Activation of complement by cell surface components of Staphylococcus aureus

Growth of Staphylococcus aureus in the presence of oleic acid shifts the glycolipid fatty acid profile and increases resistance to antimicrobial peptides

Staphylococcus aureus readily adapts to various environments and quickly develops antibiotic resistance, which has led to an increase in multidrug-resistant infections. Hence, S. aureus presents a significant global health issue and its adaptations to the host environment are crucial for understanding pathogenesis and antibiotic susceptibility. When S. aureus is grown conventionally, its membrane lipids contain a mix of branched-chain and straight-chain saturated fatty acids. However, when unsaturated fatty acids are present in the growth medium, they become a major part of the total fatty acid composition. This study explores the biophysical effects of incorporating straight-chain unsaturated fatty acids into S. aureus membrane lipids. Membrane preparations from cultures supplemented with oleic acid showed more complex differential scanning calorimetry scans than those grown in tryptic soy broth alone. When grown in the presence of oleic acid, the cultures exhibited a transition significantly above the growth temperature, attributed to the presence of glycolipids with long-chain fatty acids causing acyl chain packing frustration within the bilayer. Functional aspects of the membrane were assessed by studying the kinetics of dye release from unilamellar vesicles induced by the antimicrobial peptide mastoparan X. Dye release was slower from liposomes prepared from cells grown in oleic acid-supplemented cultures, suggesting that changes in membrane lipid composition and biophysics protect the cell membrane against peptide-induced lysis. These findings underscore the intricate relationship between the growth environment, membrane lipid composition, and the physical properties of the bacterial membrane, which should be considered when developing new strategies against S. aureus infections.

Staphylococcus aureus delta toxin modulates both extracellular membrane vesicle biogenesis and amyloid formation

IMPORTANCE

Extracellular membrane vesicles (MVs) produced by Staphylococcus aureus in planktonic cultures encapsulate a diverse cargo of bacterial proteins, nucleic acids, and glycopolymers that are protected from destruction by external factors. δ-toxin, a member of the phenol soluble modulin family, was shown to be critical for MV biogenesis. Amyloid fibrils co-purified with MVs generated by virulent, community-acquired S. aureus strains, and fibril formation was dependent on expression of the S. aureus δ-toxin gene (hld). Mass spectrometry data confirmed that the amyloid fibrils were comprised of δ-toxin. Although S. aureus MVs were produced in vivo in a localized murine infection model, amyloid fibrils were not observed in the in vivo setting. Our findings provide critical insights into staphylococcal factors involved in MV biogenesis and amyloid formation.

Lipoteichoic Acid from Staphylococcus aureus Activates the Complement System via C3 Induction and CD55 Inhibition

Staphylococcus aureus inhibits complement activity by secreting a variety of toxins. However, the underlying mechanism of complement component regulation by lipoteichoic acid (LTA), a cell wall component of S. aureus, has not been elucidated. In this study, we observed that aLTA (LTA of S. aureus) increased C3 expression in THP-1 cells. The mechanism of aLTA-mediated C3 induction includes an aLTA-toll-like receptor (TLR) 2 interaction, interleukin 1 receptor associated kinase (IRAK) 2 recruitment, and nuclear factor kappa B (NF-kB) activation. In HepG2 cells, C3 protein production begins to increase from 3 h and increases steadily until 48 h. On the other hand, CD55 levels increased up to 6 h after aLTA treatment and started to decrease after 24 h and levels were decreased at 48 h by more than 50% compared to untreated cells. The expression of CD55 in HepG2 cells was shown to be regulated by IRAK-M induced by aLTA. Serum C3 levels increased in mice injected with aLTA, which resulted in an increase in the amount and activity of the membrane attack complex (MAC). We also observed that CD55 mRNA was increased in the liver 24 h after aLTA injection, but was decreased 48 h after injection. These results suggest that aLTA increases complement levels via induction of C3 and inhibition of CD55, which may cause associated MAC-mediated liver damage.

The Role of Macrophages in Staphylococcus aureus Infection

Staphylococcus aureus is a member of the human commensal microflora that exists, apparently benignly, at multiple sites on the host. However, as an opportunist pathogen it can also cause a range of serious diseases. This requires an ability to circumvent the innate immune system to establish an infection. Professional phagocytes, primarily macrophages and neutrophils, are key innate immune cells which interact with S. aureus, acting as gatekeepers to contain and resolve infection. Recent studies have highlighted the important roles of macrophages during S. aureus infections, using a wide array of killing mechanisms. In defense, S. aureus has evolved multiple strategies to survive within, manipulate and escape from macrophages, allowing them to not only subvert but also exploit this key element of our immune system. Macrophage-S. aureus interactions are multifaceted and have direct roles in infection outcome. In depth understanding of these host-pathogen interactions may be useful for future therapeutic developments. This review examines macrophage interactions with S. aureus throughout all stages of infection, with special emphasis on mechanisms that determine infection outcome.

Lipidomic and Ultrastructural Characterization of the Cell Envelope of Staphylococcus aureus Grown in the Presence of Human Serum

Comprehensive lipidomics of S. aureus grown in the presence of human serum suggests that human serum lipids can associate with the cell envelope without being truly integrated into the lipid membrane. However, fatty acids derived from human serum lipids, including unsaturated fatty acids, can be incorporated into lipid classes that can be biosynthesized by S. aureus itself. Cholesteryl esters and triglycerides are found to be the major source of incorporated fatty acids upon hydrolysis by lipases. These findings have significant implications for the nature of the S. aureus cell surface when grown in vivo. Changes in phospholipid and glycolipid abundances and fatty acid composition could affect membrane biophysics and function and the activity of membrane-targeting antimicrobials. Finally, the association of serum lipids with the cell envelope has implications for the physicochemical nature of the cell surface and its interaction with host defense systems.

Staphylococcus aureus can incorporate exogenous straight-chain unsaturated and saturated fatty acids (SCUFAs and SCFAs, respectively) to replace some of the normally biosynthesized branched-chain fatty acids and SCFAs. In this study, the impact of human serum on the S. aureus lipidome and cell envelope structure was comprehensively characterized. When S. aureus was grown in the presence of 20% human serum, typical human serum lipids, such as cholesterol, sphingomyelin, phosphatidylethanolamines, and phosphatidylcholines, were present in the total lipid extracts. Mass spectrometry showed that SCUFAs were incorporated into all major S. aureus lipid classes, i.e., phosphatidylglycerols, lysyl-phosphatidylglycerols, cardiolipins, and diglucosyldiacylglycerols. Heat-killed S. aureus retained fewer serum lipids and failed to incorporate SCUFAs, suggesting that association and incorporation of serum lipids with S. aureus require a living or nondenatured cell. Cytoplasmic membranes isolated from lysostaphin-produced protoplasts of serum-grown cells retained serum lipids, but washing cells with Triton X-100 removed most of them. Furthermore, electron microscopy studies showed that serum-grown cells had thicker cell envelopes and associated material on the surface, which was partially removed by Triton X-100 washing. To investigate which serum lipids were preferentially hydrolyzed by S. aureus lipases for incorporation, we incubated individual serum lipid classes with S. aureus and found that cholesteryl esters (CEs) and triglycerides (TGs) are the major donors of the incorporated fatty acids. Further experiments using purified Geh lipase confirmed that CEs and TGs were the substrates of this enzyme. Thus, growth in the presence of serum altered the nature of the cell surface with implications for interactions with the host.

IMPORTANCE Comprehensive lipidomics of S. aureus grown in the presence of human serum suggests that human serum lipids can associate with the cell envelope without being truly integrated into the lipid membrane. However, fatty acids derived from human serum lipids, including unsaturated fatty acids, can be incorporated into lipid classes that can be biosynthesized by S. aureus itself. Cholesteryl esters and triglycerides are found to be the major source of incorporated fatty acids upon hydrolysis by lipases. These findings have significant implications for the nature of the S. aureus cell surface when grown in vivo. Changes in phospholipid and glycolipid abundances and fatty acid composition could affect membrane biophysics and function and the activity of membrane-targeting antimicrobials. Finally, the association of serum lipids with the cell envelope has implications for the physicochemical nature of the cell surface and its interaction with host defense systems.

Staphylococcus aureus coagulases are exploitable yet stable public goods in clinically relevant conditions

Coagulation is an innate defense mechanism intended to limit blood loss and trap invading pathogens during infection. However, Staphylococcus aureus has the ability to hijack the coagulation cascade and generate clots via secretion of coagulases. Although many S. aureus have this characteristic, some do not. The population dynamics regarding this defining trait have yet to be explored. We report here that coagulases are public goods that confer protection against antimicrobials and immune factors within a local population or community, thus promoting growth and virulence. By utilizing variants of a methicillin-resistant S. aureus we infer that the secretion of coagulases is a cooperative trait, which is subject to exploitation by invading mutants that do not produce the public goods themselves. However, overexploitation, "tragedy of the commons," does not occur at clinically relevant conditions. Our micrographs indicate this is due to spatial segregation and population viscosity. These findings emphasize the critical role of coagulases in a social evolution context and provide a possible explanation as to why the secretion of these public goods is maintained in mixed S. aureus communities.

Exposure of Staphylococcus aureus to Targocil Blocks Translocation of the Major Autolysin Atl across the Membrane, Resulting in a Significant Decrease in Autolysis

Peptidoglycan (PG) and wall teichoic acid (WTA) are the major staphylococcal cell wall components, and WTA biosynthesis has recently been explored for drug development. Targocil is a novel agent that targets the TarG subunit of the WTA translocase (TarGH) that transports WTA across the membrane to the wall. Previously we showed that targocil treatment of a methicillin-susceptible Staphylococcus aureus strain led to a rapid shut down of cellular autolysis. Targocil II, which targets the TarH subunit of TarGH, also resulted in a drastic decrease in autolysis. Here, we address the mechanism of targocil-mediated decreased autolysis. The mechanism is WTA dependent since targocil treatment decreased autolysis in methicillin-resistant strains but not in a WTA-deficient mutant. Similar to cellular autolysis, autolysin-retaining crude cell walls isolated from targocil-treated cells had vastly decreased autolytic activity compared to those from untreated cells. Purified cell walls from control and targocil-treated cells, which lack autolytic activity, were similarly susceptible to lysozyme and lysostaphin and had similar O-acetyl contents, indicating that targocil treatment did not grossly alter PG structure and chemistry. Purified cell walls from targocil-treated cells were highly susceptible to autolysin extracts, supporting the notion that targocil treatment led to decreased autolysin in the crude cell walls. Quantitative real-time PCR analysis revealed that the decrease in autolysis in the targocil-exposed cells was not due to transcriptional repression of the autolysin genes atl, lytM, lytN, and sle1 Zymographic analysis of peptidoglycan hydrolase profiles showed a deficiency of cell surface autolysins in targocil-treated cells but higher activity in cell membrane fractions. Here, we propose that the untranslocated WTA molecules in the targocil-exposed cells sequester Atl at the membrane, resulting in significantly decreased autolysis.

Application of fluorescent monocytes for probing immune complexes on antigen microarrays

Microarrayed antigens are used for identifying serum antibodies with given specificities and for generating binding profiles. Antibodies bind to these arrayed antigens forming immune complexes and are conventionally identified by secondary labelled antibodies.In the body immune complexes are identified by bone marrow derived phagocytic cells, such as monocytes. In our work we were looking into the possibility of replacing secondary antibodies with monocytoid cells for the generation of antibody profiles. Using the human monocytoid cell line U937, which expresses cell surface receptors for immune complex components, we show that cell adhesion is completely dependent on the interaction of IgG heavy chains and Fcγ receptors, and this recognition is susceptible to differences between heavy chain structures and their glycosylation. We also report data on a possible application of this system in autoimmune diagnostics.Compared to secondary antibodies, fluorescent monocytesas biosensors are superior in reflecting biological functions of microarray-bound antibodies and represent an easy and robust alternative for profiling interactions between serum proteins and antigens.

CD66b overexpression and homotypic aggregation of human peripheral blood neutrophils after activation by a gram-positive stimulus

Neutrophils represent the main component of innate immunity in the clearance of bacterial infections. To pass the tissue and to localize and reach the site of infection, the peripheral blood neutrophils have to pass through a complex receptor-mediated interaction with the endothelial layer. Under pathophysiological conditions, such as severe sepsis, this process is impaired and often characterized by neutrophil aggregation. In this study, we examined the impact of three different Staphylococcus aureus strains on the activation status of human peripheral blood neutrophils by coincubation of bacterial culture supernatant with whole blood. This complex interaction of a gram-positive stimulus with blood components leads to a special neutrophil activation phenotype, which is characterized by an overexpression of the cell-surface molecule CD66b. The process is accompanied by a strong increase of homotypic aggregates and seems to be initialized by a massive activation impulse caused by the interplay of plasma components. This maximum activation of neutrophils prior to the complex and highly regulated activation required for transmigration might play a key role in the neutrophil dysfunction in gram-positive sepsis.

A play in four acts: Staphylococcus aureus abscess formation

Staphylococcus aureus is an important human pathogen that causes skin and soft tissue abscesses. Abscess formation is not unique to staphylococcal infection and purulent discharge has been widely considered a physiological feature of healing and tissue repair. Here we present a different view, whereby S. aureus deploys specific virulence factors to promote abscess lesions that are distinctive for this pathogen. In support of this model, only live S. aureus is able to form abscesses, requiring genes that act at one or more of four discrete stages during the development of these infectious lesions. Protein A and coagulases are distinctive virulence attributes for S. aureus, and humoral immune responses specific for these polypeptides provide protection against abscess formation in animal models of staphylococcal disease.

Solution insights into the structure of the Efb/C3 complement inhibitory complex as revealed by lysine acetylation and mass spectrometry

The extracellular fibrinogen-binding protein (Efb), an immunosuppressive and anti-inflammatory protein secreted by Staphylococcus aureus, has been identified as a potent inhibitor of complement-mediated innate immunity. Efb functions by binding to and disrupting the function of complement component 3 (C3). In a recent study, we presented a high-resolution co-crystal structure of the complement inhibitory domain of Efb (Efb-C) bound to its cognate domain (C3d) from human C3 and employed a series of structure/function analyses that provided evidence for an entirely new, conformational change-based mechanism of complement inhibition. To better understand the Efb/C3 complex and its downstream effects on C3 inhibition, we investigated the solvent-accessibility and protein interface of Efb(-C)/C3d using a method of lysine acetylation, proteolytic digestion, and mass spectrometric analysis. Lysine modification in Efb was monitored by the mass increment of lysine-containing fragments. Besides confirming the binding sites observed in co-crystal structure study, the in-solution data presented here suggest additional contacting point(s) between the proteins that were not revealed by crystallography. The results of this study demonstrate that solution-based analysis of protein-protein interactions can provide important complementary information on the nature of protein-protein interactions.

Characterization of Ehp, a secreted complement inhibitory protein from Staphylococcus aureus

We report here the discovery and characterization of Ehp, a new secreted Staphylococcus aureus protein that potently inhibits the alternative complement activation pathway. Ehp was identified through a genomic scan as an uncharacterized secreted protein from S. aureus, and immunoblotting of conditioned S. aureus culture medium revealed that the Ehp protein was secreted at the highest levels during log-phase bacterial growth. The mature Ehp polypeptide is composed of 80 residues and is 44% identical to the complement inhibitory domain of S. aureus Efb (extracellular fibrinogen-binding protein). We observed preferential binding by Ehp to native and hydrolyzed C3 relative to fully active C3b and found that Ehp formed a subnanomolar affinity complex with these various forms of C3 by binding to its thioester-containing C3d domain. Site-directed mutagenesis demonstrated that Arg(75) and Asn(82) are important in forming the Ehp.C3d complex, but loss of these side chains did not completely disrupt Ehp/C3d binding. This suggested the presence of a second C3d-binding site in Ehp, which was mapped to the proximity of Ehp Asn(63). Further molecular level details of the Ehp/C3d interaction were revealed by solving the 2.7-A crystal structure of an Ehp.C3d complex in which the low affinity site had been mutationally inactivated. Ehp potently inhibited C3b deposition onto sensitized surfaces by the alternative complement activation pathway. This inhibition was directly related to Ehp/C3d binding and was more potent than that seen for Efb-C. An altered conformation in Ehp-bound C3 was detected by monoclonal antibody C3-9, which is specific for a neoantigen exposed in activated forms of C3. Our results suggest that increased inhibitory potency of Ehp relative to Efb-C is derived from the second C3-binding site in this new protein.

A structural basis for complement inhibition by Staphylococcus aureus

To provide insight into bacterial suppression of complement-mediated immunity, we present here structures of a bacterial complement inhibitory protein, both free and bound to its complement target. The 1.25-A structure of the complement component C3-inhibitory domain of Staphylococcus aureus extracellular fibrinogen-binding protein (Efb-C) demonstrated a helical motif involved in complement regulation, whereas the 2.2-A structure of Efb-C bound to the C3d domain of human C3 allowed insight into the recognition of complement proteins by invading pathogens. Our structure-function studies provided evidence for a previously unrecognized mode of complement inhibition whereby Efb-C binds to native C3 and alters the solution conformation of C3 in a way that renders it unable to participate in successful 'downstream' activation of the complement response.

The Role of TLR2 In Vivo following Challenge withStaphylococcus aureusand Prototypic Ligands

Based on a wealth of in vitro macrophage studies, immunity to Staphylococcus aureus cell wall-derived peptidoglycan (PGN) and lipoteichoic acid has been attributed to TLR2. We investigated whether the in vitro paradigm of TLR2 dominance would hold true in vivo. Using an experimental peritonitis model, we challenged mice with PGN or lipoteichoic acid and found that only PGN resulted in significant leukocyte (primarily neutrophil) accumulation in the peritoneum at 4 h. PGN-mediated leukocyte recruitment was P-/E-selectin dependent but only partially TLR2 dependent, and also involved the C5aR. Concomitant inhibition of TLR2 and C5aR resulted in a further reduction in PGN-induced peritonitis. Peritoneal neutrophilia was partially mast cell dependent; however, the defect could not be reconstituted with TLR2(-/-) or C5aR(-/-) mast cells. Interestingly, macrophage-deficient mice did not have defective neutrophil recruitment. By 24 h, the response to PGN involved primarily monocytes and was TLR2 and C5aR independent. Finally, we challenged mice with live S. aureus and found a similar degree of TLR2 involvement in leukocyte recruitment to that observed with PGN. Most importantly, bacterial clearance from the spleen and peritoneum was not altered in TLR2(-/-) mice vs wild-type mice. Morbidity was only significantly increased in S. aureus-infected mice treated with a blocking Fab against C5aR. Taken together, these studies indicate that in vivo responses to prototypic TLR2 ligands do not necessarily recapitulate the absolute necessity for TLR2 observed in vitro, and additional receptors contribute, in a significant manner, to PGN and S. aureus-mediated immune responses.

Staphylococcus aureus strains that express serotype 5 or serotype 8 capsular polysaccharides differ in virulence

Most isolates of Staphylococcus aureus produce a serotype 5 (CP5) or 8 (CP8) capsular polysaccharide. To investigate whether CP5 and CP8 differ in their biological properties, we created isogenic mutants of S. aureus Reynolds that expressed CP5, CP8, or no capsule. Biochemical analyses of CP5 and CP8 purified from the isogenic S. aureus strains were consistent with published structures. The degree of O acetylation of each polysaccharide was similar, but CP5 showed a greater degree of N acetylation. Mice challenged with the CP5(+) strain showed a significantly higher bacteremia level than mice challenged with the CP8(+) strain. Similarly, the CP5(+) strain survived preferentially in the bloodstream and kidneys of infected mice challenged with a mixed inoculum containing both strains. The enhanced virulence of the CP5(+) strain in vivo correlated with its greater resistance to in vitro killing in whole mouse blood. Likewise, in vitro opsonophagocytic killing assays with human neutrophils and sera revealed greater survival of the Reynolds (CP5) strain, even though the kinetics of opsonization by C3b and iC3b was similar for both the CP5(+) and CP8(+) strains. Electron micrographs demonstrated C3 molecules on the cell wall beneath the capsule layer for both serotype 5 and 8 strains. Purified CP5 and CP8 stimulated a modest oxidative burst in human neutrophils but failed to activate the alternative complement pathway. These results indicate that CP5 and CP8 differ in a number of biological properties, and these differences likely contribute to the relative virulence of serotype 5 and 8 S. aureus in vivo.

Increased inflammation in lysozyme M-deficient mice in response to Micrococcus luteus and its peptidoglycan

More than 70 years ago, Alexander Fleming discovered lysozyme and proposed that nonpathogenic bacteria fail to cause disease because they are very susceptible to destruction by lysozyme, an enzyme that is one of the principal proteins of phagocytes. Although much has been learned about the effects of lysozyme in vitro, its biological role in vivo has not been determined. We examined transgenic mice deficient in lysozyme M after challenge by the normally nonpathogenic and highly lysozyme-sensitive bacterium Micrococcus luteus. Despite partial compensation by newly expressed lysozyme P in macrophages, lysozyme M-deficient mice developed much more severe lesions than wild-type mice. The tissue injury was due to the failure of lysozyme M-deficient mice to inactivate peptidoglycan, resulting in an intense and prolonged inflammatory response. Our data indicate that tissue injury is normally limited by prompt degradation of bacterial macromolecules that trigger innate immunity and inflammation.

Cytokine secretion by stimulated monocytes depends on the growth phase and heat treatment of bacteria: a comparative study between lactic acid bacteria and invasive pathogens

The consumption of food containing lactic acid bacteria (LAB) has been shown to exert immunomodulatory effects in humans. The specific cellular interaction of these bacteria with immuno-competent cells has not yet been fully understood. Since the TNF-alpha secretion of stimulated monocytes is an important initial response to a bacterial challenge, we investigated the potential of LAB originating from the human intestine or fermented food in comparison to the effect of invasive pathogens. The challenge of monocytes with three LAB strains, Listeria monocytogenes or enterohaemorrhagic Escherichia coli (EHEC) elicited a strain specific, dose-dependent biphasic TNF-alpha secretion. The concentration (EDmax) of bacteria or bacterial cell wall components necessary to induce maximal TNF-alpha secretion (TNFmax) by monocytes was mathematically approximated. It was shown for exponentially growing LAB strains that the maximal TNF-alpha secretion (TNFmax) was stronger (57 to 78%) upon stimulation with living bacteria than with heat killed cells. In contrast to log-phase bacteria, the maximal TNF-alpha secretion of monocytes (TNFmax) was higher (15 to 55%) after the stimulation with heat killed, stationary-phase bacteria when compared to that of live LAB. Thus, monocyte stimulation was clearly affected by the growth phase of bacteria. Purified cell walls of LAB strains revealed only a limited potential for monocyte stimulation. LPS exhibited a higher capacity to stimulate monocytes than purified gram positive cell walls or muramyldipeptide. In comparison to pathogenic bacteria, the maximal secretory TNF-alpha response (TNFmax) was up to 2 fold higher with LAB strains. In general, the amount of bacteria (EDmax) necessary to induce maximal TNF-alpha secretion (TNFmax) was approximately 1 to 3 log higher for heat killed bacteria when compared to live bacterial cells illustrating the significant lower potential of heat killed bacteria to activate monocytes.

Staphylococcal culture supernates stimulate human phagocytes

Phagocytes play a major role in host defense against staphylococci as well as in the pathophysiology of Gram-positive septic shock. In Gram negative sepsis, the main mediator, LPS exerts its effects as easily suspendable mediator. In Gram positive sepsis the main mediator is still not found, therefore we studied the interaction of soluble staphylococcal products with phagocytes. Staphylococcus aureus supernates (SaS) were harvested from several laboratory and clinical strains that were grown to late-log phase. These supernates upregulated CD11b/CD18 expression on human neutrophils even in a 100-fold dilution. SaS also induced the release of TNF-alpha and IL-1 beta by human monocytes. Control experiments excluded peptidoglycan, lipoteichoic acid, alpha and delta toxin, leucocidin, TSST-1 and all enterotoxins as sole mediators. Endotoxin contamination was also excluded. SaS was heat-stable; incubation for 45 minutes at 100 degrees C did not affect its activity. Compared to purified peptidoglycan and intact bacteria per bacterium, SaS had a higher potency in stimulating phagocytes. We hypothesize that there are more--yet unknown--soluble staphylococcal products which are very important in phagocyte stimulation.

A pplications of genetics to studies of bacterial virulence

Classical genetic techniques have made it possible in many instances to discern which bacterial factors are directly involved in causation of infection, as opposed to those that are associated with but do not directly contribute to virulence. By use of these methods as well as monoclonal antibodies, recombinant DNA, and other new techniques it has been shown that bacterial virulence is complicated, with involvement of many different bacterial factors at each step of infection; bacterial factors that facilitate one step of infection may actually impede a subsequent step. Interestingly, a large number of genes involved in toxin production or bacterial cell-surface structure are carried on unstable elements (phage, plasmids). In addition, many chromosomal genes affecting surface antigens or appendages involved in pathogenesis are subject to high-frequency variation, enabling the bacterium to adapt rapidly to different ecological niches or to evade host immunological defences. Genetic approaches have greatly increased our appreciation for the sophistication of successful bacterial pathogens, and are rapidly being used to create exciting new vaccines.

Serum-induced potentiation of tumor necrosis factor alpha production by human monocytes in response to staphylococcal peptidoglycan: involvement of different serum factors

Peptidoglycan from a Staphylococcus epidermidis strain, isolated from a patient with septicemia, was preincubated with human serum. This mixture was then investigated for its potency to induce tumor necrosis factor (TNF) secretion by human blood monocytes. TNF was measured in the supernatants by using a bioassay and/or an enzyme-linked immunosorbent assay specific for TNF alpha (TNF-alpha). Although earlier studies indicated that staphylococcal peptidoglycan alone is a relatively poor stimulator of TNF-alpha production, the present study shows that human serum highly potentiates peptidoglycan-induced TNF-alpha release by human monocytes. In the presence of serum and in the low-dose range, peptidoglycan was almost as potent as endotoxin. At high peptidoglycan concentrations, monocytes showed an extremely high TNF-alpha response, but again only in the presence of serum. At low peptidoglycan doses, the stimulatory effect of serum was abrogated by heat treatment or depleting serum of complement components C1 and C3/C4, which suggests a role for the classical complement pathway. At high doses of peptidoglycan, the serum stimulatory effect depended mainly on immunoglobulin G.

Induction of release of tumor necrosis factor from human monocytes by staphylococci and staphylococcal peptidoglycans

The role of cytokines in gram-positive infections is still relatively poorly defined. The purpose of this study was to establish whether or not intact staphylococci and purified peptidoglycans and peptidoglycan components derived from staphylococci are capable of stimulating the release of tumor necrosis factor (TNF) by human monocytes. We show here that intact staphylococci and purified peptidoglycans, isolated from three Staphylococcus epidermidis and three S. aureus strains, were indeed able to induce secretion of TNF by human monocytes in a concentration-dependent fashion. TNF release was detected by both enzyme immunoassay and the L929 fibroblast bioassay. In the enzyme immunoassay, a minimal concentration of peptidoglycan of 1 micrograms/ml was required to detect TNF release by monocytes, whereas in the bioassay a peptidoglycan concentration of 10 micrograms/ml was needed to detect a similar amount of TNF release. Peptidoglycan components such as the stem peptide, tetra- and pentaglycine, and muramyl dipeptide were unable to induce TNF release from human monocytes.

The macrophage response to bacteria. Modulation of macrophage functional activity by peptidoglycan from Moraxella (Branhamella) catarrhalis

Moraxella (Branhamella) catarrhalis organisms have been shown to be particularly efficient in inducing in a pure population of bone marrow-derived mononuclear phagocytes secretory and cellular activities. In the present study, the ability of peptidoglycan from this Gram-negative organism to trigger a macrophage response was compared with that elicited by peptidoglycan from Staphylococcus aureus and Bacillus subtilis. The results show that the three peptidoglycans were similarly active in triggering the secretion of tumour necrosis factor and tumouricidal activity but differed considerably in their ability to induce the generation of nitrite in macrophages; in this respect, peptidoglycan from M. catarrhalis was particularly potent. The impressive capacity of M. catarrhalis peptidoglycan to induce in low concentration the secretion of tumour necrosis factor and nitrite and tumouricidal activity may, in addition to its lipopolysaccharide, contribute to the extraordinary potential of this organism to trigger the functional activities of macrophages.

The continuing importance of staphylococci as major hospital pathogens

Rates of hospital-acquired staphylococcal infection have risen substantially in the United States over the last decade. Moreover, it has been shown that bloodstream infections caused by these organisms account for significant morbidity and mortality. It is likely that the changes in medical practice and in types of patient account for these changes, and current antibiotic therapy has helped select more resistant organisms. The increasing use of implantable and temporary medical devices and the increased use of immunosuppressive therapies correlate strongly with the rising incidence of these organisms. Likewise, more patients are predisposed to these infections because of poor immune status and factors favouring colonization. Intrinsic microbiological factors such as glycocalyx production and the presence of bacterial surface proteins allow these organisms to adhere to protein coated foreign bodies and basement membranes thus enabling them to initiate infection and cause disease. Moreover, virulence factors such as encapsulation, slime production and elaboration of extracellular enzymes aid their resistance to host defences. As a group, staphylococci are a leading cause of hospital-acquired infection, and species identification is required for both treatment and control.

Induction of anti-phagocytic surface properties of Staphylococcus aureus from bovine mastitis by growth in milk whey

The respiratory burst activity of bovine polymorphonuclear (PMN) cells in response to milk whey- and TSB-grown S. aureus strains isolated from bovine mastitis was studied in whole blood chemiluminescence (CL) and in a CL system with purified bovine neutrophils. In both cases milk whey-grown S. aureus strains elicited significantly less CL than homologous strains grown in TSB. Ingestion of milk whey-grown S. aureus strains by bovine neutrophils was also considerably lower than that of the corresponding homologous organisms grown in TSB. Binding of complement factor C3 to serum-opsonized milk whey-grown S. aureus strains was lower compared with TSB-grown homologous organisms. Moreover, 5 of 6 S. aureus strains grown in milk whey were significantly more resistant to in vivo clearance from the peritoneal cavity of mice compared with homologous bacteria grown in TSB. S. aureus strains grown in TSB exhibited hydrophobic surface properties, whereas homologous strains grown in milk whey were hydrophilic.

Antiphagocytic effect of the capsule of Staphylococcus simulans

An encapsulated strain of Staphylococcus simulans was observed to be more resistant to phagocytosis by human granulocytes than was a nonencapsulated strain. Phagocytosis of the encapsulated strain was enhanced by antisera to S. simulans, but opsonic activity of antisera was removed by absorption with S. simulans capsular material. The encapsulated strain of S. simulans was also more invasive than the nonencapsulated S. simulans in vivo. More encapsulated than nonencapsulated S. simulans were found in heart blood when equal numbers of organisms were injected intraperitoneally into mice. Invasion of the bloodstreams of mice by encapsulated S. simulans was prevented by passive immunization (rabbit antiserum). Thus, the capsule of S. simulans inhibited phagocytosis in vitro and contributed to virulence in vivo.

Cell surface antigen of encapsulated Staphylococcus epidermidis SE-360 protects mice from homologous infection

Cell surface antigen was mechanically extracted from encapsulated strain SE-360 of Staphylococcus epidermidis and purified by DEAE-Sephadex A 25 (Cl- form) ion exchange chromatography. This antigen manifested type-specific activity and major sugar constituents were galactose, glucose and N-acetyl-glucosamine at the molar ratio 1.00:9.05:1.65. alpha-D-glucosyl- and N-acetyl-glucosaminyl-residues were closely correlated to the antigenic determinant. In mice, protection against homologous microorganisms could be achieved by active immunization with thus purified antigen. Type-specific opsonin in rabbit anti-SE-360 serum could also be absorbed.

Clinical significance and pathogenesis of hyperbilirubinemia associated with Staphylococcus aureus septicemia

PURPOSE

Our goal was to examine the clinical significance of hyperbilirubinemia in patients with Staphylococcus aureus endocarditis. In addition, preliminary data concerning the possible mechanism of cholestasis observed during S. aureus septicemia are presented.

PATIENTS AND METHODS

This study had two parts: a clinical investigation and a laboratory investigation. In the former, patients with endocarditis were identified through chart review. Those with admission total serum bilirubin levels of 2.0 mg/dl or greater were considered to have hyperbilirubinemia. In the latter investigation, the hepatic storage capacity and transport maximum for sulfobromophthalein (BSP), an organic dye that is rapidly taken up and excreted by the liver, were determined by measuring the change in serum concentration and the corresponding hepatic removal rate at various BSP infusion rates. Measurements were conducted before and after the infusion of Escherichia coli-derived lipopolysaccharide in some rabbits, after the infusion of resuspended S. aureus in others, and after the infusion of lipoteichoic acid in the remainder.

RESULTS

Eleven of 47 consecutive patients with S. aureus endocarditis were noted to have hyperbilirubinemia without clinical or laboratory evidence of hepatic bacterial infection. Compared with the remaining 36 patients, these 11 patients had a significantly lower mean platelet count and a higher serum creatinine level and white blood cell count. Although none of the 47 patients were hypotensive on admission, four of the 11 hyperbilirubinemic patients died of overwhelming sepsis, compared with two of the 36 remaining patients (p less than 0.05). When one of the clinical isolates of S. aureus or lipoteichoic acid was infused into conscious rabbits, there was a marked decrease in the hepatic transport maximum and an increase in the relative hepatic storage capacity of sulfobromophthalein. Similar changes were noted following the administration of lipopolysaccharide.

CONCLUSION

Our data suggest that the presence of hyperbilirubinemia in patients with S. aureus sepsis may identify persons at high risk of dying from overwhelming sepsis. It further suggests that lipoteichoic acid may play an important role in causing defective hepatic excretory function that is responsible for hyperbilirubinemia.

The role of plasmids in opsonin-independent Staphylococcus aureus-leukocyte interactions

The opsonin-independent phagocytic and bactericidal activity of human polymorphonuclear leukocytes stimulated by two Staphylococcus aureus strains and their variants with differing plasmid patterns was investigated. Interactions between staphylococci and phagocytes were evaluated by chemiluminescence and intracellular killing tests. The results obtained indicate that the presence or absence of certain plasmids can modify staphylococcal phagocytosis and their susceptibility to intracellular killing. Pretreatment of the strains investigated with subinhibitory concentrations of mezlocillin and ofloxacin (10% MIC) influenced these parameters, too.

Investigations on opsonin-independent antistaphylococcal activity of human neutrophilic granulocytes, monocytes and lymphocytes

Using cells from 20 healthy human donors the opsonin-independent staphylococcal killing abilities of peripheral blood neutrophilic granulocytes, monocytes and lymphocytes were studied. S. aureus strains T 1 and T 14, S. sciuri strain S I, S. saprophyticus strain S III and S. simulans strain S V were selected for these experiments because of their differing cell wall composition, surface hydrophobicity, protein A content and extracellular enzyme activity spectrum. We could demonstrate a very individual activity range of these cells against staphylococci. On the other hand each staphylococcal strain examined behaved in a very typical way in its susceptibility against the killing by human phagocytes and lymphocytes. Repeated tests in monthly intervals showed that the staphylococcal killing activity range of phagocytes and lymphocytes of a certain healthy donor remains constant and stable.

Interaction of purified lipoteichoic acid with the classical complement pathway

Glycerophosphate-containing lipoteichoic acids (LTAs) interact with the first component of the classical complement pathway (C1). This resulted in the activation of the classical complement pathway in serum, shown by the consumption of C1, C2, and C4. The dose-dependent interaction of LTAs with purified C1 and C1q was dependent on the negative charges of the phosphate groups of LTA. It was reduced by charge compensation through D-alanine ester substituents and by sterical hindrance through di- and trihexosyl residues linked to position 2 of the glycerol moieties. The charge density of LTA may also play a role: poly(digalactosylglycerophosphate) LTAs, in which the phosphate groups are in a greater distance from each other, were less effective, and the loss of micellar organization by deacylation of LTA drastically reduced the complement activation capacity.

Complement activation by clumping factor and protein A from Staphylococcus aureus strain E 2371

Purified surface components from Staphylococcus aureus strain E 2371, which bind to human plasma proteins, were tested for their ability in vitro to activate complement present in normal human serum. Staphylococcal clumping factor as well as protein A both isolated from strain E 2371 were capable of activate complement, while the fibronectin-binding protein showed no activity. At identical molar concentrations clumping factor was more potent than protein A to induce complement consumption. Both clumping factor and protein A were able to activate the alternative complement pathway as demonstrated in serum chelated with ethylene-glycerol-tetra-acetic acid (10 mM) in the presence of MgCl2 (10 mM).

Activation of the alternative complement pathway by pneumococcal lipoteichoic acid

Cell wall teichoic acids of some gram-positive bacteria are potent activators of the alternative pathway of complement. It is unclear, however, whether the other form of teichoic acid, cell membrane lipoteichoic acid (LTA), can also activate the alternative pathway. In the present study, radiolabelled pneumococcal LTA was found to bind spontaneously to sheep erythrocytes in a temperature- and time-dependent fashion. In addition, the presence of pneumococcal LTA on the erythrocyte surface was verified by the fact that they could be agglutinated by a myeloma protein (TEPC-15) specific for choline, a constituent of pneumococcal LTA. Pneumococcal LTA when fixed to the surface of erythrocytes was able to activate the alternative pathway of complement in both guinea pig serum deficient in the fourth component of complement and human serum deficient in the second component of complement, resulting in lysis of the sensitized erythrocytes. The sensitizing principle of the LTA preparation was removed before erythrocyte sensitization by immunoabsorption, using the choline-specific TEPC-15 myeloma protein. These data demonstrate that purified pneumococcal LTA will bind to sheep erythrocytes and endow them with the ability to activate the alternative pathway.

Protein A and staphylococcal products in neoplastic disease

Tumoricidal responses and tumor regressions have been observed after plasma perfusion over Staphylococcus aureus Cowan I (SAC), or purified protein A immobilized on solid supports. This system was initially studied in a single human patient and then extended to dogs with spontaneous mammary carcinoma, an excellent model of human breast cancer. In the single patient and dogs with mammary tumors, perfusion of plasma over protein A bearing staphylococcus resulted in tumor necrosis and tumor regression. Tumor reduction or growth retardation with similar perfusion systems has been noted in various feline and rodent tumor models. Tumoricidal responses were also observed in canine tumors after perfusion over commercial protein A which was immobilized in a collodion charcoal matrix (PACC). These responses were amplified when a subtherapeutic and nontoxic dose of cytarabine was given after perfusion. Similar tumor reduction in murine and feline tumor models has been noted after perfusion of autologous serum over protein A immobilized on various other solid supports. The PACC perfusion system was extended to five consecutive patients with advanced breast adenocarcinoma. Four of five patients showed tumor regression after perfusion of small volumes of autologous or homologous plasma over PACC. Patients also experienced pyrexia, nausea, vomiting, and significant cardiopulmonary toxicity. Detailed hemodynamic studies of these effects showed that the major pathophysiology involved a decline in total peripheral resistance associated with an increase in cardiac output. With reduction of immobilized protein A quantity and diminution in plasma perfusion rate, the cardiopulmonary toxicity associated with treatments was diminished. Chemotherapy given as FAC to a single patient shortly after concluding perfusion therapy resulted in rapid regression of residual large tumor masses. Studies focusing on the mechanism of the tumoricidal responses have examined changes in sera after incubation or perfusion over immobilized SAC or PACC. Major findings include (1) the identification of protein A leaching from PACC and SAC after serum perfusion and appearing in the effluent as Clq binding oligomers composed predominantly of IgG and protein A but also containing IgA, IgM and C3 with a molecular weight range of 600,000 to 2,000,000; (2) the identification of C3a anaphylatoxins in serum perfused over PACC or SAC; (3) the recognition that several enterotoxins, in particular enterotoxin B are present in commercial protein A preparation.(ABSTRACT TRUNCATED AT 400 WORDS)

Bacterial adherence and glycocalyx formation in osteomyelitis experimentally induced with Staphylococcus aureus

A surgical procedure allowed the placement of a silicone rubber catheter in the marrow cavity of the tibia of a rabbit and also allowed the introduction of a sclerosing agent (sodium morrhuate) and cells of Staphylococcus aureus. Osteomyelitis developed in 60% of the animals so treated, and the infecting microorganism was recovered from the infected tibias of the animals that developed this disease. All blood cultures taken 24 h after the infection were negative for S. aureus. Radiological findings consisted of osteolytic changes, the occurrence of sequestration and periosteal reactions, and sclerosis in the infected bones. Sections of bone prepared for histological examination confirmed the diagnosis of osteomyelitis. Transmission and scanning electron microscopy of samples of bone marrow, bone chips, and the catheters taken from the infected tibiae revealed gram-positive cocci embedded in a very extensive matrix of ruthenium red-staining glycocalyx adhering to the bone and the implanted catheter. It is proposed that this extensive glycocalyx served a protective function for the bacteria and was important in bacterial adherence and thus played an important role in bacterial persistence and the development of osteomyelitis in these rabbits.

Complement and the host's defense against the pneumococcus

The complement system plays a critical role in resistance to Streptococcus pneumoniae. In the last two decades, a great deal of new knowledge has been generated on both the complement system and on the pneumococcus. Not only has this new knowledge helped produce a better understanding of how the complement system serves the host in its defense against S. pneumoniae, but in a more general fashion, the lessons learned from the interaction of complement and the pneumococcus have also provided insight into how the complement system functions in the defense of the host against a wide variety of other microorganisms. The following review will attempt to summarize current knowledge about the complement system, how it interacts at the molecular level with the pneumococcus, the biologic consequences of that interaction, and their significance in pneumococcal infections.

Polymorphonuclear leukocytes: dedicated professional phagocytes

Polymorphonuclear leukocytes are termed professional phagocytes because they are specially equipped to seek and destroy invading microorganisms. Polymorphonuclear leukocytes are formed in the bone marrow and released into the circulation, where they are transported to the tissues. At sites of tissue invasion by microorganisms, humoral factors are released that induce these cells to leave the bloodstream and enter the tissues. Chemotactic substances guide polymorphonuclear leukocytes to the infecting organisms. Antibody and complement can function as opsonins and enhance the ability of polymorphonuclear leukocytes to engulf microbes. Ingested organisms are killed by oxidative or nonoxidative systems. Defects in the various aspects of polymorphonuclear leukocyte function may be found in patients with recurrent, severe, or unusual infections. Evaluation of selected patients with recurrent infections should include tests of polymorphonuclear leukocyte function.

Activation of the alternate complement pathway by peptidoglycan of Actinomyces viscosus, a potentially pathogenic oral bacterium

Peptidoglycans and cells walls from Actinomyces viscosus, Staphylococcus aureus, and group A streptococcus were compared for their relative abilities to activate the alternate complement pathway (ACP). On the dry-weight basis, the peptidoglycan from A. viscosus was 3.5 times more active than group A streptococcal peptidoglycan and 15.6 times more active than Staph. aureus peptidoglycan in activating the ACP. Consequently A. viscosus peptidoglycan is one of the most potent ACP-activators reported to date. For both A. viscosus and group A streptococcus, the peptidoglycan was a better ACP activator than cell walls from the same organism (125- and 52-fold, respectively) indicating that the peptidoglycan is probably the most important subcellular ACP-activator in these microorganisms. In contrast, cell walls from Staph, aureus were 9 times more active than peptidoglycan from Staph. aureus in activating the ACP, presumably because teichoic acids are the most important subcellular ACP activator in this microorganism.

Biological effects of the interaction of staphylococcal alpha-toxin with human serum

The alpha-toxin (hemolysin) of Staphylococcus aureus is known to be an important determinant of pathogenicity although its precise role in the process of infection is not understood. In this study, the interaction of alpha-toxin with the human complement system was evaluated in terms of its effect on the opsonic activity of serum for S. aureus. Phagocytosis by human polymorphonuclear leukocytes was studied by measuring the uptake of preopsonized radiolabeled bacteria. It was found that alpha-toxin-treated serum had reduced opsonic activity and that this change was associated with complement consumption via the classical pathway. Levels of C3 to C9 were reduced in proportion to the amount of toxin added to the reaction mixture; levels of C2 were markedly reduced but those of factors B and D of the alternative pathway were unaltered in the presence of alpha-toxin. Heat-inactivated toxin, which had no hemolytic activity, also interacted with the complement system but with a significantly reduced effect. In addition, alpha-toxin behaved as a chemotaxinogen for polymorphonuclear leukocytes: human serum was activated by the toxin. These studies demonstrate that the interaction of staphylococcus alpha-toxin with human serum affects two important aspects of the host response to the staphylococcus.

Activation of components of the alternative pathway of complement by Propionibacterium acnes cell wall carbohydrate

The trichloroacetic acid (TCA) extractable molecules in Propionibacterium acnes cell wall were tested for the ability to activate the alternative pathway of complement in human serum treated with ethyleneglycol-bis (beta-aminoethyl ether) N,N-tetracetic acid (EGTA). The extracted molecules failed to consume hemolytic activity against antibody-coated sheep erythrocytes but gave a dose-dependent consumption of rabbit erythrocyte (RE) lytic activity. Similarly, the extract produced significant cleavage of Factor B, but failed to cleave C3, as detected by immunoelectrophoresis. Adsorption of the extracted material to sheep erythrocytes did not render the cells susceptible to lysis via the alternative pathway. Sephadex G-25 chromatography yielded several fractions which were able to consume RE lytic activity from EGTA-treated serum. These fractions were analyzed and found to contain glucose, mannose, and galactose. No teichoic acid or protein was detected. The alternative pathway activator in P. acnes is thus a nonteichoic acid cell wall carbohydrate which, in its extractable form is capable of activating only alternative pathway reactants prior to C3.

Studies on bacterial hypersensitivity in man. Interrelationship between skin reactions to bacterial peptidoglycan and serum peptidoglycan antibody titers

The nature and extent of bacterially induced allergies are difficult to define. Since peptidoglycan, the main component of the cell wall of almost all bacteria, has been available in a highly purified, chemically and immunologically well-defined form, investigation of the allergological significance of this cell component is feasible. Intracutaneous tests were carried out on 181 test subjects with five different peptidoglycan (PG) preparations from Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus Pyogenes. The results of the investigation were compared with the result of determination of serum PG antibodies and serum IgE concentrations. It was shown that test subjects with dual and later reactions to three different staphylococcal PGs displayed significantly higher PG antibody titers than test subjects with negative reactions. Such a relationship could not be found with the cutaneous reactions to streptococcal PG. The total serum IgE values were very much higher in test subjects with immediate reactions to staphylococcal PG than in test subjects with a negative reaction. Typical Arthus reaction or late granulomatous reactions were not observed. Humoral antibodies are involved at least in part in the elicitation of dual and late reactions. Thus, there are interesting parallels to allergy to fungal spores and organic dusts.

Morphological examination of the glycocalyces of Staphylococcus aureus strains Wiley and Smith

The glycocalyces of gram-positive bacteria have only been studied to a limited extent, with most studies being directed at the elucidation of capsules. With modern methods of electron microscopy, it has been shown that an extensive, diffuse polyanionic matrix surrounds Staphylococcus aureus cells of the Smith and Wiley strains, both in vivo and in modified staphylococcus 110 media. This slime layer was extracapsular in the case of the Smith strain, yet appeared to be the only layer peripheral to the teichoic acid in the Wiley strain. It is proposed that these glycocalyces serve a protective function and that their production is induced not only by excess nutrients in the growth medium but also by metabolic stress.

A transient deficit in neutrophilic chemotaxis in a dog with recurrent staphylococcal pyoderma

A transient neutrophilic chemotactic deficit was confirmed in a 3 1/2-year-old castrated male dog with recurrent staphylococcal pyoderma accompanied by a persistent eosinophilia and intermittent basophilia. Neutrophilic chemotaxis was quantitatively assessed over the next seven months, and the disappearance of the chemotactic deficit correlated with complete clinical remission of the skin lesions. Aberrations of the complement system were not discovered, and the dog's serum showed increased chemoattractiveness for control neutrophil preparations.

Complement consumption gonococcal peptidoglycan

Purified peptidoglycan (PG) obtained from Neisseria gonorrhoeae was tested for the ability to consume complement in normal human sera. Sonicated PG (S-PG), a heterogeneous mixture of soluble fragments (molecular weight, greater than 10(6)), as well as intact (insoluble) PG, reduced the level of whole hemolytic complement in a pool of four human sera. The minimal concentration of S-PG required for this activity was approximately 500 micrograms of S-PG per ml of serum. Complete lysozyme digestion of S-PG, yielding PG fragments of less than 10(4) molecular weight, eliminated complement-consuming activity. S-PG-mediated complement consumption resulted in depletion of the individual complement components C4 and C3. Consumption of complement did not occur when C4-deficient human serum or normal human sera treated with Mg2+-(ethylene glycol-bis(beta-aminoethyl ether)-N,N-tetraacetic acid to specifically impair classical complement pathway activity were used. The addition of rabbit anti-PG antibody greatly enhanced gonococcal PG-mediated complement consumption. Together, the data suggested that gonococcal PG-mediated complement consumption occurred via the classical complement pathway, was dependent on the presence of anti-PG antibody, and required glycosidically linked polymers of PG. Individual human sera varied widely in the extent of gonococcal PG-mediated reduction of complement levels, presumably a reflection of either different amounts of natural antibody to gonococcal PG, different levels of human PG hydrolase(s) capable of degrading PG to inactive fragments, or both.

Protein A effect on alternative pathway complement activation and opsonization of Staphylococcus aureus

Twelve Staphylococcus aureus strains with known amounts of protein A were compared with regard to alternative pathway complement activation and opsonization in human serum. "Protein A-poor" strains (less than or equal to 0.16 ng/10(6) bacteria) were, on the average, 3. 4-fold more efficient in alternative pathway complement activation than "protein A-rich" strains (greater than or equal to 0.625 ng/10(6) bacteria) (P less than 0.001). Protein A-poor strains were significantly better phagocytized by human polymorphonuclear leukocytes after opsonization in magnesium-ethylene glycol-bis (beta-amino-ethyl ether)-N, N-tetraacetic acid-chelated serum than were the protein A-rich strains (P less than 0.001). No significant differences between protein A-poor and -rich strains were found in complement activation and opsonization in normal serum. Cell wall-bound protein A appeared to hinder alternative pathway complement activation by S. aureus, which resulted in decreased opsonization of these bacteria in the absence of an intact classical pathway. These studies suggest that protein A may cover alternative pathway complement-activating sites within the peptidoglycan matrix of the staphylococcal cell wall.

Binding of human immunoglobulin G to protein A in encapsulated Staphylococcus aureus

Recent studies of the mechanism of resistance to phagocytosis in encapsulated Staphylococcus aureus have suggested that the capsule is readily penetrated by high-molecular-weight proteins such as antibodies and complement components. S. aureus strains contain a cell wall protein, protein A, that reacts with the Fc portion of immunoglobulins. The binding of immunoglobulin G (IgG) to encapsulated and unencapsulated S. aureus strains has been studied to assess the penetrability of the S. aureus capsule by IgG. Encapsulated S. aureus strains M and Smith diffuse bound large amounts of human IgG which were comparable to amounts bound by the unencapsulated strains Cowan I, M variant, and Smith compact. Trypsin treatment of bacteria reduced their ability to bind IgG. Bound IgG was not removed by extensive washing of bacteria with buffer. A non-protein A-containing, coagulase-negative, encapsulated staphylococcal strain did not bind IgG. These observations suggest that IgG is binding to cell wall protein A in encapsulated S. aureus. No differences in the rates of IgG binding by encapsulated and unencapsulated S. aureus strains were observed. It is concluded that the S. aureus capsule is freely permeable to IgG. This is of importance in considerations of the mechanisms of resistance to phagocytosis and antigen masking in encapsulated microorganisms.