistant to the macrolide, showed similar sensitivities to evernimicin. These results suggest a use for this novel antimicrobial agent against antibiotic-resistant bacterial infections.

Macrolide antibiotic inhibition of translation and 50S ribosomal subunit assembly in methicillin-resistant Staphylococcus aureus cells

Methicillin-resistant Staphylococcus aureus cells were treated with three macrolide antibiotics to examine the inhibitory effect of the drugs on the growth rate and cell viability. Inhibition of protein synthesis and 50S ribosomal subunit assembly were also examined. The growth rate and cell viability were reduced by each antibiotic in both erythromycin-susceptible and erythromycin-resistant MRSA organisms. Translation and the formation of the 50S ribosomal subunit were inhibited to an equal extent in the erythromycin-susceptible cells, but protein synthesis was affected to a greater extent by each macrolide in the erythromycin-resistant organisms. Clarithromycin was the most inhibitory of the three compounds, followed by erythromycin and azithromycin in relative effectiveness. The use of these compounds against MRSA organisms is discussed.

Macrolide and ketolide antibiotic separation by reversed phase high performance liquid chromatography

Twenty different macrolide and ketolide antibiotics were analyzed by reversed phase high performance liquid chromatography on an ODS-2 cartridge column. Each of these compounds was uniquely separated and purified by varying the flow rate. Retention times of the individual drugs were proportional to the flow rate of the mobile phase. Recovery of antimicrobial activity for most of the drugs was greater than 90% based on a microbiological assay of material recovered from the column. Retention times were related to structural differences between these antimicrobial agents.

Molecular investigation of the postantibiotic effects of clarithromycin and erythromycin on Staphylococcus aureus cells

The kinetics of recovery after inhibition of growth by erythromycin and clarithromycin were examined in Staphylococcus aureus cells. After inhibition for one mass doubling by 0.5 microg of the antibiotics/ml, a postantibiotic effect (PAE) of 3 and 4 h duration was observed for the two drugs before growth resumed. Cell viability was reduced by 25% with erythromycin and 45% with clarithromycin compared with control cells. Erythromycin and clarithromycin treatment reduced the number of 50S ribosomal subunits to 24 and 13% of the number found in untreated cells. 30S subunit formation was not affected. Ninety minutes was required for resynthesis to give the control level of 50S particles. Protein synthesis rates were diminished for up to 4 h after the removal of the macrolides. This continuing inhibition of translation was the result of prolonged binding of the antibiotics to the 50S subunit as measured by 14C-erythromycin binding to ribosomes in treated cells. The limiting factors in recovery from macrolide inhibition in these cells, reflected as a PAE, are the time required for the synthesis of new 50S subunits and the slow loss of the antibiotics from ribosomes in inhibited cells.

Antibiotic resistance mechanisms in bacteria of oral and upper respiratory origin

Over the past 20 years, antibiotic resistance has increased in virtually every species of bacteria examined. In this paper, the main mechanisms of antibiotic resistance currently known for antibiotics used for treatment of disease caused by oral and upper respiratory bacteria will be reviewed, with an emphasis on the most commonly used antibiotics. The possible role that mercury, which is released from silver amalgams, plays in the oral/respiratory bacterial ecology is also discussed, as it relates to possible selection of antibiotic resistant bacteria.

Innovative approaches to novel antibacterial drug discovery

Increasing antibiotic resistance in microorganisms and new emerging pathogens have become a major problem in our society. Rising to satisfy this urgent medical need is a recent confluence of powerful new drug discovery technologies: combinatorial chemistry; sequence and functional genomic analysis; and novel methods of high-throughput screening. The combination of these technologies will bring to bear untapped power in the search for new antimicrobials.

50S ribosomal subunit synthesis and translation are equivalent targets for erythromycin inhibition in Staphylococcus aureus

Macrolide antibiotics like erythromycin can prevent the formation of the 50S ribosomal subunit in growing bacterial cells, in addition to their inhibitory effect on translation. The significance of this novel finding has been further investigated. The 50% inhibitory doses of erythromycin for the inhibition of translation and 50S subunit assembly in Staphylococcus aureus cells were measured and were found to be identical. Together they account quantitatively for the observed effects of erythromycin on cell growth rates. There is also a direct relationship between the loss of rRNA from the 50S subunit and its accumulation as oligoribonucleotides in cells. The importance of this second site for erythromycin inhibition of bacterial cell growth is discussed.