Inter-species genetic movement may blur the epidemiology of streptococcal diseases in endemic regions

Streptococcus dysgalactiae subsp. equisimilis (human group G streptococcus, GGS) is generally regarded as a commensal organism but can cause a spectrum of human diseases very similar to that caused by S. pyogenes (group A streptococcus, GAS). Lateral acquisition of genes between these two phylogenetically closely related species is well documented. However, the extent and mechanisms of lateral acquisitions is not known. We report here genomic subtraction between a pathogenic GGS isolate and a community GGS isolate and analyses of the gene sequences unique to the pathovar. Our results show that cross-species genetic transfers are common between GGS and two closely related human pathogens, GAS and the group B streptococcus. We also demonstrate that mobile genetic elements, such as phages and transposons, play an important role in the ongoing inter-species transfers of genetic traits between extant organisms in the community. Furthermore, lateral gene transfers between GAS and GGS may occur more frequently in geographical regions of high GAS endemicity. These observations may have important implications in understanding the epidemiology of streptococcal diseases in such regions.     

Inhibition of Streptococcus pyogenes adherence to HaCaT cells by a peptide corresponding to the streptococcal fibronectin-binding protein, SfbI, is strain dependent

Streptococcus pyogenes (group A streptococcus, GAS) is a human-specific pathogen, which employs a large number of adhesins for colonization. Fibronectin-binding proteins (FBPs) play a major role in GAS adhesion to host cells. SfbI, a major streptococcal FBP, has been well studied. A peptide (peptide-MSG) based on this adhesin inhibits fibronectin (Fn)-binding by the pathogen. To test whether this peptide also inhibits adherence of GAS to host cells, adhesion assays were performed with strains possessing different combinations of genes for three distinct FBPs. Peptide-MSG inhibited GAS adherence to human keratinocytes (HaCaT) in a strain dependent manner. There is no consistent pattern between the effect and the ability to express one or more of the FBPs. A single peptide may be insufficient to prevent GAS adherence to host cells.     

A new rapid and cost-effective method for detection of phages, ICEs and virulence factors encoded by Streptococcus pyogenes

Streptococcus pyogenes (group A Streptococcus, GAS) is a human pathogen that causes diseases of various intensity, from mild strep throat to life threatening invasive infections and postinfectional sequelae. S. pyogenes encodes multiple, often phage encoded, virulence factors and their presence is related to severity of the disease. Acquisition of mobile genetic elements, carrying virulence factors, as phages or ICEs (integrative and cojugative elements) has been shown previously to promote selection of virulent clones. We designed the system of eight low volume multi- and one singleplex PCR reactions to detect genes encoding twenty virulence factors (spd3, sdc, sdaB, sdaD, speB, spyCEP, scpA, mac, sic, speL, K, M, C, I, A, H, G, J, smeZ and ssa) and twenty one phage and ICE integration sites described so far for S. pyogenes. Classification of strains based on the phage and virulence factors absence or presence, correlates with PFGE MLST and emm typing results. We developed a novel, fast and cost effective system that can be used to detect GAS virulence factors. Moreover, this system may become an alternative and effective system to differentiate between GAS strains.     

A族β溶血性链球菌与猩红热的相关研究

A族β溶血性链球菌（beta—haemolyticgroup A Streptococcusisolate,GAS）又称为酿脓链球菌（Strepto—coccus pyogenes）,是一种常见的致病性化脓性革兰阳性球菌,猩红热是由GAS引起的儿童常见呼吸道传染病。近年来,随着严重侵袭性GAS感染在欧美一些国家再次增多,猩红热在一些国家中的发病率也在升高。简要介绍GAS的分型、超抗原及耐药与猩红热之间的关系。     

Group A streptococcus activates type I interferon production and MyD88-dependent signaling without involvement of TLR2, TLR4, and TLR9

Bacterial pathogens are recognized by the innate immune system through pattern recognition receptors, such as Toll-like receptors (TLRs). Engagement of TLRs triggers signaling cascades that launch innate immune responses. Activation of MAPKs and NF-kappaB, elements of the major signaling pathways induced by TLRs, depends in most cases on the adaptor molecule MyD88. In addition, Gram-negative or intracellular bacteria elicit MyD88-independent signaling that results in production of type I interferon (IFN). Here we show that in mouse macrophages, the activation of MyD88-dependent signaling by the extracellular Gram-positive human pathogen group A streptococcus (GAS; Streptococcus pyogenes) does not require TLR2, a receptor implicated in sensing of Gram-positive bacteria, or TLR4 and TLR9. Redundant engagement of either of these TLR molecules was excluded by using TLR2/4/9 triple-deficient macrophages. We further demonstrate that infection of macrophages by GAS causes IRF3 (interferon-regulatory factor 3)-dependent, MyD88-independent production of IFN. Surprisingly, IFN is induced also by GAS lacking slo and sagA, the genes encoding cytolysins that were shown to be required for IFN production in response to other Gram-positive bacteria. Our data indicate that (i) GAS is recognized by a MyD88-dependent receptor other than any of those typically used by bacteria, and (ii) GAS as well as GAS mutants lacking cytolysin genes induce type I IFN production by similar mechanisms as bacteria requiring cytoplasmic escape and the function of cytolysins.     

Molecular evolution of a multigene family in group A streptococci

The emm genes are members of a gene family in group A streptococci (GAS) that encode for antiphagocytic cell-surface proteins and/or immunoglobulin-binding proteins. Previously sequenced genes in this family have been named "emm," "fcrA," "enn," "arp," "protH," and "mrp"; herein they will be referred to as the "emm gene family." The genes in the emm family are located in a cluster occupying 3-6 kb between the genes mry and scpA on the chromosome of Streptococcus pyogenes. Most GAS strains contain one to three tandemly arranged copies of emm-family genes in the cluster, but the alleles within the cluster vary among different strains. Phylogenetic analysis of the conserved sequences at the 3' end of these genes differentiates all known members of this family into four evolutionarily distinct emm subfamilies. As a starting point to analyze how the different subfamilies are related evolutionarily, the structure of the emm chromosomal region was mapped in a number of diverse GAS strains by using subfamily-specific primers in the polymerase chain reaction. Nine distinct chromosomal patterns of the genes in the emm gene cluster were found. These nine chromosomal patterns support a model for the evolution of the emm gene family in which gene duplication followed by sequence divergence resulted in the generation of four major-gene subfamilies in this locus.      

Streptococcus pyogenes pili promote pharyngeal cell adhesion and biofilm formation

Group A Streptococcus (GAS, Streptococcus pyogenes) is a Gram-positive human pathogen responsible for several acute diseases and autoimmune sequelae that account for half a million deaths worldwide every year. GAS infections require the capacity of the pathogen to adhere to host tissues and assemble in cell aggregates. Furthermore, a role for biofilms in GAS pathogenesis has recently been proposed. Here we investigated the role of GAS pili in biofilm formation. We demonstrated that GAS pilus-negative mutants, in which the genes encoding either the pilus backbone structural protein or the sortase C1 have been deleted, showed an impaired capacity to attach to a pharyngeal cell line. The same mutants were much less efficient in forming cellular aggregates in liquid culture and microcolonies on human cells. Furthermore, mutant strains were incapable of producing the typical three-dimensional layer with bacterial microcolonies embedded in a carbohydrate polymeric matrix. Complemented mutants had an adhesion and aggregation phenotype similar to the wild-type strain. Finally, in vivo expression of pili was indirectly confirmed by demonstrating that most of the sera from human patients affected by GAS-mediated pharyngitis recognized recombinant pili proteins. These data support the role of pili in GAS adherence and colonization and suggest a general role of pili in all pathogenic streptococci.     

The fibronectin-binding capacity and host cell adherence of Streptococcus pyogenes strains are discordant with each other

Surface exposed fibronectin-binding proteins (FBPs) play an important role in the adherence of Streptococcus pyogenes (group A streptococcus, GAS) to host cells. This pathogen expresses numerous FBPs, of which SfbI, SfbII and PrtF2 are major surface exposed FBPs. However, GAS strains differ in the genetic potential to express these proteins. To test whether this difference reflects in differences in fibronectin (Fn) binding, a set of circulating strains previously examined for adherence to host cells was used. The 68 distinct strains were isolated from throat, skin and blood. They were analyzed for (a) the presence of genes for SfbI, SfbII and PrtF2 and (b) the extent of Fn binding. The results suggest that strains possessing two or more of the genes for these FBPs bound Fn significantly more than strains possessing none or one of the genes. No correlation between the extent of Fn binding and the tissue site of isolation was found. Furthermore, together with our previous studies on adherence capacity of these GAS strains, we found no correlation between Fn binding ability and the avidity of the strains to adhere to epithelial cells. We suggest that while Fn binding is important for adhesion, for many GAS strains the extent of Fn binding is not the critical determinant of adherence.     

The Mga virulence regulon: infection where the grass is greener

Co-ordinate regulation of virulence gene expression in response to different host environments is central to the success of the group A streptococcus (GAS, Streptococcus pyogenes) as an important human pathogen. Mga represents a ubiquitous stand-alone virulence regulator that controls genes (Mga regulon) whose products are necessary for adherence, internalization and host immune evasion. Mga highly activates a core set of virulence genes, including its own gene, by directly binding to their promoters. Yet, Mga also influences expression of over 10% of the GAS genome, primarily genes and operons involved in metabolism and sugar utilization. Expression of the Mga regulon is influenced by conditions that signify favourable growth conditions, presumably allowing GAS to take advantage of promising new niches in the host. The ability of Mga to respond to growth signals clearly involves regulation of mga expression via global regulatory networks such as RALPs, Rgg/RopB and the catabolite control protein CcpA. However, the presence of predicted PTS regulatory domains (PRDs) within Mga suggests an intriguing model whereby phosphorylation of Mga by the PTS phosphorelay might link growth and sugar utilization with virulence in GAS. As Mga homologues have been found in several important Gram-positive pathogens, the Mga regulon could provide a valuable paradigm for increasing our understanding of global virulence networks in bacteria.     

Superantigen-like gene(s) in human pathogenic Streptococcus dysgalactiae,subsp equisimilis: genomic localisation of the gene encoding streptococcal pyrogenic exotoxin G (speG(dys))

Streptococcus pyogenes (GAS) causes about 90% of streptococcal human infections while group C (GCS) and G (GGS) streptococci can be pathogenic for different mammalians. Especially the human pathogenic GCS and GGS, Streptococcus dysgalactiae, subsp. equisimilis, account for 5-8% of the human streptococcal diseases like wound infections, otitis media, purulent pharyngitis and also streptococcal toxic shock syndrome. A defined superantigen so far was not identified in GCS and GGS strains. In the present investigation we screened DNA of GCS and GGS human isolates for the presence of genes for streptococcal pyrogenic exotoxins (spe) by hybridisation with probes that stand for the GAS genes speA, speC, speZ (smeZ), speH, speG, speI, speJ and ssa. In many GCS and GGS strains we found positive reactions with the probes speG, speJ and ssa, but not with the probes for the remaining genes under investigation. PCR amplification with subsequent sequence analysis of the PCR fragments revealed only the presence of the gene speG in GCS and GGS strains, while no DNA fragments specific for speJ and ssa could be amplified. Additionally, the upstream and downstream regions flanking speG in GGS strain 39072 were sequenced. Remarkable differences were found in the neighbourhood of speG between GAS and GGS sequences. Downstream of speG we identified in strain GGS 39072 two new open reading frames encoding proteins with no similarity to protein sequences accessible in the databases so far. In the compared GAS strains SF370 and MGAS8232, this segment, apart from some small fragments, had been deleted. Our analysis suggests that a gene transfer from GGS to GAS has preceded following deletion of the two genes orf1 and orf2 in GAS.