ReducingStaphylococcus aureusresistance to lysostaphin using CRISPR‐dCas9

Recent advances in gene-editing approaches for tackling antibiotic resistance threats: a review

Antibiotic resistance, a known global health challenge, involves the flow of bacteria and their genes among animals, humans, and their surrounding environment. It occurs when bacteria evolve and become less responsive to the drugs designated to kill them, making infections harder to treat. Despite several obstacles preventing the spread of genes and bacteria, pathogens regularly acquire novel resistance factors from other species, which reduces their ability to prevent and treat such bacterial infections. This issue requires coordinated efforts in healthcare, research, and public awareness to address its impact on human health worldwide. This review outlines how recent advances in gene editing technology, especially CRISPR/Cas9, unveil a breakthrough in combating antibiotic resistance. Our focus will remain on the relationship between CRISPR/cas9 and its impact on antibiotic resistance and its related infections. Moreover, the prospects of this new advanced research and the challenges of adopting these technologies against infections will be outlined by exploring its different derivatives and discussing their advantages and limitations over others, thereby providing a corresponding reference for the control and prevention of the spread of antibiotic resistance.

CRISPR-Cas System: A New Dawn to Combat Antibiotic Resistance

Antimicrobial resistance (AMR) can potentially harm global public health. Horizontal gene transfer (HGT), which speeds up the emergence of AMR and increases the burden of drug resistance in mobile genetic elements (MGEs), is the primary method by which AMR genes are transferred across bacterial pathogens. New approaches are urgently needed to halt the spread of bacterial diseases and antibiotic resistance. Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR), an RNA-guided adaptive immune system, protects prokaryotes from foreign DNA like plasmids and phages. This approach may be essential in limiting horizontal gene transfer and halting the spread of antibiotic resistance. The CRISPR-Cas system has been crucial in identifying and understanding resistance mechanisms and developing novel therapeutic approaches. This review article investigates the CRISPR-Cas system's potential as a tool to combat bacterial AMR. Antibiotic-resistant bacteria can be targeted and eliminated by the CRISPR-Cas system. It has been proven to be an efficient method for removing carbapenem-resistant plasmids and regaining antibiotic susceptibility. The CRISPR-Cas system has enormous potential as a weapon against bacterial AMR. It precisely targets and eliminates antibiotic-resistant bacteria, facilitates resistance mechanism identification, and offers new possibilities in diagnostics and therapeutics.

Cryo-EM analysis of S. aureus TarL, a polymerase in wall teichoic acid biogenesis central to virulence and antibiotic resistance

Wall teichoic acid (WTA), a covalent adduct of Gram-positive bacterial cell wall peptidoglycan, contributes directly to virulence and antibiotic resistance in pathogenic species. Polymerization of the Staphylococcus aureus WTA ribitol-phosphate chain is catalyzed by TarL, a member of the largely uncharacterized TagF-like family of membrane-associated enzymes. We report the cryo-electron microscopy structure of TarL, showing a tetramer that forms an extensive membrane-binding platform of monotopic helices. TarL is composed of an amino-terminal immunoglobulin-like domain and a carboxyl-terminal glycosyltransferase-B domain for ribitol-phosphate polymerization. The active site of the latter is complexed to donor substrate cytidine diphosphate-ribitol, providing mechanistic insights into the catalyzed phosphotransfer reaction. Furthermore, the active site is surrounded by electropositive residues that serve to retain the lipid-linked acceptor for polymerization. Our data advance general insight into the architecture and membrane association of the still poorly characterized monotopic membrane protein class and present molecular details of ribitol-phosphate polymerization that may aid in the design of new antimicrobials.

Recent Advances in Understanding the Molecular Mechanisms of Multidrug Resistance and Novel Approaches of CRISPR/Cas9-Based Genome-Editing to Combat This Health Emergency

The rapid spread of multidrug resistance (MDR), due to abusive use of antibiotics has led to global health emergency, causing substantial morbidity and mortality. Bacteria attain MDR by different means such as antibiotic modification/degradation, target protection/modification/bypass, and enhanced efflux mechanisms. The classical approaches of counteracting MDR bacteria are expensive and time-consuming, thus, it is highly significant to understand the molecular mechanisms of this resistance to curb the problem from core level. The revolutionary approach of clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated sequence 9 (CRISPR/Cas9), considered as a next-generation genome-editing tool presents an innovative opportunity to precisely target and edit bacterial genome to alter their MDR strategy. Different bacteria possessing antibiotic resistance genes such as mecA, ermB, ramR, tetA, mqrB and blaKPC that have been targeted by CRISPR/Cas9 to re-sensitize these pathogens against antibiotics, such as methicillin, erythromycin, tigecycline, colistin and carbapenem, respectively. The CRISPR/Cas9 from S. pyogenes is the most widely studied genome-editing tool, consisting of a Cas9 DNA endonuclease associated with tracrRNA and crRNA, which can be systematically coupled as sgRNA. The targeting strategies of CRISPR/Cas9 to bacterial cells is mediated through phage, plasmids, vesicles and nanoparticles. However, the targeting approaches of this genome-editing tool to specific bacteria is a challenging task and still remains at a very preliminary stage due to numerous obstacles awaiting to be solved. This review elaborates some recent updates about the molecular mechanisms of antibiotic resistance and the innovative role of CRISPR/Cas9 system in modulating these resistance mechanisms. Furthermore, the delivery approaches of this genome-editing system in bacterial cells are discussed. In addition, some challenges and future prospects are also described.

Cellular and Enzymatic Determinants Impacting the Exolytic Action of an Anti-Staphylococcal Enzybiotic

Bacteriophage endolysins are bacteriolytic enzymes that have been explored as potential weapons to fight antibiotic-resistant bacteria. Despite several studies support the application of endolysins as enzybiotics, detailed knowledge on cellular and enzymatic factors affecting their lytic activity is still missing. The bacterial membrane proton motive force (PMF) and certain cell wall glycopolymers of Gram-positive bacteria have been implicated in some tolerance to endolysins. Here, we studied how the anti-staphylococcal endolysin Lys11, a modular enzyme with two catalytic domains (peptidase and amidase) and a cell binding domain (CBD11), responded to changes in the chemical and/or electric gradients of the PMF (ΔpH and Δψ, respectively). We show that simultaneous dissipation of both gradients enhances endolysin binding to cells and lytic activity. The collapse of ΔpH is preponderant in the stimulation of Lys11 lytic action, while the dissipation of Δψ is mainly associated with higher endolysin binding. Interestingly, this binding depends on the amidase domain. The peptidase domain is responsible for most of the Lys11 bacteriolytic activity. Wall teichoic acids (WTAs) are confirmed as major determinants of endolysin tolerance, in part by severely hindering CBD11 binding activity. In conclusion, the PMF and WTA interfere differently with the endolysin functional domains, affecting both the binding and catalytic efficiencies.

Biofilms as Battlefield Armor for Bacteria against Antibiotics: Challenges and Combating Strategies

Bacterial biofilms are formed by communities, which are encased in a matrix of extracellular polymeric substances (EPS). Notably, bacteria in biofilms display a set of 'emergent properties' that vary considerably from free-living bacterial cells. Biofilms help bacteria to survive under multiple stressful conditions such as providing immunity against antibiotics. Apart from the provision of multi-layered defense for enabling poor antibiotic absorption and adaptive persistor cells, biofilms utilize their extracellular components, e.g., extracellular DNA (eDNA), chemical-like catalase, various genes and their regulators to combat antibiotics. The response of biofilms depends on the type of antibiotic that comes into contact with biofilms. For example, excessive production of eDNA exerts resistance against cell wall and DNA targeting antibiotics and the release of antagonist chemicals neutralizes cell membrane inhibitors, whereas the induction of protein and folic acid antibiotics inside cells is lowered by mutating genes and their regulators. Here, we review the current state of knowledge of biofilm-based resistance to various antibiotic classes in bacteria and genes responsible for biofilm development, and the key role of quorum sensing in developing biofilms and antibiotic resistance is also discussed. In this review, we also highlight new and modified techniques such as CRISPR/Cas, nanotechnology and bacteriophage therapy. These technologies might be useful to eliminate pathogens residing in biofilms by combating biofilm-induced antibiotic resistance and making this world free of antibiotic resistance.

CRISPR-Cas-Based Antimicrobials: Design, Challenges, and Bacterial Mechanisms of Resistance

The emergence of antibiotic-resistant bacterial strains is a source of public health concern across the globe. As the discovery of new conventional antibiotics has stalled significantly over the past decade, there is an urgency to develop novel approaches to address drug resistance in infectious diseases. The use of a CRISPR-Cas-based system for the precise elimination of targeted bacterial populations holds promise as an innovative approach for new antimicrobial agent design. The CRISPR-Cas targeting system is celebrated for its high versatility and specificity, offering an excellent opportunity to fight antibiotic resistance in pathogens by selectively inactivating genes involved in antibiotic resistance, biofilm formation, pathogenicity, virulence, or bacterial viability. The CRISPR-Cas strategy can enact antimicrobial effects by two approaches: inactivation of chromosomal genes or curing of plasmids encoding antibiotic resistance. In this Review, we provide an overview of the main CRISPR-Cas systems utilized for the creation of these antimicrobials, as well as highlighting promising studies in the field. We also offer a detailed discussion about the most commonly used mechanisms for CRISPR-Cas delivery: bacteriophages, nanoparticles, and conjugative plasmids. Lastly, we address possible mechanisms of interference that should be considered during the intelligent design of these novel approaches.

A Review of CRISPR-Based Advances in Dermatological Diseases

Clustered regularly interspaced short palindromic repeat (CRISPR) has revolutionized biomedical research by offering novel approaches to genetic and epigenetic manipulation. In dermatology, it has significantly promoted our understanding of complex diseases, and shown great potential in therapeutic applications. In this review, we introduce the adoption of CRISPR technology as a tool to study different types of skin disorders, including monogenic genodermatoses, inflammatory disorders, and cutaneous infections. We highlight the promising preclinical results of CRISPR-mediated treatment and important mechanic discoveries in investigative studies. Future opportunities and remaining challenges are also discussed. We predict that CRISPR will be more extensively used for dermatological research and even be accessible to patients in the future.

CRISPR-Based Gene Editing in Acinetobacter baumannii to Combat Antimicrobial Resistance

Antimicrobial resistance (AMR) poses a significant threat to the health, social, environment, and economic sectors on a global scale and requires serious attention to addressing this issue. Acinetobacter baumannii was given top priority among infectious bacteria because of its extensive resistance to nearly all antibiotic classes and treatment options. Carbapenem-resistant A. baumannii is classified as one of the critical-priority pathogens on the World Health Organization (WHO) priority list of antibiotic-resistant bacteria for effective drug development. Although available genetic manipulation approaches are successful in A. baumannii laboratory strains, they are limited when employed on newly acquired clinical strains since such strains have higher levels of AMR than those used to select them for genetic manipulation. Recently, the CRISPR-Cas (Clustered regularly interspaced short palindromic repeats/CRISPR-associated protein) system has emerged as one of the most effective, efficient, and precise methods of genome editing and offers target-specific gene editing of AMR genes in a specific bacterial strain. CRISPR-based genome editing has been successfully applied in various bacterial strains to combat AMR; however, this strategy has not yet been extensively explored in A. baumannii. This review provides detailed insight into the progress, current scenario, and future potential of CRISPR-Cas usage for AMR-related gene manipulation in A. baumannii.

Role of sodium pyruvate in maintaining the survival and cytotoxicity of Staphylococcus aureus under high glucose conditions

Glucose is a crucial carbon source for the growth of Staphylococcus aureus, but an excess of glucose is detrimental and even leads to cell death. Pyruvate, the central metabolite of glycolysis, has been shown to have anti-inflammatory and antioxidant properties. This study aimed to investigate the protective effect of pyruvate on S. aureus under high glucose conditions. Sodium pyruvate greatly increased the cytotoxicity of S. aureus strain BAA-1717 to human erythrocytes and neutrophils in vitro. However, the cytotoxicity and survival of S. aureus were significantly reduced by high glucose, which was restored to normal levels by the addition of sodium pyruvate. The expression of hlg and lukS in S. aureus was higher in the LB-GP cultures than that in LB-G cultures, but there was no significant difference in cytotoxicity between LB-GP and LB-G cultures. Furthermore, the hemolytic activity of S. aureus supernatants could be inhibited by the cell-free culture medium (CFCM) of LB-G cultures, suggesting that high levels of extracellular proteases were presence in the CFCM of LB-G cultures, resulting in degradation of the hemolytic factors. The expression of sarA, which negatively regulates extracellular protease secretion, was higher in LB-GP cultures than that in LB-G cultures. Additionally, sodium pyruvate increased acetate production in S. aureus, which helps maintain cell viability under acidic environment. In conclusion, pyruvate plays an important role in the survival and cytotoxicity of S. aureus under high glucose conditions. This finding may aid in the development of effective treatments for diabetic foot infections.

CRISPR-Cas system as a promising player against bacterial infection and antibiotic resistance

The phenomenon of antibiotic resistance (AR) and its increasing global trends and destructive waves concerns patients and the healthcare system. In order to combat AR, it is necessary to explore new strategies when the current antibiotics fail to be effective. Thus, knowing the resistance mechanisms and appropriate diagnosis of bacterial infections may help enhance the sensitivity and specificity of novel strategies. On the other hand, resistance to antimicrobial compounds can spread from resistant populations to susceptible ones. Antimicrobial resistance genes (ARGs) significantly disseminate AR via horizontal and vertical gene transfer. The clustered regularly interspaced short palindromic repeats (CRISPR)-Cas system is a member of the bacterial immune system with the ability to remove the ARGs; therefore, it can be introduced as an effective and innovative strategy in the battle against AR. Here, we reviewed CRISPR-based bacterial diagnosis technologies. Moreover, the strategies to battle AR based on targeting bacterial chromosomes and resistance plasmids using the CRISPR-Cas system have been explained. Besides, we have presented the limitations of CRISPR delivery and potential solutions to help improve the future development of CRISPR-based platforms.

Lysostaphin: Engineering and Potentiation toward Better Applications

Lysostaphin is a potent bacteriolytic enzyme with endopeptidase activity against the common pathogen Staphylococcus aureus. By digesting the pentaglycine crossbridge in the cell wall peptidoglycan of S. aureus including the methicillin-resistant strains, lysostaphin initiates rapid lysis of planktonic and sessile cells (biofilms) and has great potential for use in agriculture, food industries, and pharmaceutical industries. In the past few decades, there have been tremendous efforts in potentiating lysostaphin for better applications in these fields, including engineering of the enzyme for higher potency and lower immunogenicity with longer-lasting effects, formulation and immobilization of the enzyme for higher stability and better durability, and recombinant expression for low-cost industrial production and in situ biocontrol. These achievements are extensively reviewed in this article focusing on applications in disease control, food preservation, surface decontamination, and pathogen detection. In addition, some basic properties of lysostaphin that have been controversial and only elucidated recently are summarized, including the substrate-binding properties, the number of zinc-binding sites, the substrate range, and the cleavage site in the pentaglycine crossbridge. Resistance to lysostaphin is also highlighted with a focus on various mechanisms. This article is concluded with a discussion on the limitations and future perspectives for the actual applications of lysostaphin.

CRISPR-Based Approaches for Gene Regulation in Non-Model Bacteria

CRISPR interference (CRISPRi) and CRISPR activation (CRISPRa) have become ubiquitous approaches to control gene expression in bacteria due to their simple design and effectiveness. By regulating transcription of a target gene(s), CRISPRi/a can dynamically engineer cellular metabolism, implement transcriptional regulation circuitry, or elucidate genotype-phenotype relationships from smaller targeted libraries up to whole genome-wide libraries. While CRISPRi/a has been primarily established in the model bacteria Escherichia coli and Bacillus subtilis, a growing numbering of studies have demonstrated the extension of these tools to other species of bacteria (here broadly referred to as non-model bacteria). In this mini-review, we discuss the challenges that contribute to the slower creation of CRISPRi/a tools in diverse, non-model bacteria and summarize the current state of these approaches across bacterial phyla. We find that despite the potential difficulties in establishing novel CRISPRi/a in non-model microbes, over 190 recent examples across eight bacterial phyla have been reported in the literature. Most studies have focused on tool development or used these CRISPRi/a approaches to interrogate gene function, with fewer examples applying CRISPRi/a gene regulation for metabolic engineering or high-throughput screens and selections. To date, most CRISPRi/a reports have been developed for common strains of non-model bacterial species, suggesting barriers remain to establish these genetic tools in undomesticated bacteria. More efficient and generalizable methods will help realize the immense potential of programmable CRISPR-based transcriptional control in diverse bacteria.

Synthetic antimicrobial peptides as enhancers of the bacteriolytic action of staphylococcal phage endolysins

Bacteriophage endolysins degrade the bacterial cell wall and are therefore considered promising antimicrobial alternatives to fight pathogens resistant to conventional antibiotics. Gram-positive bacteria are usually considered easy targets to exogenously added endolysins, since their cell walls are not shielded by an outer membrane. However, in nutrient rich environments these bacteria can also tolerate endolysin attack if they keep an energized cytoplasmic membrane. Hence, we have hypothesized that the membrane depolarizing action of antimicrobial peptides (AMPs), another attractive class of alternative antibacterials, could be explored to overcome bacterial tolerance to endolysins and consequently improve their antibacterial potential. Accordingly, we show that under conditions supporting bacterial growth, Staphylococcus aureus becomes much more susceptible to the bacteriolytic action of endolysins if an AMP is also present. The bactericidal gain resulting from the AMP/endolysin combined action ranged from 1 to 3 logs for different S. aureus strains, which included drug-resistant clinical isolates. In presence of an AMP, as with a reduced content of cell wall teichoic acids, higher endolysin binding to cells is observed. However, our results indicate that this higher endolysin binding alone does not fully explain the higher susceptibility of S. aureus to lysis in these conditions. Other factors possibly contributing to the increased endolysin susceptibility in presence of an AMP are discussed.

Microbial cell surface engineering for high-level synthesis of bio-products

Microbial cell surface layers, which mainly include the cell membrane, cell wall, periplasmic space, outer membrane, capsules, S-layers, pili, and flagella, control material exchange between the cell and the extracellular environment, and have great impact on production titers and yields of various bio-products synthesized by microbes. Recent research work has made exciting achievements in metabolic engineering using microbial cell surface components as novel regulation targets without direct modifications of the metabolic pathways of the desired products. This review article will summarize the accomplishments obtained in this emerging field, and will describe various engineering strategies that have been adopted in bacteria and yeasts for the enhancement of mass transfer across the cell surface, improvement of protein expression and folding, modulation of cell size and shape, and re-direction of cellular resources, all of which contribute to the construction of more efficient microbial cell factories toward the synthesis of a variety of bio-products. The existing problems and possible future directions will also be discussed.

Engineered CRISPR-Cas systems for the detection and control of antibiotic-resistant infections

Antibiotic resistance is spreading rapidly around the world and seriously impeding efforts to control microbial infections. Although nucleic acid testing is widely deployed for the detection of antibiotic resistant bacteria, the current techniques-mainly based on polymerase chain reaction (PCR)-are time-consuming and laborious. There is an urgent need to develop new strategies to control bacterial infections and the spread of antimicrobial resistance (AMR). The CRISPR-Cas system is an adaptive immune system found in many prokaryotes that presents attractive opportunities to target and edit nucleic acids with high precision and reliability. Engineered CRISPR-Cas systems are reported to effectively kill bacteria or even revert bacterial resistance to antibiotics (resensitizing bacterial cells to antibiotics). Strategies for combating antimicrobial resistance using CRISPR (i.e., Cas9, Cas12, Cas13, and Cas14) can be of great significance in detecting bacteria and their resistance to antibiotics. This review discusses the structures, mechanisms, and detection methods of CRISPR-Cas systems and how these systems can be engineered for the rapid and reliable detection of bacteria using various approaches, with a particular focus on nanoparticles. In addition, we summarize the most recent advances in applying the CRISPR-Cas system for virulence modulation of bacterial infections and combating antimicrobial resistance.

CRISPR-Cas, a Revolution in the Treatment and Study of ESKAPE Infections: Pre-Clinical Studies

One of the biggest threats we face globally is the emergence of antimicrobial-resistant (AMR) bacteria, which runs in parallel with the lack in the development of new antimicrobials. Among these AMR bacteria pathogens belonging to the ESKAPE group can be highlighted (Enterococcus spp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) due to their profile of drug resistance and virulence. Therefore, innovative lines of treatment must be developed for these bacteria. In this review, we summarize the different strategies for the treatment and study of molecular mechanisms of AMR in the ESKAPE pathogens based on the clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (Cas) proteins’ technologies: loss of plasmid or cellular viability, random mutation or gene deletion as well directed mutations that lead to a gene’s loss of function.

Electrostatic-Mediated Affinity Tuning of Lysostaphin Accelerates Bacterial Lysis Kinetics and Enhances In Vivo Efficacy

Drug-resistant bacterial pathogens are a serious threat to global health, and antibacterial lysins are at the forefront of innovative treatments for these life-threatening infections. While lysins' general mechanism of action is well understood, the design principles that might enable engineering of performance-enhanced variants are still being formulated. Here, we report a detailed analysis of molecular determinants underlying the in vivo efficacy of lysostaphin, a canonical anti-MRSA (methicillin-resistant Staphylococcus aureus) lysin. Systematic analysis of bacterial binding, growth inhibition, lysis kinetics, and in vivo therapeutic efficacy revealed that binding affinity, and not inherent catalytic firepower, is the dominant driver of lysostaphin efficacy. This insight enabled electrostatic affinity tuning of lysostaphin to produce a single point mutant that manifested dramatically enhanced processivity and lysis kinetics and trended toward improved in vivo efficacy. More generally, these studies provide important insights into the complex relationships between lysin electrostatics, bacterial targeting, cell lysis efficiency, and in vivo efficacy. The lessons learned may enable engineering of other high-performance antibacterial biocatalysts.

Endolysin-Based Autolytic E. coli System for Facile Recovery of Recombinant Proteins

Recovery of recombinant proteins from the Escherichia coli cytoplasm depends on cell disruption by mechanical, chemical, and/or enzymatic methods, which usually cause incomplete cell breakage or protein denaturation. Controllable autolytic E. coli strains have been designed to facilitate the purification of recombinant proteins; however, these strains suffer from low recovery yield, slow cell lysis, or extensive strain engineering. Herein, we report an improved, highly efficient programmable autolytic E. coli platform, in which cell lysis is initiated upon the induced expression of T4 lysozyme with N-terminal fusion of a cell-penetrating peptide. Through the engineering of the peptide sequence and copy number, and by incorporating the fusion lytic gene into the E. coli genome, more than 99.97% of cells could be lysed within 30 min of induction regardless of cell age. We further tested the expression and release of a recombinant enzyme lysostaphin (Lst) and demonstrated that 4 h induction of the lytic gene after 3 h of Lst expression resulted in 98.97% cell lysis. Lst obtained from this system had the same yield, yet 1.63-fold higher activity, compared with that obtained from cells lysed by freeze-thawing and sonication. This autolytic platform shows potential for use in large-scale microbial production of proteins and other biopolymers.

Influence of bacterial culture medium on peptidoglycan binding of cell wall lytic enzymes

The bacteriolysin lysostaphin (Lst) and endolysin PlyPH are potent modular lytic enzymes with activity against clinically-relevant Gram-positive Staphylococcus aureus and Bacillus cereus, respectively. Both enzymes possess an N-terminal catalytic domain and C-terminal binding domain, with the latter conferring significant enzyme specificity. Lst and PlyPH show reduced activity in the presence of bacterial growth-supporting conditions, such as complex media. Here, we hypothesize that Lst and PlyPH bind poorly to their targets in growth media, which may influence their use in antimicrobial applications in the food industry, as therapeutics, and for control of microbial communities. To this end, binding of isolated Lst and PlyPH binding domains to target bacteria was quantified in the presence of three increasingly complex media - phosphate buffered saline (PBS), defined growth medium (AAM) and undefined complex medium (TSB) by surface plasmon resonance (SPR) and flow cytometry. Evaluation of binding kinetics by SPR demonstrated that PlyPH binding was particularly sensitive to medium composition, with 8-fold lower association and 3.4-fold lower dissociation rate constants to B. cereus in TSB compared to PBS. Flow cytometry studies indicated a decrease in the binding-dependent fluorescent populations of S. aureus and B. cereus, for lysostaphin binding domain and PlyPH binding domain, respectively, in TSB compared to PBS. Enzyme binding behavior was consistent with the enzymes' catalytic activity in the three media, thereby suggesting that compromised enzyme binding could be responsible for poor activity in more complex growth media.

Deimmunized Lysostaphin Synergizes with Small-Molecule Chemotherapies and Resensitizes Methicillin-Resistant Staphylococcus aureus to β-Lactam Antibiotics

There is an urgent need for novel agents to treat drug-resistant bacterial infections, such as multidrug-resistant Staphylococcus aureus (MRSA). Desirable properties for new antibiotics include high potency, narrow species selectivity, low propensity to elicit new resistance phenotypes, and synergy with standard-of-care (SOC) chemotherapies. Here, we describe analysis of the antibacterial potential exhibited by F12, an innovative anti-MRSA lysin that has been genetically engineered to evade detrimental antidrug immune responses in human patients. F12 possesses high potency and rapid onset of action, it has narrow selectivity against pathogenic staphylococci, and it manifests synergy with numerous SOC antibiotics. Additionally, resistance to F12 and β-lactam antibiotics appears mutually exclusive, and, importantly, we provide evidence that F12 resensitizes normally resistant MRSA strains to β-lactams both in vitro and in vivo These results suggest that combinations of F12 and SOC antibiotics are a promising new approach to treating refractory S. aureus infections.

Wall teichoic acids: physiology and applications

Wall teichoic acids (WTAs) are charged glycopolymers containing phosphodiester-linked polyol units and represent one of the major components of Gram-positive cell envelope. WTAs have important physiological functions in cell division, gene transfer, surface adhesion, drug resistance and biofilm formation, and are critical virulence factors and vital determinants in mediating cell interaction with and tolerance to environmental factors. Here, we first briefly introduce WTA structure, biosynthesis and its regulation, and then summarize in detail four major physiological roles played by WTAs, i.e. WTA-mediated resistance to antimicrobials, virulence to mammalian cells, interaction with bacteriolytic enzymes and regulation of cell metabolism. We also review the applications of WTAs in these fields that are closely related to the human society, including antibacterial drug discovery targeting WTA biosynthesis, development of vaccines and antibodies regarding WTA-mediated pathogenicity, specific and sensitive detection of pathogens in food using WTAs as a surface epitope and regulation of WTA-related pathways for efficient microbial production of useful compounds. We also point out major problems remaining in these fields, and discuss some possible directions in the future exploration of WTA physiology and applications.

Reduced Growth of Staphylococcus aureus Under High Glucose Conditions Is Associated With Decreased Pentaglycine Expression

The high-glucose-induced cytotoxicity in diabetes has been widely recognized. Staphylococcus aureus is the most frequent pathogen isolated from diabetic foot ulcers, but the properties of this bacterium under high glucose conditions remain unclear. S. aureus grew in medium usually forms weak biofilm, and which was significantly increased by addition of glucose. However, extracellular DNA (eDNA), an important component of biofilms, was markedly decreased in presence of 15 mM glucose. The reduced eDNA content was not caused by degradation, because the nuclease activity of biofilm supernatants with glucose was significantly decreased due to the acidic pH of the medium. Under planktonic state, the growth of S. aureus was significantly decreased in the Luria-Bertani (LB) medium supplemented with 25 mM glucose, and the reduced growth of S. aureus by glucose was dose-dependent. Except for glucose, the growth of planktonic S. aureus was also markedly decreased by fructose or sucrose. Amounts of acid metabolites were produced under high glucose conditions, but the survival of planktonic S. aureus was unaffected by these acidic conditions. Cells of S. aureus from the culture medium with glucose had a thinner cell wall and highly resistant to lysostaphin compared with the bacteria cultured in LB medium. mRNA expression of genes encoding pentaglycine bridges, the substrate of lysostaphin, was significantly decreased in S. aureus by glucose. In addition to S. aureus, the growth of Staphylococcus haemolyticus and Staphylococcus epidermidis was also significantly decreased by an excess of glucose, but strains of Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa were unaffected by glucose. In conclusion, the reduced growth of S. aureus under high glucose conditions is due to impairment of the unique cell-wall structure, pentaglycine bridges.

Enzybiotics LYSSTAPH-S and LYSDERM-S as Potential Therapeutic Agents for Chronic MRSA Wound Infections

Antibacterial antibiotic therapy has played an important role in the treatment of bacterial infections for almost a century. The increasing resistance of pathogenic bacteria to antibiotics leads to an attempt to use previously neglected antibacterial therapies. Here we provide information on the two recombinantly modified antistaphylococcal enzymes derived from lysostaphin (LYSSTAPH-S) and endolysin (LYSDERM-S) derived from kayvirus 812F1 whose target sites reside in the bacterial cell wall. LYSSTAPH-S showed a stable antimicrobial effect over 24-h testing, even in concentrations lower than 1 µg/mL across a wide variety of epidemiologically important sequence types (STs) of methicillin-resistant Staphylococcus aureus (MRSA), especially in the stationary phase of growth (status comparable to chronic infections). LYSDERM-S showed a less potent antimicrobial effect that lasted only a few hours at concentrations of 15 μg/mL and higher. Our data indicate that these antimicrobial enzymes could be of substantial help in the treatment of chronic MRSA wound infections.