Studies on the chemistry and immunochemistry of cell walls of Staphylococcus aureus

Invasive Staphylococcus epidermidis uses a unique processive wall teichoic acid glycosyltransferase to evade immune recognition

Staphylococcus epidermidis expresses glycerol phosphate wall teichoic acid (WTA), but some health care-associated methicillin-resistant S. epidermidis (HA-MRSE) clones produce a second, ribitol phosphate (RboP) WTA, resembling that of the aggressive pathogen Staphylococcus aureus. RboP-WTA promotes HA-MRSE persistence and virulence in bloodstream infections. We report here that the TarM enzyme of HA-MRSE [TarM(Se)] glycosylates RboP-WTA with glucose, instead of N-acetylglucosamine (GlcNAc) by TarM(Sa) in S. aureus. Replacement of GlcNAc with glucose in RboP-WTA impairs HA-MRSE detection by human immunoglobulin G, which may contribute to the immune-evasion capacities of many invasive S. epidermidis. Crystal structures of complexes with uridine diphosphate glucose (UDP-glucose), and with UDP and glycosylated poly(RboP), reveal the binding mode and glycosylation mechanism of this enzyme and explain why TarM(Se) and TarM(Sa) link different sugars to poly(RboP). These structural data provide evidence that TarM(Se) is a processive WTA glycosyltransferase. Our study will support the targeted inhibition of TarM enzymes, and the development of RboP-WTA targeting vaccines and phage therapies.

The staphylococcal surface-glycopolymer wall teichoic acid (WTA) is crucial for complement activation and immunological defense against Staphylococcus aureus infection

Staphylococcus aureus is a Gram-positive bacterial pathogen that is decorated by glycopolymers, including wall teichoic acid (WTA), peptidoglycan, lipoteichoic acid, and capsular polysaccharides. These bacterial surface glycopolymers are recognized by serum antibodies and a variety of pattern recognition molecules, including mannose-binding lectin (MBL). Recently, we demonstrated that human serum MBL senses staphylococcal WTA. Whereas MBL in infants who have not yet fully developed adaptive immunity binds to S. aureus WTA and activates complement serum, MBL in adults who have fully developed adaptive immunity cannot bind to WTA because of an inhibitory effect of serum anti-WTA IgG. Furthermore, we showed that human anti-WTA IgGs purified from pooled adult serum IgGs triggered activation of classical complement-dependent opsonophagocytosis against S. aureus. Because the epitopes of WTA that are recognized by anti-WTA IgG and MBL have not been determined, we constructed several S. aureus mutants with altered WTA glycosylation. Our intensive biochemical studies provide evidence that the β-GlcNAc residues of WTA are required for the induction of anti-WTA IgG-mediated opsonophagocytosis and that both β- and α-GlcNAc residues are required for MBL-mediated complement activation. The molecular interactions of other S. aureus cell wall components and host recognition proteins are also discussed. In summary, in this review, we discuss the biological importance of S. aureus cell surface glycopolymers in complement activation and host defense responses.

Glycoepitopes of staphylococcal wall teichoic acid govern complement-mediated opsonophagocytosis via human serum antibody and mannose-binding lectin

Serum antibodies and mannose-binding lectin (MBL) are important host defense factors for host adaptive and innate immunity, respectively. Antibodies and MBL also initiate the classical and lectin complement pathways, respectively, leading to opsonophagocytosis. We have shown previously that Staphylococcus aureus wall teichoic acid (WTA), a cell wall glycopolymer consisting of ribitol phosphate substituted with α- or β-O-N-acetyl-d-glucosamine (GlcNAc) and d-alanine, is recognized by MBL and serum anti-WTA IgG. However, the exact antigenic determinants to which anti-WTA antibodies or MBL bind have not been determined. To answer this question, several S. aureus mutants, such as α-GlcNAc glycosyltransferase-deficient S. aureus ΔtarM, β-GlcNAc glycosyltransferase-deficient ΔtarS, and ΔtarMS double mutant cells, were prepared from a laboratory and a community-associated methicillin-resistant S. aureus strain. Here, we describe the unexpected finding that β-GlcNAc WTA-deficient ΔtarS mutant cells (which have intact α-GlcNAc) escape from anti-WTA antibody-mediated opsonophagocytosis, whereas α-GlcNAc WTA-deficient ΔtarM mutant cells (which have intact β-GlcNAc) are efficiently engulfed by human leukocytes via anti-WTA IgG. Likewise, MBL binding in S. aureus cells was lost in the ΔtarMS double mutant but not in either single mutant. When we determined the serum concentrations of the anti-α- or anti-β-GlcNAc-specific WTA IgGs, anti-β-GlcNAc WTA-IgG was dominant in pooled human IgG fractions and in the intact sera of healthy adults and infants. These data demonstrate the importance of the WTA sugar conformation for human innate and adaptive immunity against S. aureus infection.

ISOLATION AND PROPERTIES OF A GROUP ANTIGEN OF STAPHYLOCOCCUS ALBUS

An antigen composed of glycerophosphate and glucose has been isolated from the cell walls of a strain of Staphylococcus albus. The antigen reacted with homologous and heterologous S. albus antisera. Similar material was isolated from the cell walls of three other S. albus strains. The antigen did not react with S. aureus antiserum nor with normal human or rabbit serum. The antigen appeared to have a backbone structure of glycerophosphate with appended monoglucoside units. The antigenic determinant was shown to be glucose in alpha linkage.

Studies on the interactions between components of Staphylococcus aureus and Staphylococcus bacteriophage

The cell walls of Staphylococcus aureus are capable of inactivating S. aureus bacteriophage. Furthermore, the cell walls isolated from S. aureus of a given phage type inactivate a variety of different staphylococcal bacteriophages. Under the conditions employed neither the isolated mucopeptide nor teichoic acid components of the cell walls act as bacteriophage receptor.

Chemical basis for an immunological specificity of a strain of Staphylococcus aureus

Antisera, prepared against formalin-killed cells of Staphylococcus aureus, strain Copenhagen, agglutinated the cell walls of this strain. The agglutination was inhibited by the teichoic acid from the cell wall of this strain, by any degradation product of this teichoic acid which contained the alpha-acetylglucosaminyl-ribitol unit, by alpha-phenyl-acetylglucosaminide, and by N-acetylglucosamine, but not by a large number of other haptens related to the cell wall. In quantitative experiments, however, only 40 to 50 per cent of antibody adsorption to cell wall could be inhibited by teichoic acid or by N-acetylglucosamine. The alpha-acetylglucosaminyl-ribitol unit in the teichoic acid is, therefore, an important immunological determinant in the cell wall of this strain, although other immunological specificities may also exist. The cell walls were also agglutinated by heterologous antisera prepared against streptococcal Group A carbohydrate or against horse serum azophenyl-beta-acetylglucosaminide. The heterologous agglutination, however, was specific for the beta-acetylglucosaminyl-ribitol units in the teichoic acid.

SEPARATION OF TEICHOIC ACID OF STAPHYLOCOCCUS AUREUS INTO TWO IMMUNOLOGICALLY DISTINCT SPECIFIC POLYSACCHARIDES WITH ALPHA- AND BETA-N-ACETYLGLUCOSAMINYL LINKAGES RESPECTIVELY. ANTIGENICITY OF THEICHOIC ACIDS IN MAN

Human sera were found to contain antibodies precipitating with each of two samples of teichoic acid of Staphylococcus aureus prior to immunization; these antibodies were probably formed as a result of contact or infection with this microorganism. Injection of teichoic acid into two individuals resulted in a rise in circulating antibody to teichoic acid; a third subject probably had a primary response to α-teichoic acid. Quantitative precipitin and agar diffusion studies revealed the presence of two distinct antibodies in the sera and showed that each specimen of teichoic acid was a mixture of two polymers an α-linked N-acetylglucosaminyl-ribitol polymer and a β-linked N-acetylglucosaminyl-ribitol polymer, termed α- and β-teichoic acids respectively. The α-teichoic acid anti-α-teichoic acid system was inhibited best by α-linked glucosaminides and the β-anti-β-teichoic acid system was inhibited best by a β-linked glucosaminide. The α- and (β-teichoic acids could be separated from each other by specific precipitation under appropriate conditions and recovered from the washed specific precipitates. The existence of two distinct teichoic acid polymers raises important questions as to cell wall structure and the biosynthesis of the teichoic acids.

STUDIES ON HUMAN ANTIBODIES. I. STARCH GEL ELECTROPHORESIS OF THE DISSOCIATED POLYPEPTIDE CHAINS

Specific precipitates and purified human antibodies were reduced and alkylated and subjected to starch gel electrophoresis in 8 M urea to dissociate and separate the L and H polypeptide chains. Dissociated antibodies to dextran, levan, teichoic acid, blood group A substance, and tetanus toxoid showed sharp bands corresponding to L polypeptide chains. The patterns differed for antibodies of different specificities. Some differences were also seen among antibodies of the same specificity from different individuals. Purified antidextran antibodies showed particularly simple patterns resembling those of purified human γ myeloma proteins. In some cases only one L chain band was present.

STUDIES ON HUMAN ANTIBODIES. II. DISTRIBUTION OF GENETIC FACTORS

Human antibodies against dextran, teichoic acid, blood group A substance, levan, tetanus toxoid, and nuclei were isolated and analyzed for their content of Gm(a), Gm(b), and Inv(a) γ-globulin genetic factors. The majority of these antibodies contained all the genetic factors determined in the donor's whole γ-globulin, but in many antibodies at very different concentrations. In a few instances specific factors could not be detected despite their presence in the individual's whole γ-globulin. Different antibodies isolated from the serum of the same individual showed different relative concentrations of genetic factors. The distribution of genetic factors seen in certain isolated human antibodies appeared to approach the selective occurrence of these factors in myeloma proteins.

Preparation of a latex reagent for the detection of anti-Staphylococcus aureus ribitol teichoic acid antibodies

Purified S. aureus ribitol teichoic acid was covalently bound to carboxylated latex particles. The immunological properties of the polysaccharide antigen were preserved. The reagent obtained was used for the quantification of anti-ribitol teichoic acid antibodies by means of a direct and rapid agglutination test carried out on a slide. There was good correlation between the preliminary results of this test and those obtained with counter-immunoelectrophoresis (CIE). The method is faster and more sensitive than CIE.

Study of Staphylococcus aureus teichoic acid immunodominant site by help of synthetic haptens

The beta ribitol teichoic acid was extracted and purified from Staphylococcus aureus strain Wood 46 and chemically and immunologically characterised. Rabbit antiserum was prepared against formalin killed Staphylococcus aureus cells. Liquid phase immunoprecipitation of the beta ribitol teichoic acid-anti-Staphylococcus aureus serum system was studied by laser nephelometry. Various mono- and disaccharides (N-acetyl-glucosamine-ribitol with alpha- or beta-linkage and N-acetyl-glucosamine-ribitol-phosphate with beta-linkage) were prepared by organic synthesis, reproducing part of the ribitol teichoic acid molecule. Inhibition by those mono- or disaccharides of the precipitation of the beta-ribitol teichoic acid-Staphylococcus aureus antibodies system was studied quantitatively by determining inhibitory ratio of each inhibitor. Glucose, ribitol and glucosamine were weak inhibitors whereas N-acetyl-glucosamine was a better one, stronger than disaccharide with an alpha-linkage. The beta linked disaccharide and beta-methyl-N-acetyl-glucosamine gave comparable inhibition and both compounds were effective inhibitors. The most potent inhibitor was phosphorylated beta-linked disaccharide which inhibited 25% more than the same disaccharide without phosphorus. Thus, the function of phosphorus in Staphylococcus aureus beta ribitol teichoic acid recognition by antibodies was demonstrated.

Ultrastructural localization of carbohydrates on thin sections of Staphylococcus aureus with silver methenamine and wheat germ agglutinin-gold complex

Postembedding staining of intracellular carbohydrates on thin sections of Staphylococcus aureus was studied by the silver methenamine and the wheat germ agglutinin-gold techniques. Staining of silver grains was observed on both the cell wall and the cross wall. The staining was interpreted to be due to teichoic acid. Labeling by wheat germ agglutinin-gold particles was observed on both the cell wall and the cross wall, and the staining pattern resembled that of silver methenamine staining. Therefore, the labeling was considered to be due to N-acetylglucosamine of teichoic acid. The combination of two types of cytochemical techniques was useful to localize and characterize the carbohydrates of the bacterial cell.

Teichoic acid serology in staphylococcal infections of infants and children

Counterimmunoelectrophoresis and gel diffusion were utilized for the detection and titration of antibodies to staphylococcal teichoic acids in various disease states caused by coagulase-positive staphylococcus in infants and children. Serum samples were obtained on admission and serially for 2 to 12 weeks during illness. Teichoic acid antibodies were found by CIE in 12 of 21 patients (57%) with invasive CPS disease with bacteremia (Group A), in two of 17 patients (12%) with CPS infection without bacteremia (Group B), in none of 27 patients with bacteremia and/or invasive infections caused by organisms other than CPS (Group C), and in none of 24 noninfected, hospitalized patients or healthy children (Group D). Gel diffusion was useful for titrating antibodies in seropositive sera. Teichoic acid serology is a useful adjunct in the diagnosis of invasive CPS infections. The presence of these antibodies by CIE and gel diffusion may help to identify patients with endothelial or metastatic infections associated with staphylococcal bacteremia.

Teichoic acids in pathogenic Staphylococcus aureus

Twenty-six strains of Staphylococcus aureus obtained from patients with endocarditis were studied for the production of alpha- and/or beta-ribitol teichoic acid (TA), using highly specific anti-TA antibodies prepared in rabbits. A counterimmunoelectrophoretic assay was used. Beta-TA was the predominant residue produced by all strains; alpha-TA was found in all strains, but in smaller amounts and with much strain-to-strain variations. Antibodies in patients' sera were found against beta-TA in higher titers and for longer periods than were anti-alpha-TA antibodies. Antibodies against one or both TA residues were present in all but one of 26 patients.

Activation of complement by opportunist pathogens and chemotypes of Salmonella minnesota

Washed cells of Staphylococcus aureus, Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa, and Salmonella minnesota chemotypes (S, Rb, and Re) were tested for their ability to activate the alternative complement pathway (ACP). Parameters of ACP activation were (i) conversion of C3 in 10 mM ethyleneglycol-bis-(beta-aminoethyl ether)-N,N1-tetraacetic acid-treated human serum supplemented with 2.5 mM MgCl2, (ii) lysis of glutathione-treated human erythrocytes in the presence of human serum, and (iii) C3 to C9 consumption in C4-deficient guinea pig serum. With the exception of S. minnesota Re and S. aureus, all of the strains were highly active in the test systems when compared with inulin. S. minnesota Re and S. aureus initiated C3 conversion in untreated human serum, suggesting that these microorganisms were capable of activating complement by a mechanism other than the ACP. These results provide direct evidence for ACP activation by opportunist gram-negative bacilli and refute the hypothesis that the lipid A moiety of the lipopolysaccharide cell wall is responsible for ACP activation.

Studies on the immunochemistry of Staphylococcus aureus cell wall: antigenicity of pentaglycine bridges

The specific antigenicity of pentaglycine bridges in cell walls of S. aureus was investigated. The antistaphylococcal sera (against 11 Oeding strains of S. aureus) were found to contain antibodies of two different specificities against polyglycyl peptides; one type reacted with polyglycyl peptides with a free amino terminus and the other with polyglycyl peptides with a free carboxyl terminus. These antibodies were assayed by passive hemagglutination with tanned sheep red cells sensitized with N-polyglycyl-BSA (containing polyglycyl peptides with a free amino terminus) or with C-poe antibodies against N-polyglycyl peptides were absorbed by S. aureus strains and by S. epidermidis. Heterologous bacterial species failed to absorb antibodies of either specificity. Antibodies against polyglycyl peptides were used to confirm the mechanism of action of penicillin on S. aureus cell wall.

Purification and properties of lysozyme produced by Staphylococcus aureus

A method based on cold ethyl alcohol fractionation at different pH levels and ionic strengths and on gel filtration on a Sephadex G-200 column was used to concentrate and purify lysozyme from the culture supernatant fluid of Staphylococcus aureus strain 524. The final, nondialyzable product exhibited a 163-fold rise in specific activity over that of the starting material. Staphylococcal lysozyme is a glycosidase which splits N-acetylamino sugars from the susceptible substrate. Staphylococcal lysozyme was shown to be similar to egg white lysozyme in its optimal temperature for reaction, optimal pH, activation by NaCl and Ca(++) ions, inhibition by sodium citrate and ethylenediaminetetraacetate, and inactivation by Cu(++) ions and sodium dodecyl sulfate. It differs from the egg white lysozyme in its temperature susceptibility range (staphylococcal lysozyme is inactivated at 56 C). It acts on whole cells and cell walls of Micrococcus lysodeikticus, murein from S. aureus 524, and cell walls of S. epidermidis Zak. The last substrate was not susceptible to the action of egg white lysozyme in the test system used. The mechanism of action of staphylococcal lysozyme seems to be analogous to that of egg white lysozyme; however, the biological specificity of the two enzymes may be different.

Serological activity of staphylococcal polysaccharide

The polysaccharide from cell walls of coagulase-positive staphylococci coated both latex particles and tanned red cells for agglutination by human sera and by specific staphylococcal antisera. Treatment with trypsin or autoclaving destroyed the capacity of polysaccharide to coat particles but did not affect precipitation of antibody. Periodic acid destroyed both properties. The teichoic acid portion of the staphylococcal polysaccharide displayed precipitin activity similar to polysaccharide, but it did not coat either latex particles or tanned red cells. Teichoic acid did, however, inhibit specific agglutination of polysaccharide-coated particles or cells.

Electron microscopy of Staphylococcus aureus cell wall lysis

Virgilio, Rafael (Escuela de Química y Farmacia, Universidad de Chile, Santiago, Chile), C. González, Nubia Muñoz, and Silvia Mendoza. Electron microscopy of Staphylococcus aureus cell wall lysis. J. Bacteriol. 91:2018-2024. 1966.-A crude suspension of Staphylococcus aureus cell walls (strain Cowan III) in buffer solution was shown by electron microscopy to lyse slightly after 16 hr, probably owing to the action of autolysin. The lysis was considerably faster and more intense after the addition of lysozyme. A remarkable reduction in thickness and rigidity of the cell walls, together with the appearance of many irregular protrusions in their outlines, was observed after 2 hr; after 16 hr, there remained only a few recognizable cell wall fragments but many residual particulate remnants. When autolysin was previously inactivated by trypsin, there was a complete inhibition of the lytic action of lysozyme; on the other hand, when autolysin was inactivated by heat and lysozyme was added, a distinct decrease in the thickness of the cell walls was observed, but there was no destruction of the walls. The lytic action of lysozyme, after treatment with hot 5% trichloroacetic acid, gave rise to a marked dissolution of the structure of the cell walls, which became lost against the background, without, however, showing ostensible alteration of wall outlines. From a morphological point of view, the lytic action of autolysin plus lysozyme was quite different from that of trichloroacetic acid plus lysozyme, as shown by electron micrographs, but in both cases it was very intense. This would suggest different mechanisms of action for these agents.