Chemical composition and structure of cell wall teichoic acids of staphylococci

Wall teichoic acid substitution with glucose governs phage susceptibility of Staphylococcus epidermidis

The species- and clone-specific susceptibility of Staphylococcus cells for bacteriophages is governed by the structures and glycosylation patterns of wall teichoic acid (WTA) glycopolymers. The glycosylation-dependent phage-WTA interactions in the opportunistic pathogen Staphylococcus epidermidis and in other coagulase-negative staphylococci (CoNS) have remained unknown. We report a new S. epidermidis WTA glycosyltransferase TagE whose deletion confers resistance to siphoviruses such as ΦE72 but enables binding of otherwise unbound podoviruses. S. epidermidis glycerolphosphate WTA was found to be modified with glucose in a tagE-dependent manner. TagE is encoded together with the enzymes PgcA and GtaB providing uridine diphosphate-activated glucose. ΦE72 transduced several other CoNS species encoding TagE homologs, suggesting that WTA glycosylation via TagE is a frequent trait among CoNS that permits interspecies horizontal gene transfer. Our study unravels a crucial mechanism of phage-Staphylococcus interaction and horizontal gene transfer, and it will help in the design of anti-staphylococcal phage therapies.IMPORTANCEPhages are highly specific for certain bacterial hosts, and some can transduce DNA even across species boundaries. How phages recognize cognate host cells remains incompletely understood. Phages infecting members of the genus Staphylococcus bind to wall teichoic acid (WTA) glycopolymers with highly variable structures and glycosylation patterns. How WTA is glycosylated in the opportunistic pathogen Staphylococcus epidermidis and in other coagulase-negative staphylococci (CoNS) species has remained unknown. We describe that S. epidermidis glycosylates its WTA backbone with glucose, and we identify a cluster of three genes responsible for glucose activation and transfer to WTA. Their inactivation strongly alters phage susceptibility patterns, yielding resistance to siphoviruses but susceptibility to podoviruses. Many different CoNS species with related glycosylation genes can exchange DNA via siphovirus ΦE72, suggesting that glucose-modified WTA is crucial for interspecies horizontal gene transfer. Our finding will help to develop antibacterial phage therapies and unravel routes of genetic exchange.

Phage susceptibility determinants of the opportunistic pathogen Staphylococcus epidermidis

Staphylococcus epidermidis is a common member of the human skin and nose microbiomes and a frequent cause of invasive infections. Transducing phages accomplish the horizontal transfer of resistance and virulence genes by mispackaging of mobile-genetic elements, contributing to severe, therapy-refractory S. epidermidis infections. Lytic phages on the other hand can be interesting candidates for new anti-S. epidermidis phage therapies. Despite the importance of phages, we are only beginning to unravel S. epidermidis phage interactions. Recent studies shed new light on S. epidermidis phage diversity, host range, and receptor specificities. Modulation of cell wall teichoic acids, the major phage receptor structures, along with other phage defense mechanisms, are crucial determinants for S. epidermidis susceptibility to different phage groups.

Host-phage interactions and modeling for therapy

Phage are drivers of numerous ecological processes on the planet and have the potential to be developed into a therapy alternative to antibiotics. Phage at all points of their life cycle, from initiation of infection to their release, interact with their host in some manner. More importantly, to harness their antimicrobial potential it is vital to understand how phage interact with the eukaryotic environment in the context of applying phage for therapy. In this chapter, the various mechanisms of phage interplay with their hosts as part of their natural life cycle are discussed in depth for Gram-positive and negative bacteria. Further, the literature surrounding the various models utilized to develop phage as a therapeutic are examined, and how these models may improve our understanding of phage-host interactions and current progress in utilizing phage for therapy in the clinical environment.

Polysaccharides' Structures and Functions in Biofilm Architecture of Antimicrobial-Resistant (AMR) Pathogens

Bacteria and fungi have developed resistance to the existing therapies such as antibiotics and antifungal drugs, and multiple mechanisms are mediating this resistance. Among these, the formation of an extracellular matrix embedding different bacterial cells, called biofilm, is an effective strategy through which bacterial and fungal cells are establishing a relationship in a unique environment. The biofilm provides them the possibility to transfer genes conferring resistance, to prevent them from desiccation and to impede the penetration of antibiotics or antifungal drugs. Biofilms are formed of several constituents including extracellular DNA, proteins and polysaccharides. Depending on the bacteria, different polysaccharides form the biofilm matrix in different microorganisms, some of them involved in the first stage of cells' attachment to surfaces and to each other, and some responsible for giving the biofilm structure resistance and stability. In this review, we describe the structure and the role of different polysaccharides in bacterial and fungal biofilms, we revise the analytical methods to characterize them quantitatively and qualitatively and finally we provide an overview of potential new antimicrobial therapies able to inhibit biofilm formation by targeting exopolysaccharides.

Lipid Transport Across Bacterial Membranes

The movement of lipids within and between membranes in bacteria is essential for building and maintaining the bacterial cell envelope. Moving lipids to their final destination is often energetically unfavorable and does not readily occur spontaneously. Bacteria have evolved several protein-mediated transport systems that bind specific lipid substrates and catalyze the transport of lipids across membranes and from one membrane to another. Specific protein flippases act in translocating lipids across the plasma membrane, overcoming the obstacle of moving relatively large and chemically diverse lipids between leaflets of the bilayer. Active transporters found in double-membraned bacteria have evolved sophisticated mechanisms to traffic lipids between the two membranes, including assembling to form large, multiprotein complexes that resemble bridges, shuttles, and tunnels, shielding lipids from the hydrophilic environment of the periplasm during transport. In this review, we explore our current understanding of the mechanisms thought to drive bacterial lipid transport.

Bioinformatic Analysis of a Set of 14 Temperate Bacteriophages Isolated from Staphylococcus aureus Strains Highlights Their Massive Genetic Diversity

Epidemiology and virulence studies of Staphylococcus aureus showed that temperate bacteriophages are one of the most powerful drivers for its evolution not only because of their abundance but also because of the richness of their genetic payload. Here, we report the isolation, genome sequencing, and bioinformatic analysis of 14 bacteriophages induced from lysogenic S. aureus strains from human or veterinary (cattle) origin. The bacteriophages belonged to the Siphoviridae family; were of similar genome size (40 to 45 kbp); and fell into clusters B2, B3, B5, and B7 according to a recent clustering proposal. One of the phages, namely, vB_SauS_308, was the most unusual one, belonging to the sparsely populated subcluster B7 but showing differences in protein family contents compared with the rest of the members. This phage contains a type I endolysin (one catalytic domain and noncanonical cell wall domain [CBD]) and a host recognition module lacking receptor binding protein, cell wall hydrolase, and tail fiber proteins. This phage also lacked virulence genes, which is opposite to what has been reported for subcluster B6 and B7 members. None of six phages, taken as representatives of each of the four subclusters, showed activity on coagulase-negative staphylococci (excepted for two Staphylococcus hominis strains in which propagation and a very slow adsorption rate were observed) nor transducing ability. Immunity tests on S. aureus RN4220 lysogens with each of these phages showed no cross immunity. IMPORTANCE To the best of our knowledge, this set of sequenced bacteriophages is the largest one in South America. Our report describes for the first time the utilization of MultiTwin software to analyze the relationship between phage protein families. Notwithstanding the fact that most of the genetic information obtained correlated with recently published information, due to their geographical origin, the reported analysis adds up to and confirms currently available knowledge of Staphylococcus aureus temperate bacteriophages in terms of phylogeny and role in host evolution.

Antibiotics and Carbohydrate-Containing Drugs Targeting Bacterial Cell Envelopes: An Overview

Certain bacteria constitute a threat to humans due to their ability to escape host defenses as they easily develop drug resistance. Bacteria are classified into gram-positive and gram-negative according to the composition of the cell membrane structure. Gram-negative bacteria have an additional outer membrane (OM) that is not present in their gram-positive counterpart; the latter instead hold a thicker peptidoglycan (PG) layer. This review covers the main structural and functional properties of cell wall polysaccharides (CWPs) and PG. Drugs targeting CWPs are discussed, both noncarbohydrate-related (β-lactams, fosfomycin, and lipopeptides) and carbohydrate-related (glycopeptides and lipoglycopeptides). Bacterial resistance to these drugs continues to evolve, which calls for novel antibacterial approaches to be developed. The use of carbohydrate-based vaccines as a valid strategy to prevent bacterial infections is also addressed.

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.

Insight into the molecular basis of substrate recognition by the wall teichoic acid glycosyltransferase TagA

Wall teichoic acid (WTA) polymers are covalently affixed to the Gram-positive bacterial cell wall and have important functions in cell elongation, cell morphology, biofilm formation, and β-lactam antibiotic resistance. The first committed step in WTA biosynthesis is catalyzed by the TagA glycosyltransferase (also called TarA), a peripheral membrane protein that produces the conserved linkage unit, which joins WTA to the cell wall peptidoglycan. TagA contains a conserved GT26 core domain followed by a C-terminal polypeptide tail that is important for catalysis and membrane binding. Here, we report the crystal structure of the Thermoanaerobacter italicus TagA enzyme bound to UDP-N-acetyl-d-mannosamine, revealing the molecular basis of substrate binding. Native MS experiments support the model that only monomeric TagA is enzymatically active and that it is stabilized by membrane binding. Molecular dynamics simulations and enzyme activity measurements indicate that the C-terminal polypeptide tail facilitates catalysis by encapsulating the UDP-N-acetyl-d-mannosamine substrate, presenting three highly conserved arginine residues to the active site that are important for catalysis (R214, R221, and R224). From these data, we present a mechanistic model of catalysis that ascribes functions for these residues. This work could facilitate the development of new antimicrobial compounds that disrupt WTA biosynthesis in pathogenic bacteria.

Cell wall glycosylation in Staphylococcus aureus: targeting the tar glycosyltransferases

Peptidoglycan (PG) is the major structural polymer of the bacterial cell wall. The PG layer of gram-positive bacterial pathogens such as Staphylococcus aureus (S. aureus) is permeated with anionic glycopolymers known as wall teichoic acids (WTAs) and lipoteichoic acids (LTAs). In S. aureus, the WTA backbone typically consists of repeating ribitol-5-phosphate units, which are modified by enzymes that introduce glycosylation as well as amino acids at different locations. These modifications are key determinants of phage adhesion, bacterial biofilm formation and virulence of S. aureus. In this review, we examine differences in WTA structures in gram-positive bacteria, focusing in particular on three enzymes, TarM, TarS, and TarP that glycosylate the WTA of S. aureus at different locations. Infections with S. aureus pose an increasing threat to human health, particularly through the emergence of multidrug-resistant strains. Recently obtained structural information on TarM, TarS and TarP has helped to better understand the strategies used by S. aureus to establish resistance and to evade host defense mechanisms. Moreover, structures of complexes with poly-RboP and its analogs can serve as a platform for the development of new inhibitors that could form a basis for the development of antibiotic agents.

Characterization of Clinical MRSA Isolates from Northern Spain and Assessment of Their Susceptibility to Phage-Derived Antimicrobials

Methicillin-resistant Staphylococcus aureus (MRSA) is a prevalent nosocomial pathogen, causing a wide range of diseases. The increased frequency of MRSA isolates in hospitals and the emergence of vancomycin resistance have sparked the search for new control strategies. This study aimed to characterize sixty-seven MRSA isolates collected from both infected patients and asymptomatic carriers in a Spanish hospital. RAPD-PCR allowed the identification of six genetic patterns. We also investigated the presence of genes involved in producing adhesins, toxins and the capsule; the biofilm; and antimicrobial resistance. A notable percentage of the isolates carried virulence genes and showed medium-high ability to form biofilms. Next, we assessed the strains' susceptibility to two phages (phiIPLA-C1C and phiIPLA-RODI) and one endolysin (LysRODI). All strains were resistant to phiIPLA-C1C, and most (70.2%) were susceptible to phiIPLA-RODI. Regarding LysRODI, all strains displayed susceptibility, although to varying degrees. There was a correlation between endolysin susceptibility and the random amplification of polymorphic DNA (RAPD) profile or the presence of some virulence genes (fnbA, eta, etb, PVL and czr), but that was not observed with biofilm-forming ability, strain origin or phage sensitivity. Taken together, these findings can help to explain the factors influencing endolysin effectiveness, which will contribute to the development of efficient therapies targeting MRSA infections.

Our natural "makeup" reveals more than it hides: Modeling the skin and its microbiome

Skin is our primary interface with the environment. A structurally and functionally complex organ that hosts a dynamic ecosystem of microbes, and synthesizes many compounds that affect our well-being and psychosocial interactions. It is a natural platform of signal exchange between internal organs, skin resident microbes, and the environment. These interactions have gained a great deal of attention due to the increased prevalence of atopic diseases, and the co-occurrence of multiple allergic diseases related to allergic sensitization in early life. Despite significant advances in experimentally characterizing the skin, its microbial ecology, and disease phenotypes, high-levels of variability in these characteristics even for the same clinical phenotype are observed. Addressing this variability and resolving the relevant biological processes requires a systems approach. This review presents some of our current understanding of the skin, skin-immune, skin-neuroendocrine, skin-microbiome interactions, and computer-based modeling approaches to simulate this ecosystem in the context of health and disease. The review highlights the need for a systems-based understanding of this sophisticated ecosystem. This article is categorized under: Infectious Diseases > Computational Models.

Lytic Activity of Polyvalent Staphylococcal Bacteriophage PhiSA012 and Its Endolysin Lys-PhiSA012 Against Antibiotic-Resistant Staphylococcal Clinical Isolates From Canine Skin Infection Sites

The spread of antibiotic-resistant bacteria (ARB) in human and veterinary medicine is of global concern. Notably, the emergence of methicillin-resistant Staphylococcus pseudintermedius has become a serious problem. In this context, bacteriophages and their lytic enzymes, endolysins, have received considerable attention as therapeutics for infectious diseases in place of antibiotics. The aim of the present study was to investigate the antibiotic-resistance patterns of staphylococcal species isolated from canine skin at a primary care animal hospital in Tokyo, Japan and evaluate the lytic activity of the staphylococcal bacteriophage phiSA012 and its endolysin Lys-phiSA012 against isolated antibiotic-resistant staphylococcal strains. Forty clinical staphylococcal samples were isolated from infection sites of dogs (20 from skin and 20 from the external ear canal). Susceptibility to antimicrobial agents was determined by a disk diffusion method. The host range of phiSA012 was determined by using a spot test against staphylococcal isolates. Against staphylococcal isolates that showed resistance toward five classes or more of antimicrobials, the lytic activity of phiSA012 and Lys-phiSA012 was evaluated using a turbidity reduction assay. Twenty-three S. pseudintermedius, 16 Staphylococcus schleiferi, and 1 Staphylococcus intermedius were detected from canine skin and ear infections, and results revealed 43.5% methicillin resistance in S. pseudintermedius and 31.3% in S. schleiferi. In addition, the prevalence multidrug resistance (MDR) S. pseudintermedius was 65.2%. PhiSA012 could infect all staphylococcal isolates by spot testing, but showed little lytic activity by turbidity reduction assay against MDR S. pseudintermedius isolates. On the other hand, Lys-phiSA012 showed lytic activity and reduced significantly the number of staphylococcal colony-forming units. These results demonstrated that ARB issues underlying in small animal hospital and proposed substitutes for antibiotics. Lys-phiSA012 has broader lytic activity than phiSA012 against staphylococcal isolates; therefore, Lys-phiSA012 is a more potential candidate therapeutic agent for several staphylococcal infections including that of canine skin.

The C-type lectin receptor MGL senses N-acetylgalactosamine on the unique Staphylococcus aureus ST395 wall teichoic acid

Staphylococcus aureus is a common skin commensal but is also associated with various skin and soft tissue pathologies. Upon invasion, S. aureus is detected by resident innate immune cells through pattern-recognition receptors (PRRs), although a comprehensive understanding of the specific molecular interactions is lacking. Recently, we demonstrated that the PRR langerin (CD207) on epidermal Langerhans cells senses the conserved β-1,4-linked N-acetylglucosamine (GlcNAc) modification on S. aureus wall teichoic acid (WTA), thereby increasing skin inflammation. Interestingly, the S. aureus ST395 lineage as well as certain species of coagulase-negative staphylococci (CoNS) produce a structurally different WTA molecule, consisting of poly-glycerolphosphate with α-O-N-acetylgalactosamine (GalNAc) residues, which are attached by the glycosyltransferase TagN. Here, we demonstrate that S. aureus ST395 strains interact with the human Macrophage galactose-type lectin (MGL; CD301) receptor, which is expressed by dendritic cells and macrophages in the dermis. MGL bound S. aureus ST395 in a tagN- and GalNAc-dependent manner but did not interact with different tagN-positive CoNS species. However, heterologous expression of Staphylococcus lugdunensis tagN in S. aureus conferred phage infection and MGL binding, confirming the role of this CoNS enzyme as GalNAc-transferase. Functionally, the detection of GalNAc on S. aureus ST395 WTA by human monocyte-derived dendritic cells significantly enhanced cytokine production. Together, our findings highlight differential recognition of S. aureus glycoprofiles by specific human innate receptors, which may affect downstream adaptive immune responses and pathogen clearance.

Analysis host-recognition mechanism of staphylococcal kayvirus ɸSA039 reveals a novel strategy that protects Staphylococcus aureus against infection by Staphylococcus pseudintermedius Siphoviridae phages

Following the emergence of antibiotic-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus pseudintermedius (MRSP), phage therapy has attracted significant attention as an alternative to antibiotic treatment. Bacteriophages belonging to kayvirus (previously known as Twort-like phages) have broad host range and are strictly lytic in Staphylococcus spp. Previous work revealed that kayvirus ɸSA039 has a host-recognition mechanism distinct from those of other known kayviruses: most of kayviruses use the backbone of wall teichoic acid (WTA) as their receptor; by contrast, ɸSA039 uses the β-N-acetylglucosamine (β-GlcNAc) residue in WTA. In this study, we found that ɸSA039 could switch its receptor to be able to infect S. aureus lacking the β-GlcNAc residue by acquiring a spontaneous mutation in open reading frame (ORF) 100 and ORF102. Moreover, ɸSA039 could infect S. pseudintermedius, which has a different WTA structure than S. aureus. By comparison, with newly isolated S. pseudintermedius-specific phage (SP phages), we determined that glycosylation in WTA of S. pseudintermedius is essential for adsorption of SP phages, but not ɸSA039. Finally, we describe a novel strategy of S. aureus which protects the bacteria from infection of SP phages. Notably, glycosylation of ribitol phosphate (RboP) WTA by TarM or/and TarS prevents infection of S. aureus by SP phages. These findings could help to establish a new strategy for the treatment of S. aureus and S. pseudintermedius infection, as well as provide valuable insights into the biology of phage-host interactions.

Extracellular electron transfer features of Gram-positive bacteria

Electroactive microorganisms possess the unique ability to transfer electrons to or from solid phase electron conductors, e.g., electrodes or minerals, through various physiological mechanisms. The processes are commonly known as extracellular electron transfer and broadly harnessed in microbial electrochemical systems, such as microbial biosensors, microbial electrosynthesis, or microbial fuel cells. Apart from a few model microorganisms, the nature of the microbe-electrode conductive interaction is poorly understood for most of the electroactive species. The interaction determines the efficiency and a potential scaling up of bioelectrochemical systems. Gram-positive bacteria generally have a thick electron non-conductive cell wall and are believed to exhibit weak extracellular electron shuttling activity. This review highlights reported research accomplishments on electroactive Gram-positive bacteria. The use of electron-conducting polymers as mediators is considered as one promising strategy to enhance the electron transfer efficiency up to application scale. In view of the recent progress in understanding the molecular aspects of the extracellular electron transfer mechanisms of Enterococcus faecalis, the electron transfer properties of this bacterium are especially focused on. Fundamental knowledge on the nature of microbial extracellular electron transfer and its possibilities can provide insight in interspecies electron transfer and biogeochemical cycling of elements in nature. Additionally, a comprehensive understanding of cell-electrode interactions may help in overcoming insufficient electron transfer and restricted operational performance of various bioelectrochemical systems and facilitate their practical applications.

Peculiarities of Staphylococcus aureus phages and their possible application in phage therapy

Bacteriophage has become an attractive alternative for the treatment of antibiotic-resistant Staphylococcus aureus. For the success of phage therapy, phage host range is an important criterion when considering a candidate phage. Most reviews of S. aureus (SA) phages have focused on their impact on host evolution, especially their contribution to the spread of virulence genes and pathogenesis factors. The potential therapeutic use of SA phages, especially detailed characterizations of host recognition mechanisms, has not been extensively reviewed so far. In this report, we provide updates on the study of SA phages, focusing on host recognition mechanisms with the recent discovery of phage receptor-binding proteins (RBPs) and the possible applications of SA phages in phage therapy.

Potential targets for next generation antimicrobial glycoconjugate vaccines

Cell surface carbohydrates have been proven optimal targets for vaccine development. Conjugation of polysaccharides to a carrier protein triggers a T-cell-dependent immune response to the glycan moiety. Licensed glycoconjugate vaccines are produced by chemical conjugation of capsular polysaccharides to prevent meningitis caused by meningococcus, pneumococcus and Haemophilus influenzae type b. However, other classes of carbohydrates (O-antigens, exopolysaccharides, wall/teichoic acids) represent attractive targets for developing vaccines. Recent analysis from WHO/CHO underpins alarming concern toward antibiotic-resistant bacteria, such as the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) and additional pathogens such as Clostridium difficile and Group A Streptococcus. Fungal infections are also becoming increasingly invasive for immunocompromised patients or hospitalized individuals. Other emergencies could derive from bacteria which spread during environmental calamities (Vibrio cholerae) or with potential as bioterrorism weapons (Burkholderia pseudomallei and mallei, Francisella tularensis). Vaccination could aid reducing the use of broad-spectrum antibiotics and provide protection by herd immunity also to individuals who are not vaccinated.

This review analyzes structural and functional differences of the polysaccharides exposed on the surface of emerging pathogenic bacteria, combined with medical need and technological feasibility of corresponding glycoconjugate vaccines.

Staphylococcus aureus counters phosphate limitation by scavenging wall teichoic acids from other staphylococci via the teichoicase GlpQ

Staphylococcus aureus is part of the human nasal and skin microbiomes along with other bacterial commensals and opportunistic pathogens. Nutrients are scarce in these habitats, demanding effective nutrient acquisition and competition strategies. How S. aureus copes with phosphate limitation is still unknown. Wall teichoic acid (WTA), a polyol-phosphate polymer, could serve as a phosphate source, but whether S. aureus can utilize it during phosphate starvation remains unknown. S. aureus secretes a glycerophosphodiesterase, GlpQ, that cleaves a broad variety of glycerol-3-phosphate (GroP) headgroups of deacylated phospholipids, providing this bacterium with GroP as a carbon and phosphate source. Here we demonstrate that GlpQ can also use glycerophosphoglycerol derived from GroP WTA from coagulase-negative Staphylococcus lugdunensis, Staphylococcus capitis, and Staphylococcus epidermidis, which share the nasal and skin habitats with S. aureus Therefore, S. aureus GlpQ is the first reported WTA-hydrolyzing enzyme, or teichoicase, from Staphylococcus Activity assays revealed that unmodified WTA is the preferred GlpQ substrate, and the results from MS analysis suggested that GlpQ uses an exolytic cleavage mechanism. Importantly, GlpQ did not hydrolyze the ribitol-5-phosphate WTA polymers of S. aureus, underscoring its role in interspecies competition rather than in S. aureus cell wall homeostasis or WTA recycling. glpQ expression was strongly up-regulated under phosphate limitation, and GlpQ allowed S. aureus to grow in the presence of GroP WTA as the sole phosphate source. Our study reveals a novel and unprecedented strategy of S. aureus for acquiring phosphate from bacterial competitors under the phosphate-limiting conditions in the nasal or skin environments.

The Genus Macrococcus: An Insight Into Its Biology, Evolution, and Relationship With Staphylococcus

The Gram-positive genus Macrococcus is composed of eight species that are evolutionarily closely related to species of the Staphylococcus genus. In contrast to Staphylococcus species, species of Macrococcus are generally regarded to be avirulent in their animal hosts. Recent reports on Macrococcus have focused on the presence of novel methicillin resistance genes in Macrococcus caseolyticus and Macrococcus canis, with the discovery of the first plasmid-encoded methicillin resistance gene in clinical Staphylococcus aureus of probable macrococcal origin generating further interest in these organisms. Furthermore, M. caseolyticus has been associated with flavor development in certain fermented foods and its potential as a food bio-preservative has been documented. The potential application of these organisms in food seems at odds with the emerging information regarding antibiotic resistance and is prompting further examination of the potential safety issues associated with such strains, given the European Food Safety Authority framework for the safety evaluation of microorganisms in the food chain. A comprehensive understanding of the genus would also contribute to understanding the evolution of staphylococci in terms of its acquisition of antibiotic resistance and pathogenic potential. In this review, we discuss the current knowledge on Macrococcus with regard to their phenotypic capabilities, genetic diversity, and evolutionary history with Staphylococcus. Comparative genomics of the sequenced Macrococcus species will be discussed, providing insight into their unique metabolic features and the genetic structures carrying methicillin resistance. An in-depth understanding of these antibiotic resistance determinants can open the possibilities for devising better preventative strategies for an unpredictable future.

A rapid NMR-based method for discrimination of strain-specific cell wall teichoic acid structures reveals a third backbone type in Lactobacillus plantarum

The lactic acid bacterium Lactobacillus plantarum is capable of producing strain-specific structures of cell wall teichoic acid (WTA), an anionic polysaccharide found in the Gram-positive bacterial cell wall. In this study, we established a rapid, NMR-based procedure to discriminate WTA structures in this species, and applied it to 94 strains of L. plantarum. Six previously reported glycerol- and ribitol-containing WTA subtypes were successfully identified from 78 strains, suggesting that these were the dominant structures. However, the level of structural variety differed markedly among bacterial sources, possibly reflecting differences in strain-level microbial diversity. WTAs from eight strains were not identified based on NMR spectra and were classified into three groups. Structural analysis of a partial degradation product of an unidentified WTA produced by strain TUA 1496L revealed that the WTA was 1-O-β-d-glucosylglycerol. Two-dimensional NMR analysis of the polymer structure showed phosphodiester bonds between C-3 and C-6 of the glycerol and glucose residues, suggesting a polymer structure of 3,6΄-linked poly(1-O-β-d-glucosyl-sn-glycerol phosphate). This is the third WTA backbone structure in L. plantarum, following 3,6΄-linked poly(1-O-α-d-glucosyl-sn-glycerol phosphate) and 1,5-linked poly(ribitol phosphate).

Structural characterization of the lipoteichoic acid isolated from Staphylococcus sciuri W620

Lipoteichoic acid (LTA) is an important cell envelope compound of Gram-positive bacteria. LTA isolated from allergy-protective Staphylococcus sciuri W620 strain was characterized by chemical analyses as well as 1D and 2D NMR experiments. Compositional analyses indicated the presence of glycerol (Gro), phosphate-Gro, alanine-Gro, glucose (Glc) and fatty acids. The studied strain produced LTA with backbone composed of glycerol-phosphate repeating units only substituted with d-alanine (Ala) and the lipid anchor, typically for genus Staphyloccocus, possessing the structure β-d-Glcp(1→6)- β-d-Glcp(1→3)-1,2-diacyl-sn-Gro.

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).

Structure and Function of Surface Polysaccharides of Staphylococcus aureus

The major surface polysaccharides of Staphylococcus aureus include the capsular polysaccharide (CP), cell wall teichoic acid (WTA), and polysaccharide intercellular adhesin/poly-β(1-6)-N-acetylglucosamine (PIA/PNAG). These glycopolymers are important components of the staphylococcal cell envelope, but none of them is essential to S. aureus viability and growth in vitro. The overall biosynthetic pathways of CP, WTA, and PIA/PNAG have been elucidated, and the functions of most of the biosynthetic enzymes have been demonstrated. Because S. aureus CP and WTA (but not PIA/PNAG) utilize a common cell membrane lipid carrier (undecaprenyl-phosphate) that is shared by the peptidoglycan biosynthesis pathway, there is evidence that these processes are highly integrated and temporally regulated. Regulatory elements that control glycopolymer biosynthesis have been described, but the cross talk that orchestrates the biosynthetic pathways of these three polysaccharides remains largely elusive. CP, WTA, and PIA/PNAG each play distinct roles in S. aureus colonization and the pathogenesis of staphylococcal infection. However, they each promote bacterial evasion of the host immune defences, and WTA is being explored as a target for antimicrobial therapeutics. All the three glycopolymers are viable targets for immunotherapy, and each (conjugated to a carrier protein) is under evaluation for inclusion in a multivalent S. aureus vaccine. Future research findings that increase our understanding of these surface polysaccharides, how the bacterial cell regulates their expression, and their biological functions will likely reveal new approaches to controlling this important bacterial pathogen.

Bacteriophage-based latex agglutination test for rapid identification of Staphylococcus aureus

Rapid diagnosis is essential for the management of Staphylococcus aureus infections. A host recognition protein from S. aureus bacteriophage phiSLT was recombinantly produced and used to coat streptavidin latex beads to develop a latex agglutination test (LAT). The diagnostic accuracy of this bacteriophage-based test was compared with that of a conventional LAT, Pastorex Staph-Plus, by investigating a clinical collection of 86 S. aureus isolates and 128 coagulase-negative staphylococci (CoNS) from deep tissue infections. All of the clinical S. aureus isolates were correctly identified by the bacteriophage-based test. While most of the CoNS were correctly identified as non-S. aureus isolates, 7.9% of the CoNS caused agglutination. Thus, the sensitivity of the bacteriophage-based LAT for identification of S. aureus among clinical isolates was 100%, its specificity was 92.1%, its positive predictive value (PPV) was 89.6%, and its negative predictive value (NPV) was 100%. The sensitivity, specificity, PPV, and NPV of the Pastorex LAT for the identification of S. aureus were 100%, 99.2%, 98.9%, and 100%, respectively. Among the additionally tested 35 S. aureus and 91 non-S. aureus staphylococcal reference and type strains, 1 isolate was false negative by each system; 13 and 8 isolates were false positive by the bacteriophage-based and Pastorex LATs, respectively. The ability of the phiSLT protein to detect S. aureus was dependent on the presence of wall teichoic acid (WTA) and corresponded to the production of ribitol phosphate WTA, which is found in most S. aureus clones but only a small minority of CoNS. Bacteriophage-based LAT identification is a promising strategy for rapid pathogen identification. Finding more specific bacteriophage proteins would increase the specificity of this novel diagnostic approach.

Functional and structural analysis of the major amidase (Atl) in Staphylococcus

The cytoplasmic membrane of most bacteria is surrounded by a more or less thick murein layer (peptidoglycan) that protects the protoplast from mechanical damage, osmotic rupture and lysis. When bacteria are dividing processes are initiated stepwise that involve DNA replication, constriction of the membranes, cell growth, biosynthesis of new murein, and finally the generation of two daughter cells. As the daughter cells are still covalently interlinked by the murein network they must be separated by specific peptidoglycan hydrolases, also referred to as autolysins. In staphylococci, the major autolysin (Atl) and its processed products N-acetylmuramoyl-l-alanine amidase (AM) and endo-β-N-acetylglucosaminidase (GL) have been in the research focus for long time. This review addresses phenotypic consequences of atl mutants, impact of Atl in virulence, the mechanism of targeting to the septum region, regulation of atl, the structure of the amidase and the repeat regions, as well as the phylogeny of Atl and its use in Staphylococcus genus and species typing.

Extraction of cell wall-bound teichoic acids and surface proteins from Listeria monocytogenes

Gram-positive bacteria contain a cell wall consisting of a thick peptidoglycan layer decorated with surface proteins and polysaccharide-based polymers. The latter include the wall teichoic acids (WTAs), which are anionic glycopolymers covalently linked to the peptidoglycan matrix. They are constituted by a long backbone containing sugars of various sizes (trioses to hexoses) which can be reduced (polyols as in Listeria) or oxidized (uronic acids) and can undergo a variety of species- or often strain-specific modifications and substitutions. These confer unique biochemical properties to WTAs and any defect in the modification or substitution process can potentially affect their biological role in the overall cell wall physiology. Surface proteins can be associated to the cell wall by covalent bonds that anchor the protein to the peptidoglycan lattice. Due to the chemical nature of this bond, covalently bound proteins "co-purify" with peptidoglycan sacculi and are intrinsically insoluble at high temperatures and/or in the presence of ionic detergents. Analysis of this type of proteins therefore requires enzymatic digestion of peptidoglycan for the subsequent release of associated proteins. In contrast, proteins associated to the cell wall by non-covalent interactions are easier to isolate using ionic detergents. In this chapter, we describe methods for the extraction and analysis of (i) WTAs, (ii) covalently, and (iii) non-covalently cell wall-bound surface proteins from the Gram-positive pathogen Listeria monocytogenes.

Wall teichoic acids of gram-positive bacteria

The peptidoglycan layers of many gram-positive bacteria are densely functionalized with anionic glycopolymers known as wall teichoic acids (WTAs). These polymers play crucial roles in cell shape determination, regulation of cell division, and other fundamental aspects of gram-positive bacterial physiology. Additionally, WTAs are important in pathogenesis and play key roles in antibiotic resistance. We provide an overview of WTA structure and biosynthesis, review recent studies on the biological roles of these polymers, and highlight remaining questions. We also discuss prospects for exploiting WTA biosynthesis as a target for new therapies to overcome resistant infections.

Determination of strain-specific wall teichoic acid structures in Lactobacillus plantarum reveals diverse α-D-glucosyl substitutions and high structural uniformity of the repeating units

The structural diversity of wall teichoic acid (WTA) was investigated using biochemical and NMR analyses among 19 strains of Lactobacillus plantarum, of which seven were previously established to contain a glycerol-type backbone, whereas the remaining 12 strains possess ribitol-containing WTA. Despite the fact that the WTAs consisted of identical components, namely phosphoric acid, alditol (glycerol or ribitol) and glucose, comparative analysis of the (1)H and (13)C NMR spectra indicated the presence of six different structures, based on the observed differences in the anomeric signals of glucose residues. To determine the six WTA structures, their repeating units were prepared by alkaline hydrolysis, followed by fractionation on HPLC, and analysis by NMR spectroscopy using synthetic molecules as a reference. The structures of the six isolates were established as 1-α-D-glucosyl-sn-glycerol 3-phosphate, 1-α-D-kojibiosyl-sn-glycerol 3-phosphate, 1-α-D-nigerosyl-sn-glycerol 3-phosphate, 4-α-D-kojibiosylribitol 1-phosphate and 1,5-linked di-(2,4-di-α-D-glucosylribitol) phosphate. The backbone structures appeared to be 3,6'-linked poly(1-α-D-glucosyl-sn-glycerol phosphate) for the glycerol-type WTA and 1,5-linked poly(ribitol phosphate) for the ribitol-containing WTA. Moreover, in the analysis of the alkaline hydrolysates on HPLC, only single structures of repeating units were released from each WTA, indicating the high structural uniformity of the WTA in each strain. Notably, analyses of lipoteichoic acid isolated from representative strains harbouring the six different WTAs revealed the universal presence of a 1,3-linked poly(glycerol phosphate) chain, substituted at C-2 of the glycerol residues with glucose residues. These findings provide fundamental information on WTA structural variability in Lb. plantarum, which seems likely to play a pivotal role in the physiology of this bacterial species.

Effect of alkaline pH on staphylococcal biofilm formation

Biofilms are a serious problem, cause of severe inconvenience in the biomedical, food and industrial environment. Staphylococcus aureus and S. epidermidis are important pathogenic bacteria able to form thick and resistant biofilms on various surfaces. Therefore, strategies aimed at preventing or at least interfering with the initial adhesion and subsequent biofilm formation are a considerable achievement. The aim of this study was to evaluate the effect of alkaline pH on bacterial adhesion and further biofilm formation of S. aureus and S. epidermidis strains by biofilm biomass, cell-surface hydrophobicity, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) analysis. The results demonstrated that the amount of biofilm biomass formed and the surface hydrophobicity were significantly less than what were observed at higher levels of pH. SEM and CLSM images revealed a poorly structured and very thin biofilm (2.5-3 times thinner than that of the controls). The inhibiting effect of the alkaline pH on the bacterial attachment impaired the normal development of biofilm that arrested at the microcolony stage. Alkaline formulations could be promising towards the control of bacterial colonization and therefore the reduction of the biofilm-related hazard. In the clinical setting, alkaline solutions or cleaners could be promising to prevent the bacterial colonization, by treating surfaces such as catheters or indwelling medical devices, reducing the risk of biofilm related infections.

Staphylococcus aureus determinants for nasal colonization

Approximately 20% of the healthy human population is persistently colonized in the nasal cavity with Staphylococcus aureus, which constitutes a major risk for infection. S. aureus seems to predominantly colonize the anterior part of the nasal cavity by adhering to nasal surface structures and escaping the host innate and adaptive immune responses. Several bacterial and host factors that play a role in these processes have been identified in the past few years and were in part functionally evaluated in appropriate colonization models. However, the dynamics of host-pathogen crosstalk is only partially understood.

In vitro activity against Staphylococcus aureus of a novel antimicrobial agent, PRF-119, a recombinant chimeric bacteriophage endolysin

Antistaphylococcal activity of the novel chimeric endolysin PRF-119 was evaluated with the microdilution method. The MIC(50) and MIC(90) of 398 methicillin-susceptible Staphylococcus aureus isolates were 0.098 μg/ml and 0.391 μg/ml, respectively (range, 0.024 to 0.780 μg/ml). Both the MIC(50) and MIC(90) values of 776 methicillin-resistant S. aureus isolates were 0.391 μg/ml (range, 0.024 to 1.563 μg/ml). All 192 clinical isolates of coagulase-negative staphylococci exhibited MIC values of >50 μg/ml. In conclusion, PRF-119 exhibited very good activity specifically against S. aureus.

Staphylococcus aureus and Bacillus subtilis W23 make polyribitol wall teichoic acids using different enzymatic pathways

Wall teichoic acids (WTAs) are anionic polymers that play key roles in bacterial cell shape, cell division, envelope integrity, biofilm formation, and pathogenesis. B. subtilis W23 and S. aureus both make polyribitol-phosphate (RboP) WTAs and contain similar sets of biosynthetic genes. We use in vitro reconstitution combined with genetics to show that the pathways for WTA biosynthesis in B. subtilis W23 and S. aureus are different. S. aureus requires a glycerol-phosphate primase called TarF in order to make RboP-WTAs; B. subtilis W23 contains a TarF homolog, but this enzyme makes glycerol-phosphate polymers and is not involved in RboP-WTA synthesis. Instead, B. subtilis TarK functions in place of TarF to prime the WTA intermediate for chain extension by TarL. This work highlights the enzymatic diversity of the poorly characterized family of phosphotransferases involved in WTA biosynthesis in Gram-positive organisms.

Mutation of tagO reveals an essential role for wall teichoic acids in Staphylococcus epidermidis biofilm development

The icaADBC-encoded polysaccharide intercellular adhesin (PIA) and wall teichoic acids (WTA) are structural components of Staphylococcus epidermidis biofilms. Deletion of tagO, which encodes the first enzymic step in WTA biosynthesis, had pleiotropic effects, including enhanced intercellular aggregation and autolytic activity, and impaired biofilm production. The biofilm-negative phenotype of the tagO mutant, named TAGO1, was associated with increased cell surface hydrophobicity, lower rates of primary attachment to polystyrene, and reduced icaADBC operon and PIA expression. Mild acid stress induced by growth in BHI glucose media reduced rates of stationary phase autolysis and enhanced aggregation by TAGO1, leading to formation of a pellicle, which unlike a biofilm was only loosely attached to the polystyrene surface. TAGO1 pellicles were dispersed by proteinase K and DNase I but not sodium metaperiodate, implicating protein and extracellular DNA (eDNA) and not PIA in this phenotype. Substantially increased levels of eDNA were recovered from TAGO1 culture supernatants compared with the wild-type. These data indicate that WTA are essential for the primary attachment and accumulation phases of the S. epidermidis biofilm phenotype. Furthermore, in the absence of WTA, proteins and eDNA can promote cell aggregation and pellicle formation, which also appear to limit interactions with artificial surfaces.

Vibrational and electronic characterisation of Staphylococcus aureus wall teichoic acids and relevant components in thin films

This work reports an investigation of S. aureus wall teichoic acid (WTA) and compares this biopolymer with its major occurring components, D: -alanine and glycerol phosphate. Detailed insight into molecular structures and electronic properties is obtained by vibrational and photoemission spectroscopy. Calculations are performed to support the analysis of our experimental vibrational spectra. It is shown that there are contributions of positive and negative charges in WTAs, but the number of negative charges is expected to be higher. The presence of both positive and negative charges on WTA may offer a route for modification of surfaces with the objective of avoiding the formation of biofilms.

Glycosylation of wall teichoic acid in Staphylococcus aureus by TarM

Wall teichoic acid (WTA) glycopolymers are major constituents of cell envelopes in Staphylococcus aureus and related gram-positive bacteria with important roles in cell wall maintenance, susceptibility to antimicrobial molecules, biofilm formation, and host interaction. Most S. aureus strains express polyribitol phosphate WTA substituted with D-alanine and N-acetylglucosamine (GlcNAc). WTA sugar modifications are highly variable and have been implicated in bacteriophage susceptibility and immunogenicity, but the pathway and enzymes of staphylococcal WTA glycosylation have remained unknown. Revisiting the structure of S. aureus RN4220 WTA by NMR analysis revealed the presence of canonical polyribitol phosphate WTA bearing only alpha-linked GlcNAc substituents. A RN4220 transposon mutant resistant to WTA-dependent phages was identified and shown to produce altered WTA, which exhibited faster electrophoretic migration and lacked completely the WTA alpha-GlcNAc residues. Disruption of a gene of unknown function, renamed tarM, was responsible for this phenotype. Recombinant TarM was capable of glycosylating WTA in vitro in a UDP-GlcNAc-dependent manner, thereby confirming its WTA GlcNAc-transferase activity. Deletion of the last seven amino acids from the C terminus abolished the activity of TarM. tarM-related genes were found in the genomes of several WTA-producing bacteria, suggesting that TarM-mediated WTA glycosylation is a general pathway in gram-positive bacteria. Our study represents a basis for dissecting the biosynthesis and function of glycosylated WTA in S. aureus and other bacteria.

The wall teichoic acid and lipoteichoic acid polymers of Staphylococcus aureus

Staphylococci and most other Gram-positive bacteria incorporate complex teichoic acid (TA) polymers into their cell envelopes. Several crucial roles in Staphylococcus aureus fitness and cell wall maintenance have been assigned to these polymers, which are either covalently linked to peptidoglycan (wall teichoic acid, WTA) or to the cytoplasmic membrane (lipoteichoic acid, LTA). However, the exact TA structures, functions, and biosynthetic pathways are only superficially understood. Recently, most of the enzymes mediating TA biosynthesis have been identified and mutants lacking or with defined changes in WTA or LTA have become available. Their characterization has revealed crucial roles of TAs in protection against harmful molecules and environmental stresses; in control of enzymes directing cell division or morphogenesis and of cation homeostasis; and in interaction with host or bacteriophage receptors and biomaterials. Accordingly, several in vivo studies have demonstrated the importance of WTA and LTA in S. aureus colonization, infection, and immune evasion. TAs and enzymes required for TA biosynthesis represent attractive candidates for novel vaccines and antibiotics and are targeted by recently developed antibacterial therapeutics.

Discovery of a small molecule that blocks wall teichoic acid biosynthesis in Staphylococcus aureus

Both Gram-positive and Gram-negative bacteria contain bactoprenol-dependent biosynthetic pathways expressing non-essential cell surface polysaccharides that function as virulence factors. Although these polymers are not required for bacterial viability in vitro, genes in many of the biosynthetic pathways are conditionally essential: they cannot be deleted except in strains incapable of initiating polymer synthesis. We report a cell-based, pathway-specific strategy to screen for small molecule inhibitors of conditionally essential enzymes. The screen identifies molecules that prevent the growth of a wildtype bacterial strain but do not affect the growth of a mutant strain incapable of initiating polymer synthesis. We have applied this approach to discover inhibitors of wall teichoic acid (WTA) biosynthesis in Staphylococcus aureus. WTAs are anionic cell surface polysaccharides required for host colonization that have been suggested as targets for new antimicrobials. We have identified a small molecule, 7-chloro-N,N-diethyl-3-(phenylsulfonyl)-[1,2,3]triazolo[1,5-a]quinolin-5-amine (1835F03), that inhibits the growth of a panel of S. aureus strains (MIC = 1-3 microg mL(-1)), including clinical methicillin-resistant S. aureus (MRSA) isolates. Using a combination of biochemistry and genetics, we have identified the molecular target as TarG, the transmembrane component of the ABC transporter that exports WTAs to the cell surface. We also show that preventing the completion of WTA biosynthesis once it has been initiated triggers growth arrest. The discovery of 1835F03 validates our chemical genetics strategy for identifying inhibitors of conditionally essential enzymes, and the strategy should be applicable to many other bactoprenol-dependent biosynthetic pathways in the pursuit of novel antibacterials and probes of bacterial stress responses.

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

Biofilm formation in Staphylococcus aureus is usually associated with the production of the poly-N-acetylglucosamine (PNAG) exopolysaccharide, synthesized by proteins encoded by the icaADBC operon. PNAG is a linear beta-(1-6)-linked N-acetylglucosaminoglycan that has to be partially deacetylated and consequently positively charged in order to be associated with bacterial cell surfaces. Here, we investigated whether attachment of PNAG to bacterial surfaces is mediated by ionic interactions with the negative charge of wall teichoic acids (WTAs), which represent the most abundant polyanions of the Gram-positive bacterial envelope. We generated WTA-deficient mutants by in-frame deletion of the tagO gene in two genetically unrelated S. aureus strains. The DeltatagO mutants were more sensitive to high temperatures, showed a higher degree of cell aggregation, had reduced initial adherence to abiotic surfaces and had a reduced capacity to form biofilms under both steady-state and flow conditions. However, the levels as well as the strength of the PNAG interaction with the bacterial cell surface were similar between DeltatagO mutants and their corresponding wild-type strains. Furthermore, double DeltatagO DeltaicaADBC mutants displayed a similar aggregative phenotype to that of single DeltatagO mutants, indicating that PNAG is not responsible for the aggregative behaviour observed in DeltatagO mutants. Overall, the absence of WTAs in S. aureus had little effect on PNAG production or anchoring to the cell surface, but did affect the biofilm-forming capacity, cell aggregative behaviour and the temperature sensitivity/stability of S. aureus.

Teichoic acids and related cell-wall glycopolymers in Gram-positive physiology and host interactions

Most Gram-positive bacteria incorporate membrane- or peptidoglycan-attached carbohydrate-based polymers into their cell envelopes. Such cell-wall glycopolymers (CWGs) often have highly variable structures and have crucial roles in protecting, connecting and controlling the major envelope constituents. Further important roles of CWGs in host-cell adhesion, inflammation and immune activation have also been described in recent years. Identifying and harnessing highly conserved or species-specific structural features of CWGs offers excellent opportunities for developing new antibiotics, vaccines and diagnostics for use in the fight against severe infectious diseases, such as sepsis, pneumonia, anthrax and tuberculosis.

Late-stage polyribitol phosphate wall teichoic acid biosynthesis in Staphylococcus aureus

Wall teichoic acids are cell wall polymers that maintain the integrity of the cellular envelope and contribute to the virulence of Staphylococcus aureus. Despite the central role of wall teichoic acid in S. aureus virulence, details concerning the biosynthetic pathway of the predominant wall teichoic acid polymer are lacking, and workers have relied on a presumed similarity to the putative polyribitol phosphate wall teichoic acid pathway in Bacillus subtilis. Using high-resolution polyacrylamide gel electrophoresis for analysis of wall teichoic acid extracted from gene deletion mutants, a revised assembly pathway for the late-stage ribitol phosphate-utilizing enzymes is proposed. Complementation studies show that a putative ribitol phosphate polymerase, TarL, catalyzes both the addition of the priming ribitol phosphate onto the linkage unit and the subsequent polymerization of the polyribitol chain. It is known that the putative ribitol primase, TarK, is also a bifunctional enzyme that catalyzes both ribitol phosphate priming and polymerization. TarK directs the synthesis of a second, electrophoretically distinct polyribitol-containing teichoic acid that we designate K-WTA. The biosynthesis of K-WTA in S. aureus strain NCTC8325 is repressed by the accessory gene regulator (agr) system. The demonstration of regulated wall teichoic acid biosynthesis has implications for cell envelope remodeling in relation to S. aureus adhesion and pathogenesis.

Differential roles of sortase-anchored surface proteins and wall teichoic acid in Staphylococcus aureus nasal colonization

Most of the severe bacterial infections originate from the endogenous microflora of human body surfaces. However, the molecular basis of colonization, e.g. of the human nose by Staphylococcus aureus, has remained incompletely understood. Several surface-exposed proteins and wall teichoic acid (WTA) polymers have previously been implicated in S. aureus attachment to nasal epithelial cells. Here we dissect the role of these molecules in colonization using S. aureus sortase A (srtA) and tagO mutants deficient in surface protein and WTA display, respectively. Although the two mutants were similarly affected in attachment to nasal cells they were abrogated in binding to different types of epithelial ligands. Surface protein sorting, but not WTA, were required for keratin- or fibronectin-mediated interactions while only WTA-mediated binding to nasal cells was effectively inhibited by polyinosinic acid, indicating a possible role of scavenger receptor-like molecules in WTA-dependent epithelial interactions. Both mutants exhibited profound colonization defects in a cotton rat nasal colonization model, albeit at different stages of colonization (>90% reduced bacterial counts at 24h or several days after inoculation with the tagO or srtA mutant, respectively). These data indicate that S. aureus nasal colonization is a multifactorial process with various ligands affecting initial colonization and prolonged persistence in different ways. Our studies should be useful in the development of new preventive and therapeutic strategies.