Distribution of superantigens in group A streptococcal isolates from Salvador, Brazil

T-cell receptor Vβ8 for detection of biologically active streptococcal pyrogenic exotoxin type C

Streptococcus pyogenes is an important human pathogen, commonly spread by airborne droplets but also by ingestion of contaminated food. Apart from causing infection, this pathogen produces 13 distinct types of streptococcal pyrogenic exotoxins (SPE). The current method for detection cannot distinguish between the biologically active form of SPE that has been reported to cause foodborne outbreaks and the inactivated toxin that poses no health risk. To measure the biological activity of SPE type C (SPE-C), one such toxin that was linked to foodborne outbreaks associated with milk and milk products, we developed a cell-based assay that can discern between biologically active and inactive SPE-C. To the best of our knowledge, this is the first showing that SPE-C activates T-cells expressing Vβ8. With this finding, we used a T-cell line natively expressing Vβ8 that was genetically engineered to also express the luciferase reporter gene under the regulation of nuclear factor of activated T-cells response element in combination with a B-cell line to present the recombinant SPE-C (rSPE-C) toxin via major histocompatibility complex (MHC) class II to the Vβ8 T-cell receptor (TCR) in an assay to detect and to discern between biologically active and inactive rSPE-C. By using this system, we demonstrated that SPE-C induced significant IL-2 secretion after 72 h and visible light emission after only 5 h, doubling by 24 h. We utilize this finding to assess the specificity of the assay and the effect of pasteurization on SPE-C activity. We observed no cross-reactivity with SPE-B and significant loss of SPE-C biological activity in spiked phosphate-buffered saline while SPE-C spiked into milk is heat stable. Once SPE-C has formed, it is infeasible to eliminate it from milk by thermal treatment.

Molecular Genetic Characterization of Streptococcus pyogenes Strains Isolated from Patients with Various Manifestations of Streptococcal Infection

In 82 clinical strains of Streptococcus pyogenes (group A streptococci) isolated from patients with various manifestations of streptococcal infection, emm-typing revealed 27 emm-types (n=77) with a predominance of emm-89 (n=15; 18%), emm-75 (n=9; 11%), and emm-1 (n=6; 7%); types emm-3, emm-12, and emm-58 (n=4; 5% each) were found with almost equal frequency; other types were less common. The superantigen genes speC, speG, speH, speI, speJ, speK, speL, speM, smeZ, and SSA were identified in S. pyogenes strains using multiprimer PCR; the genes of the superantigen SpeA and cysteine proteinase SpeB were detected using real-time PCR. All the studied S. pyogenes strains contained superantigen genes, and 98% of the strains had several (from 2 to 7) genes. The number of variants of these sets reached 37; 2% of the strains contained only one superantigen gene. The distribution frequencies of superantigen genes in the studied strains were: speA - 43%; speC - 38%; speG - 93%; speH - 13%; speI - 6%; speJ - 24%; speK - 13%; speL and speM - 11% each; smeZ - 98%; SSA - 15%. All studied S. pyogenes strains contained the speB gene. Our studies have demonstrated that the sets of superantigen genes of group A streptococci are characterized by pronounced diversity to some extent associated with emm-type.

Assessment of the Relationship between Clinical Manifestation and Pathogenic Potential of Streptococcus pyogenes Strains-Distribution of Genes and Genotypes of Toxins

Streptococcus pyogenes is one of the most important species among beta-haemolytic streptococci, causing human infections of different localization. It is isolated from clinical specimens relatively frequently. In this study, the frequency and co-occurrence of toxin genes (speA, speB, speC, speH, speJ, speK) among 147 S. pyogenes strains were evaluated, using real-time PCR. In addition, the relationship between the occurrence of these genes and the origin of S. pyogenes strains from selected clinical material was assessed. The speB gene was present with the highest incidence (98.6%), while the speK gene was the least frequent (8.2%) among the tested strains. Based on the presence of the detected genes, the distribution of 17 genotypes was determined. The most common (21.8%), was speA (−) speB (+) speC (−) speH (−) speJ (−) speK (−) genotype. Furthermore, significant variation in the presence of some genes and genotypes of toxins in S. pyogenes strains isolated from different types of clinical material was found. There is a considerable variety and disproportion between the frequency of individual genes and genotypes of toxins in S. pyogenes strains. The relationship between the origin of S. pyogenes isolates and the presence of toxins genes indicates their pathogenic potential in the development of infections of selected localization.

Antibodies to the conserved region of the M protein and a streptococcal superantigen cooperatively resolve toxic shock-like syndrome in HLA-humanized mice

Invasive streptococcal disease (ISD) and toxic shock syndrome (STSS) result in over 160,000 deaths each year. We modelled these in HLA-transgenic mice infected with a clinically lethal isolate expressing Streptococcal pyrogenic exotoxin (Spe) C and demonstrate that both SpeC and streptococcal M protein, acting cooperatively, are required for disease. Vaccination with a conserved M protein peptide, J8, protects against STSS by causing a dramatic reduction in bacterial burden associated with the absence of SpeC and inflammatory cytokines in the blood. Furthermore, passive immunotherapy with antibodies to J8 quickly resolves established disease by clearing the infection and ablating the inflammatory activity of the M protein, which is further enhanced by addition of SpeC antibodies. Analysis of 77 recent isolates of Streptococcus pyogenes causing ISD, demonstrated that anti-J8 antibodies theoretically recognize at least 73, providing strong support for using antibodies to J8, with or without antibodies to SpeC, as a therapeutic approach.

Decoding the molecular epidemiology of group A streptococcus - an Indian perspective

PURPOSE

Unlike western countries the knowledge of group A streptococcus (GAS) epidemiology in India remains patchy and incomplete. Typing is crucial for surveillance as well as in predicting the efficacy of multivalent M protein vaccine. The present study aimed to explore the emm types of 206 invasive and non-invasive GAS isolates from South India as well as reviewing all the published literature on GAS molecular epidemiology from India thereby generating a pan-Indian data to predict the conjectural coverage of the 30-valent M-protein vaccine in this population.

METHODOLOGY

emm typing and superantigen (SAg) profiling of GAS along with reviewing literatures on GAS molecular epidemiology from India.

RESULTS

This study revealed a high diversity of emm types with emm 63, 82, 183, 85, 92, 169, 42, 44, 106, 74, 12 being frequently encountered, belonging to twenty emm clusters. The pan-Indian data on prevalent emm types further supports our study findings with 135 emm different types. Six clusters dominated accounting for 80 % of the GAS isolates: E3(26 %), E6(20 %), E2(11 %), E4(10 %), D4(7 %), E1(6 %). No significant association was noted between emm types and the nature of infection (P≥0.05) while a few SAg profiles were significantly associated with certain emm types. Pan Indian data revealed that only 16 % of the emm types encountered were included in proposed 30-valent M protein based vaccine.

CONCLUSION

The coverage among the South Indian GAS isolates was 28.2 % which increased to only 46.6 % with the cross-opsonic effect, thus highlighting the importance of developing a specific multivalent vaccine including the prevalent emm types in India or considering the use of conserved C-repeat vaccines and non-M protein based vaccines.

A Multiplex Assay for Detection of Staphylococcal and Streptococcal Exotoxins

Staphylococcal and streptococcal exotoxins, also known as superantigens, mediate a range of diseases including toxic shock syndrome, and they exacerbate skin, pulmonary and systemic infections caused by these organisms. When present in food sources they can cause enteric effects commonly known as food poisoning. A rapid, sensitive assay for the toxins would enable testing of clinical samples and improve surveillance of food sources. Here we developed a bead-based, two-color flow cytometry assay using single protein domains of the beta chain of T cell receptors engineered for high-affinity for staphylococcal (SEA, SEB and TSST-1) and streptococcal (SpeA and SpeC) toxins. Site-directed biotinylated forms of these high-affinity agents were used together with commercial, polyclonal, anti-toxin reagents to enable specific and sensitive detection with SD₅₀ values of 400 pg/ml (SEA), 3 pg/ml (SEB), 25 pg/ml (TSST-1), 6 ng/ml (SpeA), and 100 pg/ml (SpeC). These sensitivities were in the range of 4- to 80-fold higher than achieved with standard ELISAs using the same reagents. A multiplex format of the assay showed reduced sensitivity due to higher noise associated with the use of multiple polyclonal agents, but the sensitivities were still well within the range necessary for detection in food sources or for rapid detection of toxins in culture supernatants. For example, the assay specifically detected toxins in supernatants derived from cultures of Staphylococcus aureus. Thus, these reagents can be used for simultaneous detection of the toxins in food sources or culture supernatants of potential pathogenic strains of Staphylococcus aureus and Streptococcus pyogenes.