Group A Streptococcus Serotypes Research Articles

Genome sequencing gives clues to group A streptococcus virulence

By sequencing the genome of an M3 group A streptococcus (GAS) isolated from a patient with streptococcal toxic-shock syndrome, James Musser (US National Institute of Allergy and Infectious Diseases, Hamilton, MT, USA) and co-workers have gained new insights into the molecular basis of virulence of this GAS serotype, which might offer therapeutic benefits.

Molecular analysis of group A Streptococcus type emm18 isolates temporally associated with acute rheumatic fever outbreaks in Salt Lake City, Utah.

Acute rheumatic fever (ARF) and subsequent rheumatic heart disease are rare but serious sequelae of group A Streptococcus (GAS) infections in most western countries. Salt Lake City (SLC), Utah, and the surrounding intermountain region experienced a resurgence of ARF in 1985 which has persisted. The largest numbers of cases were encountered in 1985-1986 and in 1997-1998. Organisms with a mucoid colony phenotype when grown on blood agar plates were temporally associated with the higher incidence of ARF. To develop an understanding of the molecular population genetic structure of GAS strains associated with ARF in the SLC region, 964 mucoid and nonmucoid pharyngeal isolates recovered in SLC from 1984 to 1999 were studied by sequencing the emm gene. Isolates with an emm18 allele were further characterized by sequencing the spa, covR, and covS genes. Peak periods of ARF were associated with GAS isolates possessing an emm18 allele encoding the protein found in serotype M18 isolates. Among the serotype M18 isolates, the difference in the number of C repeats produced three size variants. Variation was limited in spa, a gene that encodes a streptococcal protective antigen, and covR and covS, genes that encode a two-component regulatory system that, when inactivated, results in a mucoid phenotype and enhanced virulence in mouse infection models. Pulsed-field gel electrophoresis showed a single restriction profile for serotype M18 organisms isolated during both peak periods of ARF. In SLC, the incidence of ARF coresurged with the occurrence of GAS serotype M18 isolates that have very restricted genetic variation.

Extracellular cysteine protease produced by Streptococcus pyogenes participates in the pathogenesis of invasive skin infection and dissemination in mice.

The role of an extracellular cysteine protease encoded by the speB gene in group A Streptococcus (GAS) skin infection was studied with a mouse model. Mice were injected subcutaneously with a wild-type GAS serotype M3 strain or a cysteine protease-inactivated isogenic derivative grown to stationary phase. The mortality rate of mice injected with the M3 speB mutant strain was significantly decreased (P < 0.0008) compared to that of animals injected with the wild-type parental organism. The abscesses formed in animals infected with the cysteine protease mutant strain were significantly smaller (P < 0.0001) than those caused by the wild-type organism and slowly regressed over 3 to 4 weeks. In striking contrast, infection with the wild-type GAS isolate generated necrotic lesions, and in some animals the GAS disseminated widely from the injection site and produced extensive cutaneous damage. All of these animals developed bacteremia and died. GAS dissemination was accompanied by severe tissue and blood vessel necrosis. Cysteine protease expression in the infected tissue was identified by immunogold electron microscopy. These data demonstrate that cysteine protease expression contributes to soft tissue pathology, including necrosis, and is required for efficient systemic dissemination of the organism from the initial site of skin inoculation.

Production of Stabilized Virulence Factor-Negative Variants by Group A Streptococci during Stationary Phase

Many of the virulence factors associated with fulminant group A streptococci (GAS) infection are expressed under in vitro exponential growth conditions. However, the survival of GAS in tissue and intracellularly, as well as colonization of asymptomatic carriers, has been reported for GAS. The bacteria associated with these niches may encounter high-density, low-nutrient-flowthrough conditions that may more closely mimic in vitro stationary-phase conditions than exponential growth. Therefore, the behavior of GAS in stationary-phase culture was examined. We observed that after 24 h in stationary phase, GAS serotypes M49 and M2 developed a unstable colony dimorphism of typical large and atypical small colonies. Between days 4 and 5, we isolated stabilized atypical small colonies which remained stable for up to nine passages (approximately 200 generations) on fresh medium before fully reverting to the large-colony phenotype. Upon analysis, the small colonies showed no difference in cell number per colony, growth rate, survival in prolonged stationary-phase culture, or antibiotic sensitivity. However, the small colonies showed decreased transcription of hyaluronic acid capsule, the global positive virulence factor regulator gene mga, the mga-regulated emm mRNA (M-protein structural gene), and speB (cysteine protease). Accordingly, the small colonies were completely sensitive in a traditional phagocytosis assay. The production of virulence factors and phagocytosis resistance of the small-colony isolates was recovered when, after several passages on fresh medium, the colony morphology began to revert.

Human antibodies to the conserved region of the M protein: opsonization of heterologous strains of group A streptococci

A 20-mer peptide (p145) in the carboxyl-terminal region of the M protein of group A streptococci (GAS) has previously been defined as the target of bactericidal antibodies. Sequence analysis of seven field isolates from indigenous Australians living in an area highly endemic for GAS and five laboratory reference strains (encompassing nine unique serotypes plus three nontypeables) demonstrates that this region is highly conserved (sequence identity ranging from 65 to 95%) with six of the 12 sequences being identical to p145. Most of the sequence dissimilarity is contained within the last seven amino acids of p145. Competitive ELISA demonstrates that human antibodies specific for p145 cannot discriminate between p145 and synthetic peptides representing four from four of the variant sequences tested. Ig purified from endemic sera was able to opsonize each of the GAS isolates and free p145 as well as a peptide expressing a minimal conformational epitope within p145 (requiring amino acids between positions 2 and 13 of p145), but not an irrelevant peptide, were able to partially or completely inhibit opsonization of all isolates and reference strains. Thus adult endemic sera contain antibodies which are bactericidal for multiple GAS serotypes and which are specific for a sequence of 12 amino acids contained within the p145 region of the M protein.

Group A streptococcal infections in hospitalized patients.

During the late 1980’s, a resurgence of severe group A streptococcus (GAS) infections was noted in the Western Hemisphere. Molecular and genetic studies supported the emergence of a virulent clone in a possibly non-immune population, responsible for the resurgence1. Sporadic cases of severe GAS disease were reported from around the world but the dramatic increase was confined to the Western Hemisphere. Similar increase was not documented in tropical countries where these conditions remained endemic. To date, published data on the current epidemiology and microbiology of GAS infections from such areas are scanty. In Malaysia, studies on GAS infections have been confined to teaching hospitals and populations served by them. Outcome of one such study supported the existence of as yet uncharacterized/new GAS serotypes in this region2. To obtain more comprehensive data, it is essential to study GAS infections and their sequelae in other areas and different population groups. Therefore, laboratory-based surveillance was carried out as a pilot study at a small hospital in a rice growing area. The aim was to assess the occurrence of GAS infections and their sequelae and to characterize GAS strains isolated from clinical specimens.KeywordsRheumatic FeverRheumatic Heart DiseaseWestern HemisphereStreptococcal InfectionSerum Opacity FactorThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

PCR-Mediated Amplification of Group A Streptococcal Genes Encoding Immunoglobulin-Binding Proteins

A majority of group A streptococci (GAS) express immunoglobulin (Ig)-binding proteins. The genes encoding these proteins belong to either the emm or the emm-related (fcrA and enn) gene family. The present study presents oligonucleotide primers and protocols for the specific PCR-mediated amplification of fcrA and enn genes with and without their own promoters and transcription termination sites. The PCR system appears to be applicable to virtually every GAS serotype. Using these assays, some sequence variability in the 5′ untranslated region of fcrA and at the 5′ end of enn was demonstrated for a minority of GAS serotypes. The fcrA and enn genes of GAS serotype M49 were amplified by PCR, cloned into pJLA602, and expressed in Escherichia coli. The fcrA gene of the GAS serotype M49 strain CS101, including its adjacent regulatory sequences, was sequenced using a universal primer set by means of which emm-related genes can be completely sequenced with only five sequencing reactions. The fcrA49 sequence provides further evidence that fcrA genes are a separate entity from emm-related genes and exhibit a variability at their 5′ ends similar to that of proteins encoded by emm genes.