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

Vanillin inhibits PqsR-mediated virulence in Pseudomonas aeruginosa

Vanillin, a natural phenolic aldehyde from vanilla bean, has been reported to inhibit pqs quorum sensing in Pseudomonas aeruginosa, with potential applications in combinatorial antimicrobial therapy against biofilm infections.

Bringing Community Ecology to Bear on the Issue of Antimicrobial Resistance

Antimicrobial resistance (AMR) is a global concern, pertaining not only to human health but also to the health of industry and the environment. AMR research has traditionally focused on genetic exchange mechanisms and abiotic environmental constraints, leaving important aspects of microbial ecology unresolved. The genetic and ecological aspects of AMR, however, not only contribute separately to the problem but also are interrelated. For example, mutualistic associations among microbes such as biofilms can both serve as a barrier to antibiotic penetration and a breeding ground for horizontal exchange of antimicrobial resistance genes (ARGs). In this review, we elucidate how species interactions promote and impede the establishment, maintenance, and spread of ARGs and indicate how management initiatives might benefit from leveraging the principles and tools of community ecology to better understand and manipulate the processes underlying AMR.

Structure-Activity Relationship Studies of Small Molecule Modulators of the Staphylococcal Accessory Gene Regulator

The accessory gene regulator (agr) quorum-sensing system is arguably the most important regulator of Staphylococcus virulence. The agr-system serves a crucial role in pathogenesis by triggering substantive gene expression alterations to up-regulate the production of a wide variety of virulence determinants such as exoenzymes (proteases, lipases, nucleases) and downregulate the expression of surface binding proteins. Accordingly, the agr-system represents a compelling target for the development of antivirulence therapeutics as potential adjuncts, or alternatives, to conventional bactericidal and bacteriostatic antibiotics. Despite this potential, to date, no agr-system inhibitors have progressed to the clinic; however, several promising lead compounds have been identified through screens of synthetic and natural product libraries. On the basis of the molecular components within the agr-system, the current contingent of regulating compounds can be clustered into three broad groups, AgrA-P3 activation inhibitors, AgrB-AgrD processing inhibitors, and AgrC-AIP interaction inhibitors. This review aims to provide an overview of the development, structure-activity-relationships, and limitations of compounds within each of these groups in addition to the current opportunities for developing next-generation anologs.

Current landscape in the discovery of novel antibacterial agents

BACKGROUND

Standard treatments against bacterial infections are becoming ineffective due to the rise of antibacterial resistance worldwide. Classical approaches to develop new antibacterial agents are not sufficient to fulfil the current pipeline, therefore new strategies are currently being devised in the field of antibacterial discovery.

OBJECTIVES

The objective of this narrative review is to compile the most successful strategies for drug discovery within the antibacterial context that are currently being pursued.

SOURCES

Peer-reviewed publications from the MEDLINE database with robust data addressing the discovery of new antibacterial agents in the current pipeline have been selected.

CONTENT

Several strategies to discover new antibacterials are described in this review: (i) derivatives of known antibacterial agents; the activity of a known antimicrobial agent can be improved through two strategies: (a) the modification of the original chemical structure of an antimicrobial agent to circumvent antibacterial resistance mechanisms and (b) the development of a compound that inhibits the mechanisms of resistance to an antibacterial agent; (ii) new antibacterial agents targeting new proteins; (iii) inhibitors of virulence factors; (iv) nanoparticles; (v) antimicrobial peptides and peptidomimetics; (vi) phage therapy and enzybiotics; and (vii) antisense oligonucleotides.

IMPLICATIONS

This review intends to provide a positive message affirming that several different strategies to design new antibacterial agents are currently being developed, and we are therefore confident that in the near future some of the most promising approaches will come to fruition.

Camouflaging bacteria by wrapping with cell membranes

Bacteria have been extensively utilized for bioimaging, diagnosis and therapy given their unique characteristics including genetic manipulation, rapid proliferation and disease site targeting specificity. However, clinical translation of bacteria for these applications has been largely restricted by their unavoidable side effects and low treatment efficacies. Engineered bacteria for biomedical applications ideally need to generate only a low inflammatory response, show slow elimination by macrophages, low accumulation in normal organs, and almost unchanged inherent bioactivities. Here we describe a set of stealth bacteria, cell membrane coated bacteria (CMCB), meeting these requirement. Our findings are supported by evaluation in multiple mice models and ultimately demonstrate the potential of CMCB to serve as efficient tumor imaging agents. Stealth bacteria wrapped up with cell membranes have the potential for a myriad of bacterial-mediated biomedical applications.

The use of engineered bacteria for biomedical applications is limited by side effects such as inflammatory response. Here the authors engineer cell membrane coated bacteria as in vivo tumor imaging agents, and show that these generate a lower inflammatory response and reduced macrophage clearance.

Elucidating the Hot Spot Residues of Quorum Sensing Peptidic Autoinducer PapR by Multiple Amino Acid Replacements

The quorum sensing (QS) system of Bacillus cereus, an opportunistic human pathogen, utilizes the autoinducing PapR peptide signal that mediates the activation of the pleiotropic virulence regulator PlcR. A set of synthetic 7-mer PapR-derived peptides (PapR₇; ADLPFEF) have been shown to inhibit efficiently the PlcR regulon activity and the production of virulence factors, reflected by a loss in hemolytic activity without affecting bacterial growth. Interestingly, these first potent synthetic inhibitors involved D-amino acid or alanine replacements of three amino acids; proline, glutamic acid, and phenylalanine of the heptapeptide PapR. To better understand the role of these three positions in PlcR activity, we report herein the second generation design, synthesis, and characterization of PapR₇-derived combinations, alternate double and triple alanine and D-amino acids replacement at these positions. Our findings generate a new set of non-native PapR₇-derived peptides that inhibit the PlcR regulon activity and the production of virulence factors. Using the amino acids substitution strategy, we revealed the role of proline and glutamic acid on PlcR regulon activation. Moreover, we demonstrated that the D-Glutamic acid substitution was crucial for the design of stronger PlcR antagonists. These peptides represent potent synthetic inhibitors of B. cereus QS and constitute new and readily accessible chemical tools for the study of the PlcR system. Our method might be applied to other quorum sensing systems to design new anti-virulence agents.

Drug-like Fragments Inhibit agr-Mediated Virulence Expression in Staphylococcus aureus

In response to the increasingly problematic emergence of antibiotic resistance, novel strategies for combating pathogenic bacteria are being investigated. Targeting the agr quorum sensing system, which regulates expression of virulence in Staphylococcus aureus, is one potentially useful approach for combating drug-resistant pathogens that has not yet been fully explored. A previously published study of a fragment screen resulted in the identification of five compound fragments that interact with the DNA-binding domain of the response regulator AgrA from S. aureus. We have analyzed the ability of these compounds to affect agr-mediated virulence gene expression in cultured S. aureus cells. Three of the compounds demonstrated the ability to reduce agr-driven transcription at the P2 and P3 promoters of the agr operon and increase biofilm formation, and two of these compounds also showed the ability to reduce levels of secreted toxins. The finding that the compounds tested were able to reduce agr activity suggests that they could be useful tools for probing the effects of agr inhibition. Furthermore, the characteristics of compound fragments make them good starting materials for the development of compound libraries to iteratively improve the inhibitors.

Quorum Sensing as Antivirulence Target in Cystic Fibrosis Pathogens

Cystic fibrosis (CF) is an autosomal recessive genetic disorder which leads to the secretion of a viscous mucus layer on the respiratory epithelium that facilitates colonization by various bacterial pathogens. The problem of drug resistance has been reported for all the species able to colonize the lung of CF patients, so alternative treatments are urgently needed. In this context, a valid approach is to investigate new natural and synthetic molecules for their ability to counteract alternative pathways, such as virulence regulating quorum sensing (QS). In this review we describe the pathogens most commonly associated with CF lung infections: Staphylococcus aureus, Pseudomonas aeruginosa, species of the Burkholderia cepacia complex and the emerging pathogens Stenotrophomonas maltophilia, Haemophilus influenzae and non-tuberculous Mycobacteria. For each bacterium, the QS system(s) and the molecules targeting the different components of this pathway are described. The amount of investigations published in the last five years clearly indicate the interest and the expectations on antivirulence therapy as an alternative to classical antibiotics.

Simplified Autoinducing Peptide Mimetics with Single-Nanomolar Activity Against the Staphylococcus aureus AgrC Quorum Sensing Receptor

Staphylococcus aureus is a leading cause of hospital-acquired infections worldwide, and cases of community-acquired infections are becoming more prevalent. The production of numerous virulence factors in S. aureus is under the control of the accessory gene regulator (agr) quorum sensing (QS) system. S. aureus upregulates agr at high cell density by secreting a peptide pheromone, or autoinducing peptide (AIP), which is detected by its cognate transmembrane receptor, AgrC. The extracellular AIP binding site of AgrC represents an attractive target for inhibition of the agr system and, thereby, QS-controlled virulence in S. aureus. Nonnative peptides and, more recently, peptidomimetics have been reported to inhibit the AgrC receptor and represent useful chemical tools to study the role of QS in S. aureus infections. We seek to expand beyond peptide-like scaffolds to generate AgrC modulators with enhanced stability, solubility, and synthetic accessibility relative to these compounds, while maintaining their high potencies. Toward this goal, we report herein a study of the structure-activity relationships responsible for the activity of a recently reported simplified AIP mimetic and AgrC antagonist, n7OFF, and the discovery of a new AIP mimetic, Bnc3, which has low- to sub-nanomolar inhibitory activity in all four S. aureus agr specificity groups. NMR structural studies of Bnc3 revealed hydrophobic and hydrophilic faces that are likely critical for AgrC antagonism, in agreement with prior studies of peptide-derived inhibitors. Bnc3 represents an important transition compound toward the development of small-molecule AgrC antagonists.

Sub-inhibitory membrane damage undermines Staphylococcus aureus virulence

We investigated antibacterial properties of a recently described membrane-active lipopeptide, C₁₀OOc₁₂O (decanoyl-ornithyl-ornithyl-dodecanoyl-ornithyl-amide) against Gram-positive bacteria (GPB). Minimal inhibitory concentrations (MICs) and kinetics were compared in culture media and plasma. Chemo-sensitization to antibiotics was determined using the checkerboard assay. Membrane damages were estimated using diverse membrane potential sensitive dyes. ATP levels and relevant enzymes activities were measured using commercial bioassay kits. While relatively weakly active in simple culture media, sub-MIC levels (~ten-fold) of C₁₀OOc₁₂O have significantly improved the antibacterial function of Human plasma. Mechanistic studies indicated that C₁₀OOc₁₂O-treated bacteria have sustained mild membrane damage(s) in association with rapid (within 2 min) but low (<10%) dissipation of the trans-membrane potential; Intracellular ATP levels were transiently reduced (~20%) whereas extracellular ATP increased only at MIC values; Sub-inhibitory concentrations were sufficient for inhibiting major agr-regulated virulence factors (lipase and α-toxin) and for sensitizing MRSA USA300 to the antibiotic oxacillin to the point of reverting the bacteria status from oxacillin-resistant to oxacillin-sensitive (i.e., oxacillin MIC was reduced from 32 to 0.1 mg/l). These findings argue that by means of mild depolarization, C₁₀OOc₁₂O affects the quorum sensing regulator in a manner that transiently weakens bacterial defenses, thereby enforcing studies that support the potential usefulness of fighting S. aureus (and possibly other GPB) infections, by targeting its virulence.

Apicidin Attenuates MRSA Virulence through Quorum-Sensing Inhibition and Enhanced Host Defense

Recurrent epidemics of drug-resistant Staphylococcus aureus illustrate the rapid lapse of antibiotic efficacy following clinical implementation. Over the last decade, community-associated methicillin-resistant S. aureus (MRSA) has emerged as a dominant cause of infections, and this problem is amplified by the hyper-virulent nature of these isolates. Herein, we report the discovery of a fungal metabolite, apicidin, as an innovative means to counter both resistance and virulence. Owing to its breadth and specificity as a quorum-sensing inhibitor, apicidin antagonizes all MRSA agr systems in a non-biocidal manner. In skin challenge experiments, the apicidin-mediated abatement of MRSA pathogenesis corresponds with quorum-sensing inhibition at in vivo sites of infection. Additionally, we show that apicidin attenuates MRSA-induced disease by potentiating innate effector responses, particularly through enhanced neutrophil accumulation and function at cutaneous challenge sites. Together, these results indicate that apicidin treatment represents a strategy to limit MRSA virulence and promote host defense.

Recent Advances in Anti-virulence Therapeutic Strategies With a Focus on Dismantling Bacterial Membrane Microdomains, Toxin Neutralization, Quorum-Sensing Interference and Biofilm Inhibition

Antimicrobial resistance constitutes one of the major challenges facing humanity in the Twenty-First century. The spread of resistant pathogens has been such that the possibility of returning to a pre-antibiotic era is real. In this scenario, innovative therapeutic strategies must be employed to restrict resistance. Among the innovative proposed strategies, anti-virulence therapy has been envisioned as a promising alternative for effective control of the emergence and spread of resistant pathogens. This review presents some of the anti-virulence strategies that are currently being developed, it will cover strategies focused on quench pathogen quorum sensing (QS) systems, disassemble of bacterial functional membrane microdomains (FMMs), disruption of biofilm formation and bacterial toxin neutralization.

Characterization of agr Groups of Staphylococcus pseudintermedius Isolates from Dogs in Texas

Staphylococcus pseudintermedius is an important canine pathogen implicated in an increasing number of human infections. Along with rising levels of methicillin and multidrug resistance, staphylococcal biofilms are a complicating factor for treatment and contribute to device, implant, and surgical infections. Staphylococcal virulence, including biofilm formation, is regulated in part by the quorum sensing accessory gene regulator system (agr). The signal molecule for agr, known as the autoinducing peptide molecule, contains polymorphisms that result in the formation of distinct groups. In S. pseudintermedius, 4 groups (i.e., groups I, II, III, and IV) have been identified but not comprehensively examined for associations with infection type, virulence factor carriage, or phylogenetic relationships-all of which have been found to be significant in S. aureus In this study, 160 clinical canine isolates from Texas, including isolates from healthy dogs (n = 40) and 3 different infection groups (pyoderma, urinary tract, and surgical, n = 40 each), were sequenced. The agr group, biofilm-producing capabilities, toxin gene carriage, antimicrobial resistance, and sequence type (ST) were identified for all isolates. While no significant associations were discovered among the clinical infection types and agr groups, agr II isolates were significantly less common than any other group in diseased dogs. Furthermore, agr II isolates were less likely than other agr groups to be multidrug resistant and to carry toxin genes expA and sec-canine Fifty-two (33%) of the 160 isolates were methicillin resistant, and the main sequence types (ST64, ST68, ST71, ST84, ST150, and ST155) of methicillin-resistant strains of S. pseudintermedius (MRSP) were identified for the geographic region.IMPORTANCEStaphylococcus pseudintermedius is an important disease-causing bacterium in dogs and is recognized as a growing threat to human health. Due to increasing multidrug resistance, discovery of alternative methods for treatment of these infections is vital. Interference with one target for alternative treatment, the quorum sensing system agr, has demonstrated clinical improvement of infections in S. aureus animal models. In this study, we sequenced and characterized 160 clinical S. pseudintermedius isolates and their agr systems in order to increase understanding of the epidemiology of the agr group and clarify its associations with types of infection and antimicrobial resistance. We found that isolates with agr type II were significantly less common than other agr types in diseased dogs. This provides valuable information to veterinary clinical microbiologists and clinicians, especially as less research has been performed on infection associations of agr and its therapeutic potential in S. pseudintermedius than in S. aureus.

Probiotics to prevent Staphylococcus aureus disease?

There are a plethora of probiotic formulae that supposedly benefit human health on the market. However, the scientific underpinnings of the claimed benefits have remained poorly established. Scientific evidence is now increasingly being provided that explains those benefits, for example, by immune-stimulatory effects or inter-bacterial competition between beneficial and pathogenic bacteria. In our recent study (Piewngam et al. Nature 2018), we show that Bacillus colonization of the human intestine is negatively correlated with that of the human pathogen, Staphylococcus aureus. This type of colonization resistance is achieved by secretion of a class of lipopeptides by Bacillus species that inhibits S. aureus quorum-sensing signaling, which we found is crucial for S. aureus intestinal colonization. Here, we discuss what these findings imply for the general role of S. aureus intestinal colonization, the role of quorum-sensing in that process, and potential alternative ways to control S. aureus infection.

Prenylated Diresorcinols Inhibit Bacterial Quorum Sensing

Current treatment options for bacterial infections are dependent on antibiotics that inhibit microbial growth and viability. These approaches result in the evolution of drug-resistant strains of bacteria. An anti-infective strategy that is less likely to lead to the development of resistance is the disruption of quorum sensing mechanisms, which are involved in promoting virulence. The goal of this study was to identify fungal metabolites effective as quorum sensing inhibitors. Three new prenylated diresorcinols (1-3), along with two known compounds, (4 R) -regiolone and decarboxycitrinone, were isolated from a freshwater fungus (Helotiales sp.) from North Carolina. Their structures were assigned on the basis of HRESIMS and NMR experiments. The structure of compound 1 was confirmed via X-ray diffraction analysis, and its absolute configuration was established by TDDFT-ECD and optical rotation calculations. Compounds 1-3 suppressed quorum sensing in a clinical isolate of methicillin-resistant Staphylococcus aureus (MRSA), with IC₅₀ values ranging from 0.3 to 12.5 μM. These compounds represent potential leads in the development of antivirulence therapeutics.

Commensal Staphylococci Influence Staphylococcus aureus Skin Colonization and Disease

Commensal organisms that constitute the skin microbiota play a pivotal role in the orchestration of cutaneous homeostasis and immune competence. This balance can be promptly offset by the expansion of the opportunistic pathogen Staphylococcus aureus, which is responsible for the majority of bacterial skin infections. S. aureus carriage is also known to be a precondition for its transmission and pathogenesis. Recent reports suggest that skin-dwelling coagulase-negative staphylococci (CoNS) can prime the skin immune system to limit the colonization potential of invaders, and they can directly compete through production of antimicrobial molecules or through signaling antagonism. We review recent advances in these CoNS colonization resistance mechanisms, which may serve to aid development of pharmacologic and probiotic intervention strategies to limit S. aureus skin colonization and disease.

Nonconventional Therapeutics against Staphylococcus aureus

Staphylococcus aureus is one of the most important human pathogens that is responsible for a variety of diseases ranging from skin and soft tissue infections to endocarditis and sepsis. In recent decades, the treatment of staphylococcal infections has become increasingly difficult as the prevalence of multi-drug resistant strains continues to rise. With increasing mortality rates and medical costs associated with drug resistant strains, there is an urgent need for alternative therapeutic options. Many innovative strategies for alternative drug development are being pursued, including disruption of biofilms, inhibition of virulence factor production, bacteriophage-derived antimicrobials, anti-staphylococcal vaccines, and light-based therapies. While many compounds and methods still need further study to determine their feasibility, some are quickly approaching clinical application and may be available in the near future.

Interference With Quorum-Sensing Signal Biosynthesis as a Promising Therapeutic Strategy Against Multidrug-Resistant Pathogens

Faced with the global health threat of increasing resistance to antibiotics, researchers are exploring interventions that target bacterial virulence factors. Quorum sensing is a particularly attractive target because several bacterial virulence factors are controlled by this mechanism. Furthermore, attacking the quorum-sensing signaling network is less likely to select for resistant strains than using conventional antibiotics. Strategies that focus on the inhibition of quorum-sensing signal production are especially attractive because the enzymes involved are expressed in bacterial cells but are not present in their mammalian counterparts. We review here various approaches that are being taken to interfere with quorum-sensing signal production via the inhibition of autoinducer-2 synthesis, PQS synthesis, peptide autoinducer synthesis, and N-acyl-homoserine lactone synthesis. We expect these approaches will lead to the discovery of new quorum-sensing inhibitors that can help to stem the tide of antibiotic resistance.

Thinking Outside the Box-Novel Antibacterials To Tackle the Resistance Crisis

The public view on antibiotics as reliable medicines changed when reports about "resistant superbugs" appeared in the news. While reasons for this resistance development are easily spotted, solutions for re-establishing effective antibiotics are still in their infancy. This Review encompasses several aspects of the antibiotic development pipeline from very early strategies to mature drugs. An interdisciplinary overview is given of methods suitable for mining novel antibiotics and strategies discussed to unravel their modes of action. Select examples of antibiotics recently identified by using these platforms not only illustrate the efficiency of these measures, but also highlight promising clinical candidates with therapeutic potential. Furthermore, the concept of molecules that disarm pathogens by addressing gatekeepers of virulence will be covered. The Review concludes with an evaluation of antibacterials currently in clinical development. Overall, this Review aims to connect select innovative antimicrobial approaches to stimulate interdisciplinary partnerships between chemists from academia and industry.

Small-molecule AgrA inhibitors F12 and F19 act as antivirulence agents against Gram-positive pathogens

Small-molecule antivirulence agents represent a promising alternative or adjuvant to antibiotics. These compounds disarm pathogens of disease-causing toxins without killing them, thereby diminishing survival pressure to develop resistance. Here we show that the small-molecule antivirulence agents F12 and F19 block staphylococcal transcription factor AgrA from binding to its promoter. Consequently, toxin expression is inhibited, thus preventing host cell damage by Gram-positive pathogens. Broad spectrum efficacy against Gram-positive pathogens is due to the existence of AgrA homologs in many Gram-positive bacteria. F12 is more efficacious in vitro and F19 works better in vivo. In a murine MRSA bacteremia/sepsis model, F19 treatment alone resulted in 100% survival while untreated animals had 70% mortality. Furthermore, F19 enhances antibiotic efficacy in vivo. Notably, in a murine MRSA wound infection model, combination of F19 with antibiotics resulted in bacterial load reduction. Thus, F19 could be used alone or in combination with antibiotics to prevent and treat infections of Gram-positive pathogens.

Turning off Bacillus cereus quorum sensing system with peptidic analogs

We explored quenching of the PlcR-PapR quorum-sensing system in Bacillus cereus. We generated PapR7-peptidic derivatives that inhibit this system and thus the production of virulence factors, reflected by a loss in hemolytic activity, without affecting bacterial growth. To our knowledge, these peptides represent the first potent synthetic inhibitors of quorum-sensing in B. cereus.

Probing the evolutionary robustness of two repurposed drugs targeting iron uptake in Pseudomonas aeruginosa

LAY SUMMARY

We probed the evolutionary robustness of two antivirulence drugs, gallium and flucytosine, targeting the iron-scavenging pyoverdine in the opportunistic pathogen Pseudomonas aeruginosa. Using an experimental evolution approach in human serum, we showed that antivirulence treatments are not evolutionarily robust per se, but vary in their propensity to select for resistance.

BACKGROUND AND OBJECTIVES

Treatments that inhibit the expression or functioning of bacterial virulence factors hold great promise to be both effective and exert weaker selection for resistance than conventional antibiotics. However, the evolutionary robustness argument, based on the idea that antivirulence treatments disarm rather than kill pathogens, is controversial. Here, we probe the evolutionary robustness of two repurposed drugs, gallium and flucytosine, targeting the iron-scavenging pyoverdine of the opportunistic human pathogen Pseudomonas aeruginosa.

METHODOLOGY

We subjected replicated cultures of bacteria to two concentrations of each drug for 20 consecutive days in human serum as an ex vivo infection model. We screened evolved populations and clones for resistance phenotypes, including the restoration of growth and pyoverdine production, and the evolution of iron uptake by-passing mechanisms. We whole-genome sequenced evolved clones to identify the genetic basis of resistance.

RESULTS

We found that mutants resistant against antivirulence treatments readily arose, but their selective spreading varied between treatments. Flucytosine resistance quickly spread in all populations due to disruptive mutations in upp, a gene encoding an enzyme required for flucytosine activation. Conversely, resistance against gallium arose only sporadically, and was based on mutations in transcriptional regulators, upregulating pyocyanin production, a redox-active molecule promoting siderophore-independent iron acquisition. The spread of gallium resistance was presumably hampered because pyocyanin-mediated iron delivery benefits resistant and susceptible cells alike.

CONCLUSIONS AND IMPLICATIONS

Our work highlights that antivirulence treatments are not evolutionarily robust per se. Instead, evolutionary robustness is a relative measure, with specific treatments occupying different positions on a continuous scale.

Periprosthetic bacterial biofilm and quorum sensing

Periprosthetic joint infection (PJI) is a common complication after total joint arthroplasty leading to severe morbidity and mortality. With an aging population and increasing prevalence of total joint replacement procedures, the burden of PJI will be felt not only by individual patients, but in increased healthcare costs. Current treatment of PJI is inadequate resulting in incredibly high failure rates. This is believed to be largely mediated by the presence of bacterial biofilms. These polymicrobial bacterial colonies form within secreted extracellular matrices, adhering to the implant surface and local tissue. The biofilm architecture is believed to play a complex and critical role in a variety of bacterial processes including nutrient supplementation, metabolism, waste management, and antibiotic and immune resistance. The establishment of these biofilms relies heavily on the quorum sensing communication systems utilized by bacteria. Early stage research into disrupting bacterial communication by targeting quorum sensing show promise for future clinical applications. However, prevention of the biofilm formation via early forced induction of the biofilm forming process remains yet unexplored. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:2331-2339, 2018.

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.

Developments in strategies for Quorum Sensing virulence factor inhibition to combat bacterial drug resistance

Quorum sensing (QS) is a complex bacterial intercellular communication system. It is mediated by molecules called auto-inducers (AIs) and allows coordinated responses to a variety of environmental signals by inducing alterations in gene expression. Communication through QS can tremendously stimulate the pathogenicity and virulence via multiple mechanisms in pathogenic bacteria. The present review explores the major types of multitudinous QS systems known in Gram-positive and Gram-negative bacteria and their roles in bacterial pathogenesis and drug resistance. Because bacterial resistance to antibiotics is increasingly becoming a significant clinical challenge to human health; alternate strategies to combat drug resistance are warranted. Targeting bacterial pathogenicity by interruptions in QS using natural QS inhibitors and synthetic quorum-quenching analogs are being increasingly considered for development of next generation antimicrobials. The review highlights the recent advancements in discovery of promising new QS modulators and their efficiency in controlling infections caused by multidrug-resistant bacterial pathogens.

Screening for inhibitors of mutacin synthesis in Streptococcus mutans using fluorescent reporter strains

Background

Within the polymicrobial dental plaque biofilm, bacteria kill competitors by excreting mixtures of bacteriocins, resulting in improved fitness and survival. Inhibiting their bacteriocin synthesis might therefore be a useful strategy to eliminate specific pathogens. We used Streptococcus mutans, a highly acidogenic inhabitant of dental plaque, as a model and searched for natural products that reduced mutacin synthesis. To this end we fused the promoter of mutacin VI to the GFP+ gene and integrated the construct into the genome of S. mutans UA159 by single homologous recombination.

Results

The resulting reporter strain 423p - gfp + was used to screen 297 secondary metabolites from different sources, mainly myxobacteria and fungi, for their ability to reduce the fluorescence of the fully induced reporter strain by > 50% while growth was almost unaffected (> 90% of control). Seven compounds with different chemical structures and different modes of action were identified. Erinacine C was subsequently validated and shown to inhibit transcription of all three mutacins of S. mutans. The areas of the inhibition zones of the sensor strains S. sanguinis and Lactococcus lactis were reduced by 35% to 61% in comparison to controls in the presence of erinacine C, demonstrating that the amount of active mutacins in the culture supernatants of S. mutans was reduced. Erinacines are cyathane diterpenes that were extracted from cultures of the edible mushroom Hericium erinaceus. They have anti-inflammatory, antimicrobial and neuroprotective effects. For erinacine C, a new biological activity was found here.

Conclusions

We demonstrate the successful development of a whole-cell fluorescent reporter for the screening of natural compounds and report that erinacine C suppresses mutacin synthesis in S. mutans without affecting cell viability.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1170-3) contains supplementary material, which is available to authorized users.

Transcriptional regulators: valuable targets for novel antibacterial strategies

Antibiotics have saved millions of lives over the past decades. However, the accumulation of so many antibiotic resistance genes by some clinically relevant pathogens has begun to lead to untreatable infections worldwide. The current antibiotic resistance crisis will require greater efforts by governments and the scientific community to increase the research and development of new antibacterial drugs with new mechanisms of action. A major challenge is the identification of novel microbial targets, essential for in vivo growth or pathogenicity, whose inhibitors can overcome the currently circulating resistome of human pathogens. In this article, we focus on the potential high value of bacterial transcriptional regulators as targets for the development of new antibiotics, discussing in depth the molecular role of these regulatory proteins in bacterial physiology and pathogenesis. Recent advances in the search for novel compounds that inhibit the biological activity of relevant transcriptional regulators in pathogenic bacteria are reviewed.

A Novel Antimicrobial Coating Represses Biofilm and Virulence-Related Genes in Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) has become an important cause of hospital-acquired infections worldwide. It is one of the most threatening pathogens due to its multi-drug resistance and strong biofilm-forming capacity. Thus, there is an urgent need for novel alternative strategies to combat bacterial infections. Recently, we demonstrated that a novel antimicrobial surface coating, AGXX®, consisting of micro-galvanic elements of the two noble metals, silver and ruthenium, surface-conditioned with ascorbic acid, efficiently inhibits MRSA growth. In this study, we demonstrated that the antimicrobial coating caused a significant reduction in biofilm formation (46%) of the clinical MRSA isolate, S. aureus 04-02981. To understand the molecular mechanism of the antimicrobial coating, we exposed S. aureus 04-02981 for different time-periods to the coating and investigated its molecular response via next-generation RNA-sequencing. A conventional antimicrobial silver coating served as a control. RNA-sequencing demonstrated down-regulation of many biofilm-associated genes and of genes related to virulence of S. aureus. The antimicrobial substance also down-regulated the two-component quorum-sensing system agr suggesting that it might interfere with quorum-sensing while diminishing biofilm formation in S. aureus 04-02981.

Therapeutic Targeting of the Staphylococcus aureus Accessory Gene Regulator (agr) System

Staphylococcus aureus can cause numerous different diseases, which has been attributed to its large repertoire of virulence factors, many of which are under the control of the accessory gene regulator (agr) quorum sensing system. Under conditions of high cell density, agr increases the production of many virulence factors, decreases expression of several colonization factors, and is intimately associated with the pathogenesis and biofilm formation of S. aureus. This review summarizes our current understanding of the molecular mechanisms underlying agr quorum sensing and the regulation of agr expression. The discussion also examines subgroups of agr and their association with different diseases, and concludes with an analysis of strategies for designing drugs and vaccines that target agr to combat S. aureus infections.

Targeting Virulence in Staphylococcus aureus by Chemical Inhibition of the Accessory Gene Regulator System In Vivo

Methicillin-resistant Staphylococcus aureus (MRSA) presents one of the most serious health concerns worldwide. The WHO labeled it as a “high-priority” pathogen in 2017, also citing the more recently emerged vancomycin-intermediate and -resistant strains.

Methicillin-resistant Staphylococcus aureus (MRSA) presents one of the most serious health concerns worldwide. The WHO labeled it as a “high-priority” pathogen in 2017, also citing the more recently emerged vancomycin-intermediate and -resistant strains. With the spread of antibiotic resistance due in large part to the selective pressure exerted by conventional antibiotics, the use of antivirulence strategies has been recurrently proposed as a promising therapeutic approach. In MRSA, virulence is chiefly controlled by quorum sensing (QS); inhibitors of QS are called quorum quenchers (QQ). In S. aureus, the majority of QS components are coded for by the accessory gene regulator (Agr) system. Although much work has been done to develop QQs against MRSA, only a few studies have progressed to in vivo models. Those studies include both prophylactic and curative models of infection as well as combination treatments with antibiotic. For most, high efficacy is seen at attenuating MRSA virulence and pathogenicity, with some studies showing effects such as synergy with antibiotics and antibiotic resensitization. This minireview aims to summarize and derive conclusions from the literature on the in vivo efficacy of QQ agents in MRSA infection models. In vitro data are also summarized to provide sufficient background on the hits discussed. On the whole, the reported in vivo effects of the reviewed QQs against MRSA represent positive progress at this early stage in drug development. Follow-up studies that thoroughly examine in vitro and in vivo activity are needed to propel the field forward and set the stage for lead optimization.

Methicillin-resistant Staphylococcus aureus causes sustained collecting lymphatic vessel dysfunction

Methicillin-resistant Staphylococcus aureus (MRSA) is a major cause of morbidity and mortality worldwide and is a frequent cause of skin and soft tissue infections (SSTIs). Lymphedema-fluid accumulation in tissue caused by impaired lymphatic vessel function-is a strong risk factor for SSTIs. SSTIs also frequently recur in patients and sometimes lead to acquired lymphedema. However, the mechanism of how SSTIs can be both the consequence and the cause of lymphatic vessel dysfunction is not known. Intravital imaging in mice revealed an acute reduction in both lymphatic vessel contractility and lymph flow after localized MRSA infection. Moreover, chronic lymphatic impairment is observed long after MRSA is cleared and inflammation is resolved. Associated with decreased collecting lymphatic vessel function was the loss and disorganization of lymphatic muscle cells (LMCs), which are critical for lymphatic contraction. In vitro, incubation with MRSA-conditioned supernatant led to LMC death. Proteomic analysis identified several accessory gene regulator (agr)-controlled MRSA exotoxins that contribute to LMC death. Infection with agr mutant MRSA resulted in sustained lymphatic function compared to animals infected with wild-type MRSA. Our findings suggest that agr is a promising target to preserve lymphatic vessel function and promote immunity during SSTIs.

Identification of Staphylococcal Quorum Sensing Inhibitors by Quantification of õ-Hemolysin with High Performance Liquid Chromatography

Quorum sensing plays a major role in regulation of virulence factor production by staphylococci. Chemical inhibitors that block this process and prevent the production of exotoxins and exoenzymes could have medical utility for infection prophylaxis and therapy. Here, we describe a high performance liquid chromatography method amenable to medium throughput screening for staphylococcal quorum sensing inhibitors by quantification of õ-hemolysin, a direct protein output of this system.

Virulence Factor Targeting of the Bacterial Pathogen Staphylococcus aureus for Vaccine and Therapeutics

BACKGROUND

Staphylococcus aureus is a major bacterial pathogen capable of causing a range of infections in humans from gastrointestinal disease, skin and soft tissue infections, to severe outcomes such as sepsis. Staphylococcal infections in humans can be frequent and recurring, with treatments becoming less effective due to the growing persistence of antibiotic resistant S. aureus strains. Due to the prevalence of antibiotic resistance, and the current limitations on antibiotic development, an active and highly promising avenue of research has been to develop strategies to specifically inhibit the activity of virulence factors produced S. aureus as an alternative means to treat disease.

OBJECTIVE

In this review we specifically highlight several major virulence factors produced by S. aureus for which recent advances in antivirulence approaches may hold promise as an alternative means to treating diseases caused by this pathogen. Strategies to inhibit virulence factors can range from small molecule inhibitors, to antibodies, to mutant and toxoid forms of the virulence proteins.

CONCLUSION

The major prevalence of antibiotic resistant strains of S. aureus combined with the lack of new antibiotic discoveries highlight the need for vigorous research into alternative strategies to combat diseases caused by this highly successful pathogen. Current efforts to develop specific antivirulence strategies, vaccine approaches, and alternative therapies for treating severe disease caused by S. aureus have the potential to stem the tide against the limitations that we face in the post-antibiotic era.

Coagulase-Negative Staphylococcal Strain Prevents Staphylococcus aureus Colonization and Skin Infection by Blocking Quorum Sensing

Coagulase-negative staphylococci (CoNS) and Staphylococcus aureus are part of the natural flora of humans and other mammals. We found that spent media from the CoNS species Staphylococcus caprae can inhibit agr-mediated quorum sensing by all classes of S. aureus. A biochemical assessment of the inhibitory activity suggested that the S. caprae autoinducing peptide (AIP) was responsible, and mass spectrometric analysis identified the S. caprae AIP as an eight-residue peptide (YSTCSYYF). Using a murine model of intradermal MRSA infection, the therapeutic efficacy of synthetic S. caprae AIP was evident by a dramatic reduction in both dermonecrotic injury and cutaneous bacterial burden relative to controls. Competition experiments between S. caprae and MRSA demonstrated a significant reduction in MRSA burden using murine models of both skin colonization and intradermal infection. Our findings indicate that important interactions occur between commensals that can impact disease outcomes and potentially shape the composition of the natural flora.

Staphylococcus aureus pathogenesis in diverse host environments

Staphylococcus aureus is an eminent human pathogen that can colonize the human host and cause severe life-threatening illnesses. This bacterium can reside in and infect a wide range of host tissues, ranging from superficial surfaces like the skin to deeper tissues such as in the gastrointestinal tract, heart and bones. Due to its multifaceted lifestyle, S. aureus uses complex regulatory networks to sense diverse signals that enable it to adapt to different environments and modulate virulence. In this minireview, we explore well-characterized environmental and host cues that S. aureus responds to and describe how this pathogen modulates virulence in response to these signals. Lastly, we highlight therapeutic approaches undertaken by several groups to inhibit both signaling and the cognate regulators that sense and transmit these signals downstream.

Small-Molecule Potentiators for Conventional Antibiotics against Staphylococcus aureus

Antimicrobial resistance constitutes a global health problem, while the discovery and development of novel antibiotics is stagnating. Methicillin-resistant Staphylococcus aureus, responsible for the establishment of recalcitrant, biofilm-related infections, is a well-known and notorious example of a highly resistant micro-organism. Since resistance development is unavoidable with conventional antibiotics that target bacterial viability, it is vital to develop alternative treatment options on top. Strategies aimed at more subtle manipulation of bacterial behavior have recently attracted attention. Here, we provide a literature overview of several small-molecule potentiators for antibiotics, identified for the treatment of Staphylococcus aureus infection. Typically, these potentiators are not bactericidal by themselves and function by reversing resistance mechanisms, by attenuating Staphylococcus aureus virulence, and/or by interfering with quorum sensing.

Probiotics or pro-healers: the role of beneficial bacteria in tissue repair

Probiotics are beneficial microorganisms, known to exert numerous positive effects on human health, primarily in the battle against pathogens. Probiotics have been associated with improved healing of intestinal ulcers, and healing of infected cutaneous wounds. This article reviews the latest findings on probiotics related to their pro-healing properties on gut epithelium and skin. Proven mechanisms by which probiotic bacteria exert their beneficial effects include direct killing of pathogens, competitive displacement of pathogenic bacteria, reinforcement of epithelial barrier, induction of fibroblasts, and epithelial cells' migration and function. Beneficial immunomodulatory effects of probiotics relate to modulation and activation of intraepithelial lymphocytes, natural killer cells, and macrophages through induced production of cytokines. Systemic effects of beneficial bacteria and link between gut microbiota, immune system, and cutaneous health through gut-brain-skin axes are discussed as well. In light of growing antibiotic resistance of pathogens, antibiotic use is becoming less effective in treating cutaneous and systemic infections. This review points to a new perspective and therapeutic potential of beneficial probiotic species as a safe alternative approach for treatment of patients affected by wound healing disorders and cutaneous infections.

Small bacterial and phagic proteins: an updated view on a rapidly moving field

Small proteins, that is, polypeptides of 50 amino acids (aa) or less, are increasingly recognized as important regulators in bacteria. Secreted or not, their small size make them versatile proteins, involved in a wide range of processes. They may allow bacteria to sense and to respond to stresses, to send signals and communicate, and to modulate infections. Bacteriophages also produce small proteins to influence lysogeny/lysis decisions. In this review, we update the present view on small proteins functions, and discuss their possible applications.

Structure-Activity Relationship Study Based on Autoinducing Peptide (AIP) from Dog Pathogen S. schleiferi

Herein, an effective protocol for solid-phase synthesis of peptide thiolactones by concomitant ring closure and cleavage from the solid support is reported. The strategy was applied for mapping the importance of the structural features in S. schleiferi AIP (5) by performing an alanine scan and truncation of this natural compound. This furnished some of the most potent inhibitors of accessory gene regulator (agr)-I in the human pathogen S. aureus reported to date.

Dehydrosqualene Desaturase as a Novel Target for Anti-Virulence Therapy against Staphylococcus aureus

Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA), is a life-threatening pathogen in hospital- and community-acquired infections. The golden-colored carotenoid pigment of S. aureus, staphyloxanthin, contributes to the resistance to reactive oxygen species (ROS) and host neutrophil-based killing. Here, we describe a novel inhibitor (NP16) of S. aureus pigment production that reduces the survival of S. aureus under oxidative stress conditions. Carotenoid components analysis, enzyme inhibition, and crtN mutational studies indicated that the molecular target of NP16 is dehydrosqualene desaturase (CrtN). S. aureus treated with NP16 showed increased susceptibility to human neutrophil killing and to innate immune clearance in a mouse infection model. Our study validates CrtN as a novel druggable target in S. aureus and presents a potent and effective lead compound for the development of virulence factor-based therapy against S. aureus.

S. aureus staphyloxanthin contributes substantially to pathogenesis by interfering with host immune clearance mechanisms, but it has little impact on ex vivo survival of the bacterium. Agents blocking staphyloxanthin production may discourage the establishment and maintenance of bacterial infection without exerting selective pressure for antimicrobial resistance. Our newly discovered CrtN inhibitor, NP16, may offer an effective strategy for combating S. aureus infections.

Advances in the local and targeted delivery of anti-infective agents for management of osteomyelitis

INTRODUCTION

Osteomyelitis, a common and debilitating invasive infection of bone, is a frequent complication following orthopedic surgery and causes pathologic destruction of skeletal tissues. Bone destruction during osteomyelitis results in necrotic tissue, which is poorly penetrated by antibiotics and can serve as a nidus for relapsing infection. Osteomyelitis therefore frequently necessitates surgical debridement procedures, which provide a unique opportunity for targeted delivery of antimicrobial and adjunctive therapies. Areas covered: Following surgical debridement, tissue voids require implanted materials to facilitate the healing process. Antibiotic-loaded, non-biodegradable implants have been the standard of care. However, a new generation of biodegradable, osteoconductive materials are being developed. Additionally, in the face of widespread antimicrobial resistance, alternative therapies to traditional antibiotic regimens are being investigated, including bone targeting compounds, antimicrobial surface modifications of orthopedic implants, and anti-virulence strategies. Expert commentary: Recent advances in biodegradable drug delivery scaffolds make this technology an attractive alternative to traditional techniques for orthopedic infection that require secondary operations for removal. Advances in novel treatment methods are expanding the arsenal of viable antimicrobial treatment strategies in the face of widespread drug resistance. Despite a need for large scale clinical investigations, these strategies offer hope for future treatment of this difficult invasive disease.

A broad range quorum sensing inhibitor working through sRNA inhibition

For the last decade, chemical control of bacterial virulence has received considerable attention. Ajoene, a sulfur-rich molecule from garlic has been shown to reduce expression of key quorum sensing regulated virulence factors in the opportunistic pathogen Pseudomonas aeruginosa. Here we show that the repressing effect of ajoene on quorum sensing occurs by inhibition of small regulatory RNAs (sRNA) in P. aeruginosa as well as in Staphylococcus aureus, another important human pathogen that employs quorum sensing to control virulence gene expression. Using various reporter constructs, we found that ajoene lowered expression of the sRNAs RsmY and RsmZ in P. aeruginosa and the small dual-function regulatory RNA, RNAIII in S. aureus, that controls expression of key virulence factors. We confirmed the modulation of RNAIII by RNA sequencing and found that the expression of many QS regulated genes encoding virulence factors such as hemolysins and proteases were lowered in the presence of ajoene in S. aureus. Importantly, our findings show that sRNAs across bacterial species potentially may qualify as targets of anti-virulence therapy and that ajoene could be a lead structure in search of broad-spectrum compounds transcending the Gram negative-positive borderline.

Signal Biosynthesis Inhibition with Ambuic Acid as a Strategy To Target Antibiotic-Resistant Infections

There has been major interest by the scientific community in antivirulence approaches against bacterial infections. However, partly due to a lack of viable lead compounds, antivirulence therapeutics have yet to reach the clinic. Here we investigate the development of an antivirulence lead targeting quorum sensing signal biosynthesis, a process that is conserved in Gram-positive bacterial pathogens. Some preliminary studies suggest that the small molecule ambuic acid is a signal biosynthesis inhibitor. To confirm this, we constructed a methicillin-resistant Staphylococcus aureus (MRSA) strain that decouples autoinducing peptide (AIP) production from regulation and demonstrate that AIP production is inhibited in this mutant. Quantitative mass spectrometric measurements show that ambuic acid inhibits signal biosynthesis (50% inhibitory concentration [IC₅₀] of 2.5 ± 0.1 μM) against a clinically relevant USA300 MRSA strain. Quantitative real-time PCR confirms that this compound selectively targets the quorum sensing regulon. We show that a 5-μg dose of ambuic acid reduces MRSA-induced abscess formation in a mouse model and verify its quorum sensing inhibitory activity in vivo Finally, we employed mass spectrometry to identify or confirm the structure of quorum sensing signaling peptides in three strains each of S. aureus and Staphylococcus epidermidis and single strains of Enterococcus faecalis, Listeria monocytogenes, Staphylococcus saprophyticus, and Staphylococcus lugdunensis By measuring AIP production by these strains, we show that ambuic acid possesses broad-spectrum efficacy against multiple Gram-positive bacterial pathogens but does not inhibit quorum sensing in some commensal bacteria. Collectively, these findings demonstrate the promise of ambuic acid as a lead for the development of antivirulence therapeutics.

Staphylococcus aureus Quorum Regulator SarA Targeted Compound, 2-[(Methylamino)methyl]phenol Inhibits Biofilm and Down-Regulates Virulence Genes

Staphylococcus aureus is a widely acknowledged Gram-positive pathogen for forming biofilm and virulence gene expressions by quorum sensing (QS), a cell to cell communication process. The quorum regulator SarA of S. aureus up-regulates the expression of many virulence factors including biofilm formation to mediate pathogenesis and evasion of the host immune system in the late phases of growth. Thus, inhibiting the production or blocking SarA protein might influence the down-regulation of biofilm and virulence factors. In this context, here we have synthesized 2-[(Methylamino)methyl]phenol, which was specifically targeted toward the quorum regulator SarA through in silico approach in our previous study. The molecule has been evaluated in vitro to validate its antibiofilm activity against clinical S. aureus strains. In addition, antivirulence properties of the inhibitor were confirmed with the observation of a significant reduction in the expression of representative virulence genes like fnbA, hla and hld that are governed under S. aureus QS. Interestingly, the SarA targeted inhibitor showed negligible antimicrobial activity and markedly reduced the minimum inhibitory concentration of conventional antibiotics when used in combination making it a more attractive lead for further clinical tests.

The Staphylococcal Biofilm: Adhesins, Regulation, and Host Response

The staphylococci comprise a diverse genus of Gram-positive, nonmotile commensal organisms that inhabit the skin and mucous membranes of humans and other mammals. In general, staphylococci are benign members of the natural flora, but many species have the capacity to be opportunistic pathogens, mainly infecting individuals who have medical device implants or are otherwise immunocompromised. Staphylococcus aureus and Staphylococcus epidermidis are major sources of hospital-acquired infections and are the most common causes of surgical site infections and medical device-associated bloodstream infections. The ability of staphylococci to form biofilms in vivo makes them highly resistant to chemotherapeutics and leads to chronic diseases. These biofilm infections include osteomyelitis, endocarditis, medical device infections, and persistence in the cystic fibrosis lung. Here, we provide a comprehensive analysis of our current understanding of staphylococcal biofilm formation, with an emphasis on adhesins and regulation, while also addressing how staphylococcal biofilms interact with the immune system. On the whole, this review will provide a thorough picture of biofilm formation of the staphylococcus genus and how this mode of growth impacts the host.

Different drugs for bad bugs: antivirulence strategies in the age of antibiotic resistance

The rapid evolution and dissemination of antibiotic resistance among bacterial pathogens are outpacing the development of new antibiotics, but antivirulence agents provide an alternative. These agents can circumvent antibiotic resistance by disarming pathogens of virulence factors that facilitate human disease while leaving bacterial growth pathways - the target of traditional antibiotics - intact. Either as stand-alone medications or together with antibiotics, these drugs are intended to treat bacterial infections in a largely pathogen-specific manner. Notably, development of antivirulence drugs requires an in-depth understanding of the roles that diverse virulence factors have in disease processes. In this Review, we outline the theory behind antivirulence strategies and provide examples of bacterial features that can be targeted by antivirulence approaches. Furthermore, we discuss the recent successes and failures of this paradigm, and new developments that are in the pipeline.