Wall teichoic acids are dispensable for anchoring the PNAG exopolysaccharide to the Staphylococcus aureus cell surface

Magnesium Infusion on Dental Implants and Its Impact on Osseointegration and Biofilm Development: A Review

Dental implants have gained global popularity as a treatment option for tooth loss. The success of dental implants depends on their optimal integration into the tissues of the alveolar bone and the periodontium. However, several factors can hinder the proper osseointegration of implants, with the growth of biofilm on the implant surface and subsequent peri-implant infections being significant concerns. To overcome this challenge, researchers have explored the incorporation of antimicrobial agents onto metallic implant surfaces to mitigate biofilm growth. Ideally these agents should promote osteogenesis while exhibiting antibacterial effects. Magnesium (Mg) has emerged as a promising dual-function implant coating due to its osteogenic and antibacterial properties. Despite several studies, the precise mechanisms behind osteoinductive and antimicrobial effect of Mg is unclear, as yet. This review aims to collate and discuss the utility of Mg as a dental implant coating, its impact on the osteogenic process, potential in mitigating microbial growth, and prospects for the future. A comprehensive literature search was conducted across several databases and the findings reveal the promise of Mg as a dual-function dental implant coating material, both as a standalone agent and in combination with other materials. The antibacterial effect of Mg is likely to be due to its (1) toxicity particularly at high concentrations, (2) the production or reactive oxygen species, and (3) pH modulation, while the osteoinductive effect is due to a complex series of cellular and biochemical pathways. Despite its potential both as a standalone and composite coating, challenges such as degradation rate, leaching, and long-term stability must be addressed. Further research is needed to understand the utility of Mg as an implant coating material, particularly in relation to its antibacterial activity, osseointegration, and longevity in the oral milieu.

Design, synthesis and optimization of TarO inhibitors as multifunctional antibiotics against Methicillin-resistant Staphylococcus aureus

UDP-N-acetylglucosamine-undecaprenyl-phosphate N-acetylglucosaminephosphotransferase (TarO) has been found to simultaneously contribute to β-lactam resistance and virulence of Methicillin-resistant Staphylococcus aureus (MRSA). However, optimization of hit compounds targeting TarO has been hindered due to their high lipophilicity and the poor correlation between the enzyme activity inhibition and β-lactam sensitization. In this study, 31 analogues of Tarocin A were designed, synthesized and evaluated by a luminescence-based reporter preliminary screening. In the subsequent β-lactams synergy test, a good correlation was observed between the results obtained from these two methods. Finally, analog 18a with more potential against TarO and an improved hydrophilicity (clogP = 3.2) was obtained. Compared with Tarocin A, 18a shows stronger β-lactam sensitizing and anti-biofilm activities in vitro, as well as potent anti-virulence and synergistic potency with imipenem in vivo. These results suggest that TarO is a promising target for combating MRSA, and 18a can serve as a lead molecule.

Cryo-EM analyses unveil details of mechanism and targocil-II mediated inhibition of S. aureus WTA transporter TarGH

Wall teichoic acid (WTA) is a polyol phosphate polymer that covalently decorates peptidoglycan of gram-positive bacteria, including Staphylococcus aureus. Central to WTA biosynthesis is flipping of lipid-linked precursors across the cell membrane by TarGH, a type V ABC transporter. Here, we present cryo-EM structures of S. aureus TarGH in the presence of targocil-II, a promising small-molecule lead with β-lactam antibiotic synergistic action. Targocil-II binds to the extracellular dimerisation interface of TarG, we suggest mimicking flipped but not yet released substrate. In absence of targocil-II and in complex with ATP analogue ATPγS, determined at 2.3 Å resolution, the ATPase active site is allosterically inhibited. This is due to a so far undescribed D-loop conformation, potentially minimizing spurious ATP hydrolysis in the absence of substrate. Targocil-II binding comparatively causes local and remote conformational changes through to the TarH active site, with the D-loop now optimal for ATP hydrolysis. These structures suggest an ability to modulate ATP hydrolysis in a WTA substrate dependent manner and a jammed ATPase cycle as the basis of the observed inhibition by targocil-II. The molecular insights provide an unprecedented basis for development of TarGH targeted therapeutics for treatment of multidrug-resistant S. aureus and other gram-positive bacterial infections.

Mapping protein-exopolysaccharide binding interaction in Staphylococcus epidermidis biofilms by live cell proximity labeling

Bacterial biofilms consist of cells encased in an extracellular polymeric substance (EPS) composed of exopolysaccharides, extracellular DNA, and proteins that are critical for cell-cell adhesion and protect the cells from environmental stress, antibiotic treatments, and the host immune response. Degrading EPS components or blocking their production have emerged as promising strategies for prevention or dispersal of bacterial biofilms, but we still have little information about the specific biomolecular interactions that occur between cells and EPS components and how those interactions contribute to biofilm production. Staphylococcus epidermidis is a leading cause of nosocomial infections as a result of producing biofilms that use the exopolysaccharide poly-(1→6)-β-N-acetylglucosamine (PNAG) as a major structural component. In this study, we have developed a live cell proximity labeling approach combined with quantitative mass spectrometry-based proteomics to map the PNAG interactome of live S. epidermidis biofilms. Through these measurements we discovered elastin-binding protein (EbpS) as a major PNAG-interacting protein. Using live cell binding measurements, we found that the lysin motif (LysM) domain of EbpS specifically binds to PNAG present in S. epidermidis biofilms. Our work provides a novel method for the rapid identification of exopolysaccharide-binding proteins in live biofilms that will help to extend our understanding of the biomolecular interactions that are required for bacterial biofilm formation.

Impact of the pentose phosphate pathway on metabolism and pathogenesis of Staphylococcus aureus

Staphylococcus aureus is an important pathogen that leads to significant disease through multiple routes of infection. We recently published a transposon sequencing (Tn-seq) screen in a mouse acute pneumonia model and identified a hypothetical gene (SAUSA300_1902, pgl) with similarity to a lactonase of Escherichia coli involved in the pentose phosphate pathway (PPP) that was conditionally essential. Limited studies have investigated the role of the PPP in physiology and pathogenesis of S. aureus. We show here that mutation of pgl significantly impacts ATP levels and respiration. RNA-seq analysis of the pgl mutant and parent strains identified compensatory changes in gene expression for glucose and gluconate as well as reductions in the pyrimidine biosynthesis locus. These differences were also evident through unbiased metabolomics studies and 13C labeling experiments that showed mutation of pgl led to reductions in pyrimidine metabolism including decreases in ribose-5P, UMP and GMP. These nucleotide reductions impacted the amount of extracellular DNA in biofilms and reduced biofilm formation. Mutation also limited the capacity of the strain to resist oxidant damage induced by hydrogen peroxide and paraquat and subsequent intracellular survival inside macrophages. Changes in wall teichoic acid impacted susceptibility to hydrogen peroxide. We demonstrated the importance of these changes on virulence in three different models of infection, covering respiratory, skin and septicemia, demonstrating the need for proper PPP function in all models. This work demonstrates the multifaceted role metabolism can play in multiple aspects of S. aureus pathogenesis.

A genetic regulatory see-saw of biofilm and virulence in MRSA pathogenesis

Staphylococcus aureus is one of the most common opportunistic human pathogens causing several infectious diseases. Ever since the emergence of the first methicillin-resistant Staphylococcus aureus (MRSA) strain decades back, the organism has been a major cause of hospital-acquired infections (HA-MRSA). The spread of this pathogen across the community led to the emergence of a more virulent subtype of the strain, i.e., Community acquired Methicillin resistant Staphylococcus aureus (CA-MRSA). Hence, WHO has declared Staphylococcus aureus as a high-priority pathogen. MRSA pathogenesis is remarkable because of the ability of this "superbug" to form robust biofilm both in vivo and in vitro by the formation of polysaccharide intercellular adhesin (PIA), extracellular DNA (eDNA), wall teichoic acids (WTAs), and capsule (CP), which are major components that impart stability to a biofilm. On the other hand, secretion of a diverse array of virulence factors such as hemolysins, leukotoxins, enterotoxins, and Protein A regulated by agr and sae two-component systems (TCS) aids in combating host immune response. The up- and downregulation of adhesion genes involved in biofilm formation and genes responsible for synthesizing virulence factors during different stages of infection act as a genetic regulatory see-saw in the pathogenesis of MRSA. This review provides insight into the evolution and pathogenesis of MRSA infections with a focus on genetic regulation of biofilm formation and virulence factors secretion.

Combining bacteriophage and vancomycin is efficacious against MRSA biofilm-like aggregates formed in synovial fluid

Background

Biofilm formation is a major clinical challenge contributing to treatment failure of periprosthetic joint infection (PJI). Lytic bacteriophages (phages) can target biofilm associated bacteria at localized sites of infection. The aim of this study is to investigate whether combination therapy of phage and vancomycin is capable of clearing Staphylococcus aureus biofilm-like aggregates formed in human synovial fluid.

Methods

In this study, S. aureus BP043, a PJI clinical isolate was utilized. This strain is a methicillin-resistant S. aureus (MRSA) biofilm-former. Phage Remus, known to infect S. aureus, was selected for the treatment protocol. BP043 was grown as aggregates in human synovial fluid. The characterization of S. aureus aggregates was assessed for structure and size using scanning electron microscopy (SEM) and flow cytometry, respectively. Moreover, the formed aggregates were subsequently treated in vitro with: (a) phage Remus [∼10⁸ plaque-forming units (PFU)/ml], (b) vancomycin (500 μg/ml), or (c) phage Remus (∼10⁸ PFU/ml) followed by vancomycin (500 μg/ml), for 48 h. Bacterial survival was quantified by enumeration [colony-forming units (CFU)/ml]. The efficacy of phage and vancomycin against BP043 aggregates was assessed in vivo as individual treatments and in combination. The in vivo model utilized Galleria mellonella larvae which were infected with BP043 aggregates pre-formed in synovial fluid.

Results

Scanning electron microscopy (SEM) images and flow cytometry data demonstrated the ability of human synovial fluid to promote formation of S. aureus aggregates. Treatment with Remus resulted in significant reduction in viable S. aureus residing within the synovial fluid aggregates compared to the aggregates that did not receive Remus (p < 0.0001). Remus was more efficient in eliminating viable bacteria within the aggregates compared to vancomycin (p < 0.0001). Combination treatment of Remus followed by vancomycin was more efficacious in reducing bacterial load compared to using either Remus or vancomycin alone (p = 0.0023, p < 0.0001, respectively). When tested in vivo, this combination treatment also resulted in the highest survival rate (37%) 96 h post-treatment, compared to untreated larvae (3%; p < 0.0001).

Conclusion

We demonstrate that combining phage Remus and vancomycin led to synergistic interaction against MRSA biofilm-like aggregates in vitro and in vivo.

Hitchhiking motility of Staphylococcus aureus involves the interaction between its wall teichoic acids and lipopolysaccharide of Pseudomonas aeruginosa

Staphylococcus aureus, which lacks pili and flagella, is nonmotile. However, it hitchhikes motile bacteria, such as Pseudomonas aeruginosa, to migrate in the environment. This study demonstrated that the hitchhiking motility of S. aureus SA113 was reduced after the tagO, which encodes an enzyme for wall teichoic acids (WTA) synthesis, was deleted. The hitchhiking motility was restored after the mutation was complemented by transforming a plasmid expressing TagO into the mutant. We also showed that adding purified lipopolysaccharide (LPS) to a culture that contains S. aureus SA113 and P. aeruginosa PAO1, reduced the movement of S. aureus, showing that WTA and LPS are involved in the hitchhiking motility of S. aureus. This study also found that P. aeruginosa promoted the movement of S. aureus in the digestive tract of Caenorhabditis elegans and in mice. In conclusion, this study reveals how S. aureus hitchhikes P. aeruginosa for translocation in an ecosystem. The results from this study improve our understanding on how a nonmotile pathogen moves in the environment and spreads in animals.

Horizontal transfer and evolution of wall teichoic acid gene cassettes in Bacillus subtilis

Background: Wall teichoic acid (WTA) genes are essential for production of cell walls in gram-positive bacteria and necessary for survival and variability in the cassette has led to recent antibiotic resistance acquisition in pathogenic bacteria. 

Methods: Using a pan-genome approach, we examined the evolutionary history of WTA genes in  Bacillus subtilis ssp.  subtilis. 

Results: Our analysis reveals an interesting pattern of evolution from the type-strain WTA gene cassette possibly resulting from horizontal acquisition from organisms with similar gene sequences. The WTA cassettes have a high level of variation which may be due to one or more independent horizontal transfer events during the evolution of  Bacillus subtilis ssp.  subtilis. This swapping of entire WTA cassettes and smaller regions within the WTA cassettes is an unusual feature in the evolution of the  Bacillus subtilis genome and highlights the importance of horizontal transfer of gene cassettes through homologous recombination within  B. subtilis or other bacterial species. 

Conclusions: Reduced sequence conservation of these WTA cassettes may indicate a modified function like the previously documented WTA ribitol/glycerol variation. An improved understanding of high-frequency recombination of gene cassettes has ramifications for synthetic biology and the use of  B. subtilis in industry.

Using Knock-Out Mutants to Investigate the Adhesion of Staphylococcus aureus to Abiotic Surfaces

The adhesion of Staphylococcus aureus to abiotic surfaces is crucial for establishing device-related infections. With a high number of single-cell force spectroscopy measurements with genetically modified S. aureus cells, this study provides insights into the adhesion process of the pathogen to abiotic surfaces of different wettability. Our results show that S. aureus utilizes different cell wall molecules and interaction mechanisms when binding to hydrophobic and hydrophilic surfaces. We found that covalently bound cell wall proteins strongly interact with hydrophobic substrates, while their contribution to the overall adhesion force is smaller on hydrophilic substrates. Teichoic acids promote adhesion to hydrophobic surfaces as well as to hydrophilic surfaces. This, however, is to a lesser extent. An interplay of electrostatic effects of charges and protein composition on bacterial surfaces is predominant on hydrophilic surfaces, while it is overshadowed on hydrophobic surfaces by the influence of the high number of binding proteins. Our results can help to design new models of bacterial adhesion and may be used to interpret the adhesion of other microorganisms with similar surface properties.

A Staphylococcus aureus clpX Mutant Used as a Unique Screening Tool to Identify Cell Wall Synthesis Inhibitors that Reverse β-Lactam Resistance in MRSA

Staphylococcus aureus is a leading cause of bacterial infections world-wide. Staphylococcal infections are preferentially treated with β-lactam antibiotics, however, methicillin-resistant S. aureus (MRSA) strains have acquired resistance to this superior class of antibiotics. We have developed a growth-based, high-throughput screening approach that directly identifies cell wall synthesis inhibitors capable of reversing β-lactam resistance in MRSA. The screen is based on the finding that S. aureus mutants lacking the ClpX chaperone grow very poorly at 30°C unless specific steps in teichoic acid synthesis or penicillin binding protein (PBP) activity are inhibited. This property allowed us to exploit the S. aureus clpX mutant as a unique screening tool to rapidly identify biologically active compounds that target cell wall synthesis. We tested a library of ∼50,000 small chemical compounds and searched for compounds that inhibited growth of the wild type while stimulating growth of the clpX mutant. Fifty-eight compounds met these screening criteria, and preliminary tests of 10 compounds identified seven compounds that reverse β-lactam resistance of MRSA as expected for inhibitors of teichoic acid synthesis. The hit compounds are therefore promising candidates for further development as novel combination agents to restore β-lactam efficacy against MRSA.

Influence of sugars on biofilm formation of Staphylococcus epidermidis

The problem of biofilm formation by clinical strains of opportunistic bacteria is one of the most significant for medicine, because in a state of biofilm bacteria become more resistant to environmental factors, including antibiotics, a situation that can cause failure of treatment. Among opportunistic pathogens staphylococci are of special interest. Knowledge about the peculiarities of biofilm formation of these strains, in particular the polysaccharide biosynthesis, can be used for creation of a strategy of prophylaxis of different lesions that bind with staphylococci. The effect of different concentrations of the most widespread sugars (glucose, sucrose, lactose, galactose) on the activity of biofilm formation by strains of Staphylococcus epidermidis was investigated. Strains of S. epidermidis (n = 7) were isolated from the reproductive tract of women with dysbiosis. The cultures were grown in universal synthetic media with concentration of one of the listed sugars (0.5–3.0%) during 72 h. Results were obtained colorimetrically. We studied the number of cells in biofilm and the index of biofilm formation. The largest number of cells in the biofilm was observed when the culture incubated in a medium with 2.0% of glucose (increase of 25.3 times compared to control). The amount of CFU in the control biofilm was 9.96 lg CFU/mL. The glucose concentration of 3.0% inhibited the biofilm formation: the number of cells in the biofilm was 569 times less compared to the control. The highest value of biofilm formation index was 7.2, which was 1.3 times higher than the control (5.4). In the presence of lactose and galactose in nutrient medium in concentrations from 1.0% a decrease in the number of cells and biofilm formation index were observed. The received data show that process of biofilm formation is significantly dependent on external sources of sugars, which can indicate the possibility of their use as antibiofilm drug compounds, which inhibit membrane transport of sugars in bacteria.

iTRAQ-based quantitative proteomic analysis of the antimicrobial mechanism of lactobionic acid against Staphylococcus aureus

Staphylococcus aureus is a common pathogenic microorganism that causes foodborne diseases. Lactobionic acid (LBA) is a natural polyhydroxy acid widely used in the food industry. To understand the antibacterial action of LBA against S. aureus better and identify 274 differentially expressed proteins upon LBA treatment, an isobaric tag was used for relative and absolute quantification-based quantitative proteomics. Combined with ultrastructural observations, results suggested that LBA inhibited S. aureus by disrupting cell wall and membrane integrity, regulating adenosine triphosphate binding cassette transporter expression, affecting cellular energy metabolism, attenuating S. aureus virulence and reducing infection, and decreasing the levels of proteins involved in stress and starvation responses. Quantitative real-time polymerase chain reaction analysis was used to validate the proteomic data. The results provide new insights into the inhibitory effects of LBA on S. aureus and suggest that LBA application may be a promising method to ensure food and pharmaceutical product safety.

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.

Environmentally Relevant Concentration of Bisphenol S Shows Slight Effects on SIHUMIx

Bisphenol S (BPS) is an industrial chemical used in the process of polymerization of polycarbonate plastics and epoxy resins and thus can be found in various plastic products and thermal papers. The microbiota disrupting effect of BPS on the community structure of the microbiome has already been reported, but little is known on how BPS affects bacterial activity and function. To analyze these effects, we cultivated the simplified human intestinal microbiota (SIHUMIx) in bioreactors at a concentration of 45 µM BPS. By determining biomass, growth of SIHUMIx was followed but no differences during BPS exposure were observed. To validate if the membrane composition was affected, fatty acid methyl esters (FAMEs) profiles were compared. Changes in the individual membrane fatty acid composition could not been described; however, the saturation level of the membranes slightly increased during BPS exposure. By applying targeted metabolomics to quantify short-chain fatty acids (SCFA), it was shown that the activity of SIHUMIx was unaffected. Metaproteomics revealed temporal effect on the community structure and function, showing that BPS has minor effects on the structure or functionality of SIHUMIx.

Microbial Biofilms: Human T-cell Leukemia Virus Type 1 First in Line for Viral Biofilm but Far Behind Bacterial Biofilms

Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus associated with adult T-cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). To date, it is the unique published example of a virus able to form a biofilm at the surface of infected cells. Deeply studied in bacteria, bacterial biofilms represent multicellular assemblies of bacteria in contact with a surface and shielded by the extracellular matrix (ECM). Microbial lifestyle in biofilms, either viral or bacterial, is opposed structurally and physiologically to an isolated lifestyle, in which viruses or bacteria freely float in their environment. HTLV-1 biofilm formation is believed to be promoted by viral proteins, mainly Tax, through remodeling of the ECM of the infected cells. HTLV-1 biofilm has been linked to cell-to-cell transmission of the virus. However, in comparison to bacterial biofilms, very little is known on kinetics of viral biofilm formation or dissemination, but also on its pathophysiological roles, such as escape from immune detection or therapeutic strategies, as well as promotion of leukemogenesis. The switch between production of cell-free isolated virions and cell-associated viral biofilm, although not fully apprehended yet, remains a key step to understand HTLV-1 infection and pathogenesis.

Force-Averaging DLVO Model Predictions of the Adhesion Strengths Quantified for Pathogenic Listeria monocytogenes EGDe Grown under Variable pH Stresses

The roles of the bacterial surface biopolymers of pathogenic Listeria monocytogenes EGDe grown under variable pH conditions in governing their adhesion to a model surface of silicon nitride were investigated using atomic force microscopy under water. Our results indicated that the adhesion forces were the highest for cells cultured in media adjusted to pH 7 followed by 1.39, 1.49, 1.57, and 2.18-fold reductions at pH 6, 8, 9, and 5, respectively. Adhesion energies followed the same trends with 1.35, 1.67, 2.20, and 2.79-fold reductions in energies at pH 6, 8, 9, and 5, respectively, compared to the energy measured at pH 7. Furthermore, the structural properties of the bacterial surface biopolymer brush represented by the biopolymer brush thickness (L_o) and the molecular density (Γ) were determined by fitting a steric model of repulsion to the approach force-distance data. The L_o values followed the same trends as adhesion forces and energies, with thickness being highest at pH 7 followed by 1.82, 2.99, 3.11, and 4.66-fold reductions at pH 6, 8, 9, and 5, respectively. Γ was the highest at pH 5 and was followed by 1.26, 1.27, 1.70, and 2.82-fold reductions at pH 8, 9, 6, and 7, respectively. Our results indicated that bacterial adhesion forces and energies increased linearly with the product of L_o and Γ representing the number of biopolymers per unit length of the bacterial surface. To predict the adhesion forces and energies measured, a force-averaging model of the soft-particle analysis of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was used. In addition to the standard parameters accounted for in the soft-particle analysis of the DLVO theory such as surface potential, hydrophobicity, and size, this averaging model incorporates in it structural bacterial parameters such as L_o and Γ as well as a surface coverage factor (ϕ) that represents the fraction of the bacterial surface covered by biopolymers. When the soft-particle analysis of DLVO was considered, repulsive hydrogen bond strengths were predicted at close distances of approach (<0.3 nm). In comparison, the force-averaging model predicted that attractive hydrogen bonds dominate the bacterial adhesion strengths quantified. The highest adhesion quantified for cells grown at pH 7 was related to longer and more spaced biopolymers, higher contents of cellular carbohydrates, and more hydrophilic biopolymers, each of which contributes to higher possibilities for hydrogen bonding formation. These results are significant in designing new strategies that aim at controlling bacterial adhesion to surfaces.

Surface Proteins of Staphylococcus epidermidis

Staphylococcus epidermidis is a ubiquitous commensal of human skin. The widespread use of indwelling medical devices in modern medicine provides an opportunity for it to cause infections. Disease causing isolates can come from many different genetic backgrounds. Multiply antibiotic resistant strains have spread globally. S. epidermidis has a smaller repertoire of cell wall anchored (CWA) surface proteins than Staphylococcus aureus. Nevertheless, these CWA proteins promote adhesion to components of the extracellular matrix including collagen, fibrinogen, and fibronectin and contribute to the formation of biofilm. The A domain of the accumulation associated protein Aap can promote adhesion to unconditioned biomaterial but must be removed proteolytically to allow accumulation to proceed by homophilic Zn²⁺-dependent interactions. Mature biofilm contains amyloid structures formed by Aap and the small basic protein (Sbp). The latter contributes to the integrity of both protein and polysaccharide biofilm matrices. Several other CWA proteins can also promote S. epidermidis biofilm formation.

The role of magnesium in biomaterials related infections

Magnesium is currently increasing interest in the field of biomaterials. An extensive bibliography on this material in the last two decades arises from its potential for the development of biodegradable implants. In addition, many researches, motivated by this progress, have analyzed the performance of magnesium in both in vitro and in vivo assays with gram-positive and gram-negative bacteria in a very broad range of conditions. This review explores the extensive literature in recent years on magnesium in biomaterials-related infections, and discusses the mechanisms of the Mg action on bacteria, as well as the competition of Mg²⁺ and/or synergy with other divalent cations in this subject.

Genetic and Biochemical Analysis of CodY-Mediated Cell Aggregation in Staphylococcus aureus Reveals an Interaction between Extracellular DNA and Polysaccharide in the Extracellular Matrix

The global regulator CodY links nutrient availability to the regulation of virulence factor gene expression in Staphylococcus aureus, including many genes whose products affect biofilm formation. Antithetical phenotypes of both biofilm deficiency and accumulation have been reported for codY-null mutants; thus, the role of CodY in biofilm development remains unclear. codY mutant cells of a strain producing a robust biofilm elaborate proaggregation surface-associated features not present on codY mutant cells that do not produce a robust biofilm. Biochemical analysis of the clinical isolate SA564, which aggregates when deficient for CodY, revealed that these features are sensitive to nuclease treatment and are resistant to protease exposure. Genetic analyses revealed that disrupting lgt (the diacylglycerol transferase gene) in codY mutant cells severely weakened aggregation, indicating a role for lipoproteins in the attachment of the biofilm matrix to the cell surface. An additional and critical role of IcaB in producing functional poly-N-acetylglucosamine (PIA) polysaccharide in extracellular DNA (eDNA)-dependent biofilm formation was shown. Moreover, overproducing PIA is sufficient to promote aggregation in a DNA-dependent manner regardless of source of nucleic acids. Taken together, our results point to PIA synthesis as the primary determinant of biofilm formation when CodY activity is reduced and suggest a modified electrostatic net model for matrix attachment whereby PIA associates with eDNA, which interacts with the cell surface via covalently attached membrane lipoproteins. This work counters the prevailing view that polysaccharide- and eDNA/protein-based biofilms are mutually exclusive. Rather, we demonstrate that eDNA and PIA can work synergistically to form a biofilm.IMPORTANCEStaphylococcus aureus remains a global health concern and exemplifies the ability of an opportunistic pathogen to adapt and persist within multiple environments, including host tissue. Not only does biofilm contribute to persistence and immune evasion in the host environment, it also may aid in the transition to invasive disease. Thus, understanding how biofilms form is critical for developing strategies for dispersing biofilms and improving biofilm disease-related outcomes. Using biochemical, genetic, and cell biology approaches, we reveal a synergistic interaction between PIA and eDNA that promotes cell aggregation and biofilm formation in a CodY-dependent manner in S. aureus We also reveal that envelope-associated lipoproteins mediate attachment of the biofilm matrix to the cell surface.

Disruption of l-Rhamnose Biosynthesis Results in Severe Growth Defects in Streptococcus mutans

The rhamnose-glucose cell wall polysaccharide (RGP) of Streptococcus mutans plays a significant role in cell division, virulence, and stress protection. Prior studies examined function of the RGP using strains carrying deletions in the machinery involved in RGP assembly. In this study, we explored loss of the substrate for RGP, l-rhamnose, via deletion of rmlD (encoding the protein responsible for the terminal step in l-rhamnose biosynthesis). We demonstrate that loss of rhamnose biosynthesis causes a phenotype similar to strains with disrupted RGP assembly (ΔrgpG and ΔrgpF strains). Deletion of rmlD not only caused a severe growth defect under nonstress growth conditions but also elevated susceptibility of the strain to acid and oxidative stress, common conditions found in the oral cavity. A genetic complement of the ΔrmlD strain completely restored wild-type levels of growth, whereas addition of exogenous rhamnose did not. The loss of rhamnose production also significantly disrupted biofilm formation, an important aspect of S. mutans growth in the oral cavity. Further, we demonstrate that loss of either rmlD or rgpG results in ablation of rhamnose content in the S. mutans cell wall. Taken together, these results highlight the importance of rhamnose production in both the fitness and the ability of S. mutans to overcome environmental stresses.IMPORTANCE Streptococcus mutans is a pathogenic bacterium that is the primary etiologic agent of dental caries, a disease that affects billions yearly. Rhamnose biosynthesis is conserved not only in streptococcal species but in other Gram-positive, as well as Gram-negative, organisms. This study highlights the importance of rhamnose biosynthesis in RGP production for protection of the organism against acid and oxidative stresses, the two major stressors that the organism encounters in the oral cavity. Loss of RGP also severely impacts biofilm formation, the first step in the onset of dental caries. The high conservation of the rhamnose synthesis enzymes, as well as their importance in S. mutans and other organisms, makes them favorable antibiotic targets for the treatment of disease.

The ClpX chaperone controls autolytic splitting of Staphylococcus aureus daughter cells, but is bypassed by β-lactam antibiotics or inhibitors of WTA biosynthesis

β-lactam antibiotics interfere with cross-linking of the bacterial cell wall, but the killing mechanism of this important class of antibiotics is not fully understood. Serendipitously we found that sub-lethal doses of β-lactams rescue growth and prevent spontaneous lysis of Staphylococcus aureus mutants lacking the widely conserved chaperone ClpX, and we reasoned that a better understanding of the clpX phenotypes could provide novel insights into the downstream effects of β-lactam binding to the PBP targets. Super-resolution imaging revealed that clpX cells display aberrant septum synthesis, and initiate daughter cell separation prior to septum completion at 30°C, but not at 37°C, demonstrating that ClpX becomes critical for coordinating the S. aureus cell cycle as the temperature decreases. FtsZ localization and dynamics were not affected in the absence of ClpX, suggesting that ClpX affects septum formation and autolytic activation downstream of Z-ring formation. Interestingly, oxacillin antagonized the septum progression defects of clpX cells and prevented lysis of prematurely splitting clpX cells. Strikingly, inhibitors of wall teichoic acid (WTA) biosynthesis that work synergistically with β-lactams to kill MRSA synthesis also rescued growth of the clpX mutant, as did genetic inactivation of the gene encoding the septal autolysin, Sle1. Taken together, our data support a model in which Sle1 causes premature splitting and lysis of clpX daughter cells unless Sle1-dependent lysis is antagonized by β-lactams or by inhibiting an early step in WTA biosynthesis. The finding that β-lactams and inhibitors of WTA biosynthesis specifically prevent lysis of a mutant with dysregulated autolytic activity lends support to the idea that PBPs and WTA biosynthesis play an important role in coordinating cell division with autolytic splitting of daughter cells, and that β-lactams do not kill S. aureus simply by weakening the cell wall.

The bacterium Staphylococcus aureus is a major cause of human disease, and the rapid spread of S. aureus strains that are resistant to almost all β-lactam antibiotics has made treatment increasingly difficult. β-lactams interfere with cross-linking of the bacterial cell wall but the killing mechanism of this important class of antibiotics is not fully understood. Here we provide novel insight into this topic by examining a defined S. aureus mutant that has the unusual property of growing markedly better in the presence of β-lactams. Without β-lactams this mutant dies spontaneously at a high frequency due to premature separation of daughter cells during cell division. Cell death of the mutant can, however, be prevented either by exposure to β-lactam antibiotics or by inhibiting synthesis of wall teichoic acid, a major component of the cell wall in Gram-positive bacteria with a conserved role in activation of autolytic splitting of daughter cells. The finding that β-lactam antibiotics can prevent lysis of a mutant with deregulated activity of autolytic enzymes involved in daughter cell splitting, emphasizes the idea that β-lactams interfere with the coordination between cell division and daughter cell splitting, and do not kill S. aureus simply by weakening the cell wall.

Redundant and Distinct Roles of Secreted Protein Eap and Cell Wall-Anchored Protein SasG in Biofilm Formation and Pathogenicity of Staphylococcus aureus

Chronic and fatal infections caused by Staphylococcus aureus are sometimes associated with biofilm formation. Secreted proteins and cell wall-anchored proteins (CWAPs) are important for the development of polysaccharide-independent biofilms, but functional relationships between these proteins are unclear. In the present study, we report the roles of the extracellular adherence protein Eap and the surface CWAP SasG in S. aureus MR23, a clinical methicillin-resistant isolate that forms a robust protein-dependent biofilm and accumulates a large amount of Eap in the extracellular matrix. Double deletion of eap and sasG, but not single eap or sasG deletion, reduced the biomass of the formed biofilm. Mutational analysis demonstrated that cell wall anchorage is essential for the role of SasG in biofilm formation. Confocal laser scanning microscopy revealed that MR23 formed a rugged and thick biofilm; deletion of both eap and sasG reduced biofilm ruggedness and thickness. Although sasG deletion did not affect either of these features, eap deletion reduced the ruggedness but not the thickness of the biofilm. This indicated that Eap contributes to the rough irregular surface structure of the MR23 biofilm and that both Eap and SasG play roles in biofilm thickness. The level of pathogenicity of the Δeap ΔsasG strain in a silkworm larval infection model was significantly lower (P < 0.05) than those of the wild type and single-deletion mutants. Collectively, these findings highlight the redundant and distinct roles of a secreted protein and a CWAP in biofilm formation and pathogenicity of S. aureus and may inform new strategies to control staphylococcal biofilm infections.

Redundant and Distinct Roles of Secreted Protein Eap and Cell Wall-Anchored Protein SasG in Biofilm Formation and Pathogenicity of Staphylococcus aureus

Chronic and fatal infections caused by Staphylococcus aureus are sometimes associated with biofilm formation. Secreted proteins and cell wall-anchored proteins (CWAPs) are important for the development of polysaccharide-independent biofilms, but functional relationships between these proteins are unclear. In the present study, we report the roles of the extracellular adherence protein Eap and the surface CWAP SasG in S. aureus MR23, a clinical methicillin-resistant isolate that forms a robust protein-dependent biofilm and accumulates a large amount of Eap in the extracellular matrix. Double deletion of eap and sasG, but not single eap or sasG deletion, reduced the biomass of the formed biofilm. Mutational analysis demonstrated that cell wall anchorage is essential for the role of SasG in biofilm formation. Confocal laser scanning microscopy revealed that MR23 formed a rugged and thick biofilm; deletion of both eap and sasG reduced biofilm ruggedness and thickness. Although sasG deletion did not affect either of these features, eap deletion reduced the ruggedness but not the thickness of the biofilm. This indicated that Eap contributes to the rough irregular surface structure of the MR23 biofilm and that both Eap and SasG play roles in biofilm thickness. The level of pathogenicity of the Δeap ΔsasG strain in a silkworm larval infection model was significantly lower (P < 0.05) than those of the wild type and single-deletion mutants. Collectively, these findings highlight the redundant and distinct roles of a secreted protein and a CWAP in biofilm formation and pathogenicity of S. aureus and may inform new strategies to control staphylococcal biofilm infections.

Staphylococcal Biofilms

Staphylococci, with the leading species Staphylococcus aureus and Staphylococcus epidermidis, are the most frequent causes of infections on indwelling medical devices. The biofilm phenotype that those bacteria adopt during device-associated infection facilitates increased resistance to antibiotics and host immune defenses. This review presents and discusses the molecular mechanisms contributing to staphylococcal biofilm development and their in-vivo importance. Furthermore, it summarizes current strategies for the development of therapeutics against staphylococcal biofilm-associated infection.

l-Rhamnosylation of wall teichoic acids promotes efficient surface association of Listeria monocytogenes virulence factors InlB and Ami through interaction with GW domains

Wall teichoic acids (WTAs) are important surface glycopolymers involved in various physiological processes occurring in the Gram-positive cell envelope. We previously showed that the decoration of Listeria monocytogenes (Lm) WTAs with l-rhamnose conferred resistance against antimicrobial peptides. Here, we show that WTA l-rhamnosylation also contributes to physiological levels of autolysis in Lm through a mechanism that requires efficient association of Ami, a virulence-promoting autolysin belonging to the GW protein family, to the bacterial cell surface. Importantly, WTA l-rhamnosylation also controls the surface association of another GW protein, the invasin internalin B (InlB), that promotes Lm invasion of host cells. Whereas WTA N-acetylglucosaminylation is not a prerequisite for GW protein surface association, lipoteichoic acids appear to also play a role in the surface anchoring of InlB. Strikingly, while the GW domains of Ami, InlB and Auto (another autolysin contributing to cell invasion and virulence) are sufficient to mediate surface association, this is not the case for the GW domains of the remaining six uncharacterized Lm GW proteins. Overall, we reveal WTA l-rhamnosylation as a bacterial surface modification mechanism that contributes to Lm physiology and pathogenesis by controlling the surface association of GW proteins involved in autolysis and infection.

Tunicamycin Mediated Inhibition of Wall Teichoic Acid Affects Staphylococcus aureus and Listeria monocytogenes Cell Morphology, Biofilm Formation and Virulence

The emergence of bacterial resistance to therapeutic antibiotics limits options for treatment of common microbial diseases. Subinhibitory antibiotics dosing, often aid in the emergence of resistance, but its impact on pathogen's physiology and pathogenesis is not well understood. Here we investigated the effect of tunicamycin, a cell wall teichoic acid (WTA) biosynthesis inhibiting antibiotic at the subinhibitory dosage on Staphylococcus aureus and Listeria monocytogenes physiology, antibiotic cross-resistance, biofilm-formation, and virulence. Minimum inhibitory concentration (MIC) of tunicamycin to S. aureus and L. monocytogenes was 20-40 μg/ml and 2.5-5 μg/ml, respectively, and the subinhibitory concentration was 2.5-5 μg/ml and 0.31-0.62 μg/ml, respectively. Tunicamycin pre-exposure reduced cellular WTA levels by 18-20% and affected bacterial cell wall ultrastructure, cell membrane permeability, morphology, laser-induced colony scatter signature, and bacterial ability to form biofilms. It also induced a moderate level of cross-resistance to tetracycline, ampicillin, erythromycin, and meropenem for S. aureus, and ampicillin, erythromycin, vancomycin, and meropenem for L. monocytogenes. Pre-treatment of bacterial cells with subinhibitory concentrations of tunicamycin also significantly reduced bacterial adhesion to and invasion into an enterocyte-like Caco-2 cell line, which is supported by reduced expression of key virulence factors, Internalin B (InlB) and Listeria adhesion protein (LAP) in L. monocytogenes, and a S. aureus surface protein A (SasA) in S. aureus. Tunicamycin-treated bacteria or the bacterial WTA preparation suppressed NF-κB and inflammatory cytokine production (TNFα, and IL-6) from murine macrophage cell line (RAW 264.7) indicating the reduced WTA level possibly attenuates an inflammatory response. These results suggest that at the subinhibitory dosage, tunicamycin-mediated inhibition of WTA biosynthesis interferes with cell wall structure, pathogens infectivity and inflammatory response, and ability to form biofilms but promotes the development of antibiotic cross-resistance.

Salt-Induced Stress Stimulates a Lipoteichoic Acid-Specific Three-Component Glycosylation System in Staphylococcus aureus

Lipoteichoic acid (LTA) in Staphylococcus aureus is a poly-glycerophosphate polymer anchored to the outer surface of the cell membrane. LTA has numerous roles in cell envelope physiology, including regulating cell autolysis, coordinating cell division, and adapting to environmental growth conditions. LTA is often further modified with substituents, including d-alanine and glycosyl groups, to alter cellular function. While the genetic determinants of d-alanylation have been largely defined, the route of LTA glycosylation and its role in cell envelope physiology have remained unknown, in part due to the low levels of basal LTA glycosylation in S. aureus We demonstrate here that S. aureus utilizes a membrane-associated three-component glycosylation system composed of an undecaprenol (Und) N-acetylglucosamine (GlcNAc) charging enzyme (CsbB; SAOUHSC_00713), a putative flippase to transport loaded substrate to the outside surface of the cell (GtcA; SAOUHSC_02722), and finally an LTA-specific glycosyltransferase that adds α-GlcNAc moieties to LTA (YfhO; SAOUHSC_01213). We demonstrate that this system is specific for LTA with no cross recognition of the structurally similar polyribitol phosphate containing wall teichoic acids. We show that while wild-type S. aureus LTA has only a trace of GlcNAcylated LTA under normal growth conditions, amounts are raised upon either overexpressing CsbB, reducing endogenous d-alanylation activity, expressing the cell envelope stress responsive alternative sigma factor SigB, or by exposure to environmental stress-inducing culture conditions, including growth media containing high levels of sodium chloride.IMPORTANCE The role of glycosylation in the structure and function of Staphylococcus aureus lipoteichoic acid (LTA) is largely unknown. By defining key components of the LTA three-component glycosylation pathway and uncovering stress-induced regulation by the alternative sigma factor SigB, the role of N-acetylglucosamine tailoring during adaptation to environmental stresses can now be elucidated. As the dlt and glycosylation pathways compete for the same sites on LTA and induction of glycosylation results in decreased d-alanylation, the interplay between the two modification systems holds implications for resistance to antibiotics and antimicrobial peptides.

A Systematic Evaluation of the Two-Component Systems Network Reveals That ArlRS Is a Key Regulator of Catheter Colonization by Staphylococcus aureus

Two-component systems (TCS) are modular signal transduction pathways that allow cells to adapt to prevailing environmental conditions by modifying cellular physiology. Staphylococcus aureus has 16 TCSs to adapt to the diverse microenvironments encountered during its life cycle, including host tissues and implanted medical devices. S. aureus is particularly prone to cause infections associated to medical devices, whose surfaces coated by serum proteins constitute a particular environment. Identification of the TCSs involved in the adaptation of S. aureus to colonize and survive on the surface of implanted devices remains largely unexplored. Here, using an in vivo catheter infection model and a collection of mutants in each non-essential TCS of S. aureus, we investigated the requirement of each TCS for colonizing the implanted catheter. Among the 15 mutants in non-essential TCSs, the arl mutant exhibited the strongest deficiency in the capacity to colonize implanted catheters. Moreover, the arl mutant was the only one presenting a major deficit in PNAG production, the main exopolysaccharide of the S. aureus biofilm matrix whose synthesis is mediated by the icaADBC locus. Regulation of PNAG synthesis by ArlRS occurred through repression of IcaR, a transcriptional repressor of icaADBC operon expression. Deficiency in catheter colonization was restored when the arl mutant was complemented with the icaADBC operon. MgrA, a global transcriptional regulator downstream ArlRS that accounts for a large part of the arlRS regulon, was unable to restore PNAG expression and catheter colonization deficiency of the arlRS mutant. These findings indicate that ArlRS is the key TCS to biofilm formation on the surface of implanted catheters and that activation of PNAG exopolysaccharide production is, among the many traits controlled by the ArlRS system, a major contributor to catheter colonization.

Impact of Cell Surface Molecules on Conjugative Transfer of the Integrative and Conjugative Element ICESt3 of Streptococcus thermophilus

Integrative conjugative elements (ICEs) are chromosomal elements that are widely distributed in bacterial genomes, hence contributing to genome plasticity, adaptation, and evolution of bacteria. Conjugation requires a contact between both the donor and the recipient cells and thus likely depends on the composition of the cell surface envelope. In this work, we investigated the impact of different cell surface molecules, including cell surface proteins, wall teichoic acids, lipoteichoic acids, and exopolysaccharides, on the transfer and acquisition of ICESt3 from Streptococcus thermophilus The transfer of ICESt3 from wild-type (WT) donor cells to mutated recipient cells increased 5- to 400-fold when recipient cells were affected in lipoproteins, teichoic acids, or exopolysaccharides compared to when the recipient cells were WT. These mutants displayed an increased biofilm-forming ability compared to the WT, suggesting better cell interactions that could contribute to the increase of ICESt3 acquisition. Microscopic observations of S. thermophilus cell surface mutants showed different phenotypes (aggregation in particular) that can also have an impact on conjugation. In contrast, the same mutations did not have the same impact when the donor cells, instead of recipient cells, were mutated. In that case, the transfer frequency of ICESt3 decreased compared to that with the WT. The same observation was made when both donor and recipient cells were mutated. The dominant effect of mutations in donor cells suggests that modifications of the cell envelope could impair the establishment or activity of the conjugation machinery required for DNA transport.IMPORTANCE ICEs contribute to horizontal gene transfer of adaptive traits (for example, virulence, antibiotic resistance, or biofilm formation) and play a considerable role in bacterial genome evolution, thus underlining the need of a better understanding of their conjugative mechanism of transfer. While most studies focus on the different functions encoded by ICEs, little is known about the effect of host factors on their conjugative transfer. Using ICESt3 of S. thermophilus as a model, we demonstrated the impact of lipoproteins, teichoic acids, and exopolysaccharides on ICE transfer and acquisition. This opens up new avenues to control gene transfer mediated by ICEs.

RgpF Is Required for Maintenance of Stress Tolerance and Virulence in Streptococcus mutans

Bacterial cell wall dynamics have been implicated as important determinants of cellular physiology, stress tolerance, and virulence. In Streptococcus mutans, the cell wall is composed primarily of a rhamnose-glucose polysaccharide (RGP) linked to the peptidoglycan. Despite extensive studies describing its formation and composition, the potential roles for RGP in S. mutans biology have not been well investigated. The present study characterizes the impact of RGP disruption as a result of the deletion of rgpF, the gene encoding a rhamnosyltransferase involved in the construction of the core polyrhamnose backbone of RGP. The ΔrgpF mutant strain displayed an overall reduced fitness compared to the wild type, with heightened sensitivities to various stress-inducing culture conditions and an inability to tolerate acid challenge. The loss of rgpF caused a perturbation of membrane-associated functions known to be critical for aciduricity, a hallmark of S. mutans acid tolerance. The proton gradient across the membrane was disrupted, and the ΔrgpF mutant strain was unable to induce activity of the F₁F_o ATPase in cultures grown under low-pH conditions. Further, the virulence potential of S. mutans was also drastically reduced following the deletion of rgpF The ΔrgpF mutant strain produced significantly less robust biofilms, indicating an impairment in its ability to adhere to hydroxyapatite surfaces. Additionally, the ΔrgpF mutant lost competitive fitness against oral peroxigenic streptococci, and it displayed significantly attenuated virulence in an in vivoGalleria mellonella infection model. Collectively, these results highlight a critical function of the RGP in the maintenance of overall stress tolerance and virulence traits in S. mutansIMPORTANCE The cell wall of Streptococcus mutans, the bacterium most commonly associated with tooth decay, is abundant in rhamnose-glucose polysaccharides (RGP). While these structures are antigenically distinct to S. mutans, the process by which they are formed and the enzymes leading to their construction are well conserved among streptococci. The present study describes the consequences of the loss of RgpF, a rhamnosyltransferase involved in RGP construction. The deletion of rgpF resulted in severe ablation of the organism's overall fitness, culminating in significantly attenuated virulence. Our data demonstrate an important link between the RGP and cell wall physiology of S. mutans, affecting critical features used by the organism to cause disease and providing a potential novel target for inhibiting the pathogenesis of S. mutans.

Targeting Wall Teichoic Acid in Situ with Branched Polyethylenimine Potentiates β-Lactam Efficacy against MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) is a medical concern. Here, we show that branched polyethylenimine (BPEI), a nontoxic, cationic polymer, restores MRSA's susceptibility to β-lactam antibiotics. Checkerboard assays with MRSA demonstrated synergy between BPEI and β-lactam antibiotics. A time-killing curve showed BPEI to be bactericidal in combination with oxacillin. BPEI did not potentiate efficacy with vancomycin, chloramphenicol, or linezolid. When exposed to BPEI, MRSA increased in size and had difficulty forming septa. BPEI electrostatically binds to wall teichoic acid (WTA), a cell wall anionic polymer of Gram-positive bacteria that is important for localization of certain cell wall proteins. Lack of potentiation in a WTA knockout mutant supports the WTA-based mechanism. These data suggest that BPEI may prevent proper localization of cell wall machinery by binding to WTA; leading to cell death when administered in combination with β-lactam antibiotics. Negligible in vitro toxicity suggests the combination could be a viable treatment option.

Cell differentiation defines acute and chronic infection cell types in Staphylococcus aureus

A central question to biology is how pathogenic bacteria initiate acute or chronic infections. Here we describe a genetic program for cell-fate decision in the opportunistic human pathogen Staphylococcus aureus, which generates the phenotypic bifurcation of the cells into two genetically identical but different cell types during the course of an infection. Whereas one cell type promotes the formation of biofilms that contribute to chronic infections, the second type is planktonic and produces the toxins that contribute to acute bacteremia. We identified a bimodal switch in the agr quorum sensing system that antagonistically regulates the differentiation of these two physiologically distinct cell types. We found that extracellular signals affect the behavior of the agr bimodal switch and modify the size of the specialized subpopulations in specific colonization niches. For instance, magnesium-enriched colonization niches causes magnesium binding to S. aureusteichoic acids and increases bacterial cell wall rigidity. This signal triggers a genetic program that ultimately downregulates the agr bimodal switch. Colonization niches with different magnesium concentrations influence the bimodal system activity, which defines a distinct ratio between these subpopulations; this in turn leads to distinct infection outcomes in vitro and in an in vivo murine infection model. Cell differentiation generates physiological heterogeneity in clonal bacterial infections and helps to determine the distinct infection types.

While in hospital, patients can be unwittingly exposed to bacteria that can cause disease. These hospital-associated bacteria can lead to potentially life-threatening infections that may also complicate the treatment of the patients’ existing medical conditions. Staphylococcus aureus is one such bacterium, and it can cause several types of infection including pneumonia, blood infections and long-term infections of prosthetic devices.

It is thought that S. aureus is able to cause so many different types of infection because it is capable of colonizing distinct tissues and organs in various parts of the body. Understanding the biological processes that drive the different infections is crucial to improving how these infections are treated.

S. aureus lives either as an independent, free-swimming cell or as part of a community known as a biofilm. These different lifestyles dictate the type of infection the bacterium can cause, with free-swimming cells producing toxins that contribute to intense, usually short-lived, infections and biofilms promoting longer-term infections that are difficult to eradicate. However, it is not clear how a population of S. aureus cells chooses to adopt a particular lifestyle and whether there are any environmental signals that influence this decision.

Here, Garcia-Betancur et al. found that S. aureus populations contain small groups of cells that have already specialized into a particular lifestyle. These groups of cells collectively influence the choice made by other cells in the population. While both lifestyles will be represented in the population, environmental factors influence the numbers of cells that initially adopt each type of lifestyle, which ultimately affects the choice made by the rest of the population. For example, if the bacteria colonize a tissue or organ that contains high levels of magnesium ions, the population is more likely to form biofilms.

In the future, the findings of Garcia-Betancur et al. may help us to predict how an infection may develop in a particular patient, which may help to diagnose the infection more quickly and allow it to be treated more effectively.

Role of de-N-acetylase PgaB from Aggregatibacter actinomycetemcomitans in exopolysaccharide export in biofilm mode of growth

Aggregatibacter actinomycetemcomitans, a Gram-negative bacterium, is the causative agent of localized aggressive periodontitis. Attachment to a biotic surface is a critical first step in the A. actinomycetemcomitans infection process for which exopolysaccharides have been shown to be essential. In addition, the pga operon, containing genes encoding for biosynthetic proteins for poly-N-acetyl glucosamine (PNAG), plays a key role in A. actinomycetemcomitans virulence, as a mutant strain lacking the pga operon induces significantly less bone resorption. Among the genes in the pga operon, pgaB codes for a de-N-acetylase that is responsible for the deacetylation of the PNAG exopolysaccharide. Here we report the role of PgaB in regulation of virulence genes using a markerless, scarless deletion mutant targeting the coding region of the N-terminal catalytic domain of PgaB. The results demonstrate that the N-terminal, catalytic domain of PgaB is crucial for exopolysaccharide export.

Inhibitory effects of antibiofilm compound 1 against Staphylococcus aureus biofilms

A novel benzimidazole molecule that was identified in a small-molecule screen and is known as antibiofilm compound 1 (ABC-1) has been found to prevent bacterial biofilm formation by multiple bacterial pathogens, including Staphylococcus aureus, without affecting bacterial growth. Here, the biofilm inhibiting ability of 156 μM ABC-1 was tested in various biofilm-forming strains of S. aureus. It was demonstrated that ABC-1 inhibits biofilm formation by these strains at micromolar concentrations regardless of the strains' dependence on Polysaccharide Intercellular Adhesin (PIA), cell wall-associated protein dependent or cell wall- associated extracellular DNA (eDNA). Of note, ABC-1 treatment primarily inhibited Protein A (SpA) expression in all strains tested. spa gene disruption showed decreased biofilm formation; however, the mutants still produced more biofilm than ABC-1 treated strains, implying that ABC-1 affects not only SpA but also other factors. Indeed, ABC-1 also attenuated the accumulation of PIA and eDNA on cell surface. Our results suggest that ABC-1 has pleotropic effects on several biofilm components and thus inhibits biofilm formation by S. aureus.

Wall teichoic acid is an essential component of Staphylococcus aureus for the induction of human dendritic cell maturation

Staphylococcus aureus is a Gram-positive pathogen that can cause chronic skin inflammation, pneumonia, and septic shock. The immunomodulatory functions of wall teichoic acid (WTA), a glycopolymer abundantly expressed on the Gram-positive bacterial cell wall, are poorly understood. Here, we investigated the role of WTA in the phenotypic and functional activation of human monocyte-derived dendritic cells (DCs) treated with ethanol-killed S. aureus. WTA-deficient S. aureus mutant (ΔtagO) exhibited attenuated binding and internalization to DCs compared to the wild-type. ΔtagO induced lower expression of maturation markers on and cytokines in DCs than the wild-type S. aureus. Furthermore, autologous human peripheral blood mononuclear cells cocultured with ΔtagO-treated DCs exhibited a marked reduction in T cell proliferative activity, the expression of activation markers, and the production of cytokines compared to the wild-type S. aureus-stimulated DCs. Collectively, these results suggest that WTA is an important cell wall component of S. aureus for the induction of DC maturation and activation.

MALDI-TOF Mass Spectrometry Enables a Comprehensive and Fast Analysis of Dynamics and Qualities of Stress Responses of Lactobacillus paracasei subsp. paracasei F19

Lactic acid bacteria (LAB) are widely used as starter cultures in the manufacture of foods. Upon preparation, these cultures undergo various stresses resulting in losses of survival and fitness. In order to find conditions for the subsequent identification of proteomic biomarkers and their exploitation for preconditioning of strains, we subjected Lactobacillus (Lb.) paracasei subsp. paracasei TMW 1.1434 (F19) to different stress qualities (osmotic stress, oxidative stress, temperature stress, pH stress and starvation stress). We analysed the dynamics of its stress responses based on the expression of stress proteins using MALDI-TOF mass spectrometry (MS), which has so far been used for species identification. Exploiting the methodology of accumulating protein expression profiles by MALDI-TOF MS followed by the statistical evaluation with cluster analysis and discriminant analysis of principle components (DAPC), it was possible to monitor the expression of low molecular weight stress proteins, identify a specific time point when the expression of stress proteins reached its maximum, and statistically differentiate types of adaptive responses into groups. Above the specific result for F19 and its stress response, these results demonstrate the discriminatory power of MALDI-TOF MS to characterize even dynamics of stress responses of bacteria and enable a knowledge-based focus on the laborious identification of biomarkers and stress proteins. To our knowledge, the implementation of MALDI-TOF MS protein profiling for the fast and comprehensive analysis of various stress responses is new to the field of bacterial stress responses. Consequently, we generally propose MALDI-TOF MS as an easy and quick method to characterize responses of microbes to different environmental conditions, to focus efforts of more elaborate approaches on time points and dynamics of stress responses.

Effects of Total Alkaloids of Sophora alopecuroides on Biofilm Formation in Staphylococcus epidermidis

Staphylococcus epidermidis (S. epidermidis) is an opportunistic pathogen with low pathogenicity and a cause of the repeated outbreak of bovine mastitis in veterinary clinical settings. In this report, a biofilm model of S. epidermidis was generated and the minimal inhibitory concentration (MIC) and sub-MIC (SMIC) on bacterial cultures were assessed for the following agents: total alkaloids of Sophora alopecuroides (TASA), ciprofloxacin (CIP), and erythromycin (ERY). The formation and characteristic parameters of biofilm were analyzed in terms of XTT assay, silver staining, and confocal laser scanning microscope (CLSM). Results showed that a sub-MIC of TASA could inhibit 50% biofilm of bacterial activity, while 250-fold MIC of CIP and ERY MICs only inhibited 50% and 47% of biofilm formation, respectively. All three agents could inhibit the biofilm formation at an early stage, but TASA showed a better inhibitory effect on the late stage of biofilm thickening. A morphological analysis using CLSM further confirmed the destruction of biofilm by these agents. These results thus suggest that TASA has an inhibitory effect on biofilm formation of clinic S. epidermidis, which may be a potential agent warranted for further study on the treatment prevention of infection related to S. epidermidis in veterinary clinic.

Chemical Genetic Analysis and Functional Characterization of Staphylococcal Wall Teichoic Acid 2-Epimerases Reveals Unconventional Antibiotic Drug Targets

Here we describe a chemical biology strategy performed in Staphylococcus aureus and Staphylococcus epidermidis to identify MnaA, a 2-epimerase that we demonstrate interconverts UDP-GlcNAc and UDP-ManNAc to modulate substrate levels of TarO and TarA wall teichoic acid (WTA) biosynthesis enzymes. Genetic inactivation of mnaA results in complete loss of WTA and dramatic in vitro β-lactam hypersensitivity in methicillin-resistant S. aureus (MRSA) and S. epidermidis (MRSE). Likewise, the β-lactam antibiotic imipenem exhibits restored bactericidal activity against mnaA mutants in vitro and concomitant efficacy against 2-epimerase defective strains in a mouse thigh model of MRSA and MRSE infection. Interestingly, whereas MnaA serves as the sole 2-epimerase required for WTA biosynthesis in S. epidermidis, MnaA and Cap5P provide compensatory WTA functional roles in S. aureus. We also demonstrate that MnaA and other enzymes of WTA biosynthesis are required for biofilm formation in MRSA and MRSE. We further determine the 1.9Å crystal structure of S. aureus MnaA and identify critical residues for enzymatic dimerization, stability, and substrate binding. Finally, the natural product antibiotic tunicamycin is shown to physically bind MnaA and Cap5P and inhibit 2-epimerase activity, demonstrating that it inhibits a previously unanticipated step in WTA biosynthesis. In summary, MnaA serves as a new Staphylococcal antibiotic target with cognate inhibitors predicted to possess dual therapeutic benefit: as combination agents to restore β-lactam efficacy against MRSA and MRSE and as non-bioactive prophylactic agents to prevent Staphylococcal biofilm formation.

Staphylococcus aureus and Staphylococcus epidermidis cause life-threatening infections that are commonly acquired in hospitals as well as the community and remain difficult to treat with current antibiotics. In part, this is due to the emergence of methicillin-resistant S. aureus and S. epidermidis (MRSA and MRSE), which exhibit broad resistance to β-lactams such as penicillin and other members of this important founding class of antibiotics. Compounding this problem, Staphylococci commonly colonize the surface of catheters and other medical devices, forming bacterial communities that are intrinsically resistant to antibiotics. Here we functionally characterize a family of 2-epimerases, named MnaA and Cap5P, that we demonstrate by genetic, biochemical, and X-ray crystallography means are essential for wall teichoic acid biosynthesis and that upon their genetic inactivation render methicillin-resistant Staphylococci unable to form biofilms as well as broadly hypersusceptible to β-lactam antibiotics both in vitro and in a host infection setting. WTA 2-epimerases therefore constitute a novel class of methicillin-resistant Staphylococcal drug targets.

Sticky Matrix: Adhesion Mechanism of the Staphylococcal Polysaccharide Intercellular Adhesin

The development of bacterial biofilms on surfaces leads to hospital-acquired infections that are difficult to fight. In Staphylococci, the cationic polysaccharide intercellular adhesin (PIA) forms an extracellular matrix that connects the cells together during biofilm formation, but the molecular forces involved are unknown. Here, we use advanced force nanoscopy techniques to unravel the mechanism of PIA-mediated adhesion in a clinically relevant methicillin-resistant Staphylococcus aureus (MRSA) strain. Nanoscale multiparametric imaging of the structure, adhesion, and elasticity of bacteria expressing PIA shows that the cells are surrounded by a soft and adhesive matrix of extracellular polymers. Cell surface softness and adhesion are dramatically reduced in mutant cells deficient for the synthesis of PIA or under unfavorable growth conditions. Single-cell force spectroscopy demonstrates that PIA promotes cell-cell adhesion via the multivalent electrostatic interaction with polyanionic teichoic acids on the S. aureus cell surface. This binding mechanism rationalizes, at the nanoscale, the well-known ability of PIA to strengthen intercellular adhesion in staphylococcal biofilms. Force nanoscopy offers promising prospects for understanding the fundamental forces in antibiotic-resistant biofilms and for designing anti-adhesion compounds targeting matrix polymers.

Analysis of Cell Wall Teichoic Acids in Staphylococcus aureus

Most bacterial cells are surrounded by a surface composed mainly of peptidoglycan (PGN), a glycopolymer responsible for ensuring the bacterial shape and a telltale molecule that betrays the presence of bacteria to the host immune system. In Staphylococcus aureus, as in most gram-positive bacteria, peptidoglycan is concealed by covalently linked molecules of wall teichoic acids (WTA)-phosphate rich molecules made of glycerol and ribitol phosphates which may be tailored by different amino acids and sugars.In order to analyze and compare the composition of WTA produced by different S. aureus strains, we describe methods to: (1) quantify the total amount of WTA present at the bacterial cell surface, through the determination of the inorganic phosphate present in phosphodiester linkages of WTA; (2) identify which sugar constituents are present in the assembled WTA molecules, by detecting the monosaccharides, released by acid hydrolysis, through an high-performance anion exchange chromatography analysis coupled with pulsed amperometric detection (HPAEC-PAD) and (3) compare the polymerization degree of WTA found at the cell surface of different S. aureus strains, through their different migration in a polyacrylamide gel electrophoresis (PAGE).

Role of the Pre-neck Appendage Protein (Dpo7) from Phage vB_SepiS-phiIPLA7 as an Anti-biofilm Agent in Staphylococcal Species

Staphylococcus epidermidis and Staphylococcus aureus are important causative agents of hospital-acquired infections and bacteremia, likely due to their ability to form biofilms. The production of a dense exopolysaccharide (EPS) matrix enclosing the cells slows the penetration of antibiotic down, resulting in therapy failure. The EPS depolymerase (Dpo7) derived from bacteriophage vB_SepiS-phiIPLA7, was overexpressed in Escherichia coli and characterized. A dose dependent but time independent response was observed after treatment of staphylococcal 24 h-biofilms with Dpo7. Maximum removal (>90%) of biofilm-attached cells was obtained with 0.15 μM of Dpo7 in all polysaccharide producer strains but Dpo7 failed to eliminate polysaccharide-independent biofilm formed by S. aureus V329. Moreover, the pre-treatment of polystyrene surfaces with Dpo7 reduced the biofilm biomass by 53–85% in the 67% of the tested strains. This study supports the use of phage-encoded EPS depolymerases to prevent and disperse staphylococcal biofilms, thereby making bacteria more susceptible to the action of antimicrobials.

Intra- and inter-species interactions within biofilms of important foodborne bacterial pathogens

A community-based sessile life style is the normal mode of growth and survival for many bacterial species. Under such conditions, cell-to-cell interactions are inevitable and ultimately lead to the establishment of dense, complex and highly structured biofilm populations encapsulated in a self-produced extracellular matrix and capable of coordinated and collective behavior. Remarkably, in food processing environments, a variety of different bacteria may attach to surfaces, survive, grow, and form biofilms. Salmonella enterica, Listeria monocytogenes, Escherichia coli, and Staphylococcus aureus are important bacterial pathogens commonly implicated in outbreaks of foodborne diseases, while all are known to be able to create biofilms on both abiotic and biotic surfaces. Particularly challenging is the attempt to understand the complexity of inter-bacterial interactions that can be encountered in such unwanted consortia, such as competitive and cooperative ones, together with their impact on the final outcome of these communities (e.g., maturation, physiology, antimicrobial resistance, virulence, dispersal). In this review, up-to-date data on both the intra- and inter-species interactions encountered in biofilms of these pathogens are presented. A better understanding of these interactions, both at molecular and biophysical levels, could lead to novel intervention strategies for controlling pathogenic biofilm formation in food processing environments and thus improve food safety.

Biofilms in chronic rhinosinusitis: what is new and where next?

Background:

Chronic rhinosinusitis is a common, heterogeneous condition. An effective means of mitigating disease in chronic rhinosinusitis patients remains elusive. A variety of causes have been implicated, with the biofilm theory gaining increasing prominence.

Objective:

This article reviews the literature on the role of biofilms in chronic rhinosinusitis, in terms of pathophysiology and with regard to avenues for future treatment.

Methods:

A systematic review of case series was performed using databases with independently developed search strategies, including Medline, Embase, Cumulative Index to Nursing and Allied Health Literature, Cochrane library, and Zetoc, in addition to conference proceedings and a manual search of literature, with the last search conducted on 18 January 2014. The search terms included the following, used in various combinations to maximise the yield of articles identified: ‘biofilms’, ‘chronic rhinosinusitis’, ‘DNase’, ‘extracellular DNA’ and ‘biofilm dispersal’.

Results:

The existing evidence lends further support for the role of biofilms (particularly the Staphylococcus aureus phenotype) in more severe, recalcitrant disease and poorer surgical outcomes.

Conclusion:

Multimodality treatment, with a shift in paradigm to incorporate anti-biofilm strategies, is likely to form the mainstay of future recalcitrant chronic rhinosinusitis management.

Enzymatic modifications of exopolysaccharides enhance bacterial persistence

Biofilms are surface-attached communities of bacterial cells embedded in a self-produced matrix that are found ubiquitously in nature. The biofilm matrix is composed of various extracellular polymeric substances, which confer advantages to the encapsulated bacteria by protecting them from eradication. The matrix composition varies between species and is dependent on the environmental niche that the bacteria inhabit. Exopolysaccharides (EPS) play a variety of important roles in biofilm formation in numerous bacterial species. The ability of bacteria to thrive in a broad range of environmental settings is reflected in part by the structural diversity of the EPS produced both within individual bacterial strains as well as by different species. This variability is achieved through polymerization of distinct sugar moieties into homo- or hetero-polymers, as well as post-polymerization modification of the polysaccharide. Specific enzymes that are unique to the production of each polymer can transfer or remove non-carbohydrate moieties, or in other cases, epimerize the sugar units. These modifications alter the physicochemical properties of the polymer, which in turn can affect bacterial pathogenicity, virulence, and environmental adaptability. Herein, we review the diversity of modifications that the EPS alginate, the Pel polysaccharide, Vibrio polysaccharide, cepacian, glycosaminoglycans, and poly-N-acetyl-glucosamine undergo during biosynthesis. These are EPS produced by human pathogenic bacteria for which studies have begun to unravel the effect modifications have on their physicochemical and biological properties. The biological advantages these polymer modifications confer to the bacteria that produce them will be discussed. The expanding list of identified modifications will allow future efforts to focus on linking these modifications to specific biosynthetic genes and biofilm phenotypes.

Equilibrium binding behavior of magnesium to wall teichoic acid

Peptidoglycan and teichoic acids are the major cell wall components of Gram-positive bacteria that obtain and sequester metal ions required for biochemical processes. The delivery of metals to the cytoplasmic membrane is aided by anionic binding sites within the peptidoglycan and along the phosphodiester polymer of teichoic acid. The interaction with metals is a delicate balance between the need for attraction and ion diffusion to the membrane. Likewise, metal chelation from the extracellular fluid must initially have strong binding energetics that weaken within the cell wall to enable ion release. We employed atomic absorption and equilibrium dialysis to measure the metal binding capacity and metal binding affinity of wall teichoic acid and Mg2+. Data show that Mg2+ binds to WTA with a 1:2Mg2+ to phosphate ratio with a binding capacity of 1.27 μmol/mg. The affinity of Mg2+ to WTA was also found to be 41×10(3) M(-1) at low metal concentrations and 1.3×10(3) M(-1) at higher Mg2+ concentrations due to weakening electrostatic effects. These values are lower than the values describing Mg2+ interactions with peptidoglycan. However, the binding capacity of WTA is 4 times larger than peptidoglycan. External WTA initially binds metals with positive cooperativity, but metal binding switches to negative cooperativity, whereas interior WTA binds metals with only negative cooperativity. The relevance of this work is to describe changes in metal binding behavior depending on environment. When metals are sparse, chelation is strong to ensure survival yet the binding weakens when essential minerals are abundant.

Biofilms of microorganisms and their role for the formation of resistance to anti-bacterial drugs

The article describes current concepts of mechanisms of the formation of biofilms - a supracellular colonial prokaryotic form of microorganisms causing infectious urogenital pathologies. The authors describe the role of signal molecules and extracellular genetic material for the biofilm formation as well as synergy and antagonism between different types of bacteria. The article presents possible mechanisms of existence of prokaryotes causing torpidity to the therapy and resulting in a longterm chronic infection.

An 18 kDa scaffold protein is critical for Staphylococcus epidermidis biofilm formation

Virulence of the nosocomial pathogen Staphylococcus epidermidis is crucially linked to formation of adherent biofilms on artificial surfaces. Biofilm assembly is significantly fostered by production of a bacteria derived extracellular matrix. However, the matrix composition, spatial organization, and relevance of specific molecular interactions for integration of bacterial cells into the multilayered biofilm community are not fully understood. Here we report on the function of novel 18 kDa Small basic protein (Sbp) that was isolated from S. epidermidis biofilm matrix preparations by an affinity chromatographic approach. Sbp accumulates within the biofilm matrix, being preferentially deposited at the biofilm–substratum interface. Analysis of Sbp-negative S. epidermidis mutants demonstrated the importance of Sbp for sustained colonization of abiotic surfaces, but also epithelial cells. In addition, Sbp promotes assembly of S. epidermidis cell aggregates and establishment of multilayered biofilms by influencing polysaccharide intercellular-adhesin (PIA) and accumulation associated protein (Aap) mediated intercellular aggregation. While inactivation of Sbp indirectly resulted in reduced PIA-synthesis and biofilm formation, Sbp serves as an essential ligand during Aap domain-B mediated biofilm accumulation. Our data support the conclusion that Sbp serves as an S. epidermidis biofilm scaffold protein that significantly contributes to key steps of surface colonization. Sbp-negative S. epidermidis mutants showed no attenuated virulence in a mouse catheter infection model. Nevertheless, the high prevalence of sbp in commensal and invasive S. epidermidis populations suggests that Sbp plays a significant role as a co-factor during both multi-factorial commensal colonization and infection of artificial surfaces.

Biofilm formation is a key phenotype allowing the otherwise harmless skin commensal S. epidermidis to establish chronic implant-associated infections, affecting millions of patients worldwide. S. epidermidis biofilm assembly relies on the production of an extracellular matrix that serves as glue to stabilize the multilayered bacterial architecture. Here we identified novel 18 kDa Small basic protein (Sbp) as a key component of the extracellular matrix that promotes pivotal steps of bacterial biofilm formation in vitro. Importantly, Sbp is deposited specifically at the interface between biofilm and substrate, as well as in larger humps interspersed within the bacterial cell architecture, thereby forming a proteinaceous biofilm scaffold. This localization enables Sbp to foster stable S. epidermidis interactions with an artificial surface and also contributes to S. epidermidis cell aggregation mechanisms, i.e., polysaccharide intercellular adhesin (PIA) and accumulation associated protein (Aap). In fact, by demonstrating direct Sbp-Aap interactions we provide the first evidence supporting the idea that specific molecular interactions between S. epidermidis and matrix components are involved in S. epidermidis biofilm accumulation. In conclusion, we here show that Sbp promotes key phenotypic features important for S. epidermidis to evolve as an opportunistic pathogen.