Limited repertoire of the C-terminal region of the M protein inStreptococcus pyogenes

Molecular epidemiological investigation of an outbreak of invasive beta-haemolytic streptococcal infection in western Norway

During a decade-long, high endemic situation with severe group A streptococcal disease in western Norway, a cluster of 16 patients with invasive streptococcal disease was hospitalized during a period of 11 weeks. A study including clinical characteristics and molecular epidemiology of the outbreak was initiated. Relevant clinical information was obtained from the medical records of the patients. Nine of the 16 patients had soft tissue infection, and seven of these had streptococcal toxic shock syndrome (STSS). Mortality, both overall and among those with STSS, was 25%. Streptococcal isolates from these patients were characterized by serogrouping and emm sequence typing. The emm amplicons were further characterized by sequence analysis and restriction fragment length polymorphism (emm RFLP) analysis. The streptococci were identified as group A streptococcus (GAS) in 11 patients and group G streptococcus (GGS) in four patients. The patients with GGS infection were older than the patients with GAS infection, and all patients infected with GGS had predisposing comorbidities. Isolates from 13 patients were available for emm gene analysis and found to belong to nine different emm types. Similar differentiation was obtained with emm RFLP in GAS. Hence, the outbreak was polyclonal. Results suggestive of horizontal gene transfer and recombination between the emm genes of GAS, group C streptococcus and GGS were found in the isolates from seven patients. Such genetic recombination events suggest a possible role in pathogenesis.

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.

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.

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

Streptococcal diseases, namely, acute glomerulonephritis and acute rheumatic fever, are common features in the aboriginal population of the Northern Territory of Australia. We examined the group A streptococcal M types identified during various surveys conducted since 1987. Streptococci were predominantly isolated from skin infections. A high proportion of the isolates could not be serotyped by conventional means and were designated M nontypeable (MNT). M-specific DNA sequences from the MNT isolates were examined, and sequence types were proposed for the classification of MNTs. This allowed a more precise estimate of the M types present in a population study.

Heptad motifs within the distal subdomain of the coiled-coil rod region of M protein from rheumatic fever and nephritis associated serotypes of group A streptococci are distinct from each other: nucleotide sequence of the M57 gene and relation of the deduced amino acid sequence to other M proteins

Streptococcal M protein, a dimeric alpha helical coiled-coil molecule, is an antigenically variable virulence factor on the surface of the bacteria. Our recent conformational analysis of the complete sequence of the M6 protein led us to propose a basic model for the M protein consisting of an extended central coiled-coil rod domain flanked by a variable N-terminal and a conserved C-terminal end domains. The central coiled-coil rod domain of M protein, which constitutes the major part of the M molecule, is made up of repeating heptads of the generalized sequence a-b-c-d-e-f-g, wherein "a" and "d" are predominantly apolar residues. Based on the differences in the heptad pattern of apolar residues and internal sequence homology, the central coiled-coil rod domain of M protein could be further divided into three subdomains I, II, and III. The streptococcal sequelae rheumatic fever (RF) and acute glomerulonephritis (AGN) have been known to be associated with distinct serotypes. Consistent with this, we observed that the AGN associated M49 protein exhibits a heptad motif that is distinct from the RF associated M5 and M6 proteins. Asn and Leu predominated in the "a" and "d" positions, respectively, in subdomain I of the M5 and M6 proteins, whereas apolar residues predominated in both these positions in the M49 protein. To establish whether the heptad motif of M49 is unique to this protein, or is a general characteristic of nephritis-associated serotypes, the amino acid sequence of M57, another nephritis-associated serotype, has now been examined. The gene encoding M57 was amplified by PCR, cloned into pUC19 vector, and sequenced. The C-terminal half of M57 is highly homologous to other M proteins (conserved region). In contrast, its N-terminal half (variable region) revealed no significant homology with any of the M proteins. Heptad periodicity analysis of the M57 sequence revealed that the basic design principles, consisting of distinct domains observed in the M6 protein, are also conserved in the M57 molecule. However, the heptad motif within the coiled-coil subdomain I of M57 was distinct from M5 and M6 but similar to M49. Similar analyses of the heptad characteristics within the reported sequences of M1, M12, and M24 proteins further confirmed the conservation of the overall architectural design of sequentially distinct M proteins.(ABSTRACT TRUNCATED AT 400 WORDS)