Streptococcus pyogenes activates human plasmacytoid and myeloid dendritic cells

Human peripheral blood contains two major dendritic cell (DC) populations, namely CD11c(-)CD123+ plasmacytoid DCs (PDCs) and CD11c+CD123(-) myeloid DCs (MDCs). Although the activation of these DC types by various TLR ligands has been relatively well-characterized, less is known about the ability of whole live bacteria to induce PDC and MDC activation. In the present report, we have compared the activation of human PDCs and MDCs in response to major human bacterial pathogen Streptococcus pyogenes (group A streptococci) and influenza A virus. S. pyogenes stimulation resulted in the maturation of both DC types, as evidenced by enhanced expression of costimulatory molecules and production of proinflammatory cytokines and chemokines. Furthermore, S. pyogenes-stimulated PDCs and MDCs activated na?ve CD4+ T cells and enhanced their Th1 cytokine production. Influenza A virus infection induced rapid PDC activation, whereas MDCs were extremely sensitive to influenza A virus-induced cell death. The most significant differences between DC types were seen in the production of IL-10 and IL-12, which were only produced by S. pyogenes-stimulated MDCs. Although S. pyogenes was able to induce PDC activation, only influenza A virus infection resulted in detectable IFN-alpha production. Our results show that depending on the infecting microbe, the functions of PDCs and MDCs may be partially overlapping, suggesting a considerable flexibility of the human DC system.     

Invasive infections by Streptococcus pyogenes

Invasive infections by Streptococcus pyogenes continually increase both in France and in others industrialized countries. Because of the seriousness, the rapidity of the evolution and the epidemic potentialities, guidelines for managing these infections are requested by the Superior Council of Public Hygiene of France. The authors report herein a case of an adult stricken down by a violent evolution due to Streptococcus pyogenes. They point up how diagnosis, treatment and prophylaxis for family circle are difficult.     

Immune modulation of human dendritic cells by complement

Deficiency in complement proteins such as C1q is associated with the development of systemic lupus erythematosus (SLE). Here, we show that the differentiation of dendritic cells (DC) in the presence of C1q (C1qDC) gives rise to CD1a(+)/DC-SIGN(+) cells with high phagocytic capacity and low expression of CD80, CD83 and CD86. Further, when C1qDC were exposed to LPS, a significant reduction in the production of IL-6, TNF-alpha and IL-10 occurred with a limited up-regulation of CD80, CD83 and CD86. In addition, C1qDC were less responsive to activation by CD40L in terms of IL-12p70 secretion and CD86 expression. C1qDC showed an impaired ability to stimulate alloreactive T cells, with a reduced production of IFN-gamma. In conclusion, we have shown that C1q is a potent modulator of DC, resulting in cells characterized by an impaired capacity of cytokine production and an impaired up-regulation of costimulatory molecules, leading to a limited T cell response. Therefore, we hypothesize that, next to a pivotal role in the safe clearance of apoptotic cells, C1q regulates the threshold of DC activation and thereby prevents hyperactivation of the overall immune response.     

Recurrent sepsis caused by Streptococcus pyogenes

I report that a 75-year-old man with severe atherosclerosis experienced two episodes of bacteremia with Streptococcus pyogenes of type emm87. Recurrent sepsis with S. pyogenes is extremely rare, and a foot ulcer was the suspected point of entry. The patient did not develop opsonizing antibodies to the isolate.     

Platelet aggregation by Streptococcus pyogenes.

Heat-killed group A Streptococcus pyogenes induced platelet aggregation in platelet-rich plasma. Aggregation was dependent upon the ratio of platelets to bacteria, with maximal aggregation occurring at 0.8 platelets per bacterium (final concentration, 300,000 per microliter). Inhibition of the reaction by 3 mM EDTA indicated it was a true aggregation and not merely adhesion and agglutination. Lactic acid dehydrogenase assays indicated lysis of platelets did not occur during a 6-min incubation period. Aggregation was inhibited in a dose-dependent manner by acetylsalicylic acid (100 microM to 10 mM) and quinacrine (15.6 to 250 microM), with no decrease in aggregation at the lowest concentration of inhibitor tested. S. pyogenes induced the release of [14C]serotonin, which was maximal (50%) at 2.4 min, when aggregation was nearly complete. Gel-filtered platelets were not aggregated unless fibrinogen (final concentration, 1.8 mg/ml) was included in the reaction mixture. Staphylococcus aureus, a group B streptococcus, and Escherichia coli were unable to induce aggregation in platelet-rich plasma under the conditions used for S. pyogenes.     

The signal recognition particle pathway is required for virulence in Streptococcus pyogenes

The signal recognition particle (SRP) pathway is a universally conserved pathway for targeting polypeptides for secretion via the cotranslational pathway. In particular, the SRP pathway is thought to be the main mechanism for targeting polypeptides in gram-positive bacteria, including a number of important human pathogens. Though widely considered to be an essential cellular component, recent advances have indicated this pathway may be dispensable in gram-positive bacteria of the genus Streptococcus under in vitro conditions. However, its importance for the pathogenesis of streptococcal disease is unknown. In this study, we investigated the importance of the SRP pathway for virulence factor secretion in the human pathogen Streptococcus pyogenes. While the SRP pathway was not found to be essential for viability in vitro, SRP mutants demonstrated a medium-specific growth defect that could be rescued by the addition of glucose. We also observed that a distinct subset of virulence factors were dependent upon the SRP pathway for secretion, whereas others were completely independent of this pathway. Significantly, deletion of the SRP pathway resulted in mutants that were highly attenuated in both a zebrafish model of necrotic myositis and a murine subcutaneous ulcer model, highlighting the importance of this pathway in vivo. These studies emphasize the importance of the SRP pathway for the in vivo survival and pathogenesis of S. pyogenes.     

Typing of Streptococcus pyogenes by pyrolysis mass spectrometry

Strains of Streptococcus pyogenes from an outbreak in an oncology ward (13) and routine isolates from sporadic cases (6) were examined blind by pyrolysis mass spectrometry (Py-MS), extending previous work on epidemiological typing. This outbreak appeared more complex than one reported previously, but Py-MS and conventional typing results were in complete agreement. The results confirm the potential of Py-MS as a rapid method for identification at strain level in studies of cross infection.     

Detection of Streptococcus pyogenes by Use of Illumigene Group A Streptococcus Assay

The performance of the Illumigene group A Streptococcus assay was evaluated by comparing it to culture using 437 consecutive throat swabs. The Illumigene assay was also directly compared to PCR with 161 samples. This Illumigene assay is rapid and easy to perform. The assay also has high sensitivity (100%) compared to culture or PCR and high specificity (99.2%) compared to PCR. A total of 8.8% of the isolates were erythromycin resistant, and 6.9% were clindamycin resistant.     

Streptococcal erythrogenic toxin B abrogates fibronectin-dependent internalization of Streptococcus pyogenes by cultured mammalian cells

Streptococcus pyogenes secretes several proteins that influence host-pathogen interactions. A tissue-culture model was used to study the influence of the secreted cysteine protease streptococcal erythrogenic toxin B (SPE B) on the interaction between S. pyogenes strain NZ131 (serotype M49) and mammalian cells. Inactivation of the speB gene enhanced fibronectin-dependent uptake of the pathogen by Chinese hamster ovary (CHO-K1) cells compared to that in the isogenic wild-type strain. Preincubation of the NZ131 speB mutant with purified SPE B protease significantly inhibited fibronectin-dependent uptake by both CHO-K1 and CHO-pgs745 cells. The effect was attributed to an abrogation of fibronectin binding to the surface of the bacteria that did not involve either the M49 protein or the streptococcal fibronectin-binding protein SfbI. In contrast, pretreatment of the NZ131 speB mutant with SPE B did not influence sulfated polysaccharide-mediated uptake by CHO-pgs745 cells. The results indicate that the SPE B protease specifically alters bacterial cell surface proteins and thereby influences pathogen uptake.     

Immune recognition of irradiated cancer cells

Ionizing irradiation has been extensively employed for the clinical management of solid tumors, with therapeutic or palliative intents, for decades. Until recently, radiation therapy (RT) was believed to mediate antineoplastic activity mostly (if not only) as a consequence of cancer cell-intrinsic effects. Indeed, the macromolecular damage imposed to malignant cells by RT initiates one or multiple signal transduction cascades that drive a permanent proliferative arrest (cellular senescence) or regulated cell death. Both these phenomena show a rather linear dose-response correlation. However, RT also mediates consistent immunological activity, not only as an “on-target effect” originating within irradiated cancer cells, but also as an “off-target effect” depending on the interaction between RT and stromal, endothelial, and immune components of the tumor microenvironment. Interestingly, the immunological activity of RT does not exhibit linear dose-response correlation. Here, we discuss the mechanisms whereby RT alters the capacity of the immune system to recognize and eliminate irradiated cancer cells, either as an “on-target” or as on “off-target” effect. In particular, we discuss the antagonism between the immunostimulatory and immunosuppressive effects of RT as we delineate combinatorial strategies to boost the former at the expenses of the latter.     

Epidemiological typing of Streptococcus pyogenes by pyrolysis mass spectrometry

Strains of Streptococcus pyogenes from an outbreak of infection on a burns unit (15), a collection of routine isolates from another hospital(12) and isolates from a national survey of throat infections in children in the community(4) were examined blind by pyrolysis-mass spectrometry (Py-MS). The outbreak strains (M22 T12) previously found to give identical typing results in conventional tests, formed a closely similar cluster and were distinct from other hospital and community strains. One hospital and one community strain were loosely associated with this cluster. Another cluster comprised six antibiotic-susceptible strains and two community strains. Six strains did not fall within the clusters; four were antibiotic-resistant strains isolated in hospital, one an antibiotic-resistant strain isolated in the community, and one a susceptible hospital strain. Results show that Py-MS is a potentially valuable method for rapid comparison of strains in studies of infection.     

Experimental arthritis induced by atypical strains of Streptococcus pyogenes

Experimental arthritis was induced in Sprague-Dawley rats by intraarticular injection of whole-cell sonicates, heat-killed cells and cell-wall preparations of typical and atypical strains of Group-A streptococci (Streptococcus pyogenes). The non-haemolytic nitrosoguanidine-derived mutant and the naturally occurring Lowry strain induced a similar but less severe form of arthritis. Direct immunofluorescent staining demonstrated maximum fluorescence in the sections of articular joint taken 60 days after injection. The level of immune complexes increased for up to 90 days after injection of cell walls or whole-cell sonicates and correlated well with the development of the chronic stage of arthritis observed in haematoxylin and eosin and fluorescence staining of thin tissue sections.     

Hydrogen peroxide-mediated killing of Caenorhabditis elegans by Streptococcus pyogenes

Caenorhabditis elegans is currently introduced as a new, facile, and cheap model organism to study the pathogenesis of gram-negative bacteria such as Pseudomonas aeruginosa and Salmonella enterica serovar Typhimurium. The mechanisms of killing involve either diffusible exotoxins or infection-like processes. Recently, it was shown that also some gram-positive bacteria kill C. elegans, although the precise mechanisms of killing remained open. We examined C. elegans as a pathogenesis model for the gram-positive bacterium Streptococcus pyogenes, a major human pathogen capable of causing a wide spectrum of diseases. We demonstrate that S. pyogenes kills C. elegans, both on solid and in liquid medium. Unlike P. aeruginosa and S. enterica serovar Typhimurium, the killing by S. pyogenes is solely mediated by hydrogen peroxide. Killing required live streptococci; the killing capacity depends on the amount of hydrogen peroxide produced, and killing can be inhibited by catalase. Major exotoxins of S. pyogenes are not involved in the killing process as confirmed by using specific toxin inhibitors and knockout mutants. Moreover, no accumulation of S. pyogenes in C. elegans is observed, which excludes the involvement of infection-like processes. Preliminary results show that S. pneumoniae can also kill C. elegans by hydrogen peroxide production. Hydrogen peroxide-mediated killing might represent a common mechanism by which gram-positive, catalase-negative pathogens kill C. elegans.     

Cytokine production by murine cells activated by erythrogenic toxin type A superantigen of Streptococcus pyogenes.

The mode of pathogenic action of the Steptococcus pyogenes superantigen erythrogenic toxin type A (ETA) in causing toxic shock-like syndrome in humans is thought to be mediated by massive release of cytokines by patients immune cells. The cytokine-inducing capacity of ETA as an extracellular protein was compared with that of lipopolysaccharide (LPS), a component of cell wall of gram-negative bacteria. Peritoneal macrophages and splenocytes of BALB/c and C3H/HeJ mice were stimulated by ETA and LPS. Tumor necrosis factor (TNF), interleukin 3 (IL-3) and interleukin 6 (IL-6) activities in the supernatants of stimulated cells were evaluated. In contrast to LPS, ETA induced only low amounts of IL-6 and no detectable TNF activities in peritoneal macrophage supernatants. ETA-triggered BALB/c and C3H/HeJ splenocytes produced great amounts of IL-6. ETA triggered the production of IL-3 by both mice strains splenocytes in a dose dependent manner. The amounts of IL-3 in supernatants were comparable to those induced by concanavalin A. The simultaneous presence of ETA and LPS in macrophage and splenocyte cultures induced a slight enhancement above an additive value after 72-96 h. Challenge of BALB/c mice with ETA 6 h before the harvest of peritoneal macrophages led to an enhanced production of IL-6 upon stimulation with ETA as well as with LPS. Splenocytes of nude BALB/c mice did not produce IL-6 upon stimulation with ETA, whereas LPS-induced IL-6 production was similar in these mice and in their littermates. The pathogenic effect of ETA on host's immune cells could most likely be explained as a consequence of T cell activation. The results confirm also that LPS- and ETA-induced shock is mediated by different cell types.     

Moraxella catarrhalis coaggregates with Streptococcus pyogenes and modulates interactions of S. pyogenes with human epithelial cells

The pathogens Streptococcus pyogenes and Moraxella catarrhalis colonize overlapping regions of the human nasopharynx. We have found that M. catarrhalis can dramatically increase S. pyogenes adherence to human epithelial cells and that species-specific coaggregation of these bacteria correlates with this enhanced adherence.     

Review of 17 Cases of Pneumonia Caused by Streptococcus pyogenes

 Streptococcus pyogenes is an uncommon cause of community-acquired pneumonia and there have been few recent specific accounts of the condition. To describe the current nature of this disease in the UK, data was gathered on patients with clinical pneumonia from whom Streptococcus pyogenes was cultured principally from blood or other relevant normally sterile sites. In the Harrogate and Northallerton districts of North Yorkshire, pneumonia accounted for nine (20%) cases and a quarter of all deaths in a complete sequence of 45 patients with Streptococcus pyogenes bacteraemia detected during the 16-year-period 1981–1996. An analysis is presented of those cases together with eight recent cases from counties York, Durham and Isle of Wight during 1995–1997. Of the total 17 cases, nine occurred in women and eight in men; the age range was 30–92 years. The organism was isolated from blood culture in 15 (88%) patients. Eight (47%) patients died, five within 1 day of hospitalisation. Fourteen (82%) cases occurred in the winter months October to March, including all the fatal cases and all eight in which a clinical 'viral' prodrome was observed. Predisposing medical or surgical conditions were present in 65% of the patients. Major complications included septicaemia, pleural reaction, shock, pulmonary cavitation, osteomyelitis and metastatic abscesses. Seven serotypes of Streptococcus pyogenes were encountered, with M-type 1 predominating (the cause in 60% of cases). All infections were community acquired; two small clusters of fatal pneumonia were seen.     

Rapidly fatal necrotising fasciitis caused by Streptococcus pyogenes.

AIMS--To describe the morbid anatomical and bacteriological features in a series of five cases of rapidly fatal Streptococcus pyogenes necrotising fasciitis. METHODS--Post mortem and bacteriological examinations were made of five patients dying within 48 hours from rapidly fatal necrotising fasciitis. RESULTS--All five cases died rapidly from a toxic Streptococcus toxin syndrome as a result of developing necrotising fasciitis following trivial injury. CONCLUSIONS--Necrotising fasciitis caused by Streptococcus pyogenes infection can be rapidly fatal. This is probably the result of a toxic shock syndrome. Rapid, early diagnosis and swift and probably empirical treatment is required to avoid a fatal outcome.