Dynamics of the immune response against extracellular products of group A streptococci during infection

Molecular pathogenesis of necrotizing fasciitis

Necrotizing fasciitis, also known as the flesh-eating disease, is a severe invasive infection associated with very high rates of human morbidity and mortality. It is most commonly caused by group A Streptococcus(GAS), a versatile human pathogen that causes diseases ranging in severity from uncomplicated pharyngitis (or strep throat) to life-threatening infections such as necrotizing fasciitis. Herein, we review recent discoveries bearing on the molecular pathogenesis of GAS necrotizing fasciitis. Importantly, the integration of new technologies and the development of human-relevant animal models have markedly expanded our understanding of the key pathogen-host interactions underlying GAS necrotizing fasciitis. For example, we now know that GAS organisms secrete a variety of proteases that disrupt host tissue and that these proteolytic enzymes are regulated by multiple transcriptional and posttranslational processes. This pathogenesis knowledge will be crucial to supporting downstream efforts that seek to develop novel vaccines and therapeutic agents for this serious human infection.

Superantigen gene profile diversity among clinical group A streptococcal isolates

This study examines the diversity of superantigen gene profiles between and within emm-genotypes of 92 clinical group A streptococcal isolates (30 STSS, 24 sepsis, 25 erysipelas, and 12 tonsillitis) collected in Sweden between 1986 and 2001. The emm-genotype and the distribution of smeZ, speG, speJ, speA, speC, speH, speI, speK/L, speL/M, speM, and ssa genes, and the smeZ allelic variant were determined using PCR and DNA sequencing. Forty-five emm1 isolates revealed 10 superantigen gene profiles. One profile dominated and was identified in 22 isolates collected over 14 years. The results indicate that a selective advantage maintained this genotype in circulation. The superantigen content among the emm1 isolates ranged from three to seven, with smeZ-1, speG, and speA present in all but one profile. The 47 isolates of 27 other emm-genotypes exhibited 29 superantigen gene profiles. Thus, the distribution of superantigen genes was highly variable within isolates regardless of emm-genotype. Two novel emm1 subtypes and 14 novel smeZ allelic variants were identified. The 22 smeZ alleles were generally linked to the emm-genotype. The results of the investigation show that superantigen gene profiling is useful for tracking spread of clones in the community.

Molecular mechanisms underlying group A streptococcal pathogenesis

Group A Streptococcus (GAS) is a versatile human pathogen causing diseases ranging from uncomplicated mucosal infections to life-threatening invasive disease. The development of human-relevant animal models of GAS infection and introduction of new technologies have markedly accelerated the pace of discoveries related to GAS host-pathogen interactions. For example, recently investigators have identified pili on the GAS cell surface and learned that they are key components for adherence to eukaryotic cell surfaces. Similarly, the recent development of a transgenic mouse expressing human plasminogen has resulted in new understanding of the molecular processes contributing to invasive infection. Improved understanding of the molecular mechanisms underlying the pathogenesis of GAS pharyngeal, invasive and other infections holds the promise of assisting with the development of novel preventive or therapeutic agents for this prevalent human pathogen.