Can we learn from the pathogenetic strategies of group A hemolytic streptococci how tissues are injured and organs fail in post-infectious and inflammatory sequelae?

Evaluation of post-infectious inflammatory reactions in a retrospective study of 3 common invasive bacterial infections in pediatrics

Infectious diseases can result in unanticipated post-infectious inflammatory reactions (PIIR). Our aim was to explore PIIR in 3 frequent pediatric bacterial invasive infections in France by a retrospective monocentric study. We included children hospitalized between 2003 and 2012 for Streptococcus pneumoniae (SP), Neisseria meningitidis (NM), or Streptococcus pyogenes invasive infections. The PIIR had to have occurred between 3 and 15 days without fever despite an individually tailored antibiotic therapy. A descriptive analysis was carried out to determine PIIR risk factors. We included 189 patients, of whom 72, 79, and 38 exhibited invasive infections caused by S pyogenes, SP, and NM, respectively. The mean age was 44 months. PIIR were observed in 39 cases, occurring after a median of 8 days (5-12), with a median duration of 3 days (2-6). Fever, arthritis, and pleural effusion were observed in 87%, 28.2%, and 25.6%, respectively. In multivariate analysis, PIIR were associated with pleuropneumonia, hospitalization in an intensive care unit (ICU), and elevated C-reactive protein (CRP). PIIR were observed in 20% of children after SP, NM, or S pyogenes invasives infections. Their occurrence was associated with the initial severity but not the etiological microorganism. Further studies are warranted to confirm these findings.

Mechanism by which immune complexes are deposited in hosts tissue

We offer an explanation how immune complexes are deposited in tissues of auto-immune disorders in humans. These disorders are characterized by the accumulation in tissues of large numbers of neutrophils, which can shed out long extracellular traps (NETs) rich in a nucleosome and in highly opsonic poly cations, histone, LL37, defensins and elastase possessing properties similar to antibodies. These can bind by strong electrostatic forces to negatively charged domains in immune globulins, thus facilitating their deposition and internalization by tissue cells. However, the main cause for tissue damage in auto-immune patients is inflicted by the plethora of toxic pro-inflammatory agents released by activated neutrophils. To ameliorate tissue damage and the cytokine storms, it is recommended to administer to patients highly anionic heparins accompanied by steroids, methotrexate, colchicine, copaxone, and also by additional agents which retarded neutrophil functions.

A Novel Hypothetical Approach to Explain the Mechanisms of Pathogenicity of Rheumatic Arthritis

The autoimmune disorder rheumatoid arthritis (RA) is a relapsing and chronic inflammatory disease that affects the synovial cells, cartilage, bone, and muscle. It is characterised by the accumulation of huge numbers of polymorphonuclear neutrophils (PMNs) and macrophages in the synovia. Auto-antibodies are deposited in the joint via the activity of highly cationic histones released from neutrophil extracellular traps (NETs) in a phenomenon termed NETosis. The cationic histones function as opsonic agents that bind to negatively charged domains in autoantibodies and complement compounds via strong electrostatic forces, facilitating their deposition and endocytosis by synovial cells. However, eventually the main cause of tissue damage is the plethora of toxic pro-inflammatory substances released by activated neutrophils recruited by cytokines. Tissue damage in RA can also be accompanied by infections which, upon bacteriolysis, release cell-wall components that are toxic to tissues. Some amelioration of the damaged cells and tissues in RA may be achieved by the use of highly anionic heparins, which can neutralize cationic histone activity, provided that these polyanions are co-administrated with anti-inflammatory drugs such as steroids, colchicine, or methotrexate, low molecular weight antioxidants, proteinase inhibitors, and phospholipase A2 inhibitors.

A novel aspect may explain the mechanisms of pathogenicity of rheumatic fever, a multifactorial, autoimmune, infectious and inflammatory disorder which "licks the joints and bites the heart": A working hypothesis

A novel hypothesis is presented to explain the pathogenesis of the multifactorial autoimmune disorder rheumatic fever (RF). It involves a synergistic interaction among streptococcal toxins, their cell wall components, M protein, immune complexes, complement components, cationic histones. These agents can act with cationic histones released by neutrophils during NETosis and bacteriolysis and can function as opsonic agents possessing properties similar to antibodies. Cationic histones can interact by strong electrostatic forces with negatively- charged domains on immune complexes and complement components. This allows their deposition and endocytosis in the myocardium, the heart valves, and in the joints. However, the main cause of cell and tissue damage observed in RF is due to a synergism among the plethora of pro-inflammatory substances released by activated neutrophils and macrophages. Cell damage may be mitigated to some extent by anionic heparins, heparinoids, and by anti-inflammatory drugs such as corticosteroids which counteract neutrophils and macrophage chemotaxis induced by cytokines.

Pro-inflammatory agents released by pathogens, dying host cells, and neutrophils act synergistically to destroy host tissues: a working hypothesis

We postulate that the extensive cell and tissue damage inflicted by many infectious, inflammatory and post-inflammatory episodes is an enled result of a synergism among the invading microbial agents, host neutrophils and dead and dying cells in the nidus. Microbial toxins and other metabolites along with the plethora of pro-inflammatory agents released from activated neutrophils massively recruited to the infectious sites and high levels of cationic histones, other cationic peptides, proteinases and Th1 cytokines released from activated polymorphonuclear neutrophils (PMNs) and from necrotized tissues may act in concert (synergism) to bring about cell killing and tissue destruction. Multiple, diverse interactions among the many potential pro-inflammatory moieties have been described in these complex lesions. Such infections are often seen in the skin and aerodigestive tract where the tissue is exposed to the environment, but can occur in any tissue. Commonly, the tissue-destructive infections are caused by group A streptococci, pneumococci, Staphylococcus aureus, meningococci, Escherichia coli and Shigella, although many other microbial species are seen on occasion. All these microbial agents are characterized by their ability to recruit large numbers of PMNs. Given the complex nature of the disease process, it is proposed that, to treat these multifactorial disorders, a "cocktail" of anti-inflammatory agents combined with non-bacteriolytic antibiotics and measures to counteract the critical toxic role of cationic moieties might prove more effective than a strategy based on attacking the bacteria alone.

Lipoteichoic acids as a major virulence factor causing inflammatory responses via Toll-like receptor 2

Lipoteichoic acid (LTA), a major cell wall component of Gram-positive bacteria, is associated with various inflammatory diseases ranging from minor skin diseases to severe sepsis. It is known that LTA is recognized by Toll-like receptor 2 (TLR2), leading to the initiation of innate immune responses and further development of adaptive immunity. However, excessive immune responses may result in the inflammatory sequelae that are involved in severe diseases such as sepsis. Although numerous studies have tried to identify the molecular basis for the pathophysiology of Gram-positive bacterial infection, the exact role of LTA during the infection has not been clearly elucidated. This review provides an overview of LTA structure and host recognition by TLR2 that leads to the activation of innate immune responses. Emphasis is placed on differential immunostimulating activities of LTAs of various Gram-positive bacteria at the molecular level.

The role of CRISPR-Cas systems in virulence of pathogenic bacteria

Clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated (Cas) genes are present in many bacterial and archaeal genomes. Since the discovery of the typical CRISPR loci in the 1980s, well before their physiological role was revealed, their variable sequences have been used as a complementary typing tool in diagnostic, epidemiologic, and evolutionary analyses of prokaryotic strains. The discovery that CRISPR spacers are often identical to sequence fragments of mobile genetic elements was a major breakthrough that eventually led to the elucidation of CRISPR-Cas as an adaptive immunity system. Key elements of this unique prokaryotic defense system are small CRISPR RNAs that guide nucleases to complementary target nucleic acids of invading viruses and plasmids, generally followed by the degradation of the invader. In addition, several recent studies have pointed at direct links of CRISPR-Cas to regulation of a range of stress-related phenomena. An interesting example concerns a pathogenic bacterium that possesses a CRISPR-associated ribonucleoprotein complex that may play a dual role in defense and/or virulence. In this review, we describe recently reported cases of potential involvement of CRISPR-Cas systems in bacterial stress responses in general and bacterial virulence in particular.

[Multifocal inflammatory syndrome after invasive infection due to an M1 strain of Streptococcus pyogenes]

We report on a case of Streptococcus pyogenes invasive disease with toxic shock syndrome due to an M1 strain producing SpeA and SmeZ superantigenic toxins. Post-streptococcal sequelae included several episodes of reactive arthritis and orchitis whose outcome was favorable with corticosteroid therapy. Invasive streptococcal infections are increasingly reported and may associate septic, toxinic, and immunological diseases. High-grade systemic inflammation may induce nonsuppurative complications and autoimmune diseases by molecular mimicry. Among them, reactive arthritis has been recognized as a separate entity from acute rheumatic fever and post-streptococcal orchitis has not been described before. Treatment should be quickly started and should be effective on the etiologic agent but also on its toxins due to the severity of the invasive infections associated with the spread of highly virulent bacterial clones and the potential development of multifocal nonsuppurative sequelae.

Interplay among oxidants, antioxidants, and cytokines in skin disorders: Present status and future considerations

The pathogenicity of skin disorders involves a complexity of physiological, immunological, environmental, and genetic phenomena. This review focuses on cross-talks between two main agents, the oxidants and cytokines network, which have recently been found to play important roles in the pathophysiology of a large variety of skin disorders, including carcinogenesis, UVB irradiation damages, inflammatory processes, and a series of diseases such as, psoriasis, pyoderma gangrenosum, atopic dermatitis, irritant contact dermatitis, and bacterial skin infections. In particular the review discusses the question how an interplay between oxidants and cytokines might be beneficial in wound-healing and in therapeutic strategies in clinical settings. These involve topical applications and oral administration of antioxidant and inflammatory-cytokines-neutralizing antibodies. Monitoring cytokine expression in skin disorders (inflammatory versus anti-inflammatory, or Th1 versus Th2 types of cytokines) will definitely help to evaluate the severity of injury, its type, and its role in therapy. Furthermore, it is expected that future studies should explore the possible roles of the synergistic interactions between antioxidants and cytokines and their impact on the Th1/Th2 cytokine networks balances.

Bactericidal cationic peptides can also function as bacteriolysis-inducing agents mimicking beta-lactam antibiotics?; it is enigmatic why this concept is consistently disregarded

Although there is a general consensus that highly cationic peptides kill bacteria primarily by injuring their membranes, an additional hypothesis is proposed suggesting that a large variety of cationic peptides might also render bacteria non viable by activating their autolytic wall enzymes - muramidases (a "Trojan Horse" phenomenon), resulting in bacteriolysis. This group of cationic peptides includes: lysozyme, lactoferrin, neutrophil-derived permeability increasing peptides, defensins, elastase, cathepsin G, and secretory phopholipase A2. In this respect, cationic peptides mimic the bactericidal/bacteriolytic effects exerted by of beta-lactam antibiotics. Bacteriolysis results in a massive release of the pro-inflammatory cell-wall components, endotoxin (LPS), lipoteichoic acid (LTA) and peptidoglycan (PPG), which if not effectively controlled, can trigger the coagulation and complement cascades, the release from phagocytes of inflammatory cytokines, reactive oxygen and nitrogen species, and proteinases. Synergism (a "cross-talk") among such agonists released following bacteriolysis, is probably the main cause for septic shock and multiple organ failure. It is proposed that a use of bacteriolysis-inducing antibiotics should be avoided in bacteremic patients and particularly in those patients already suspected of developing shock symptoms as these might further enhance bacteriolysis and the release of LPS, LTA and PPG. Furthermore, in additonal to the supportive regimen exercised in intensive care settings, a use of non bacteriolysis-inducing antibiotics when combined with highly sulfated compounds (e.g. heparin, and other clinically certified polysufates) should be considered instead, as these might prevent the activation of the microbial own autolytic systems induced either by highly cationic peptides released by activated phagocytes or by the highly bacteriolytic beta-lactams. Polysulfates might also depress the deleterious effects of the complement cascade and the use of combinations among anti-oxidants ( N-acetyl cysteine), proteinase inhibitors and phospholipids might prove effective to depress the synergistic cytotoxic effects induced by inflammatory agonists. Also, a use of gamma globulin enriched either in anti-LPS or in anti-LTA activities might serve to prevent the binding of these toxins to receptors upon macrophage which upon activation generate inflammatory cytokines. Thus, a use of "cocktails" of anti-inflammatory agents might replace the unsuccessful use of single antagonists proven in scores of clinical trials of sepsis to by ineffective in prolonging the lives of patients. It is enigmatic why the concept, and the publications which support a role for cationic peptides also as potent inducers of bacteriolysis, an arch evil and a deleterious phenomenon which undoubtedly plays a pivotal role in the pathophysiology of post-infectious sequelae, has been consistently disregarded.

Contribution of CsrR-regulated virulence factors to the progress and outcome of murine skin infections by Streptococcus pyogenes

Streptococcus pyogenes with null mutations in the csrRS regulatory locus are highly virulent in mice due to derepression of hyaluronic acid capsule synthesis and exotoxins, e.g., streptolysin S (SLS) and pyrogenic exotoxin B (SpeB). We generated derivatives of a DeltacsrRS strain that also carry deletions in hasAB (leading to an acapsular phenotype) or in sagA (phenotypically SLS-) or an interruption of speB (SpeB-) to test the relative contributions of these factors to the development of necrotic skin lesions. Inoculation of 2 x 10(6) to 4 x 10(6) CFU of either acapsular or SLS- strains into hairless mice resulted in lesions approximately 70% smaller than those of the DeltacsrRS parent strain. Elimination of SLS also reduced lethality from 100% to 0% at this inoculum (P < 10(-7); Fisher exact test). In contrast, SLS+ SpeB- mutants yielded lesions that were only 41% smaller than the parent strain (t = 2.2; P = 0.04), but only 3 the 17 lesions had dermal sloughing (P = 10(-5)). The nonulcerative lesions associated with SpeB- strains appeared pale with surrounding erythema. We conclude that capsule and SLS contribute to the subcutaneous spread of S. pyogenes and to a fatal outcome of infection. SpeB facilitates early dermal ulceration but has minor influence on lesion size and mortality. Large ulcerative lesions are observed only when both toxins are present.

Streptococcal beta-hemolysins: genetics and role in disease pathogenesis

A zone of beta-hemolysis surrounding colonies on blood-agar media is a hallmark phenotypic feature of the pathogens group A Streptococcus (GAS) and group B Streptococcus (GBS). In each case, lysis of red blood cells reflects the action of a potent protein exotoxin. Although these toxins have been the subjects of numerous investigations over the years, their purification and molecular identification have proven elusive. These difficulties reflect the instability of hemolytic activity, as both toxins function only in the context of the bacterial surface or certain high molecular weight 'stabilizer' molecules. This review highlights the recent discoveries of two markedly distinct genetic loci, necessary and sufficient for the beta-hemolytic phenotypes of GAS and GBS, respectively. The generation of isogenic GAS and GBS beta-hemolysin-deficient mutants and their analysis using in vitro and in vivo model systems has shown that both toxins function as virulence factors in the pathogenesis of invasive infections.

The role of bacteriolysis in the pathophysiology of inflammation, infection and post-infectious sequelae

The literature dealing with the biochemical basis of bacteriolysis and its role in inflammation, infection and in post-infectious sequelae is reviewed and discussed. Bacteriolysis is an event that may occur when normal microbial multiplication is altered due to an uncontrolled activation of a series of autolytic cell-wall breaking enzymes (muramidases). While a low-level bacteriolysis sometimes occurs physiologically, due to "mistakes" in cell separation, a pronounced cell wall breakdown may occur following bacteriolysis induced either by beta-lactam antibiotics or by a large variety of bacteriolysis-inducing cationic peptides. These include spermine, spermidine, bactericidal peptides defensins, bacterial permeability increasing peptides from neutrophils, cationic proteins from eosinophils, lysozyme, myeloperoxidase, lactoferrin, the highly cationic proteinases elastase and cathepsins, PLA2, and certain synthetic polyamino acids. The cationic agents probably function by deregulating lipoteichoic acid (LTA) in Gram-positive bacteria and phospholipids in Gram-negative bacteria, the presumed regulators of the autolytic enzyme systems (muramidases). When bacteriolysis occurs in vivo, cell-wall- and -membrane-associated lipopolysaccharide (LPS (endotoxin)), lipoteichoic acid (LTA) and peptidoglycan (PPG), are released. These highly phlogistic agents can act on macrophages, either individually or in synergy, to induce the generation and release of reactive oxygen and nitrogen species, cytotoxic cytokines, hydrolases, proteinases, and also to activate the coagulation and complement cascades. All these agents and processes are involved in the pathophysiology of septic shock and multiple organ failure resulting from severe microbial infections. Bacteriolysis induced in in vitro models, either by polycations or by beta-lactams, could be effectively inhibited by sulfated polysaccharides, by D-amino acids as well as by certain anti-bacteriolytic antibiotics. However, within phagocytic cells in inflammatory sites, bacteriolysis tends to be strongly inhibited presumably due to the inactivation by oxidants and proteinases of the bacterial muramidases. This might results in a long persistence of non-biodegradable cell-wall components causing granulomatous inflammation. However, persistence of microbial cell walls in vivo may also boost innate immunity against infections and against tumor-cell proliferation. Therapeutic strategies to cope with the deleterious effects of bacteriolysis in vivo include combinations of autolysin inhibitors with combinations of certain anti-inflammatory agents. These might inhibit the synergistic tissue- and- organ-damaging "cross talks" which lead to septic shock and to additional post-infectious sequelae.

Role of lipoteichoic acid in infection and inflammation

Lipoteichoic acid (LTA) is a surface-associated adhesion amphiphile from Gram-positive bacteria and regulator of autolytic wall enzymes (muramidases). It is released from the bacterial cells mainly after bacteriolysis induced by lysozyme, cationic peptides from leucocytes, or beta-lactam antibiotics. It binds to target cells either non-specifically, to membrane phospholipids, or specifically, to CD14 and to Toll-like receptors. LTA bound to targets can interact with circulating antibodies and activate the complement cascade to induce a passive immune kill phenomenon. It also triggers the release from neutrophils and macrophages of reactive oxygen and nitrogen species, acid hydrolases, highly cationic proteinases, bactericidal cationic peptides, growth factors, and cytotoxic cytokines, which may act in synergy to amplify cell damage. Thus, LTA shares with endotoxin (lipopolysaccharide) many of its pathogenetic properties. In animal studies, LTA has induced arthritis, nephritis, uveitis, encephalomyelitis, meningeal inflammation, and periodontal lesions, and also triggered cascades resulting in septic shock and multiorgan failure. Binding of LTA to targets can be inhibited by antibodies, phospholipids, and specific antibodies to CD14 and Toll, and in vitro its release can be inhibited by non-bacteriolytic antibiotics and by polysulphates such as heparin, which probably interfere with the activation of autolysis. From all this evidence, LTA can be considered a virulence factor that has an important role in infections and in postinfectious sequelae caused by Gram-positive bacteria. The future development of effective antibacteriolitic drugs and multidrug strategies to attenuate LTA-induced secretion of proinflammatory agonists is of great importance to combat septic shock and multiorgan failure caused by Gram-positive bacteria.

Role of streptolysin O in a mouse model of invasive group A streptococcal disease

Many of the virulence factors that have been characterized for group A streptococci (GAS) are not expressed in all clinical isolates. One putative virulence factor that is present among most is streptolysin O (Slo), a protein with well-characterized cytolytic activity for many eukaryotic cells types. In other bacterial pathogens, proteins homologous to Slo have been shown to be essential for virulence, but the role of Slo in GAS had not been previously examined. To investigate the role of Slo in GAS virulence, we examined both revertible and stable slo mutants in a mouse model of invasive disease. When the revertible slo mutant was used to infect mice, the reversion frequency of bacteria isolated from the wounds and spleens of infected animals was more than 100 times that of the inoculum, indicating that there was selective pressure in the animal for Slo(+) GAS. Experiments with the stable slo mutant demonstrated that Slo was not necessary for the formation of necrotic lesions, nor was it necessary for escape from the lesion to cause disseminated infection. Bacteria were present in the spleens of 50% of the mice that survived infection with the stable slo mutant, indicating that dissemination of Slo(-) GAS does not always cause disease. Finally, mice infected with the stable slo mutant exhibited a significant decrease in mortality rates compared to mice infected with wild-type GAS (P < 0.05), indicating that Slo plays an important role in GAS virulence.

Is streptolysin S of group A streptococci a virulence factor?

The possible role played by streptolysin S (SLS) of group A streptococci in the pathophysiology of streptococcal infections and in post-streptococcal sequelae is discussed. The following properties of SLS justify its definition as a distinct virulence factor: 1) its presence on the streptococcus surface in a cell-bound form, 2) its continuous and prolonged synthesis by resting streptococci, 3) its non-immunogenicity, 4) its extractability by serum proteins (albumin, alpha lipoprotein), 5) its ability to become transferred directly to target cells while being protected from inhibitory agents in the milieu of inflammation, 6) its ability to bore holes in the membrane phospholipids in a large variety of mammalian cells, 7) its ability to synergize with oxidants, proteolytic enzymes, and with additional host-derived proinflammatory agonists, and 8) its absence in streptococcal mutants associated with a lower pathogenicity for animals. Because tissue damage in streptococcal and post-streptococcal sequelae might be the end result of a distinct synergism between streptococcal and host-derived proinflammatory agonists it is proposed that only cocktails of anti-inflammatory agents including distinct inhibitors of SLS (phospholipids), gamma globulin, inhibitors of reactive oxygen species, proteinases, cationic proteins cytokines etc., will be effective in inhibiting the multiple synergistic interactions which lead to fasciitis, myositis and the flesh-eating syndromes, and often develop into sepsis, septic shock and multiple organ failure. The creation of mutants deficient in SLS and in proteases will help shed light on the specific role played by SLS in the virulence of group A hemolytic streptococci.

Multi-drug strategies are necessary to inhibit the synergistic mechanism causing tissue damage and organ failure in post infectious sequelae

The paper discusses the principal evidence that supports the concept that cell and tissue injury in infectious and post-infectious and inflammatory sequelae might involve a deleterious synergistic interaction among microbial- and host-derived pro-inflammatory agonists. Experimental models had proposed that a rapid cell and tissue injury might be induced by combinations among subtoxic amounts of three major groups of agonists generated both by microorganisms and by the host's own defense systems. These include: (1) oxidants: Superoxide, H(2)O(2), OH', oxidants generated by xanthine-xanthine-oxidase, ROO; HOC1, NO, OONO'-, (2) the membrane-injuring and perforating agents, microbial hemolysins, phospholipases A(2) and C, lysophosphatides, bactericidal cationic proteins, fatty acids, bile salts and the attack complex of complement a, certain xenobics and (3) the highly cationic proteinases, elastase and cathepsin G, as well as collagenase, plasmin, trypsin and a variety of microbial proteinases. Cell killing by combinations among the various agonists also results in the release of membrane-associated arachidonate and metabolites. Cell damage might be further enhanced by certain cytokines either acting directly on targets or through their capacity to prime phagocytes to generate excessive amounts of oxidants. The microbial cell wall components, lipoteichoic acid (LTA), lipopolysaccharides (LPS) and peptidoglycan (PPG), released following bacteriolysis, induced either by cationic proteins from neutrophils and eosinophils or by beta lactam antibiotics, are potent activators of macrophages which can release oxidants, cytolytic cytokines and NO. The microbial cell wall components can also activate the cascades of coagulation, complement and fibrinolysis. All these cascades might further synergize with microbial toxins and metabolites and with phagocyte-derived agonsits to amplify tissue damage and to induce septic shock, multiple organ failure, 'flesh-eating' syndromes, etc. The long persistence of non-biodegradable bacterial cell wall components within activated macrophages in granulomatous inflammation might be the result of the inactivation by oxidants and proteinases of bacterial autolytic wall enzymes (muramidases). The unsuccessful attempts in recent clinical trials to prevent septic shock by the administration of single antagonists is disconcerting. It does suggest however that, since tissue damage in post-infectious syndromes is most probably the end result of synergistic interactions among a multiplicity of agents, only agents which might depress bacteriolysis in vivo and 'cocktails' of appropriate antagonists, but not single antagonists, if administered at the early phases of infection especially to patients at high risk, might help to control the development of post-infectious syndromes. However, the use of adequate predictive markers for sepsis and other post-infectious complications is highly desirable. Although it is conceivable that anti-inflammatory strategies might also be counter-productive as they might act as 'double-edge swords', intensive investigations to devise combination therapies are warranted. The present review also lists the major anti-inflammatory agents and strategies and combinations among them which have been proposed in the last few years for clinical treatments of sepsis and other post-infectious complications.