Further insights into the mode of action of the lipoglycopeptide telavancin through global gene expression studies

Guarding the walls: the multifaceted roles of Bce modules in cell envelope stress sensing and antimicrobial resistance

Bacteria have developed diverse strategies for defending their cell envelopes from external threats. In Firmicutes, one widespread strategy is to use Bce modules-membrane protein complexes that unite a peptide-detoxifying ABC transporter with a stress response coordinating two-component system. These modules provide specific, front-line defense for a wide variety of antimicrobial peptides and small molecule antibiotics as well as coordinate responses for heat, acid, and oxidative stress. Because of these abilities, Bce modules play important roles in virulence and the development of antibiotic resistance in a variety of pathogens, including Staphylococcus, Streptococcus, and Enterococcus species. Despite their importance, Bce modules are still poorly understood, with scattered functional data in only a small number of species. In this review, we will discuss Bce module structure in light of recent cryo-electron microscopy structures of the B. subtilis BceABRS module and explore the common threads and variations-on-a-theme in Bce module mechanisms across species. We also highlight the many remaining questions about Bce module function. Understanding these multifunctional membrane complexes will enhance our understanding of bacterial stress sensing and may point toward new therapeutic targets for highly resistant pathogens.

Antibacterial activity of recently approved antibiotics against methicillin-resistant Staphylococcus aureus (MRSA) strains: A systematic review and meta-analysis

Background

Methicillin-resistant Staphylococcus aureus (MRSA) infections are considered an important public health problem, and treatment options are limited. Accordingly, in this meta-analysis, we analyzed published studies to survey in vitro activity of recently approved antibiotics against MRSA isolates.

Methods

We searched electronic databases; PubMed, Scopus, and Web of Science to identify relevant studies (until November 30, 2020) that have focused on the in vitro activity of telavancin, dalbavancin, oritavancin, and tedizolid against MRSA isolates. Statistical analyses were conducted using STATA software (version 14.0).

Results

Thirty-eight studies were included in this meta-analysis. Overall in vitro activity of tedizolid on 12,204 MRSA isolates was 0.250 and 0.5 µg/mL for MIC₅₀ and MIC₉₀, (minimum inhibitory concentration at which 50% and 90% of isolates were inhibited, respectively), respectively. The overall antibacterial activity of dalbavancin on 28539 MRSA isolates was 0.060 and 0.120 µg/mL for MIC₅₀ and MIC₉₀, respectively. The overall antibacterial activity of oritavancin on 420 MRSA isolates was 0.045 and 0.120 µg/mL for MIC₅₀ and MIC₉₀, respectively. The overall antibacterial activity of telavancin on 7353 MRSA isolates was 0.032 and 0.060 µg/mL for MIC₅₀ and MIC₉₀, respectively. The pooled prevalence of tedizolid, telavancin, and dalbavancin susceptibility was 100% (95% CI: 100–100).

Conclusion

Telavancin, dalbavancin, oritavancin, and tedizolid had potent in vitro activity against MRSA isolates. The low MICs and high susceptibility rates of these antibiotics recommend a hopeful direction to introduce useful antibiotics in treating MRSA infections in the future.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12941-022-00529-z.

Two Novel Semisynthetic Lipoglycopeptides Active against Staphylococcus aureus Biofilms and Cells in Late Stationary Growth Phase

The increase in antibiotic resistance among Gram-positive bacteria underscores the urgent need to develop new antibiotics. New antibiotics should target actively growing susceptible bacteria that are resistant to clinically accepted antibiotics including bacteria that are not growing or are protected in a biofilm environment. In this paper, we compare the in vitro activities of two new semisynthetic glycopeptide antibiotics, MA79 and ERJ390, with two clinically used glycopeptide antibiotics-vancomycin and teicoplanin. The new antibiotics effectively killed not only exponentially growing cells of Staphylococcus aureus, but also cells in the stationary growth phase and biofilm.

Sterol Sponge Mechanism Is Conserved for Glycosylated Polyene Macrolides

Amphotericin-like glycosylated polyene macrolides (GPMs) are a clinically and industrially important family of natural products, but the mechanisms by which they exert their extraordinary biological activities have remained unclear for more than half a century. Amphotericin B exerts fungicidal action primarily via self-assembly into an extramembranous sponge that rapidly extracts ergosterol from fungal membranes, but it has remained unclear whether this mechanism is applicable to other GPMs. Using a highly conserved polyene-hemiketal region of GPMs that we hypothesized to represent a conserved ergosterol-binding domain, we bioinformatically mapped the entirety of the GPM sequence-function space and expanded the number of GPM biosynthetic gene clusters (BGCs) by 10-fold. We further leveraged bioinformatic predictions and tetrazine-based reactivity screening targeting the electron-rich polyene region of GPMs to discover a first-in-class methyltetraene- and diepoxide-containing GPM, kineosporicin, and to assign BGCs to many new producers of previously reported members. Leveraging a range of structurally diverse known and newly discovered GPMs, we found that the sterol sponge mechanism of fungicidal action is conserved.

Clinical Pharmacokinetics and Pharmacodynamics of Telavancin Compared with the Other Glycopeptides

Telavancin was discovered by modifying the chemical structure of vancomycin and belongs to the group of lipoglycopeptides. It employs its antimicrobial potential through two distinct mechanisms of action: inhibition of bacterial cell wall synthesis and induction of bacterial membrane depolarization and permeabilization. In this article we review the clinically relevant pharmacokinetic and pharmacodynamic data of telavancin. For comparison, the pharmacokinetic and pharmacodynamic data of the other glycopeptides are presented. Although, in contrast to the newer lipoglycopeptides, telavancin demonstrates a relatively short half-life and rapid total clearance, its apparent volume of distribution (V_d) is almost identical to that of dalbavancin. The accumulation of telavancin after repeated dosing is only marginal, whereas the pharmacokinetic values of the other glycopeptides show much greater differences after administration of multiple doses. Despite its high plasma-protein binding of 90% and relatively low V_d of approximately 11 L, telavancin shows near complete equilibration of the free fraction in plasma with soft tissue. The ratio of the area under the plasma concentration-time curve from time zero to 24 h (AUC₂₄) of unbound plasma concentrations to the minimal inhibitory concentration (MIC) required to inhibit growth of 90% of organisms (MIC₉₀) of Staphylococcus aureus and S. epidermidis of telavancin are sufficiently high to achieve pharmacokinetic/pharmacodynamic targets indicative for optimal bacterial killing. Considering both the AUC₂₄/MIC ratios of telavancin and the near complete equilibration of the free fraction in plasma with soft tissue, telavancin is an appropriate antimicrobial agent to treat soft tissue infections caused by Gram-positive pathogens. Although the penetration of telavancin into epithelial lining fluid (ELF) requires further investigations, the AUC₂₄/MIC ratio for S. aureus indicates that bactericidal activity in the ELF could be expected.

Activity of Telavancin against Staphylococcus aureus Isolates, Including Those with Decreased Susceptibility to Ceftaroline, from Cystic Fibrosis Patients

Methicillin-resistant Staphylococcus aureus (MRSA) acquisition in cystic fibrosis (CF) patients confers a clinical outcome worse than that in non-CF patients with an increased rate of declined lung function. Telavancin, an approved lipoglycopeptide used to treat infections due to S. aureus, has a dual mode of action causing inhibition of peptidoglycan synthesis and membrane depolarization. MRSA infections in CF patients remain an important problem with no foreseeable decline in prevalence rates. Although telavancin is currently in clinical use for the treatment of complicated skin infections and hospital-acquired pneumonia, the activity against S. aureus infections in CF patients has not been investigated. In this work, we studied the activity of telavancin against CF patient-derived S. aureus strains collected from geographically diverse CF centers in the United States. We found that the telavancin MIC90 was 0.06 μg/ml, 8-fold lower than the ceftaroline or daptomycin MIC90 and 25-fold lower than the linezolid and vancomycin MIC90 We demonstrate that telavancin at serum free concentrations has rapid bactericidal activity, with a decrease of more than 3 log10 CFU/ml being achieved during the first 4 to 6 h of treatment, performing better in this assay than vancomycin and ceftaroline, including against S. aureus strains resistant to ceftaroline. Telavancin resistance was infrequent (0.3%), although we found that it can occur in vitro in both CF- and non-CF patient-derived S. aureus strains by progressive passages with subinhibitory concentrations. Genetic analysis of telavancin-resistant in vitro mutants showed gene polymorphisms in cell wall and virulence genes and increased survival in a Galleria mellonella infection model. Thus, we conclude that telavancin represents a promising therapeutic option for infections in CF patients with potent in vitro activity and a low resistance development potential.

The hidden lipoproteome of Staphylococcus aureus

Lipoproteins are attached to the outer leaflet of the membrane by a di- or tri-acylglyceryl moiety and are thus positioned in the membrane-cell wall interface. Consequently, lipoproteins are involved in many surface associated functions, including cell wall synthesis, electron transport, uptake of nutrients, surface stress response, signal transduction, and they represent a reservoir of bacterial virulence factors. Inspection of 123 annotated Staphylococcus aureus genome sequences in the public domain revealed that this organism devotes about 2-3% of its coding capacity to lipoproteins, corresponding to about 70 lipoproteins per genome. 60 of these lipoproteins were identified in 95% of the genomes analyzed, which thus constitute the core lipoproteome of S. aureus. 30% of the conserved staphylococcal lipoproteins are substrate-binding proteins of ABC transporters with roles in nutrient transport. With a few exceptions, much less is known about the function of the remaining lipoproteins, representing a large gap in our knowledge of this functionally important group of proteins. Here, we summarize current knowledge, and integrate information from genetic context analysis, expression and regulatory data, domain architecture, sequence and structural information, and phylogenetic distribution to provide potential starting points for experimental evaluation of the biological function of the poorly or uncharacterized lipoproteome of S. aureus.

Ethanol-induced stress response of Staphylococcus aureus

Transcriptional profiles of 2 unrelated clinical methicillin-resistant Staphylococcus aureus (MRSA) isolates were analyzed following 10% (v/v) ethanol challenge (15 min), which arrested growth but did not reduce viability. Ethanol-induced stress (EIS) resulted in differential gene expression of 1091 genes, 600 common to both strains, of which 291 were upregulated. With the exception of the downregulation of genes involved with osmotic stress functions, EIS resulted in the upregulation of genes that contribute to stress response networks, notably those altered by oxidative stress, protein quality control in general, and heat shock in particular. In addition, genes involved with transcription, translation, and nucleotide biosynthesis were downregulated. relP, which encodes a small alarmone synthetase (RelP), was highly upregulated in both MRSA strains following ethanol challenge, and relP inactivation experiments indicated that this gene contributed to EIS growth arrest. A number of persistence-associated genes were also upregulated during EIS, including those that encode toxin-antitoxin systems. Overall, transcriptional profiling indicated that the MRSA investigated responded to EIS by entering a state of dormancy and by altering the expression of elements from cross protective stress response systems in an effort to protect preexisting proteins.

Telavancin activity tested against Gram-positive clinical isolates from European, Russian and Israeli hospitals (2011-2013) using a revised broth microdilution testing method: redefining the baseline activity of telavancin

OBJECTIVES

To reassess the activity of telavancin when tested against Gram-positive clinical pathogens recovered from hospitalized patients in European and adjacent regions using a revised broth microdilution method.

METHODS

11 601 consecutive, non-duplicate isolates originating from 36 institutions among 18 countries recovered between 2011 and 2013 were tested for susceptibility using a revised broth microdilution method for telavancin. Interpretive telavancin breakpoints appropriate for the method were those recently approved by the FDA and EUCAST, as available.

RESULTS

Telavancin (MIC50/90, 0.03/0.06 mg/l; 100.0% susceptible) was equally potent against methicillin-susceptible ((MSSA) and methicillin-resistant (MRSA) Staphylococcus aureus. All Enterococcus faecalis was susceptible to telavancin (MIC50/90, 0.12/0.12 mg/l) and inhibited at the susceptibility breakpoint (i.e. ≤ 0.25 mg/l), except for VanA-phenotype vancomycin-resistant isolates (telavancin MIC, >1 mg/l). Telavancin ( ≤ 0.015/0.03 mg/l) was active against vancomycin-susceptible Enterococcus faecium, while higher MIC values were obtained for VanA strains. Telavancin (both MIC50 and MIC90, ≤ 0.015 mg/l) was potent against Streptococcus pneumoniae, beta-haemolytic streptococci (MIC50/90, ≤ 0.015/0.06 mg/l) and viridans group streptococci (MIC50/90, ≤ 0.015/0.03 mg/l).

CONCLUSIONS

Telavancin exhibited potent activity against this contemporary (2011-2013) collection of organisms, inhibiting indicated pathogens at or below the FDA/EUCAST-approved breakpoints for susceptibility. VanA-phenotype enterococci were less susceptible to telavancin, a feature observed using the previous testing method. These results redefine telavancin's activity against isolates from Europe.

Combined Systems Approaches Reveal a Multistage Mode of Action of a Marine Antimicrobial Peptide against Pathogenic Escherichia coli and Its Protective Effect against Bacterial Peritonitis and Endotoxemia

A marine arenicin-3 derivative, N4, displayed potent antibacterial activity against Gram-negative bacteria, but its antibacterial mode of action remains elusive. The mechanism of action of N4 against pathogenic Escherichia coli was first researched by combined cytological and transcriptomic techniques in this study. The N4 peptide permeabilized the outer membrane within 1 min, disrupted the plasma membrane after 0.5 h, and localized in the cytoplasm within 5 min. Gel retardation and circular dichroism (CD) spectrum analyses demonstrated that N4 bound specifically to DNA and disrupted the DNA conformation from the B type to the C type. N4 inhibited 21.1% of the DNA and 20.6% of the RNA synthesis within 15 min. Several hallmarks of apoptosis-like cell death were exhibited by N4-induced E. coli, such as cell cycle arrest in the replication (R) and division(D) phases, reactive oxygen species production, depolarization of the plasma membrane potential, and chromatin condensation within 0.5 h. Deformed cell morphology, disappearance of the plasma membrane, leakage of the contents, and ghost cell formation were demonstrated by transmission electron microscopy, and nearly 100% of the bacteria were killed by N4. A total of 428 to 663 differentially expressed genes are involved in the response to N4, which are associated mainly with membrane biogenesis (53.9% to 56.7%) and DNA binding (13.3% to 14.9%). N4-protected mice that were lethally challenged with lipopolysaccharide (LPS) exhibited reduced levels of interleukin-6 (IL-6), IL-1β, and tumor necrosis factor alpha (TNF-α) in serum and protected the lungs from LPS-induced injury. These data facilitate an enhanced understanding of the mechanisms of marine antimicrobial peptides (AMPs) against Gram-negative bacteria and provide guidelines in developing and applying novel multitarget AMPs in the field of unlimited marine resources as therapeutics.

Microarray Analysis to Monitor Bacterial Cell Wall Homeostasis

Transcriptomics, the genome-wide analysis of gene transcription, has become an important tool for characterizing and understanding the signal transduction networks operating in bacteria. Here we describe a protocol for quantifying and interpreting changes in the transcriptome of Streptomyces coelicolor that take place in response to treatment with three antibiotics active against different stages of peptidoglycan biosynthesis. The results defined the transcriptional responses associated with cell envelope homeostasis including a generalized response to all three antibiotics involving activation of transcription of the cell envelope stress sigma factor σ(E), together with elements of the stringent response, and of the heat, osmotic, and oxidative stress regulons. Many antibiotic-specific transcriptional changes were identified, representing cellular processes potentially important for tolerance to each antibiotic. The principles behind the protocol are transferable to the study of cell envelope homeostatic mechanisms probed using alternative chemical/environmental insults or in other bacterial strains.

Telavancin: mechanisms of action, in vitro activity, and mechanisms of resistance

Telavancin is a semisynthetic lipoglycopeptide derivative of vancomycin. Telavancin has a dual mechanism of antibacterial action, disrupting peptidoglycan synthesis and cell membrane function. In 2014, the Clinical and Laboratory Standards Institute (CLSI) revised the antimicrobial susceptibility testing method for telavancin, resulting in minimum inhibitory concentration (MIC) determinations that are more accurate and reproducible and demonstrate greater in vitro potency than shown with the previous testing method. The CLSI testing method changes coincided with revised telavancin MIC interpretive break point criteria for susceptibility approved by the US Food and Drug Administration for Staphylococcus aureus (≤0.12 µg/mL), Streptococcus pyogenes (≤0.12 µg/mL), Streptococcus agalactiae (≤0.12 µg/mL), Streptococcus anginosus group (≤0.06 µg/mL), and Enterococcus faecalis (vancomycin susceptible, ≤0.25 µg/mL). Telavancin is equally potent against methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). It demonstrates activity against isolates of heterogeneous vancomycin-intermediate S. aureus and vancomycin-intermediate S. aureus but is poorly active against vancomycin-resistant S. aureus. It also demonstrates potent activity against Staphylococcus epidermidis and Streptococcus spp. (MIC90 ≤0.03 µg/mL). Thus far, it has not been possible to select for high-level telavancin resistance in the laboratory using serially passaged clinical isolates of MRSA and MSSA.

Telavancin (VIBATIV) for the treatment of complicated skin and skin structure infections

Methicillin-resistant Staphylococcus aureus has emerged as a major causative pathogen in complicated skin and skin structure infections (cSSSIs). Unfortunately, treatment failure with vancomycin has been increasingly reported. Over the past decade, several alternative antimicrobial agents have been studied and approved for the treatment of cSSSIs. One such agent is the lipoglycopeptide telavancin, which was approved by the US FDA 2009. Given its dual mechanism of action, telavancin is characterized by a highly bactericidal activity and low potential for resistance selection. In addition, in clinical trials, it was efficacious and safe in the treatment of cSSSI. The purpose of this review is to give a background overview of telavancin, highlighting its microbiological, pharmacokinetic and pharmacodynamics characteristics, to summarize the available evidence for its use in the treatment of cSSSIs, and to provide an updated evaluation of its safety profile.

ω-Hydroxyemodin limits staphylococcus aureus quorum sensing-mediated pathogenesis and inflammation

Antibiotic-resistant pathogens are a global health threat. Small molecules that inhibit bacterial virulence have been suggested as alternatives or adjuncts to conventional antibiotics, as they may limit pathogenesis and increase bacterial susceptibility to host killing. Staphylococcus aureus is a major cause of invasive skin and soft tissue infections (SSTIs) in both the hospital and community settings, and it is also becoming increasingly antibiotic resistant. Quorum sensing (QS) mediated by the accessory gene regulator (agr) controls virulence factor production essential for causing SSTIs. We recently identified ω-hydroxyemodin (OHM), a polyhydroxyanthraquinone isolated from solid-phase cultures of Penicillium restrictum, as a suppressor of QS and a compound sought for the further characterization of the mechanism of action. At concentrations that are nontoxic to eukaryotic cells and subinhibitory to bacterial growth, OHM prevented agr signaling by all four S. aureus agr alleles. OHM inhibited QS by direct binding to AgrA, the response regulator encoded by the agr operon, preventing the interaction of AgrA with the agr P2 promoter. Importantly, OHM was efficacious in a mouse model of S. aureus SSTI. Decreased dermonecrosis with OHM treatment was associated with enhanced bacterial clearance and reductions in inflammatory cytokine transcription and expression at the site of infection. Furthermore, OHM treatment enhanced the immune cell killing of S. aureus in vitro in an agr-dependent manner. These data suggest that bacterial disarmament through the suppression of S. aureus QS may bolster the host innate immune response and limit inflammation.

Microarray analysis of the transcriptional responses of Porphyromonas gingivalis to polyphosphate

BACKGROUND

Polyphosphate (polyP) has bactericidal activity against a gram-negative periodontopathogen Porphyromonas gingivalis, a black-pigmented gram-negative anaerobic rod. However, current knowledge about the mode of action of polyP against P. gingivalis is incomplete. To elucidate the mechanisms of antibacterial action of polyP against P. gingivalis, we performed the full-genome gene expression microarrays, and gene ontology (GO) and protein-protein interaction network analysis of differentially expressed genes (DEGs).

RESULTS

We successfully identified 349 up-regulated genes and 357 down-regulated genes (>1.5-fold, P < 0.05) in P. gingivalis W83 treated with polyP75 (sodium polyphosphate, Na(n+2)P(n)O3(n+1); n = 75). Real-time PCR confirmed the up- and down-regulation of some selected genes. GO analysis of the DEGs identified distinct biological themes. Using 202 DEGs belonging to the biological themes, we generated the protein-protein interaction network based on a database of known and predicted protein interactions. The network analysis identified biological meaningful clusters related to hemin acquisition, energy metabolism, cell envelope and cell division, ribosomal proteins, and transposon function.

CONCLUSIONS

polyP probably exerts its antibacterial effect through inhibition of hemin acquisition by the bacterium, resulting in severe perturbation of energy metabolism, cell envelope biosynthesis and cell division, and elevated transposition. Further studies will be needed to elucidate the exact mechanism by which polyP induces up-regulation of the genes related to ribosomal proteins. Our results will shed new light on the study of the antibacterial mechanism of polyP against other related bacteria belonging to the black-pigmented Bacteroides species.

Comparative mechanistic studies of brilacidin, daptomycin, and the antimicrobial peptide LL16

Brilacidin (PMX30063) has shown potent bactericidal activity against drug-resistant and -susceptible strains of multiple Gram-negative and Gram-positive pathogens. In this study, we demonstrate that brilacidin causes membrane depolarization in the Gram-positive bacterium Staphylococcus aureus, to an extent comparable to that caused by the lipopeptidic drug daptomycin. Transcriptional profiling of Staphylococcus aureus by deep sequencing shows that the global response to brilacidin treatment is well correlated to those of treatment with daptomycin and the cationic antimicrobial peptide LL37 and mostly indicates abrogation of cell wall and membrane functions. Furthermore, the upregulation of various chaperones and proteases by brilacidin and daptomycin indicates that cytoplasmic protein misfolding stress may be a contributor to the mechanism of action of these drugs. These stress responses were orchestrated mainly by three two-component systems, GraSR, VraSR, and NsaSR, which have been implicated in virulence and drug resistance against other clinically available antibiotics.

Selective chemical inhibition of agr quorum sensing in Staphylococcus aureus promotes host defense with minimal impact on resistance

Bacterial signaling systems are prime drug targets for combating the global health threat of antibiotic resistant bacterial infections including those caused by Staphylococcus aureus. S. aureus is the primary cause of acute bacterial skin and soft tissue infections (SSTIs) and the quorum sensing operon agr is causally associated with these. Whether efficacious chemical inhibitors of agr signaling can be developed that promote host defense against SSTIs while sparing the normal microbiota of the skin is unknown. In a high throughput screen, we identified a small molecule inhibitor (SMI), savirin (S. aureusvirulence inhibitor) that disrupted agr-mediated quorum sensing in this pathogen but not in the important skin commensal Staphylococcus epidermidis. Mechanistic studies employing electrophoretic mobility shift assays and a novel AgrA activation reporter strain revealed the transcriptional regulator AgrA as the target of inhibition within the pathogen, preventing virulence gene upregulation. Consistent with its minimal impact on exponential phase growth, including skin microbiota members, savirin did not provoke stress responses or membrane dysfunction induced by conventional antibiotics as determined by transcriptional profiling and membrane potential and integrity studies. Importantly, savirin was efficacious in two murine skin infection models, abating tissue injury and selectively promoting clearance of agr+ but not Δagr bacteria when administered at the time of infection or delayed until maximal abscess development. The mechanism of enhanced host defense involved in part enhanced intracellular killing of agr+ but not Δagr in macrophages and by low pH. Notably, resistance or tolerance to savirin inhibition of agr was not observed after multiple passages either in vivo or in vitro where under the same conditions resistance to growth inhibition was induced after passage with conventional antibiotics. Therefore, chemical inhibitors can selectively target AgrA in S. aureus to promote host defense while sparing agr signaling in S. epidermidis and limiting resistance development.

New approaches are needed to lessen the burden of antibiotic resistant bacterial infections. One strategy is to develop therapies that target virulence which rely on host defense elements to clear the bacteria rather than direct antimicrobial killing. Quorum sensing is a bacterial signaling mechanism that often regulates virulence in medically relevant bacterial pathogens. Therefore, drugs that inhibit quorum sensing can promote host defense by rendering the pathogenic bacteria avirulent and/or less fit for survival within the host. Our work addressed this strategy in the pathogen Staphylococcus aureus which is the major cause of acute bacterial skin and soft tissue infections. We conducted a high throughput screen to identify compounds that could inhibit signaling by the quorum sensing operon, agr. We found a compound that we termed savirin (S. aureusvirulence inhibitor) that could inhibit signaling by this operon. The drug helped the innate immune system in animals to clear bacteria that express this operon without affecting clearance of bacteria that do not have this operon. We addressed the mechanism of action of this compound and whether resistance or tolerance to this compound would likely develop. Our data indicate for the first time that host defense against S. aureus skin infections can be enhanced by chemical inhibition of agr-mediated quorum sensing.

Natural product and natural product derived drugs in clinical trials

The 25 Natural Product (NP)-derived drugs launched since 2008 and the 100 NP-derived compounds and 33 Antibody Drug Conjugates (ADCs) in clinical trials or in registration at the end of 2013 are reviewed.

The cell wall-targeting antibiotic stimulon of Enterococcus faecalis

Enterococcus faecalis is an opportunistic nosocomial pathogen that is highly resistant to a variety of environmental insults, including an intrinsic tolerance to antimicrobials that target the cell wall (CW). With the goal of determining the CW-stress stimulon of E. faecalis, the global transcriptional profile of E. faecalis OG1RF exposed to ampicillin, bacitracin, cephalotin or vancomycin was obtained via microarrays. Exposure to the β-lactams ampicillin and cephalotin resulted in the fewest transcriptional changes with 50 and 192 genes differentially expressed 60 min after treatment, respectively. On the other hand, treatment with bacitracin or vancomycin for 60 min affected the expression of, respectively, 377 and 297 genes. Despite the differences in the total number of genes affected, all antibiotics induced a very similar gene expression pattern with an overrepresentation of genes encoding hypothetical proteins, followed by genes encoding proteins associated with cell envelope metabolism as well as transport and binding proteins. In particular, all drug treatments, most notably bacitracin and vancomycin, resulted in an apparent metabolic downshift based on the repression of genes involved in translation, energy metabolism, transport and binding. Only 19 genes were up-regulated by all conditions at both the 30 and 60 min time points. Among those 19 genes, 4 genes encoding hypothetical proteins (EF0026, EF0797, EF1533 and EF3245) were inactivated and the respective mutant strains characterized in relation to antibiotic tolerance and virulence in the Galleria mellonella model. The phenotypes obtained for two of these mutants, ΔEF1533 and ΔEF3245, support further characterization of these genes as potential candidates for the development of novel preventive or therapeutic approaches.

Studies on the mechanism of telavancin decreased susceptibility in a laboratory-derived mutant

Telavancin is a novel semisynthetic lipoglycopeptide derivative of vancomycin with a dual mode of action. This study sought to understand the mechanisms of decreased telavancin susceptibility in a laboratory-derived Staphlococcus aureus mutant Tlv(DS)MED1952. There were extensive changes in the transcriptome of Tlv(DS)MED1952 compared to the susceptible parent strain MED1951. Genes upregulated included cofactor biosynthesis genes, cell wall-related genes, fatty acid biosynthesis genes, and stress genes. Downregulated genes included lysine operon biosynthesis genes and lrgB, which are induced by telavancin in susceptible strains, agr and kdpDE genes, various cell surface protein genes, phenol-soluble modulin genes, several protease genes, and genes involved in anaerobic metabolism. The decreased susceptibility mutant had somewhat thicker cell walls and a decreased autolytic activity that may be related to decreased proteolytic peptidoglycan hydrolase processing. Membrane fatty acid changes correlated with increased membrane fluidity were observed. It seems likely that there are multiple genetic changes associated with the development of decreased telavancin susceptibility. The Tlv(DS) mutant showed some similar features to vancomycin-intermediate S. aureus and decreased daptomycin susceptibility strains, but also exhibited its own unique features.

Mechanisms of daptomycin resistance in Staphylococcus aureus: role of the cell membrane and cell wall

The bactericidal, cell membrane-targeting lipopeptide antibiotic daptomycin (DAP) is an important agent in treating invasive Staphylococcus aureus infections. However, there have been numerous recent reports of development of daptomycin resistance (DAP-R) during therapy with this agent. The mechanisms of DAP-R in S. aureus appear to be quite diverse. DAP-R strains often exhibit progressive accumulation of single nucleotide polymorphisms in the multipeptide resistance factor gene (mprF) and the yycFG components of the yycFGHI operon. Both loci are involved in key cell membrane (CM) events, with mprF being responsible for the synthesis and outer CM translocation of the positively charged phospholipid, lysyl-phosphotidylglycerol (L-PG), while the yyc operon is involved in the generalized response to stressors such as antimicrobials. In addition, other perturbations of the CM have been identified in DAP-R strains, including extremes in CM order, resistance to CM depolarization and permeabilization, and reduced surface binding of DAP. Moreover, modifications of the cell wall (CW) appear to also contribute to DAP-R, including enhanced expression of the dlt operon (involved in d-alanylation of CW teichoic acids) and progressive CW thickening.