Streptococcal Pyrogenic Exotoxin A, Streptolysin O, Exoenzymes, Serotype and Biotype Profiles of Streptococcus pyogenes Isolates from Patients with Toxic Shock Syndrome and other Severe Infections

Group A Streptococcus Vaccine Targeting the Erythrogenic Toxins SpeA and SpeB Is Safe and Immunogenic in Rabbits and Does Not Induce Antibodies Associated with Autoimmunity

Group A streptococcus (GAS) is a global pathogen associated with significant morbidity and mortality for which there is currently no licensed vaccine. Vaccine development has been slow, mostly due to safety concerns regarding streptococcal antigens associated with autoimmunity and related complications. For a GAS vaccine to be safe, it must be ensured that the antigens used in the vaccine do not elicit an antibody response that can cross-react with host tissues. In this study, we evaluated the safety of our GAS vaccine candidate called VaxiStrep in New Zealand White rabbits. VaxiStrep is a recombinant fusion protein comprised of streptococcal pyrogenic exotoxin A (SpeA) and exotoxin B (SpeB), also known as erythrogenic toxins, adsorbed to an aluminum adjuvant. The vaccine elicited a robust immune response against the two toxins in the rabbits without any adverse events or toxicity. No signs of autoimmune pathology were detected in the rabbits' brains, hearts, and kidneys via immunohistochemistry, and serum antibodies did not cross-react with cardiac or neuronal tissue proteins associated with rheumatic heart disease or Sydenham chorea (SC). This study further confirms that VaxiStrep does not elicit autoantibodies and is safe to be tested in a first-in-human trial.

Prevalence and Characterization ofStreptococcus pyogenesClinical Isolates from Different Hospitals and Clinics in Mansoura

Streptococcus pyogenesare associated with many bacterial diseases in both humans and animals and are capable of causing a multitude of human diseases.S. pyogenesisolates were identified by their bacitracin sensitivity, positivespy1258detection, and positive GAS latex agglutination. Different isolates were typed serotypically and genotypically by BOX-PCR. Different virulence factors were identified inS. pyogenesisolates. In addition, antimicrobial resistance was tested to eleven different antibiotics. Furthermore, the resistance mechanisms were determined phenotypically by the disc diffusion method. Finally, the correlation between both molecular and serotypes identified and the profile of virulence factors and clinical and geographical sources was determined for all isolates. Thirty-eightS. pyogenesisolates were collected from different clinical sources. Resistance testing indicated high resistance to mostly used antibiotics except amoxicillin/clavulanic acid, amoxicillin, and ampicillin. Serotyping results indicated five different serotypes, M1, M2, M3, M4, and M6, inS. pyogenesisolates, while six isolates were identified as untypeable. In addition, positive PCR results identified most of the tested SAgs genes in whichspeJgene was mostly identified followed byspeI, speC,andssagenes being identified in 81.6%, 63.3%, 60.5%, and 60.5%, respectively. However,speHwas the least detected. In contrast,speL, speM, andsmeZgenes could not be detected in all tested isolates. Finally, BOX-PCR molecular typing was a more effective clustering method when compared to the serotyping method in allS. pyogenes.In conclusion, the isolates in this study were highly resistant to mostly used antibiotics. M1 was the most identified serotype. No significant association was found between serotypes, BOX-PCR cluster groups, and SAgs genes profiles. However, by the application of BOX-PCR, effective molecular typing was obtained.

Staphylococcal and streptococcal superantigens: molecular, biological and clinical aspects

Superantigens (SAgs) include a class of certain bacterial and viral proteins exhibiting highly potent lymphocyte-transforming (mitogenic) activity towards human and or other mammalian T lymphocytes. Unlike conventional antigens, SAgs bind to certain regions of major histocompatibility complex (MHC) class II molecules of antigen-presenting cells (APCs) outside the classical antigen-binding groove and concomitantly bind in their native form to T cells at specific motifs of the variable region of the beta chain (Vbeta) of the T cell receptor (TcR). This interaction triggers the activation (proliferation) of the targeted T lymphocytes and leads to the in vivo or in vitro release of high amounts of various cytokines and other effectors by immune cells. Each SAg interacts specifically with a characteristic set of Vbeta motifs. The review summarizes our current knowledge on S. aureus and S. pyogenes superantigen proteins. The repertoire of the staphylococcal and streptococcal SAgs comprises 24 and 8 proteins, respectively. The staphylococcal SAgs include (i) the classical enterotoxins A, B, C (and antigenic variants), D, E, and the recently discovered enterotoxins G to Q, (ii) toxic shock syndrome toxin-1, (iii) exfoliatins A and B. The streptococcal SAgs include the classical pyrogenic exotoxins A and C and the newly identified pyrogenic toxins, G, H, I, J, SMEZ, and SSA. The structural and genomic aspects of these toxins and their molecular relatedness are described as well as the available 3-D crystal structure of some of them and that of certain of their complexes with MHC class II molecules and the TcR, respectively. The pathophysiological properties and clinical disorders related to these SAgs are reviewed.

Chemokine production by rat macrophages stimulated with streptolysin O from Streptococcus pyogenes

The contribution of streptolysin O (SLO) from Streptococcus pyogenes to neutrophil infiltration in inflammatory lesions was determined by production of cytokine-induced neutrophil chemoattractant (CINC)-1, -2 and -3, and macrophage inflammatory protein (MIP)-1alpha by rat macrophages stimulated with SLO in culture. Active SLO induced the production of CINCs and MIP-1alpha in dose- and time-dependent manners. These inductions were ascertained by chemokine mRNA expression in macrophages. Streptolysin S was without effect. The SLO-cholesterol complex induced the chemokine production in proportion to the residual hemolytic activity of the complex. In addition, the effects of SLO on the chemokine production were confirmed by the injection of active SLO into the preformed air pouch on the back of rats. The infiltration of neutrophils into the pouch fluid (exudate) increased steadily with a lag phase of about 2 hr. The major chemokine found in exudates was MIP-1alpha but not CINCs. In this study, it became clear that active SLO, but not the inactive one, contributed to the production of MIP-1alpha and CINCs in the conditioned medium and in exudates.

Pyrogenicity and cytokine-inducing properties of Streptococcus pyogenes superantigens: comparative study of streptococcal mitogenic exotoxin Z and pyrogenic exotoxin A

Streptococcal mitogenic exotoxin Z (SMEZ), a superantigen derived from Streptococcus pyogenes, provoked expansion of human lymphocytes expressing the Vbeta 2, 4, 7 and 8 motifs of T-cell receptor. SMEZ was pyrogenic in rabbits and stimulated the expression of the T-cell activation markers CD69 and cutaneous lymphocyte-associated antigen. A variety of cytokines was released by human mononuclear leukocytes stimulated with SMEZ, which was 10-fold more active than streptococcal pyrogenic exotoxin A. Th2-derived cytokines were elicited only by superantigens and not by streptococcal cells.

Inverse relation between disease severity and expression of the streptococcal cysteine protease, SpeB, among clonal M1T1 isolates recovered from invasive group A streptococcal infection cases

The streptococcal cysteine protease (SpeB) is one of the major virulence factors produced by group A streptococci (GAS). In this study we investigated if differences exist in SpeB production by clonally related M1T1 clinical isolates derived from patients with invasive infections. Twenty-nine of these isolates were from nonsevere cases and 48 were from severe cases, including streptococcal toxic shock syndrome (STSS) and necrotizing fasciitis (NF) cases. The expression and amount of the 28-kDa SpeB protein produced were determined by quantitative Western blotting, and protease activity was measured by a fluorescent enzymatic assay. A high degree of variation in SpeB expression was seen among the isolates, and this variation seemed to correlate with the severity and/or clinical manifestation of the invasive infection. The mean amount of 28-kDa SpeB protein and cysteine protease activity produced by isolates from nonsevere cases was significantly higher than that from STSS cases (P = 0.001). This difference was partly due to the fact that 41% of STSS isolates produced little or no SpeB compared to only 14% of isolates recovered in nonsevere cases. Moreover, the cysteine protease activity among those isolates that expressed SpeB was significantly lower for STSS isolates than for isolates from nonsevere cases (P = 0.001). Increased SpeB production was also inversely correlated with intact M protein expression, and inhibition of cysteine protease activity blocked the cleavage of the surface M protein. Together, the data support the existence of both an "on-off" and a posttranslational regulatory mechanism(s) controlling SpeB production, and they suggest that isolates with the speB gene in the "off" state are more likely to spare the surface M protein and to be isolated from cases of severe rather than nonsevere invasive infection. These findings may have important implications for the role of SpeB in host-pathogen interactions via regulation of the expression of GAS virulence genes and the severity of invasive disease.

Superantigen YPMa exacerbates the virulence of Yersinia pseudotuberculosis in mice

Yersinia pseudotuberculosis, a gram-negative bacterium responsible for enteric and systemic infection in humans, produces a superantigenic toxin designated YPMa (Y. pseudotuberculosis-derived mitogen). To assess the role of YPMa in the pathogenesis of Y. pseudotuberculosis, we constructed a superantigen-deficient mutant and compared its virulence in a mouse model of infection to the virulence of the wild-type strain. Determination of the survival rate after intravenous (i.v.) bacterial inoculation of OF1 mice clearly showed that inactivation of ypmA, encoding YPMa, reduced the virulence of Y. pseudotuberculosis. Mice infected i.v. with 10(4) and 10(5) wild-type bacteria died within 9 days, whereas mice infected with the ypmA mutant survived 12 and 3 days longer, respectively. This decreased virulence of the ypmA mutant strain was not due to an impaired colonization of the spleen, liver, or lungs. In contrast to i.v. challenge, bacterial inoculation by the intragastric (i.g.) route did not reveal any difference in virulence between wild-type Y. pseudotuberculosis and the ypmA mutant since the 50% lethal doses were identical for both strains. Moreover, inactivation of ypmA gene did not affect the bacterial growth of Y. pseudotuberculosis in Peyer's patches, mesenteric lymph nodes (MLNs), and spleen after oral infection. Histological studies of spleen, liver, lungs, heart, Peyer's patches, and MLNs after i.v. or i.g. challenge with the wild type or the ypmA mutant did not reveal any feature that can be specifically related to YPMa. Our data show that the superantigenic toxin YPMa contributes to the virulence of Y. pseudotuberculosis in systemic infection in mice.