Identification of sequence types among the M-nontypeable group A streptococci

Unexpected relationships between frequency of antimicrobial resistance, disease phenotype and emm type in group A Streptococcus

Despite universal susceptibility to β-lactams, resistance to second-line antimicrobials (e.g. erythromycin) is increasingly common among group A Streptococcus (GAS). To better understand the frequency of regional GAS antimicrobial resistance, we screened a previously described GAS strain collection from Houston, TX, USA, for resistance to commonly used antimicrobials. A total of 100/929 (10.8 %) showed resistance to at least one antimicrobial. Tetracycline resistance was identified in 52 (5.6 %) GAS strains. The cumulative frequency of erythromycin and clindamycin resistance [macrolide (M) and macrolide-lincosamide-streptogramin (MLS) phenotypes] was greatest among invasive GAS strains (9.9 %) compared to that of strains derived from any other infection type (5.9 %, P=0.045). We identified emm types 11, 75, 77 and 92 as the only emm types with high (e.g. >50 %) within-emm type resistance and contributing to the majority (24/26; 92 %) of erythromycin/clindamycin resistance in invasive GAS. High-frequency resistance emm types were also significantly overrepresented in invasive GAS strains as indicated by invasive index. We performed whole-genome sequencing to define genetic elements associated with resistance among emm types 11, 75, 77 and 92. Diverse mobile elements contributed to GAS resistance including transposons, integrative conjugative elements, prophage and a plasmid. Phylogenetic analysis suggests recent clonal emergence of emm92 GAS strains. Our findings indicate that less frequently encountered GAS emm types disproportionately contribute to resistance phenotypes, are defined by diverse mobile genetic elements and may favour invasive disease.

Complement inhibition by Sarcoptes scabiei protects Streptococcus pyogenes - An in vitro study to unravel the molecular mechanisms behind the poorly understood predilection of S. pyogenes to infect mite-induced skin lesions

Background

On a global scale scabies is one of the most common dermatological conditions, imposing a considerable economic burden on individuals, communities and health systems. There is substantial epidemiological evidence that in tropical regions scabies is often causing pyoderma and subsequently serious illness due to invasion by opportunistic bacteria. The health burden due to complicated scabies causing cellulitis, bacteraemia and sepsis, heart and kidney diseases in resource-poor communities is extreme. Co-infections of group A streptococcus (GAS) and scabies mites is a common phenomenon in the tropics. Both pathogens produce multiple complement inhibitors to overcome the host innate defence. We investigated the relative role of classical (CP), lectin (LP) and alternative pathways (AP) towards a pyodermic GAS isolate 88/30 in the presence of a scabies mite complement inhibitor, SMSB4.

Methodology/Principal findings

Opsonophagocytosis assays in fresh blood showed baseline immunity towards GAS. The role of innate immunity was investigated by deposition of the first complement components of each pathway, specifically C1q, FB and MBL from normal human serum on GAS. C1q deposition was the highest followed by FB deposition while MBL deposition was undetectable, suggesting that CP and AP may be mainly activated by GAS. We confirmed this result using sera depleted of either C1q or FB, and serum deficient in MBL. Recombinant SMSB4 was produced and purified from Pichia pastoris. SMSB4 reduced the baseline immunity against GAS by decreasing the formation of CP- and AP-C3 convertases, subsequently affecting opsonisation and the release of anaphylatoxin.

Conclusions/Significance

Our results indicate that the complement-inhibitory function of SMSB4 promotes the survival of GAS in vitro and inferably in the microenvironment of the mite-infested skin. Understanding the tripartite interactions between host, parasite and microbial pathogens at a molecular level may serve as a basis to develop improved intervention strategies targeting scabies and associated bacterial infections.

The molecular mechanisms that underpin the link between scabies and bacterial pathogens were unknown. We proposed that scabies mites play a role in the establishment, proliferation and transmission of opportunistic pathogens. We investigated here the synergy between mites and one of the most recognised mite associated pathogens, Streptococcus pyogenes. As part of the innate immune response mammals have a pre-programmed ability to recognise and immediately act against substances derived from fungal and bacterial microorganisms. This is mediated through a sequential biochemical cascade involving over 30 different proteins (complement system) which as a result of signal amplification triggers a rapid killing response. The complement cascade produces peptides that attract immune cells, increases vascular permeability, coats (opsonises) the surfaces of a pathogen, marking it for destruction, and directly disrupts foreign plasma membranes. To prevent complement mediated damage of their gut cells, scabies mites secrete several classes of complement inhibiting proteins into the mite gut and excrete them into the epidermal mite burrows. Furthermore, these inhibitors also provide protection for S. pyogenes. We verified here specifically the impact of the mite complement inhibitor SMSB4, to identify the molecular mechanisms behind the long recognised tendency of S. pyogenes to infect mite-induced skin lesions.

Molecular characterization and evaluation of the emerging antibiotic-resistant Streptococcus pyogenes from eastern India

Background

Group A Streptococcus strains causing wide variety of diseases, recently became noticeable in eastern India, are not amenable to standard treatment protocol thus enhancing the possibility of disease morbidity by becoming antibiotic resistance.

Methods

The association of Lancefield group A Streptococcal variation with degree of vir architectural diversity was evaluated using emm typing and restriction fragment length polymorphism analyses. The antibiotic sensitivity patterns were examined by modified Kirby-Bauer method of disk diffusion. Percentage calculations, 95% confidence interval and one-way ANOVA were used to assess differences in proportions.

Results

Our observations revealed 20 different emm types and 13 different HaeIII vir typing patterns. A 1.2 kb fragment was found in all HaeIII typing pattern. Fragments of 1.2 kb and 550 bp were conserved in majority of the isolates. HinfI digestion was found proficient in differentiating the strains of same vir typing patterns. Strong predominance of speC (85%) and speF (80%) genes have been observed encoding exotoxins production. 4 isolates were found to be erythromycin resistant and were of genotype emm49. High degree of tetracycline resistance was shown by 53.57% isolates which belonged to 12 different emm genotypes.

Conclusions

These findings suggested that in addition to emm typing, sequential application of HaeIII and HinfI restriction enzymes in vir typing analysis is an effective tool for group A streptococcal molecular characterization associated with antibiotic resistance.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-2079-9) contains supplementary material, which is available to authorized users.

High diversity of group A streptococcal emm types among healthy schoolchildren in Ethiopia

BACKGROUND

Although the prevalence of rheumatic heart disease in Ethiopia is one of the highest in the world, the epidemiology of group A streptococci (GAS) in this country is little known. GAS typing is a hallmark of both the epidemiology and understanding of diseases caused by these organisms. We have therefore conducted this study to investigate the emm (M-protein gene) type distribution of GAS carriers among Ethiopian schoolchildren.

METHODS

In the present study, we performed emm typing of 82 GAS isolates collected from the throats of healthy schoolchildren (6-14 years of age) residing in 3 different urban sites in Ethiopia: Addis Ababa, Gondar, and Dire Dawa.

RESULTS

We report high diversity of GAS isolates recovered from healthy schoolchildren. Eighty-two isolates represented 43 different sequence types. Thirteen newly described subtypes were detected in this study. Of the emm types prevalent in the study communities, 46% were not included in the 26-valent GAS vaccine.

CONCLUSIONS

The high diversity of emm types encountered within 3 months of collection suggest that production of a vaccine candidate based on the M-protein amino termini appears to be impractical for this population. We suggest that investigations of other vaccine candidates, including the C5a peptidase, GAS carbohydrate, and fibronectin-binding proteins, as well as conserved M-protein region vaccines, should be intensified to address the needs of this population.

Plasminogen binding by group A streptococcal isolates from a region of hyperendemicity for streptococcal skin infection and a high incidence of invasive infection

Reports of resurgence in invasive group A streptococcal (GAS) infections come mainly from affluent populations with infrequent exposure to GAS. In the Northern Territory (NT) of Australia, high incidence of invasive GAS disease is secondary to endemic skin infection, serotype M1 clones are rare in invasive infection, the diversity and level of exposure to GAS strains are high, and no particular strains dominate. Expression of a plasminogen-binding GAS M-like protein (PAM) has been associated with skin infection in isolates elsewhere (D. Bessen, C. M. Sotir, T. M. Readdy, and S. K. Hollingshead, J. Infect. Dis. 173:896-900, 1996), and subversion of the host plasminogen system by GAS is thought to contribute to invasion in animal models. Here, we describe the relationship between plasminogen-binding capacity of GAS isolates, PAM genotype, and invasive capacity in 29 GAS isolates belonging to 25 distinct strains from the NT. In the presence of fibrinogen and streptokinase, invasive isolates bound more plasminogen than isolates from uncomplicated infections (P < or = 0.004). Only PAM-positive isolates bound substantial levels of plasminogen by a fibrinogen-streptokinase-independent pathway (direct binding). Despite considerable amino acid sequence variation within the A1 repeat region of PAM where the plasminogen-binding domain maps, the critical lysine residue was conserved.

emm Typing of group A streptococcus clinical isolates: identification of dominant types for throat and skin isolates

T and emm types were determined for group A streptococci isolated from patients with various infections during 1990-1999 in Toyama Prefecture, Japan. Out of 906 isolates, 872 isolates were divided into 20 T serotypes, and 34 isoltes were T nontypeable (TNT). T12, T1, and T4 were dominant among 699 throat isolates; on the other hand, T11, T28, TB3264, and TNT were dominant among 80 skin isolates. The emm types of 190 isolates were determined following specific PCR amplification and sequencing of the products. Twenty T serotypes were divided into 34 T type/emm type combinations. Thirty-four TNT isolates were divided into 14 emm types, in which emm58 was the most common (38%). Among 82 throat isolates randomly selected, predominant T types T12, T1, and T4 isolates were of the respective same numbers in emm type. T11/emm89, T28/emm28, TB3264/emm13w, and TNT/emm58 were predominant among 80 skin isolates. emm-type distribution observed in the present study was that usually reported in the western world. To our knowledge, 3 T/emm is a novel combination. These results show that emm typing allows the characterization of group A streptococci from various sources.

Extension of the Lancefield classification for group A streptococci by addition of 22 new M protein gene sequence types from clinical isolates: emm103 to emm124

Classic M protein serotyping has been invaluable during the past 60 years for the determination of relationships between different group A streptococci (GAS) strains and the varied clinical manifestations inflicted by these organisms worldwide. Nonetheless, during the past 20 years, the difficulties of continued expansion of the serology-based Lancefield classification scheme for GAS have become increasingly apparent. By use of a less demanding sequence-based methodology that closely adheres to previously established strain criteria while being predictive of known M protein serotypes, we recently added types emm94-emm102 to the Lancefield scheme. Continued expansion by the addition of types emm103 to emm124 are now proposed. As with types emm94-emm102, each of these new emm types was represented by multiple independent isolates recovered from serious disease manifestations, each was M protein nontypeable with all typing sera stocks available to international GAS reference laboratories, and each demonstrated antiphagocytic properties in vitro by multiplying in normal human blood.

Immunological response mounted by Aboriginal Australians living in the Northern Territory of Australia against Streptococcus pyogenes serum opacity factor

Streptococcus pyogenes (Group A streptococcus) interacts with host fibronectin via a number of distinct surface components. The streptococcal serum opacity factor (SOF) is a cell-surface protein of S. pyogenes which causes opalescence of human serum and mediates bacterial binding to fibronectin. In this study, hexahistidyl-tagged fusion proteins encompassing full-length SOF, and domains of SOF encompassing opacity factor activity and fibronectin-binding regions, were used in the characterization of the Aboriginal immune response to SOF. Anti-SOF serum IgG responses were found to be significantly higher (P<0.0001) in Aboriginal adults and children when compared to a non-Aboriginal adult group. The Aboriginal immune response against the fibronectin-binding region of SOF was significantly reduced when compared to the response against the whole SOF protein and N-terminal domains examined in this study (P<0.001). This pattern of immune response was also observed in rabbits immunized with recombinant SOF. Comparison of the deduced amino acid sequence of SOF from a number of common Australian isolates with other SOF sequences revealed that the N-terminus of SOF exhibits sequence similarity values ranging from 42.9% to 96.5%. The C-terminus containing the fibronectin-binding domain and membrane-spanning regions was more highly conserved, exhibiting sequence similarity values ranging from 84.6% to 100% within the fibronectin-binding repeats. These data suggest that the immune response against SOF is directed toward the variable N-terminus of the SOF protein. Phylogenetic analysis indicated that the sof genes of S. pyogenes do not exhibit geographical variation.

Systemic and mucosal immunizations with fibronectin-binding protein FBP54 induce protective immune responses against Streptococcus pyogenes challenge in mice

The purpose of this study was to examine the suitability of fibronectin-binding protein FBP54 as a putative vaccine for Streptococcus pyogenes infections. When the distribution of the fbp54 gene among the clinical isolates representing various M serotypes was tested by PCR and Southern blot assays, it was found that all of the strains possess this gene. Furthermore, a significant increase in immunoglobulin G (IgG) antibody titers against FBP54 was observed in sera from patients with S. pyogenes infections compared with those from healthy volunteers (P < 0.005). Mice were immunized with FBP54 subcutaneously, orally, or nasally. An enzyme-linked immunosorbent assay revealed that antigen-specific IgG antibodies were induced in the sera of immunized mice, while high salivary levels of IgA antibodies were detected after oral and nasal immunizations. Mice subcutaneously or orally immunized with FBP54 survived significantly longer following the challenge with S. pyogenes than did nonimmunized mice (P < 0.001). These results indicate that FBP54 is a promising vaccine for the prevention of S. pyogenes infections.

Protective and nonprotective epitopes from amino termini of M proteins from Australian aboriginal isolates and reference strains of group A streptococci

The M protein is the primary vaccine candidate to prevent group A streptococcal (GAS) infection and the subsequent development of rheumatic fever (RF). However, the large number of serotypes have made it difficult to design a vaccine against all strains. We have taken an approach of identifying amino-terminal M protein epitopes from GAS isolates that are highly prevalent in GAS-endemic populations within the Northern Territory (NT) of Australia. Australian Aboriginals in the NT experience the highest incidence of RF worldwide. To develop a vaccine for this population, 39 peptides were synthesized, representing the amino-terminal region of the M protein from endemic GAS. Mice immunized with these peptides covalently linked to tetanus toxoid and emulsified in complete Freund's adjuvant raised high-titer antibodies. Over half of these sera reduced bacterial colony counts by >80% against the homologous isolate of GAS. Seven of the peptide antisera also cross-reacted with at least three other heterologous peptides by enzyme-linked immunosorbent assay. Antiserum to one peptide, BSA10(1-28), could recognize six other peptides, and five of these peptides could inhibit opsonization mediated by BSA10(1-28) antiserum. Cross-opsonization studies showed that six of these sera could opsonize at least one heterologous isolate of GAS. These data reveal vaccine candidates specific to a GAS-endemic area and show the potential of some to cross-opsonize multiple isolates of GAS. This information will be critical when considering which epitopes may be useful in a multiepitope vaccine to prevent GAS infection.

New multi-determinant strategy for a group A streptococcal vaccine designed for the Australian Aboriginal population

Infection with group A streptococci can result in acute and post-infectious pathology, including rheumatic fever and rheumatic heart disease. These diseases are associated with poverty and are increasing in incidence, particularly in developing countries and amongst indigenous populations, such as Australia's Aboriginal population, who suffer the highest incidence worldwide. Immunity to group A streptococci is mediated by antibodies against the M protein, a coiled-coil alpha helical surface protein of the bacterium. Vaccine development faces two substantial obstacles. Although opsonic antibodies directed against the N terminus of the protein are mostly responsible for serotypic immunity, more than 100 serotypes exist. Furthermore, whereas the pathogenesis of rheumatic fever is not well understood, increasing evidence indicates an autoimmune process. To develop a suitable vaccine candidate, we first identified a minimum, helical, non-host-cross-reactive peptide from the conserved C-terminal half of the protein and displayed this within a non-M-protein peptide sequence designed to maintain helical folding and antigenicity, J14 (refs. 8,9). As this region of the M protein is identical in only 70% of group A streptococci isolates, the optimal candidate might consist of the conserved determinant with common N-terminal sequences found in communities with endemic group A streptococci. We linked seven serotypic peptides with J14 using a new chemistry technique that enables the immunogen to display all the individual peptides pendant from an alkane backbone. This construct demonstrated excellent immunogenicity and protection in mice.

Bacterial and viral etiology of severe infection in children less than three months old in the highlands of Papua New Guinea

OBJECTIVE

Determine the bacterial and viral etiology of severe infection in young Papua New Guinean infants as part of a multicenter study in four developing countries aimed at improving case management guidelines.

METHODS

Between March, 1991, and April, 1993, children aged <3 months were recruited at the outpatient department of Goroka Base Hospital, Papua New Guinea (PNG). Children with pre-defined inclusion criteria were enrolled, a history was taken and clinical examination was performed. Blood and urine were collected from children with signs suggestive of severe disease together with eye, umbilical and pernasal swabs as appropriate. Nasopharyngeal aspirates (NPAs) were collected from children with and without signs of severe disease for identification of viruses and Chlamydia trachomatis by direct fluorescent antibody staining.

RESULTS

3280 infants were triaged and 2168 enrolled, among whom 968 had signs suggestive of severe disease. Group A Streptococcus (Streptococcus pyogenes) and Staphylococcus aureus were the most important bacterial pathogens isolated from children < 1 month old with severe infections, and Streptococcus pneumoniae, S. pyogenes and Staphylococcus aureus were most important in older children. Of 292 eye swabs 19 (7%) grew Neisseria gonorrhoeae. Of 116 umbilical swabs 51 (44%) grew S. pyogenes and 45 (39%) grew Staphylococcus aureus. Respiratory syncytial virus was the most important viral cause of acute lower respiratory infection.

CONCLUSIONS

S. pyogenes, S. pneumoniae and Staphylococcus aureus are important causes of severe infection in young children in the PNG highlands. It is necessary to improve access to clean water, promote hand-washing in the hospital and at home and investigate further the use of maternal immunization for the prevention of severe disease in young infants.

Vaccine strategies to prevent rheumatic fever

Group A streptococci (GAS) are responsible for numerous human illnesses, ranging from pharyngitis to severe invasive infections, such as necrotizing fascitis and toxic shock syndrome to the postinfectious sequelae, acute rheumatic fever (ARF), and glomerulonephritis. To date, to develop a vaccine, studies have focused on the M protein. However, designing a vaccine to prevent GAS infection based on this molecule has been hampered by the vast number of M protein serotypes and the possibility that it may induce potentially harmful autoimmune reactions. In this article, the authors discuss recent approaches to overcoming the problems of an M protein-based vaccine. In addition, recent studies identifying the protective properties of other streptococcal antigens and their potential as vaccine candidates are discussed.

emm typing and validation of provisional M types for group A streptococci

This report discusses the following issues related to typing of group A streptococci (GAS): The development and use of the 5' emm variable region sequencing (emm typing) in relation to the existing serologic typing system; the designation of emm types in relation to M types; a system for validation of new emm types; criteria for validation of provisional M types to new M-types; a list of reference type cultures for each of the M-type or emm-type strains of GAS; the results of the first culture exchange program for a quality control testing system among the national and World Health Organization collaborating centers for streptococci; and dissemination of new approaches to typing of GAS to the international streptococcal community.

Group A streptococcal Vir types are M-protein gene (emm) sequence type specific

The M-protein genes (emm genes) of 103 separate impetiginous Streptococcus pyogenes isolates were sequenced and the sequence types were compared to the types obtained by Vir typing. Vir typing is based on restriction fragment length polymorphism (RFLP) analysis of a 4- to 7-kb pathogenicity island encoding emm and other virulence genes. By using both HaeIII and HinfI to generate RFLP profiles, complete concordance between Vir type and emm sequence type was found. Comparison of the emm sequences with those in GenBank revealed new sequence types sharing less than 90% identity with known types. Diversity in the emm sequence was generated by corrected frameshift mutations, point mutations, and small in-frame mutations.

Characterization of group A Streptococcus strains recovered from Mexican children with pharyngitis by automated DNA sequencing of virulence-related genes: unexpectedly large variation in the gene (sic) encoding a complement-inhibiting protein

Sequence variation was studied in several target genes in 54 strains of group A Streptococcus (GAS) cultured from children with pharyngitis in Mexico City. Although 16 distinct emm alleles were identified, only 4 had not been previously described. Virtually all bacteria (31 of 33 [94%] with the streptococcal pyrogenic exotoxin gene (speA) had emm1-related, emm3, or emm6 alleles. The gene (sic) encoding an extracellular GAS protein that inhibits complement function was unusually variable among isolates with the emm1 family of alleles, with a total of seven variants identified. The data suggest that many GAS strains infecting Mexican children are genetically similar to organisms commonly encountered in the United States and western Europe. Sequence variation in the sic gene is useful for rapid differentiation among GAS isolates with the emm1 family of alleles.

Survey of emm gene sequences and T-antigen types from systemic Streptococcus pyogenes infection isolates collected in San Francisco, California; Atlanta, Georgia; and Connecticut in 1994 and 1995

The variable 5' emm (M-protein gene) sequences and T-antigen types were determined from 340 systemic group A streptococcal (GAS) isolates taken from hospitalized patients in San Francisco, Calif.; Atlanta, Ga.; and Connecticut in 1994 and 1995. Eighty percent of these isolates had emm sequences and T-antigen types in agreement with previously recorded M- and T-antigen associations. Most of the remaining strains either were T nontypeable (11%) or contained emm genes encoding M proteins for which T-antigen associations have not been made (6%). One newly encountered emm gene, designated ST2974, from each of 13 isolates had the T type 8/25/Imp19. Another new emm gene, ST2967, from 8 of 11 isolates was T nontypeable. Six other unique emm gene sequences from seven isolates were encountered. Sequencing of the variable region of the emm gene of GAS isolates (emm typing) is effective for surveying the sequence variability of the M virulence protein, and combined with T typing, emm typing is useful for monitoring GAS strain diversity.

Immunologic and clinical correlations in rheumatic fever and rheumatic heart disease

The intimate relationship of Streptococcus pyogenes and rheumatic fever is well-established, but the precise pathogenesis of rheumatic fever and rheumatic heart disease continues to elude intense investigative efforts by students of the disease worldwide. Technologic advances in molecular biology, not thought possible two decades ago, have given additional insight into the immunologic aspects of the disease. On the clinical side echocardiography has proved to be a marvelous, non-invasive technique to evaluate cardiac anatomy and function. We are now able to gain a closer correlation of the clinical presentation and the autoimmune response. The increased understanding acquired both from the "bench" and the "bedside" are making this perplexing disease somewhat less mysterious. We seem tantalizingly close to grasping a complete understanding of the pathogenesis of rheumatic fever and rheumatic heart disease.

Molecular epidemiology of impetiginous group A streptococcal infections in aboriginal communities of northern Australia

Group A streptococcal infections among the Aboriginal communities of the Northern Territory of Australia are endemic, with a concurrently high rate of the postinfection sequelae of rheumatic fever and acute post-streptococcal glomerulonephritis. The majority of the group A streptococcal isolates from the Northern Territory are not typeable by M typing. We recently developed a novel genotyping method, Vir typing. A preliminary study using this method discriminated all the M-nontypeable (MNT) isolates. Vir typing is based on restriction fragment length polymorphisms of the 4- to 7-kb Vir regulon of group A streptococci, which contains a number of genes, including emm (the gene for M protein). A total of 407 isolates of group A streptococci obtained from four Aboriginal communities over a 4-year period were typed by this genotyping method. Forty-two distinct genotypes were found among the isolates, including 22 among the MNT isolates. The correlation between Vir type and M type was good. This genotyping method allows the characterization of all group A streptococcal isolates from Aboriginal communities in the Northern Territory. We also propose that Vir typing be used in conjunction with M typing for epidemiological surveillance in geographical regions where the majority of isolates are MNT.

Multiple strains of Streptococcus pyogenes in skin sores of aboriginal Australians

A molecular technique (random amplification of polymorphic DNA) was used to characterize group A streptococcal (GAS) strains among 194 isolates from 55 swabs from 12 Australian Aboriginal children and adults with multiple pyoderma lesions. Ninety-three percent of the lesions contained only one strain of GAS, but 8 of 12 individuals were infected with more than one strain. We conclude that accurate epidemiologic surveys require that more than one swab specimen be obtained from each person, whereas typing of more than one colony per swab is less informative. Characterization of GAS strains by random amplification of polymorphic DNA analysis should help to provide important insights into the epidemiology of GAS, particularly in tropical populations where many isolates are M nontypeable, and into the mechanisms of genetic variation of GAS in such populations.

Protective immunity to the group A Streptococcus may be only strain specific

M protein enables Group A streptococci to resist phagocytosis. Protective immunity is considered to be mediated by opsonic antibodies directed against this M protein. In recent studies we have shown that genetically distinct populations exist within an M-type. The question asked in this study was whether human and rabbit type specific M1 antibody was opsonic for all strains of M-type 1, irrespective of their restriction fragment length polymorphism type. When locating a blood donor from among our staff for use in the indirect bactericidal test, selective variation in opsonic ability was demonstrated by one person. Subsequent testing of 44 randomly selected human sera revealed that 11 (25%) had opsonic antibody. Of these 11, 6 opsonised all seven strains and 5 demonstrated selective opsonisation. We conclude that opsonic antibody is not necessarily type specific but may be strain specific.

Towards a vaccine for rheumatic fever: identification of a conserved target epitope on M protein of group A streptococci

Rheumatic fever and rheumatic heart disease remain very common in developing countries, and a vaccine to protect against these disorders would have a great impact on public health. A vaccine must target the M protein of group A streptococci (Streptococcus pyogenes), but until lately immunity was thought to be strain-specific and dependent on antibodies to the variable serotype-specific regions of the protein. Experiments in animals have suggested the conserved region of the M protein as a possible alternative target for protective antibodies. We constructed a 20-aminoacid peptide (peptide 145) within the conserved region of the carboxyl terminus of the protein. In mice the peptide induced serum antibodies that could opsonise reference type 5 streptococci. By enzyme-linked immunosorbent assay, positive responses to peptide 145 were obtained with serum from 77 (90%) of 86 Aboriginal subjects and 135 (81%) of 167 Thai subjects living in areas with high exposure to streptococci. Only 10 (14%) of 71 Caucasian subjects with low exposure to streptococci showed positive responses. There was no difference in the proportion positive between subjects with rheumatic heart disease and control groups (other or no heart disease). Antibodies to peptide 145 were able to opsonise isolates of streptococci from Aboriginal and Thai subjects with acute rheumatic fever as well as reference strains. This highly conserved part of the M protein may be a suitable target for vaccines to prevent streptococcal infections and their sequelae.

Antigenic diversity within a family of M proteins from group A streptococci: evidence for the role of frameshift and compensatory mutations

The genes (emm) encoding M proteins, from isolates of group-A streptococci (GAS) serotyped as M52, M53, M80 and M nontypeable (MNT; serologically related to M53 and M80), were examined. Characterization of emm from these GAS revealed some discrepancies with serotyping, illustrating the difficulty in serotype determination when cross-reactions occur. DNA sequences corresponding to the N-terminal region of M proteins from the isolates showed considerable similarity both in the hypervariable region and the repeat regions. We propose that these serotypes form a family of closely related M types. Frameshift mutations in the hypervariable region followed by a corrective (compensatory) frameshift were observed. This may be an effective mechanism for generating antigenic diversity in the M protein.