Staphylococcus aureus hyaluronidase is a CodY-regulated virulence factor

Hyaluronic acid-based hydrogel microspheres with multi-responsive properties for antibacterial therapy and bone regeneration in Staphylococcus aureus-infected skull defects

This study introduces hyaluronic acid-based (HA) hydrogel microspheres loaded with zinc oxide nanoparticles (ZnO-NPs) for the treatment of infectious bone defects. The microspheres were fabricated using a 3D-printing process, with a formulation consisting of 6 wt% HAD (methacrylated HA), 3 wt% AOHA (AMP-conjugated oxidized HA), 1 % BOHA (phenylboric acid-conjugated HA), 0.5 % photoinitiator, and 0.05 % ZnO-NPs. In vitro, the hydrogel microspheres demonstrated significant antibacterial activity against Staphylococcus aureus, with colony counts and biofilm inhibition assays showing a marked reduction in bacterial growth after 12 and 24 h. The release of antimicrobial peptides (AMPs) was enhanced in acidic conditions and in the presence of hyaluronidase. The microspheres also promoted osteogenic differentiation of bone marrow stromal cells (BMSCs), as evidenced by increased expression of osteogenic markers (ALP, OCN, OPN, and COL-1). In vivo, the hydrogel microspheres were tested in a rat skull defect model, showing significant bone regeneration, improved angiogenesis, and an anti-inflammatory response. These results indicate that ABOHA@ZnO hydrogel microspheres provide a promising strategy for treating infectious bone defects by combining antimicrobial, osteogenic.

Impact of extracellular enzymes on Staphylococcus aureus host tissue adaptation and infection

Staphylococcus aureus is a multi-host pathogen that can colonize and infect both humans and livestock in a tissue-specific manner. This amazing feature of the pathogen is mainly facilitated by the surplus virulence agents produced upon necessity and favorable environmental factors. These factors are adept at damaging cellular barriers, manipulating host immune factors, and circumventing the host complement system. The delicate balance between the timely release of virulent factors and the regulation of their production underscores the significance of the exoenzyme network. Moreover, the intricate relationship between the pathogen and host tissue highlights the importance of understanding tissue-specific phenotypes for effective therapeutic strategies. Here, we provide a review on the diverse role played by the extracellular enzymes of S. aureus in tissue-specific infection and systemic colonization leading to distinctive diseased conditions. The article highlights the need to study the role of staphylococcal exoenzymes in various systemic invasions, their impact on the deterioration of host tissue, and the regulation of S. aureus virulence factors.

HylS', a fragment of truncated hyaluronidase of Streptococcus suis, contributes to immune evasion by interaction with host complement factor C3b

Pathogenic bacteria have evolved many strategies to evade surveillance and attack by complements. Streptococcus suis is an important zoonotic pathogen that infects humans and pigs. Hyaluronidase (HylA) has been reported to be a potential virulence factor of S. suis. However, in this study, it was discovered that the genomic region encoding HylA of the virulent S. suis strain SC19 and other ST1 strains was truncated into four fragments when aligned with a strain containing intact HylA and possessing hyaluronidase activity. As a result, SC19 had no hyaluronidase activity, but one truncated HylA fragment, designated as HylS,' directly interacted with complement C3b, as confirmed by western ligand blotting, pull-down, and ELISA assays. The deposition of C3b and membrane attack complex (MAC) formation on the surface of a HylS'-deleted mutant (ΔhylS') was significantly increased compared to wild-type SC19. In human sera and whole blood, ΔhylS' survival was significantly reduced compared to that in SC19. The resistance of ΔhylS' to macrophages and human polymorphonuclear neutrophil PMNs also decreased. In a mouse infection model, ΔhylS' showed reduced lethality and lower bacterial load in the organs compared to that of SC19. We conclude that the truncated hyaluronidase HylS' fragment contributes to complement evasion and the pathogenesis of S. suis.

Genomic Characterization and Comparative Analysis of Streptococcus zhangguiae sp. nov. Isolated from the Respiratory Tract of Marmota Himalayana

Two Gram-stain-positive, oxidase-negative, non-motile, facultative anaerobic, α-hemolytic, coccus-shaped bacteria (zg-86T and zg-70) were isolated from the respiratory tracts of marmots (Marmota Himalayana) on the Qinghai-Tibet Plateau of China. Phylogenetic analysis of the 16S rRNA gene and 545 core genes revealed that these two strains belong to the Streptococcus genus. These strains were most closely related to Streptococcus respiraculi HTS25T, Streptococcus cuniculi CCUG 65085T, and Streptococcus marmotae HTS5T. The average nucleotide identity (ANI) and digital DNA‒DNA hybridization (dDDH) were below the threshold for species delineation. The predominant cellular fatty acids (CFAs) in this novel species were C16:0, C18:0, and C18:1ω9c, whereas the primary polar lipids were phosphatidylglycerol (PG), phosphatidylethanolamine (PE) and an unknown phosphoglycolipid (PGL). The optimal growth conditions for the strains were 37 °C, pH 7.0, and 0.5% (w/v) NaCl on brain-heart infusion (BHI) agar supplemented with 5% defibrinated sheep blood. Comparative genomics analyses revealed the potential pathogenicity of strain zg-86T through comparisons with suis subclade strains in terms of virulence factors, pathogen-host interactions (PHIs) and mobile genetic factors (MGEs). Based on the phenotypic characteristics and phylogenetic analyses, we propose that these two isolates represent novel species in the genus Streptococcus, for which the names Streptococcus zhangguiae sp. nov. (the type strain zg-86T=GDMCC 1.1758T=JCM 34273T) is proposed.

Contribution of staphylococcal virulence factors in the pathogenesis of thrombosis

Staphylococci are responsible for many infections in humans, starting with skin and soft tissue infections and finishing with invasive diseases such as endocarditis, sepsis and pneumonia, which lead to high mortality. Patients with sepsis often demonstrate activated clotting pathways, decreased levels of anticoagulants, decreased fibrinolysis, activated endothelial surfaces and activated platelets. This results in disseminated intravascular coagulation and formation of a microthrombus, which can lead to a multiorgan failure. This review describes various staphylococcal virulence factors that contribute to vascular thrombosis, including deep vein thrombosis in infected patients. The article presents mechanisms of action of different factors released by bacteria in various host defense lines, which in turn can lead to formation of blood clots in the vessels.

Genomic insights into clostridia in bioenergy production: Comparison of metabolic capabilities and evolutionary relationships

Bacteria from diverse genera, including Acetivibrio, Bacillus, Cellulosilyticum, Clostridium, Desulfotomaculum, Lachnoclostridium, Moorella, Ruminiclostridium, and Thermoanaerobacterium, have attracted significant attention due to their versatile metabolic capabilities encompassing acetogenic, cellulolytic, and C1-metabolic properties, and acetone-butanol-ethanol fermentation. Despite their biotechnological significance, a comprehensive understanding of clostridial physiology and evolution has remained elusive. This study reports an extensive comparative genomic analysis of 48 fully sequenced bacterial genomes from these genera. Our investigation, encompassing pan-genomic analysis, central carbon metabolism comparison, exploration of general genome features, and in-depth scrutiny of Cluster of Orthologous Groups genes, has established a holistic whole-genome-based phylogenetic framework. We have classified these strains into acetogenic, butanol-producing, cellulolytic, CO2-fixating, chemo(litho/organo)trophic, and heterotrophic categories, often exhibiting overlaps. Key outcomes include the identification of misclassified species and the revelation of insights into metabolic features, energy conservation, substrate utilization, stress responses, and regulatory mechanisms. These findings can provide guidance for the development of efficient microbial systems for sustainable bioenergy production. Furthermore, by addressing fundamental questions regarding genetic relationships, conserved genomic features, pivotal enzymes, and essential genes, this study has also contributed to our comprehension of clostridial biology, evolution, and their shared metabolic potential.

Marine polysaccharides: Biological activities and applications in drug delivery systems

The ocean is the common home of a large number of marine organisms, including plants, animals, and microorganisms. Researchers can extract thousands of important bioactive components from the oceans and use them extensively to treat and prevent diseases. In contrast, marine polysaccharide macromolecules such as alginate, carrageenan, Laminarin, fucoidan, chitosan, and hyaluronic acid have excellent physicochemical properties, good biocompatibility, and high bioactivity, which ensures their wide applications and strong therapeutic potentials in drug delivery. Drug delivery systems (DDS) based on marine polysaccharides and modified marine polysaccharide molecules have emerged as an innovative technology for controlling drug distribution on temporal, spatial, and dosage scales. They can detect and respond to external stimuli such as pH, temperature, and electric fields. These properties have led to their wide application in the design of novel drug delivery systems such as hydrogels, polymeric micelles, liposomes, microneedles, microspheres, etc. In addition, marine polysaccharide-based DDS not only have smart response properties but also can combine with the unique biological properties of the marine polysaccharide base to exert synergistic therapeutic effects. The biological activities of marine polysaccharides and the design of marine polysaccharide-based DDS are reviewed. Marine polysaccharide-based responsive DDS are expected to provide new strategies and solutions for disease treatment.

Progress of stimulus responsive nanosystems for targeting treatment of bacterial infectious diseases

In recent decades, due to insufficient concentration at the lesion site, low bioavailability and increasingly serious resistance, antibiotics have become less and less dominant in the treatment of bacterial infectious diseases. It promotes the development of efficient drug delivery systems, and is expected to achieve high absorption, targeted drug release and satisfactory therapy effects. A variety of endogenous stimulation-responsive nanosystems have been constructed by using special infection microenvironments (pH, enzymes, temperature, etc.). In this review, we firstly provide an extensive review of the current research progress in antibiotic treatment dilemmas and drug delivery systems. Then, the mechanism of microenvironment characteristics of bacterial infected lesions was elucidated to provide a strong theoretical basis for bacteria-targeting nanosystems design. In particular, the discussion focuses on the design principles of single-stimulus and dual-stimulus responsive nanosystems, as well as the use of endogenous stimulus-responsive nanosystems to deliver antimicrobial agents to target locations for combating bacterial infectious diseases. Finally, the challenges and prospects of endogenous stimulus-responsive nanosystems were summarized.

Fabrication of poly(β-amino ester) and hyaluronic acid based pH responsive nanocomplex as an antibiotic release system

World Health Organization (WHO) warns about antimicrobial resistance (AMR) considered as the most serious threats to global health, food security, and development. There are various efforts for elimination of this serious issue. These efforts include education of individuals, new policies, development of new antimicrobials and new materials for effective delivery. Novel drug delivery systems with ability of local and on-demand delivery are one of the promising approaches for prevention of AMR. In this regard, a pH-responsive antibiotic delivery system based on pH-responsive poly(β-amino ester) (PBAE) and enzyme responsive hyaluronic acid (HA). The polymeric nanocomplexes were obtained via electrostatic complexation of PBAE and HA in the presence of a model antibiotics, colistin and vancomycin. The particle sizes at pH 7.4 were determined in the range of 131-730 nm and 120-400 nm by DLS and STEM, respectively. When pH was switched from 7.4 to 5.5, the hydrodynamic diameter increased 2.5-32 fold. The drug release performances were tested using FITC-labeled antibiotics via fluorescence spectroscopy. The nanocomplexes released the drugs more at pH 5.5 compared to pH 7.4. Antibacterial activity of the system was evaluated on various bacteria. The nanocomplex loaded with the antibiotics exhibited significantly greater efficacy against E. coli and S. aureus.

Smart stimuli-responsive strategies for titanium implant functionalization in bone regeneration and therapeutics

With the increasing and aging of global population, there is a dramatic rise in the demand for implants or substitutes to rehabilitate bone-related disorders which can considerably decrease quality of life and even endanger lives. Though titanium and its alloys have been applied as the mainstream material to fabricate implants for load-bearing bone defect restoration or temporary internal fixation devices for bone fractures, it is far from rare to encounter failed cases in clinical practice, particularly with pathological factors involved. In recent years, smart stimuli-responsive (SSR) strategies have been conducted to functionalize titanium implants to improve bone regeneration in pathological conditions, such as bacterial infection, chronic inflammation, tumor and diabetes mellitus, etc. SSR implants can exert on-demand therapeutic and/or pro-regenerative effects in response to externally applied stimuli (such as photostimulation, magnetic field, electrical and ultrasound stimulation) or internal pathology-related microenvironment changes (such as decreased pH value, specific enzyme secreted by bacterial and excessive production of reactive oxygen species). This review summarizes recent progress on the material design and fabrication, responsive mechanisms, and in vitro and in vivo evaluations for versatile clinical applications of SSR titanium implants. In addition, currently existing limitations and challenges and further prospective directions of these strategies are also discussed.

The Staphylococcus aureus CamS lipoprotein is a repressor of toxin production that shapes host-pathogen interaction

Lipoproteins of the opportunistic pathogen Staphylococcus aureus play a crucial role in various cellular processes and host interactions. Consisting of a protein and a lipid moiety, they support nutrient acquisition and anchor the protein to the bacterial membrane. Recently, we identified several processed and secreted small linear peptides that derive from the secretion signal sequence of S. aureus lipoproteins. Here, we show, for the first time, that the protein moiety of the S. aureus lipoprotein CamS has a biological role that is distinct from its associated linear peptide staph-cAM373. The small peptide was shown to be involved in interspecies horizontal gene transfer, the primary mechanism for the dissemination of antibiotic resistance among bacteria. We provide evidence that the CamS protein moiety is a potent repressor of cytotoxins, such as α-toxin and leukocidins. The CamS-mediated suppression of toxin transcription was reflected by altered disease severity in in vivo infection models involving skin and soft tissue, as well as bloodstream infections. Collectively, we have uncovered the role of the protein moiety of the staphylococcal lipoprotein CamS as a previously uncharacterized repressor of S. aureus toxin production, which consequently regulates virulence and disease outcomes. Notably, the camS gene is conserved in S. aureus, and we also demonstrated the muted transcriptional response of cytotoxins in 2 different S. aureus lineages. Our findings provide the first evidence of distinct biological functions of the protein moiety and its associated linear peptide for a specific lipoprotein. Therefore, lipoproteins in S. aureus consist of 3 functional components: a lipid moiety, a protein moiety, and a small linear peptide, with putative different biological roles that might not only determine the outcome of host-pathogen interactions but also drive the acquisition of antibiotic resistance determinants.

Elucidating the CodY regulon in Staphylococcus aureus USA300 substrains TCH1516 and LAC

CodY is a conserved broad-acting transcription factor that regulates the expression of genes related to amino acid metabolism and virulence in Gram-positive bacteria. Here, we performed the first in vivo determination of CodY target genes using a novel CodY monoclonal antibody in methicillin-resistant Staphylococcus aureus (MRSA) USA300. Our results showed (i) the same 135 CodY promoter binding sites regulating the 165 target genes identified in two closely related virulent S. aureus USA300 TCH1516 and LAC strains; (ii) the differential binding intensity for the same target genes under the same conditions was due to sequence differences in the same CodY-binding site in the two strains; (iii) a CodY regulon comprising 72 target genes that are differentially regulated relative to a CodY deletion strain, representing genes that are mainly involved in amino acid transport and metabolism, inorganic ion transport and metabolism, transcription and translation, and virulence, all based on transcriptomic data; and (iv) CodY systematically regulated central metabolic flux to generate branched-chain amino acids (BCAAs) by mapping the CodY regulon onto a genome-scale metabolic model of S. aureus. Our study performed the first system-level analysis of CodY in two closely related USA300 TCH1516 and LAC strains, revealing new insights into the similarities and differences of CodY regulatory roles between the closely related strains. IMPORTANCE With the increasing availability of whole-genome sequences for many strains within the same pathogenic species, a comparative analysis of key regulators is needed to understand how the different strains uniquely coordinate metabolism and expression of virulence. To successfully infect the human host, Staphylococcus aureus USA300 relies on the transcription factor CodY to reorganize metabolism and express virulence factors. While CodY is a known key transcription factor, its target genes are not characterized on a genome-wide basis. We performed a comparative analysis to describe the transcriptional regulation of CodY between two dominant USA300 strains. This study motivates the characterization of common pathogenic strains and an evaluation of the possibility of developing specialized treatments for major strains circulating in the population.

Research on the biological mechanism and potential application of CEMIP

Cell migration-inducing protein (CEMIP), also known as KIAA1199 and hyaluronan-binding protein involved in hyaluronan depolymerization, is a new member of the hyaluronidase family that degrades hyaluronic acid (HA) and remodels the extracellular matrix. In recent years, some studies have reported that CEMIP can promote the proliferation, invasion, and adhesion of various tumor cells and can play an important role in bacterial infection and arthritis. This review focuses on the pathological mechanism of CEMIP in a variety of diseases and expounds the function of CEMIP from the aspects of inhibiting cell apoptosis, promoting HA degradation, inducing inflammatory responses and related phosphorylation, adjusting cellular microenvironment, and regulating tissue fibrosis. The diagnosis and treatment strategies targeting CEMIP are also summarized. The various functions of CEMIP show its great potential application value.

Revisiting ESKAPE Pathogens: virulence, resistance, and combating strategies focusing on quorum sensing

The human-bacterial association is long-known and well-established in terms of both augmentations of human health and attenuation. However, the growing incidents of nosocomial infections caused by the ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter sp.) call for a much deeper understanding of these organisms. Adopting a holistic approach that includes the science of infection and the recent advancements in preventing and treating infections is imperative in designing novel intervention strategies against ESKAPE pathogens. In this regard, this review captures the ingenious strategies commissioned by these master players, which are teamed up against the defenses of the human team, that are equally, if not more, versatile and potent through an analogy. We have taken a basketball match as our analogy, dividing the human and bacterial species into two teams playing with the ball of health. Through this analogy, we make the concept of infectious biology more accessible.

Comparative genomic analysis of ovine and other host associated isolates of Staphylococcus aureus exhibit the important role of mobile genetic elements and virulence factors in host adaptation

Staphylococcus aureus is the main etiological agent of mastitis in small ruminants worldwide. This disease has a difficult cure and possible relapse, leading to significant economic losses in production, milk quality and livestock. This study performed comparative genomic analyses between 73 S. aureus genomes from different hosts (human, bovine, pig and others). This work isolated and sequenced 12 of these genomes from ovine. This study contributes to the knowledge of genomic specialization and the role of specific genes in establishing infection in ovine mastitis-associated S. aureus. The genomes of S. aureus isolated from sheep maintained a higher representation when grouped with clonal complexes 130 and 133. The genomes showed high genetic similarity, the species pan-genome consisting of 4200 genes (central = 2008, accessory = 1559 and unique = 634). Among these, 277 unique genes were related to the genomes isolated from sheep, with 39.6 % as hypothetical proteins, 6.4 % as phages, 6.4 % as toxins, 2.9 % as transporters, and 44.7 % as related to other proteins. Furthermore, at the pathogen level, they showed 80 genes associated with virulence factors and 19 with antibiotic resistance shared in almost all isolates. Although S. aureus isolated from ovine showed susceptibility to antimicrobials in vitro, ten genes were predicted to be associated with antibiotic inactivation and efflux pump, suggesting resistance to gentamicin and penicillin. This work may contribute to identifying genes acquired by horizontal transfer and their role in host adaptation, virulence, bacterial resistance, and characterization of strains affecting ovine.

Identification and characterization of the causative agents of Focal Ulcerative Dermatitis in commercial laying hens

Focal Ulcerative Dermatitis (FUDS) is an emerging dermatological disease that affects cage-free laying flocks, it is characterized by the development of a lesion on the dorsum of the birds; FUDS is sporadic in nature and can result in a drop in egg production and up to 50% of cumulative mortality. A total of two cage-free flocks (flock 1: no history of FUDS; flock 2: birds affected with FUDS) from a commercial laying hen operation in the mid-west U.S. were sampled in this study. The microbial composition of skin, cloacal, cecal, and ileal samples from each bird was characterized through next generation sequencing (NGS). Results identified Staphylococcus aureus and Staphylococcus agnetis as the potential causative agents of FUDS, being the most predominant in FUDS positive birds. These results were confirmed by plating, with both staphylococci as the only pathogens isolated from lesions of FUDS positive birds. A total of 68 confirmed Staphylococcus isolates from skin and environmental samples were further analyzed by whole genome sequencing (WGS) for the presence of antimicrobial resistance (AMR) genes and virulence factors that could have contributed to the development of FUDS. Forty-four-point one-two percent of the isolates had between one and four acquired AMR genes encoding for macrolides, lincosamides, spectrogramines, and beta-lactams resistance. Six classes of virulence factors associated with adherence, enzyme, immune evasion, secretion system, toxin, and iron uptake were identified. The antimicrobial effect of 4 proprietary Bacillus Direct Fed Microbial (DFM) combinations was evaluated against the Staphylococcus aureus and Staphylococcus agnetis isolates, by agar well-diffusion (AWD) assay and competitive exclusion (CE) on broth culture. Through this antimicrobial screening, a particular two-strain combination of Bacillus pumilus was identified as the most effective inhibitor of both staphylococci. A customized Bacillus pumilus product is being used at different farms with history of FUDS resulting in the successful inhibition of both Staphylococcus aureus and Staphylococcus agnetis, decreasing FUDS mortalities, and improving harvestable eggs.

Secretory proteins in the orchestration of microbial virulence: The curious case of Staphylococcus aureus

Microbial virulence showcases an excellent model for adaptive changes that enable an organism to survive and proliferate in a hostile environment and exploit host resources to its own benefit. In Staphylococcus aureus, an opportunistic pathogen of the human host, known for the diversity of the disease conditions it inflicts and the rapid evolution of antibiotic resistance, virulence is a consequence of having a highly plastic genome that is amenable to quick reprogramming and the ability to express a diverse arsenal of virulence factors. Virulence factors that are secreted to the host milieu effectively manipulate the host conditions to favor bacterial survival and growth. They assist in colonization, nutrient acquisition, immune evasion, and systemic spread. The structural and functional characteristics of the secreted virulence proteins have been shaped to assist S. aureus in thriving and disseminating effectively within the host environment and exploiting the host resources to its best benefit. With the aim of highlighting the importance of secreted virulence proteins in bacterial virulence, the present chapter provides a comprehensive account of the role of the major secreted proteins of S. aureus in orchestrating its virulence in the human host.

The Complex Bridge between Aquatic and Terrestrial Life: Skin Changes during Development of Amphibians

Amphibian skin is a particularly complex organ that is primarily responsible for respiration, osmoregulation, thermoregulation, defense, water absorption, and communication. The skin, as well as many other organs in the amphibian body, has undergone the most extensive rearrangement in the adaptation from water to land. Structural and physiological features of skin in amphibians are presented within this review. We aim to procure extensive and updated information on the evolutionary history of amphibians and their transition from water to land-that is, the changes seen in their skin from the larval stages to adulthood from the points of morphology, physiology, and immunology.

An Inflamed and Infected Reconstructed Human Epidermis to Study Atopic Dermatitis and Skin Care Ingredients

Atopic dermatitis (AD), the most common inflammatory skin disorder, is a multifactorial disease characterized by a genetic predisposition, epidermal barrier disruption, a strong T helper (Th) type 2 immune reaction to environmental antigens and an altered cutaneous microbiome. Microbial dysbiosis characterized by the prevalence of Staphylococcus aureus (S. aureus) has been shown to exacerbate AD. In recent years, in vitro models of AD have been developed, but none of them reproduce all of the pathophysiological features. To better mimic AD, we developed reconstructed human epidermis (RHE) exposed to a Th2 pro-inflammatory cytokine cocktail and S. aureus. This model well reproduced some of the vicious loops involved in AD, with alterations at the physical, microbial and immune levels. Our results strongly suggest that S. aureus acquired a higher virulence potential when the epidermis was challenged with inflammatory cytokines, thus later contributing to the chronic inflammatory status. Furthermore, a topical application of a Castanea sativa extract was shown to prevent the apparition of the AD-like phenotype. It increased filaggrin, claudin-1 and loricrin expressions and controlled S. aureus by impairing its biofilm formation, enzymatic activities and inflammatory potential.

Therapeutic Inhibition of Staphylococcus aureus ArlRS Two-Component Regulatory System Blocks Virulence

Staphylococcus aureus is a common cause of severe infections, and its widespread antibiotic resistance necessitates search for alternative therapies, such as inhibition of virulence. As S. aureus produces multiple individual virulence factors, inhibition of an entire regulatory system might provide better effects than targeting each virulence factor separately. Herein, we describe two novel inhibitors of S. aureus two-component regulatory system ArlRS: 3,4'-dimethoxyflavone and homopterocarpin. Unlike other putative ArlRS inhibitors previously identified, these two compounds were effective and specific. In vitro kinase assays indicated that 3,4'-dimethoxyflavone directly inhibits ArlS autophosphorylation, while homopterocarpin did not exhibit such effect, suggesting that two inhibitors work through distinct mechanisms. Application of the inhibitors to methicillin-resistant S. aureus (MRSA) in vitro blocked ArlRS signaling, inducing an abnormal gene expression pattern that was reflected in changes at the protein level, enhanced sensitivity to oxacillin, and led to the loss of numerous cellular virulence traits, including the ability to clump, adhere to host ligands, and evade innate immunity. The pleiotropic antivirulence effect of inhibiting a single regulatory system resulted in a marked therapeutic potential, demonstrated by the ability of inhibitors to decrease severity of MRSA infection in mice. Altogether, this study demonstrated the feasibility of ArlRS inhibition as anti-S. aureus treatment, and identified new lead compounds for therapeutic development.

Neutralizing Staphylococcus aureus Virulence with AZD6389, a Three mAb Combination, Accelerates Closure of a Diabetic Polymicrobial Wound

Nonhealing diabetic foot ulcers (DFU), a major complication of diabetes, are associated with high morbidity and mortality despite current standard of care. Since Staphylococcus aureus is the most common pathogen isolated from nonhealing and infected DFU, we hypothesized that S. aureus virulence factors would damage tissue, promote immune evasion and alter the microbiome, leading to bacterial persistence and delayed wound healing. In a diabetic mouse polymicrobial wound model with S. aureus, Pseudomonas aeruginosa, and Streptococcus pyogenes, we report a rapid bacterial proliferation, prolonged pro-inflammatory response and large necrotic lesions unclosed for up to 40 days. Treatment with AZD6389, a three-monoclonal antibody combination targeting S. aureus alpha toxin, 4 secreted leukotoxins, and fibrinogen binding cell-surface adhesin clumping factor A resulted in full skin re-epithelization 21 days after inoculation. By neutralizing multiple virulence factors, AZD6389 effectively blocked bacterial agglutination and S. aureus-mediated cell killing, abrogated S. aureus-mediated immune evasion and targeted the bacteria for opsonophagocytic killing. Neutralizing S. aureus virulence not only facilitated S. aureus clearance in lesions, but also reduced S. pyogenes and P. aeruginosa numbers, damaging inflammatory mediators and markers for neutrophil extracellular trap formation 14 days post initiation. Collectively, our data suggest that AZD6389 holds promise as an immunotherapeutic approach against DFU complications.

IMPORTANCE Diabetic foot ulcers (DFU) represent a major complication of diabetes and are associated with poor quality of life and increased morbidity and mortality despite standard of care. They have a complex pathogenesis starting with superficial skin lesions, which often progress to deeper tissue structures up to the bone and ultimately require limb amputation. The skin microbiome of diabetic patients has emerged as having an impact on DFU occurrence and chronicity. DFU are mostly polymicrobial, and the Gram-positive bacterium Staphylococcus aureus detected in more than 95% of cases. S. aureus possess a collection of virulence factors which participate in disease progression and may facilitate growth of other pathogens. Here we show in a diabetic mouse wound model that targeting some specific S. aureus virulence factors with a multimechanistic antibody combination accelerated wound closure and promoted full skin re-epithelization. This work opens promising new avenues for the treatment of DFU.

Mechanisms and Implications of Bacterial Invasion across the Human Skin Barrier

Atopic dermatitis (AD) is associated with a deficiency of skin lipids, increased populations of Staphylococcus aureus in the microbiome, and structural defects in the stratum corneum (SC), the outermost layer of human skin. However, the pathogenesis of AD is ambiguous, as it is unclear whether observed changes are the result of AD or contribute to the pathogenesis of the disease. Previous studies have shown that S. aureus is capable of permeating across isolated human SC tissue when lipids are depleted to levels consistent with AD conditions. In this study, we expand upon this discovery to determine the mechanisms and implications of bacterial penetration into the SC barrier. Specifically, we establish if bacteria are permeating intercellularly or employing a combination of both inter- and intracellular travel. The mechanical implications of bacterial invasion, lipid depletion, and media immersion are also evaluated using a newly developed, physiologically relevant, temperature-controlled drip chamber. Results reveal for the first time that S. aureus can be internalized by corneocytes, indicating transcellular movement through the tissue during permeation, consistent with previous theoretical models. S. aureus also degrades the mechanical integrity of human SC, particularly when the tissue is partially depleted of lipids. These observed mechanical changes are likely the cause of broken or ruptured tissue seen as exudative lesions in AD flares. This work further highlights the necessity of lipids in skin microbial barrier function.

IMPORTANCE Millions of people suffer from the chronic inflammatory skin disease atopic dermatitis (AD), whose symptoms are associated with a deficiency of skin lipids that exhibit antimicrobial functions and increased populations of the opportunistic pathogen Staphylococcus aureus. However, the pathogenesis of AD is ambiguous, and it remains unclear if these observed changes are merely the result of AD or contribute to the pathogenesis of the disease. In this article, we demonstrate the necessity of skin lipids in preventing S. aureus from penetrating the outermost barrier of human skin, thereby causing a degradation in tissue integrity. This bacterial permeation into the viable epidermis could act as an inflammatory trigger of the disease. When coupled with delipidated AD tissue conditions, bacterial permeation can also explain increased tissue fragility, potentially causing lesion formation in AD patients that results in further enhancing bacterial permeability across the stratum corneum and the development of chronic conditions.

Screening for Virulence-Related Genes via a Transposon Mutant Library of Streptococcus suis Serotype 2 Using a Galleria mellonella Larvae Infection Model

Streptococcus suis (S. suis) is a zoonotic bacterial pathogen causing lethal infections in pigs and humans. Identification of virulence-related genes (VRGs) is of great importance in understanding the pathobiology of a bacterial pathogen. To identify novel VRGs, a transposon (Tn) mutant library of S. suis strain SC19 was constructed in this study. The insertion sites of approximately 1700 mutants were identified by Tn-seq, which involved 417 different genes. A total of 32 attenuated strains were identified from the library by using a Galleria mellonella larvae infection model, and 30 novel VRGs were discovered, including transcription regulators, transporters, hypothetical proteins, etc. An isogenic deletion mutant of hxtR gene (ΔhxtR) and its complementary strain (CΔhxtR) were constructed, and their virulence was compared with the wild-type strain in G. mellonella larvae and mice, which showed that disruption of hxtR significantly attenuated the virulence. Moreover, the ΔhxtR strain displayed a reduced survival ability in whole blood, increased sensitivity to phagocytosis, increased chain length, and growth defect. Taken together, this study performed a high throughput screening for VRGs of S. suis using a G. mellonella larvae model and further characterized a novel critical virulence factor.

Design of Smart Size-, Surface-, and Shape-Switching Nanoparticles to Improve Therapeutic Efficacy

Multiple biological barriers must be considered in the design of nanomedicines, including prolonged blood circulation, efficient accumulation at the target site, effective penetration into the target tissue, selective uptake of the nanoparticles into target cells, and successful endosomal escape. However, different particle sizes, surface chemistries, and sometimes shapes are required to achieve the desired transport properties at each step of the delivery process. In response, this review highlights recent developments in the design of switchable nanoparticles whose size, surface chemistry, shape, or a combination thereof can be altered as a function of time, a disease-specific microenvironment, and/or via an externally applied stimulus to enable improved optimization of nanoparticle properties in each step of the delivery process. The practical use of such nanoparticles in chemotherapy, bioimaging, photothermal therapy, and other applications is also discussed.

The Candidate Antigens to Achieving an Effective Vaccine against Staphylococcus aureus

Staphylococcus aureus (S. aureus) is an opportunistic pathogen that causes various inflammatory local infections, from those of the skin to postinfectious glomerulonephritis. These infections could result in serious threats, putting the life of the patient in danger. Antibiotic-resistant S. aureus could lead to dramatic increases in human mortality. Antibiotic resistance would explicate the failure of current antibiotic therapies. So, it is obvious that an effective vaccine against S. aureus infections would significantly reduce costs related to care in hospitals. Bacterial vaccines have important impacts on morbidity and mortality caused by several common pathogens, however, a prophylactic vaccine against staphylococci has not yet been produced. During the last decades, the efforts to develop an S. aureus vaccine have faced two major failures in clinical trials. New strategies for vaccine development against S. aureus has supported the use of multiple antigens, the inclusion of adjuvants, and the focus on various virulence mechanisms. We aimed to present a compressive review of different antigens of S. aureus and also to introduce vaccine candidates undergoing clinical trials, from which can help us to choose a suitable and effective candidate for vaccine development against S. aureus.

Human monoclonal antibodies against Staphylococcus aureus surface antigens recognize in vitro and in vivo biofilm

Implant-associated Staphylococcus aureus infections are difficult to treat because of biofilm formation. Bacteria in a biofilm are often insensitive to antibiotics and host immunity. Monoclonal antibodies (mAbs) could provide an alternative approach to improve the diagnosis and potential treatment of biofilm-related infections. Here, we show that mAbs targeting common surface components of S. aureus can recognize clinically relevant biofilm types. The mAbs were also shown to bind a collection of clinical isolates derived from different biofilm-associated infections (endocarditis, prosthetic joint, catheter). We identify two groups of antibodies: one group that uniquely binds S. aureus in biofilm state and one that recognizes S. aureus in both biofilm and planktonic state. Furthermore, we show that a mAb recognizing wall teichoic acid (clone 4497) specifically localizes to a subcutaneously implanted pre-colonized catheter in mice. In conclusion, we demonstrate the capacity of several human mAbs to detect S. aureus biofilms in vitro and in vivo.

Branched-chain amino acid metabolism controls membrane phospholipid structure in Staphylococcus aureus

Branched-chain amino acids (primarily isoleucine) are important regulators of virulence and are converted to precursor molecules used to initiate fatty acid synthesis in Staphylococcus aureus. Defining how bacteria control their membrane phospholipid composition is key to understanding their adaptation to different environments. Here, we used mass tracing experiments to show that extracellular isoleucine is preferentially metabolized by the branched-chain ketoacid dehydrogenase complex, in contrast to valine, which is not efficiently converted to isobutyryl-CoA. This selectivity creates a ratio of anteiso:iso C₅-CoAs that matches the anteiso:iso ratio in membrane phospholipids, indicating indiscriminate utilization of these precursors by the initiation condensing enzyme FabH. Lipidomics analysis showed that removal of isoleucine and leucine from the medium led to the replacement of phospholipid molecular species containing anteiso/iso 17- and 19-carbon fatty acids with 18- and 20-carbon straight-chain fatty acids. This compositional change is driven by an increase in the acetyl-CoA:C₅-CoA ratio, enhancing the utilization of acetyl-CoA by FabH. The acyl carrier protein (ACP) pool normally consists of odd carbon acyl-ACP intermediates, but when branched-chain amino acids are absent from the environment, there was a large increase in even carbon acyl-ACP pathway intermediates. The high substrate selectivity of PlsC ensures that, in the presence or the absence of extracellular Ile/Leu, the 2-position is occupied by a branched-chain 15-carbon fatty acid. These metabolomic measurements show how the metabolism of isoleucine and leucine, rather than the selectivity of FabH, control the structure of membrane phospholipids.

The small RNA RsaF regulates the expression of secreted virulence factors in Staphylococcus aureus Newman

The pathogenesis of Staphylococcus aureus, from local infections to systemic dissemination, is mediated by a battery of virulence factors that are regulated by intricate mechanisms, which include regulatory proteins and small RNAs (sRNAs) as key regulatory molecules. We have investigated the involvement of sRNA RsaF, in the regulation of pathogenicity genes hyaluronate lyase (hysA) and serine proteaselike protein D (splD), by employing S. aureus strains with disruption and overexpression of rsaF. Staphylococcus aureus strain with disruption of rsaF exhibited marked down-regulation of hysA transcripts by 0.2 to 0.0002 fold, and hyaluronate lyase activity by 0.2-0.1 fold, as well as increased biofilm formation, during growth from log phase to stationery phase. These mutants also displayed down-regulation of splD transcripts by 0.8 to 0.005 fold, and reduced activity of multiple proteases by zymography. Conversely, overexpression of rsaF resulted in a 2- to 4- fold increase in hysA mRNA levels and hyaluronidase activity. Both hysA and splD mRNAs demonstrated an increased stability in RsaF⁺ strains. In silico RNA-RNA interaction indicated a direct base pairing of RsaF with hysA and splD mRNAs, which was established in electrophoretic mobility shift assays. The findings demonstrate a positive regulatory role for small RNA RsaF in the expression of the virulence factors, HysA and SplD.

Integrated Multi-omics, Virtual Screening and Molecular Docking Analysis of Methicillin-Resistant Staphylococcus aureus USA300 for the Identification of Potential Therapeutic Targets: An In-Silico Approach

Staphylococcus aureus infection is a leading cause of mortality and morbidity in community, hospital and live-stock sectors, especially with the widespread emergence of methicillin-resistant S. aureus (MRSA) strains. To identify new drug molecules to treat MRSA patients, we have undertaken to search essential proteins that are indispensable for their survival but non-homologous to human host proteins. The current study utilizes a subtractive genome and proteome approach to screen the possible therapeutic targets against S. aureus USA300. Bacterial essential genes are obtained from the DEG database and are compared to avoid cross-reactivity with human host genes. In silico analysis shows 198 proteins that may be considered as therapeutic candidates. Depending on their sub-cellular localization, proteins are grouped as either vaccine or drug targets or both. Extracellular proteins such as cell division proteins (Q2FZ91, Q2FZ95), penicillin-binding proteins (Q2FZ94, Q2FYI0) of the bacterial cell wall, phosphoglucomutase (Q2FE11) and lipoteichoic acid synthase (Q2FIS2) are considered as vaccine targets, and their epitopes have been mapped. Altogether, 53 drug targets are identified, which have shown similarity with the drug targets available in the DrugBank database. Predicted drug targets belong to the common metabolic pathways of MRSA, such as fatty acid biosynthesis, folate biosynthesis, peptidoglycan biosynthesis, ribosome, etc. Protein-protein interaction analysis emphasizing peptidoglycan biosynthesis reveals the connection between penicillin-binding proteins, mur-family proteins and FemXAB proteins. In this study, staphylococcal FemA protein (P0A0A5) is subjected to structure-based virtual screening for the drug repurposing approach. There are 20 residues missing in the crystal structure of FemA, and 12 of these residues are located at the catalytic site. The missing residues are modelled, and stereochemistry is checked. FDA approved drugs available in the DrugBank database have been used in virtual screening with FemA in search of potential repurposed molecules. This approach provides us with 10 drugs that may be used in the treatment of methicillin-resistant staphylococcal mediated diseases. AutoDock 4.2 is used for in silico screening and shows a comparable inhibition constant (Ki) for all 10 FDA-approved drugs towards FemA. Most of these drugs are used in the treatment of various cancers, migraines and leukaemia. Protein-drug interaction analysis shows that the drugs mostly interact with hydrophobic residues of FemA. Moreover, Tyr328 and Lys383 contribute largely to hydrogen bondings during interactions. All interacting amino acids that bind to the drugs are part of the active site cavity of FemA.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10989-021-10287-9.

A naturally occurring point mutation in the hyaluronidase gene (hysA1) of Staphylococcus aureus UAMS-1 results in reduced enzymatic activity

Hyaluronic acid is a high-molecular-weight polysaccharide that is widely distributed in animal tissues. Bacterial hyaluronidases degrade hyaluronic acid as secreted enzymes and have been shown to contribute to infection. Staphylococcus aureus UAMS-1 is a clinical isolate that codes for two hyaluronidases (hysA1 and hysA2). Previous research has shown the presence of a full-length HysA1 protein from the S. aureus UAMS-1 strain with no evidence of enzymatic activity. In this study, the coding and upstream promoter regions of hysA1 from the S. aureus UAMS-1 strain were cloned, sequenced, and compared to the hysA1 gene from the S. aureus Sanger 252 strain. A single base change resulting in an E480G amino acid change was identified in the hysA1 gene from the S. aureus UAMS-1 strain when compared to the hysA1 gene from S. aureus Sanger 252. A plasmid copy of hysA1 from S. aureus Sanger 252 transduced into an S. aureus UAMS-1 hysA2 deletion mutant strain restored near wild-type levels of enzymatic activity. Homology modeling of the HysA1 hyaluronidase was performed with SWISS-MODEL using hyaluronidase from Streptococcus pneumoniae as the template, followed by a series of structural analyses using PyMOL, PLIP, PDBsum, and HOPE servers. This glutamic acid is highly conserved among hyaluronidases from Staphylococcus and other gram-positive bacteria. A series of structural analyses suggested that Glu-480 in HysA1 is critically responsible for maintaining the structural and functional ensemble of the catalytic and tunnel-forming residues, which are essential for enzyme activity. The missense mutation of Glu-480 to Gly introduces a loss of side chain hydrogen bond interactions with key residues Arg-360 and Arg-364, which are responsible for the tunnel topology, resulting in displacement of the substrate from an ideal position for catalysis through a localized conformational change of the active site. There is a high degree of relatedness among several gram-positive bacterial hyaluronidases; the loss of enzymatic activity of HysA1 in the S. aureus UAMS-1 strain is most likely caused by the mutation identified in our study. The role of hyaluronidase in staphylococcal infection and the redundancy of this gene are yet to be determined.

Methicillin-Resistant Staphylococcus aureus (MRSA) Infection of Diabetic Foot Ulcers at a Tertiary Care Hospital in Accra, Ghana

Aim: This study investigated the spectrum of bacteria infecting the ulcers of individuals with diabetes at the Korle Bu Teaching Hospital in Accra, Ghana, focusing on Staphylococcus aureus (S. aureus) and methicillin-resistant S. aureus (MRSA), with respect to their prevalence, factors predisposing to their infection of the ulcers, and antimicrobial resistance patterns. Methodology: This cross-sectional study was conducted at The Ulcer Clinic, Department of Surgery, Korle Bu Teaching Hospital, involving 100 diabetic foot ulcer patients. The ulcer of each study participant was swabbed and cultured bacteriologically, following standard procedures. Antimicrobial susceptibility testing was done for all S. aureus isolated, using the Kirby-Bauer method. Results: In total, 96% of the participants had their ulcers infected—32.3% (n = 31) of these had their ulcers infected with one bacterium, 47.9% (n = 46) with two bacteria, 18.8% (n = 18) with three bacteria, and 1.0% (n = 1) with four bacteria. The prevalence of S. aureus and MRSA were 19% and 6%, respectively. The distribution of the other bacteria was as follows: coagulase-negative Staphylococci (CoNS) (54%), Escherichia coli (24%), Pseudomonas spp. (19%), Citrobacter koseri and Morganella morgana (12% each), Klebsiella oxytoca (11%), Proteus vulgaris (8%), Enterococcus spp. (6%), Klebsiella pneumoniae (5%), Proteus mirabilis and Enterobacter spp. (4%), Klebsiella spp. (2%), and Streptococcus spp. (1%). The resistance rates of S. aureus decreased across penicillin (100%, n = 19), tetracycline (47.4%, n = 9), cotrimoxazole (42.1%, n = 8), cefoxitin (31.6%, n = 6), erythromycin and clindamycin (26.3% each, n = 5), norfloxacin and gentamicin (15.8% each, n = 3), rifampicin (10.5%, n = 2), linezolid (5.3%, n = 1), and fusidic acid (0.0%, n = 0). The proportion of multidrug resistance was 47.4% (n = 9). Except for foot ulcer infection with coagulase-negative Staphylococci, which was protective of S. aureus infection of the ulcers (OR = 0.029, p = 0.001, 95% CI = 0.004–0.231), no predictor of S. aureus, MRSA, or polymicrobial ulcer infection was identified. Conclusions: The prevalence of S. aureus and MRSA infection of the diabetic foot ulcers were high, but lower than those of the predominant infector, coagulase-negative Staphylococci and the next highest infecting agent, E. coli. Diabetic foot ulcers’ infection with coagulase-negative Staphylococci protected against their infection with S. aureus. The prevalence of multidrug resistance was high, highlighting the need to further intensify antimicrobial stewardship programmes.

Intelligent Nanoparticle-Based Dressings for Bacterial Wound Infections

Conventional wound dressing materials containing free antibiotics for bacterial wound infections are presented with several limitations, that is, lack of controlled and triggered release capabilities, and may often not be adequate to address the complex bacteria microenvironment of such infections. Additionally, the improper usage of antibiotics may also result in the emergence of drug resistant strains. While delivery systems (i.e., nanoparticles) that encapsulate antibiotics may potentially overcome some of these limitations, their therapeutic outcomes are still less than desirable. For example, premature drug release or unintended drug activation may occur, which would greatly reduce treatment efficacy. To address this, responsive nanoparticle-based antimicrobial therapies could be a promising strategy. Such nanoparticles can be functionalized to react to a single stimulus or multi stimulus within the bacteria microenvironment and subsequently elicit a therapeutic response. Such "intelligent" nanoparticles can be designed to respond to the microenvironment, that is, an acidic pH, the presence of specific enzymes, bacterial toxins, etc. or to an external stimulus, for example, light, thermal, etc. These responsive nanoparticles can be further incorporated into wound dressings to better promote wound healing. This review summarizes and highlights the recent progress on such intelligent nanoparticle-based dressings as potential wound dressings for bacteria-infected wounds, along with the current challenges and prospects for these technologies to be successfully translated into the clinic.

In Vitro Antibacterial, Anti-Adhesive and Anti-Biofilm Activities of Krameria lappacea (Dombey) Burdet & B.B. Simpson Root Extract against Methicillin-Resistant Staphylococcus aureus Strains

Methicillin-resistant Staphylococcus aureus (MRSA) represents a serious threat to public health, due to its large variety of pathogenetic mechanisms. Accordingly, the present study aimed to investigate the anti-MRSA activities of Krameria lappacea, a medicinal plant native to South America. Through Ultra-High-Performance Liquid Chromatography coupled with High-Resolution Mass spectrometry, we analyzed the chemical composition of Krameria lappacea root extract (KLRE). The antibacterial activity of KLRE was determined by the broth microdilution method, also including the minimum biofilm inhibitory concentration and minimum biofilm eradication concentration. Besides, we evaluated the effect on adhesion and invasion of human lung carcinoma A549 cell line by MRSA strains. The obtained results revealed an interesting antimicrobial action of this extract, which efficiently inhibit the growth, biofilm formation, adhesion and invasion of MRSA strains. Furthermore, the chemical analysis revealed the presence in the extract of several flavonoid compounds and type-A and type-B proanthocyanidins, which are known for their anti-adhesive effects. Taken together, our findings showed an interesting antimicrobial activity of KLRE, giving an important contribution to the current knowledge on the biological activities of this plant.

Endothelial Heparan Sulfate Proteoglycans in Sepsis: The Role of the Glycocalyx

There is increasing recognition of the importance of the endothelial glycocalyx and its in vivo manifestation, the endothelial surface layer, in vascular homeostasis. Heparan sulfate proteoglycans (HSPGs) are a major structural constituent of the endothelial glycocalyx and serve to regulate vascular permeability, microcirculatory tone, leukocyte and platelet adhesion, and hemostasis. During sepsis, endothelial HSPGs are shed through the induction of "sheddases" such as heparanase and matrix metalloproteinases, leading to loss of glycocalyx integrity and consequent vascular dysfunction. Less well recognized is that glycocalyx degradation releases HSPG fragments into the circulation, which can shape the systemic consequences of sepsis. In this review, we will discuss (1) the normal, homeostatic functions of HSPGs within the endothelial glycocalyx, (2) the pathological changes in HSPGs during sepsis and their consequences on the local vascular bed, and (3) the systemic consequences of HSPG degradation. In doing so, we will identify potential therapeutic targets to improve vascular function during sepsis as well as highlight key areas of uncertainty that require further mechanistic investigation.

Genome-Wide Analysis of Staphylococcus aureus Sequence Type 72 Isolates Provides Insights Into Resistance Against Antimicrobial Agents and Virulence Potential

Staphylococcus aureus sequence type 72 (ST72) is a major community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) that has rapidly entered the hospital setting in Korea, causing mild superficial skin wounds to severe bloodstream infections. In this study, we sequenced and analyzed the genomes of one methicillin-resistant human isolate and one methicillin-sensitive human isolate of ST72 from Korea, K07-204 and K07-561, respectively. We used a subtractive genomics approach to compare these two isolates to other 27 ST72 isolates to investigate antimicrobial resistance (AMR) and virulence potential. Furthermore, we validated genotypic differences by phenotypic characteristics analysis. Comparative and subtractive genomics analysis revealed that K07-204 contains methicillin (mecA), ampicillin (blaZ), erythromycin (ermC), aminoglycoside (aadD), and tetracycline (tet38, tetracycline efflux pump) resistance genes while K07-561 has ampicillin (blaZ) and tetracycline (tet38) resistance genes. In addition to antibiotics, K07-204 was reported to show resistance to lysostaphin treatment. K07-204 also has additional virulence genes (adsA, aur, hysA, icaABCDR, lip, lukD, sdrC, and sdrE) compared to K07-561, which may explain the differential virulence potential of these human isolates of ST72. Unexpectedly, the virulence potential of K07-561 was higher in an in vivo wax-worm infection model than that of K07-204, putatively due to the presence of a 20-fold higher staphyloxanthin concentration than K07-204. Comprehensive genomic analysis of these two human isolates, with 27 ST72 isolates, and S. aureus USA300 (ST8) suggested that acquisition of both virulence and antibiotics resistance genes by ST72 isolates might have facilitated their adaptation from a community to a hospital setting where the selective pressure imposed by antibiotics selects for more resistant and virulent isolates. Taken together, the results of the current study provide insight into the genotypic and phenotypic features of various ST72 clones across the globe, delivering more options for developing therapeutics and rapid molecular diagnostic tools to detect resistant bacteria.

Bacteria and Host Interplay in Staphylococcus aureus Septic Arthritis and Sepsis

Staphylococcus aureus (S. aureus) infections are a major healthcare challenge and new treatment alternatives are needed. S. aureus septic arthritis, a debilitating joint disease, causes permanent joint dysfunction in almost 50% of the patients. S. aureus bacteremia is associated with higher mortalities than bacteremia caused by most other microbes and can develop to severe sepsis and death. The key to new therapies is understanding the interplay between bacterial virulence factors and host immune response, which decides the disease outcome. S. aureus produces numerous virulence factors that facilitate bacterial dissemination, invasion into joint cavity, and cause septic arthritis. Monocytes, activated by several components of S. aureus such as lipoproteins, are responsible for bone destructions. In S. aureus sepsis, cytokine storm induced by S. aureus components leads to the hyperinflammatory status, DIC, multiple organ failure, and later death. The immune suppressive therapies at the very early time point might be protective. However, the timing of treatment is crucial, as late treatment may aggravate the immune paralysis and lead to uncontrolled infection and death.

On-Demand Antimicrobial Agent Release from Functionalized Conjugated Oligomer-Hyaluronic Acid Nanoparticles for Tackling Antimicrobial Resistance

Controllable drug release is promising for fighting against antimicrobial resistance, which is a critical threat to human health worldwide. Herein, new hyaluronidase-responsive conjugated oligo(thiophene ethynylene) (OTE)-covalently modified hyaluronic acid (OTE-HA) nanoparticles for on-demand release of antimicrobial agents are reported. The synthesis of amphiphilic OTE-HA was carried out by esterification reaction. The resulting macromolecules were self-assembled in water to form nanoparticles, in which the hydrophobic OTE section, as bactericides, formed "cores" and the hydrophilic hyaluronic acid (HA) formed "shells". The OTE-HA nanoparticles avoid bactericide premature leakage and effectively block the dark cytotoxicity of the OTE section, possessing excellent biocompatibility. Using methicillin-resistant Staphylococcus aureus (MRSA) as an example, hyaluronidase, largely secreted by MRSA, can in situ trigger the release of OTE via hydrolyzing OTE-HA nanoparticles into fragments, even disaccharides linked with OTE. Importantly, the OTE section could effectively break cell membranes, leading to bacterial death. The half-maximal inhibitory concentration of the nanoparticles against MRSA is 3.3 μg/mL. The great antibacterial activity of OTE-HA nanoparticles against Gram-positive bacteria Streptococcus pneumoniae further confirms the controllable bactericide delivery mechanism. OTE-HA nanoparticles coated on a surface can also effectively inhibit the growth of bacteria, which holds a remarkable promise in biomedical applications. Therefore, this work provides a favorable strategy of on-demand and in situ drug release for sterilization and defeating antimicrobial resistance.

Hyaluronan Degradation by Cemip Regulates Host Defense against Staphylococcus aureus Skin Infection

Staphylococcus aureus is a major human bacterial pathogen responsible for deep tissue skin infections. Recent observations have suggested that rapid, localized digestion of hyaluronic acid in the extracellular matrix (ECM) of the dermis may influence bacterial invasion and tissue inflammation. In this study we find that cell migration-inducing protein (Cemip) is the major inducible gene responsible for hyaluronan catabolism in mice. Cemip^−/− mice failed to digest hyaluronan and had significantly less evidence of infection after intradermal bacterial challenge by S. aureus. Stabilization of large-molecular-weight hyaluronan enabled increased expression of cathelicidin antimicrobial peptide (Camp) that was due in part to enhanced differentiation of preadipocytes to adipocytes, as seen histologically and by increased expression of Pref1, PPARg, and Adipoq. Cemip^−/− mice challenged with S. aureus also had greater IL-6 expression and neutrophil infiltration. These observations describe a mechanism for hyaluronan in the dermal ECM to regulate tissue inflammation and host antimicrobial defense.

In this paper, Dokoshi et al. describe how the mammalian hyaluronidase Cemip is induced in the dermis during S. aureus infection. Cemip digests hyaluronan in the skin to regulate reactive adipogenesis and subsequent antimicrobial activity and skin inflammation.

Layer-by-Layer Biomaterials for Drug Delivery

Controlled drug delivery formulations have revolutionized treatments for a range of health conditions. Over decades of innovation, layer-by-layer (LbL) self-assembly has emerged as one of the most versatile fabrication methods used to develop multifunctional controlled drug release coatings. The numerous advantages of LbL include its ability to incorporate and preserve biological activity of therapeutic agents; coat multiple substrates of all scales (e.g., nanoparticles to implants); and exhibit tuned, targeted, and/or responsive drug release behavior. The functional behavior of LbL films can be related to their physicochemical properties. In this review, we highlight recent advances in the development of LbL-engineered biomaterials for drug delivery, demonstrating their potential in the fields of cancer therapy, microbial infection prevention and treatment, and directing cellular responses. We discuss the various advantages of LbL biomaterial design for a given application as demonstrated through in vitro and in vivo studies.

Processing, Export, and Identification of Novel Linear Peptides from Staphylococcus aureus

Staphylococcus aureus can colonize the human host and cause a variety of superficial and invasive infections. The success of S. aureus as a pathogen derives from its ability to modulate its virulence through the release, sensing of and response to cyclic signaling peptides. Here we provide, for the first time, evidence that S. aureus processes and secretes small linear peptides through a specialized pathway that converts a lipoprotein leader into an extracellular peptide signal. We have identified and confirmed the machinery for each step and demonstrate that the putative membrane metalloprotease Eep and the EcsAB transporter are required to complete the processing and secretion of the peptides. In addition, we have identified several linear peptides, including the interspecies signaling molecule staph-cAM373, that are dependent on this processing and secretion pathway. These findings are particularly important because multiple Gram-positive bacteria rely on small linear peptides to control bacterial gene expression and virulence.IMPORTANCE Here, we provide evidence indicating that S. aureus secretes small linear peptides into the environment via a novel processing and secretion pathway. The discovery of a specialized pathway for the production of small linear peptides and the identification of these peptides leads to several important questions regarding their role in S. aureus biology, most interestingly, their potential to act as signaling molecules. The observations in this study provide a foundation for further in-depth studies into the biological activity of small linear peptides in S. aureus.

The Staphylococcus aureus ArlRS two-component system regulates virulence factor expression through MgrA

The Gram-positive bacterium, Staphylococcus aureus, is a versatile pathogen that can sense and adapt to a wide variety of environments within the human host, in part through its 16 two-component regulatory systems. The ArlRS two-component system has been shown to affect many cellular processes in S. aureus, including autolysis, biofilm formation, capsule synthesis and virulence. Yet the molecular details of this regulation remained largely unknown. We used RNA sequencing to identify the ArlRS regulon, and found 70% overlap with that of the global regulator MgrA. These genes included cell wall-anchored adhesins (ebh, sdrD), polysaccharide and capsule synthesis genes, cell wall remodeling genes (lytN, ddh), the urease operon, genes involved in metal transport (feoA, mntH, sirA), anaerobic metabolism genes (adhE, pflA, nrdDG) and a large number of virulence factors (lukSF, lukAB, nuc, gehB, norB, chs, scn and esxA). We show that ArlR directly activates expression of mgrA and identify a probable ArlR-binding site (TTTTCTCAT-N4 -TTTTAATAA). A highly similar sequence is also found in the spx P2 promoter, which was recently shown to be regulated by ArlRS. We also demonstrate that ArlS has kinase activity toward ArlR in vitro, although it has slower kinetics than other similar histidine kinases.

Analysis of the CodY RNome reveals RsaD as a stress-responsive riboregulator of overflow metabolism in Staphylococcus aureus

In Staphylococcus aureus, the transcription factor CodY modulates the expression of hundreds of genes, including most virulence factors, in response to the availability of key nutrients like GTP and branched-chain amino acids. Despite numerous studies examining how CodY controls gene expression directly or indirectly, virtually nothing is known about the extent to which CodY exerts its effect through small regulatory RNAs (sRNAs). Herein, we report the first set of sRNAs under the control of CodY. We reveal that staphylococcal sRNA RsaD is overexpressed >20-fold in a CodY-deficient strain in three S. aureus clinical isolates and in S. epidermidis. We validated the CodY-dependent regulation of rsaD and demonstrated that CodY directly represses rsaD expression by binding the promoter. Using a combination of molecular techniques, we show that RsaD posttranscriptionally regulates alsS (acetolactate synthase) mRNA and enzyme levels. We further show that RsaD redirects carbon overflow metabolism, contributing to stationary phase cell death during exposure to weak acid stress. Taken together, our data delineate a role for CodY in controlling sRNA expression in a major human pathogen and indicate that RsaD may integrate nutrient depletion and other signals to mount a response to physiological stress experienced by S. aureus in diverse environments.

The Staphylococcus aureus Transcriptome during Cystic Fibrosis Lung Infection

Laboratory models have been invaluable for the field of microbiology for over 100 years and have provided key insights into core aspects of bacterial physiology such as regulation and metabolism. However, it is important to identify the extent to which these models recapitulate bacterial physiology within a human infection environment. Here, we performed transcriptomics (RNA-seq), focusing on the physiology of the prominent pathogen Staphylococcus aureusin situ in human cystic fibrosis (CF) infection. Through principal-component and hierarchal clustering analyses, we found remarkable conservation in S. aureus gene expression in the CF lung despite differences in the patient clinic, clinical status, age, and therapeutic regimen. We used a machine learning approach to identify an S. aureus transcriptomic signature of 32 genes that can reliably distinguish between S. aureus transcriptomes in the CF lung and in vitro The majority of these genes were involved in virulence and metabolism and were used to improve a common CF infection model. Collectively, these results advance our knowledge of S. aureus physiology during human CF lung infection and demonstrate how in vitro models can be improved to better capture bacterial physiology in infection.IMPORTANCE Although bacteria have been studied in infection for over 100 years, the majority of these studies have utilized laboratory and animal models that often have unknown relevance to the human infections they are meant to represent. A primary challenge has been to assess bacterial physiology in the human host. To address this challenge, we performed transcriptomics of S. aureus during human cystic fibrosis (CF) lung infection. Using a machine learning framework, we defined a "human CF lung transcriptome signature" that primarily included genes involved in metabolism and virulence. In addition, we were able to apply our findings to improve an in vitro model of CF infection. Understanding bacterial gene expression within human infection is a critical step toward the development of improved laboratory models and new therapeutics.

Characterization and Comparative Analysis of the Staphylococcus aureus Genomic Island vSaβ: an In Silico Approach

Staphylococcus aureus is a widespread opportunistic pathogen to humans and animals. Of its genome, 20 to 25% varies between strains and consists of phages, pathogenicity islands, transposons, and genomic islands. S. aureus harbors up to three genomic islands, vSaα, vSaβ, and vSaγ. The vSaβ region of S. aureus can encode a number of virulence-associated factors, such as serine proteases, leukocidins, enterotoxins, bacteriocins, or a hyaluronate lyase. In this study, the vSaβ regions of 103 clinically relevant S. aureus strains were characterized in silico and compared to the three predefined vSaβ types. We here suggest a superordinate system of 15 different vSaβ types, of which 12 were newly defined. Each vSaβ type has a distinct structure with a distinct set of genes, which are both highly conserved. Between the different types, gene content and composition vary substantially. Based on our data, a strain's vSaβ type is strongly coupled with its clonal complex, suggesting that vSaβ was acquired in an ancestral S. aureus strain, arguably by phage mediation, before differentiation into clonal complexes. In addition, we addressed the issue of ambiguous nomenclature in the serine protease gene cluster and propose a novel, phylogeny-based nomenclature of the cluster contained in the vSaβ region.IMPORTANCE With the rapid increase of available sequencing data on clinically relevant bacterial species such as S. aureus, the genomic basis of clinical phenotypes can be investigated in much more detail, allowing a much deeper understanding of the mechanisms involved in disease. We characterized in detail the S. aureus genomic island vSaβ and defined a superordinate system to categorize S. aureus strains based on their vSaβ type, providing information about the strains' virulence-associated genes and clinical potential.

Streptococcal phosphotransferase system imports unsaturated hyaluronan disaccharide derived from host extracellular matrices

Certain bacterial species target the polysaccharide glycosaminoglycans (GAGs) of animal extracellular matrices for colonization and/or infection. GAGs such as hyaluronan and chondroitin sulfate consist of repeating disaccharide units of uronate and amino sugar residues, and are depolymerized to unsaturated disaccharides by bacterial extracellular or cell-surface polysaccharide lyase. The disaccharides are degraded and metabolized by cytoplasmic enzymes such as unsaturated glucuronyl hydrolase, isomerase, and reductase. The genes encoding these enzymes are assembled to form a GAG genetic cluster. Here, we demonstrate the Streptococcus agalactiae phosphotransferase system (PTS) for import of unsaturated hyaluronan disaccharide. S. agalactiae NEM316 was found to depolymerize and assimilate hyaluronan, whereas its mutant with a disruption in the PTS genes included in the GAG cluster was unable to grow on hyaluronan, while retaining the ability to depolymerize hyaluronan. Using toluene-treated wild-type cells, the PTS activity for import of unsaturated hyaluronan disaccharide was significantly higher than that observed in the absence of the substrate. In contrast, the PTS mutant was unable to import unsaturated hyaluronan disaccharide, indicating that the corresponding PTS is the only importer of fragmented hyaluronan, which is suitable for PTS to phosphorylate the substrate at the C-6 position. This is distinct from Streptobacillus moniliformis ATP-binding cassette transporter for import of sulfated and non-sulfated fragmented GAGs without substrate modification. The three-dimensional structure of streptococcal EIIA, one of the PTS components, was found to contain a Rossman-fold motif by X-ray crystallization. Docking of EIIA with another component EIIB by modeling provided structural insights into the phosphate transfer mechanism. This study is the first to identify the substrate (unsaturated hyaluronan disaccharide) recognized and imported by the streptococcal PTS. The PTS and ABC transporter for import of GAGs shed light on bacterial clever colonization/infection system targeting various animal polysaccharides.

A Yersinia ruckeri TIR Domain-Containing Protein (STIR-2) Mediates Immune Evasion by Targeting the MyD88 Adaptor

TIR domain-containing proteins are essential for bacterial pathogens to subvert host defenses. This study describes a fish pathogen, Yersinia ruckeri SC09 strain, with a novel TIR domain-containing protein (STIR-2) that affects Toll-like receptor (TLR) function. STIR-2 was identified in Y. ruckeri by bioinformatics analysis. The toxic effects of this gene on fish were determined by in vivo challenge experiments in knockout mutants and complement mutants of the stir-2 gene. In vitro, STIR-2 downregulated the expression and secretion of IL-6, IL-1β, and TNF-α. Furthermore, the results of NF-κB-dependent luciferase reporter system, co-immunoprecipitation, GST pull-down assays, and yeast two-hybrid assay indicated that STIR-2 inhibited the TLR signaling pathway by interacting with myeloid differentiation factor 88 (MyD88). In addition, STIR-2 promoted the intracellular survival of pathogenic Yersinia ruckeri SC09 strain by binding to the TIR adaptor protein MyD88 and inhibiting the pre-inflammatory signal of immune cells. These results showed that STIR-2 increased virulence in Y. ruckeri and suppressed the innate immune response by inhibiting TLR and MyD88-mediated signaling, serving as a novel strategy for innate immune evasion.

Role of staphylococci in mastitis in sheep

Staphylococci have been isolated from various sites of the body of healthy sheep, as well as from many infections of those animals, the main one being mastitis. The objective of this review is to appraise the importance and significance of staphylococci in causing mastitis in ewes. The review includes a brief classification and taxonomy of staphylococci and describes the procedures for their isolation and identification, as well as their virulence determinants and the mechanisms of resistance to antibacterial agents. Various staphylococcal species have been implicated in staphylococcal mastitis and the characteristics of isolates are discussed with regards to potential virulence factors. Staphylococcal mastitis is explicitly described, with reference to sources of infection, the course of the disease and the relevant control measures. Finally, the potential significance of staphylococci present in ewes' milk for public health is discussed briefly.

Electrical Evaluation of Bacterial Virulence Factors Using Nanopores

In this work, we propose a novel methodology for electrical monitoring using nanoporous alumina membranes of virulence factors secreted by bacterial pathogens. Bacterial hyaluronidase (HYAL), which is produced by a number of invasive Gram-positive bacteria, is selected as a model compound to prove the concept. Our electrochemical setup takes advantage of the flat surface of indium tin oxide/poly(ethylene terephthalate) (ITO/PET) electrodes for their assembly with the nanoporous membrane. The proposed analytical method, based on the electrical monitoring of the steric/electrostatic nanochannels blocked upon formation of an antibody-HYAL immunocomplex, reached detection limits as low as 64 UI/mL (17.3 U/mg) HYAL. The inert surface of the ITO/PET electrodes together with the anti-biofilm properties of the 20 nm pore-sized alumina membranes allows for culturing the bacteria, capturing the secreted enzymes inside the nanochannels, and removing the cells before the electrochemical measurement. Secreted HYAL at levels of 1000 UI/mL (270 U/mg) are estimated in Gram-positive Staphylococcus aureus cultures, whereas low levels are detected for Gram-negative Pseudomonas aeruginosa (used as a negative control). Finally, HYAL secretion inhibition by RNAIII-inhibiting peptide (YSPWTNF-NH₂) is also monitored, opening the way for further applications of the developed monitoring system for evaluation of the antivirulence potential of different compounds. This label-free method is rapid and cheap, avoiding the use of the time-consuming sandwich assays. We envisage future applications for monitoring of bacterial virulence/invasion as well as for testing of novel antimicrobial/antivirulence agents.

Staphylococcus saccharolyticus Isolated From Blood Cultures and Prosthetic Joint Infections Exhibits Excessive Genome Decay

The slow-growing, anaerobic, coagulase-negative species Staphylococcus saccharolyticus is found on human skin and in clinical specimens but its pathogenic potential is unclear. Here, we investigated clinical isolates and sequenced the genomes of seven strains of S. saccharolyticus. Phylogenomic analyses showed that the closest relative of S. saccharolyticus is Staphylococcus capitis with an average nucleotide identity of 80%. Previously sequenced strains assigned to S. saccharolyticus are misclassified and belong to S. capitis. Based on single nucleotide polymorphisms of the core genome, the population of S. saccharolyticus can be divided into two clades that also differ in a few larger genomic islands as part of the flexible genome. An unexpected feature of S. saccharolyticus is extensive genome decay, with over 300 pseudogenes, indicating ongoing reductive evolution. Many genes of the core metabolism are not functional, rendering the species auxotrophic for several amino acids, which could explain its slow growth and need for fastidious growth conditions. Secreted proteins of S. saccharolyticus were determined; they include stress response proteins such as heat and oxidative stress-related factors, as well as immunodominant staphylococcal surface antigens and enzymes that can degrade host tissue components. The strains secrete lipases and a hyaluronic acid lyase. Hyaluronidase as well as urease activities were detected in biochemical assays, with clade-specific differences. Our study revealed that S. saccharolyticus has adapted its genome, possibly due to a recent change of habitat; moreover, the data imply that the species has tissue-invasive potential and might cause prosthetic joint infections.

Staphylococcus aureus Secreted Toxins and Extracellular Enzymes

Staphylococcus aureus is a formidable pathogen capable of causing infections in different sites of the body in a variety of vertebrate animals, including humans and livestock. A major contribution to the success of S. aureus as a pathogen is the plethora of virulence factors that manipulate the host's innate and adaptive immune responses. Many of these immune modulating virulence factors are secreted toxins, cofactors for activating host zymogens, and exoenzymes. Secreted toxins such as pore-forming toxins and superantigens are highly inflammatory and can cause leukocyte cell death by cytolysis and clonal deletion, respectively. Coagulases and staphylokinases are cofactors that hijack the host's coagulation system. Exoenzymes, including nucleases and proteases, cleave and inactivate various immune defense and surveillance molecules, such as complement factors, antimicrobial peptides, and surface receptors that are important for leukocyte chemotaxis. Additionally, some of these secreted toxins and exoenzymes can cause disruption of endothelial and epithelial barriers through cell lysis and cleavage of junction proteins. A unique feature when examining the repertoire of S. aureus secreted virulence factors is the apparent functional redundancy exhibited by the majority of the toxins and exoenzymes. However, closer examination of each virulence factor revealed that each has unique properties that have important functional consequences. This chapter provides a brief overview of our current understanding of the major secreted virulence factors critical for S. aureus pathogenesis.