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New virulence factors of the invasive human pathogen Group A Streptococcus


Group A Streptococcus (GAS) is an important Gram-positive bacterial pathogen. Found in chains, this bacterium colonizes the throat and skin of healthy individuals, and as a pathogen, primarily causes infections of the upper respiratory tract and the skin, including pharyngitis, scarlet fever, and impetigo. In addition, GAS disease can lead to several post-infection sequelae, including acute rheumatic fever and subsequent heart disease, acute glomerulonephritis, arthritis, and neurological conditions. In the past 30 years, a significant increase in invasive infections caused by GAS has been observed, in particular, necrotizing fasciitis and streptococcal toxic shock syndrome. Virulence factors of GAS promote adherence to and invasion of host tissues, injury to host cells, and evasion of the complex human immune response. This work describes the elucidation of a virulence factor involved in degradation of the human chemoattractant cytokine, interleukin 8, which is responsible for the recruitment of neutrophils to the site of bacterial infection. In addition, we describe a two gene locus found upstream of the streptolysin S operon of GAS which is involved in the pathogenesis of invasive disease. This locus includes ralp3, a member of the rofA-like family of transcriptional regulators, involved in the negative regulation of several virulence factors. Phenotypic analysis of a ralp3 mutant strain of M1T1 GAS highlights its involvement in the control of genes responsible for adherence and invasion of host epithelial cells, survival during exposure to human whole blood or antimicrobial peptides, and ultimately, full virulence of the bacteria in an in vivo mouse model of invasive infection. Divergently transcribed upstream of ralp3 is the gene we have named lsap, for Large Surface- Anchored Protein, due to its status as the largest predicted ORF in the M1 GAS genome and its predicted C- terminal LPXSG surface-anchor motif. This gene is involved in the internalization of bacteria into host cells and their resistance to host antimicrobial peptides. Allelic exchange mutagenesis of lsap shows that it is crucial for virulence in a mouse model of invasive infection. The characterization of these genes has important implications in the control of bacterial virulence factor expression, and the identification of future vaccine targets

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