Rapid selection of complement-inhibiting protein variants in group A Streptococcus epidemic waves

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120

115

Molecular factors that contribute to the emergence of new virulent bacterial subclones and epidemics are poorly understood. We hypothesized that analysis of a population-based strain sample of serotype M3 group A Streptococcus (GAS) recovered from patients with invasive infection by using genome-wide investigative methods would provide new insight into this fundamental infectious disease problem. Serotype M3 GAS strains (n ‫؍‬ 255) cultured from patients in Ontario, Canada, over 11 years and representing two distinct infection peaks were studied. Genetic diversity was indexed by pulsed-field gel electrophoresis, DNA-DNA microarray, whole-genome PCR scanning, prophage genotyping, targeted gene sequencing, and single-nucleotide polymorphism genotyping. All variation in gene content was attributable to acquisition or loss of prophages, a molecular process that generated unique combinations of proven or putative virulence genes. Distinct serotype M3 genotypes experienced rapid population expansion and caused infections that differed significantly in character and severity. Molecular genetic analysis, combined with immunologic studies, implicated a 4-aa duplication in the extreme N terminus of M protein as a factor contributing to an epidemic wave of serotype M3 invasive infections. This finding has implications for GAS vaccine research. Genome-wide analysis of population-based strain samples cultured from clinically well defined patients is crucial for understanding the molecular events underlying bacterial epidemics.population genetics ͉ evolution ͉ phage ͉ subclone

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Genome-wide molecular dissection of serotype M3 group A Streptococcus strains causing two epidemics of invasive infections

Beres

Sylva

Sturdevant

et al. 2004

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120

115

“…The Sic gene is present predominantly in serotype M1 GAS strains (3,11). To determine whether the ability of Sic to inhibit the adherence of GAS was restricted to M1 serotype organisms, we incubated two serotype M3 GAS isolates (these organisms do not have the sic gene) with A549 cells in the presence or absence of purified Sic.…”

Section: Resultsmentioning

confidence: 99%

Insight into the molecular basis of pathogen abundance: Group AStreptococcusinhibitor of complement inhibits bacterial adherence and internalization into human cells

Hoe

Ireland

DeLeo

et al. 2002

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Streptococcal inhibitor of complement (Sic) is a secreted protein made predominantly by serotype M1 Group A Streptococcus (GAS), which contributes to persistence in the mammalian upper respiratory tract and epidemics of human disease. Unexpectedly, an isogenic sic-negative mutant adhered to human epithelial cells significantly better than the wild-type parental strain. Purified Sic inhibited the adherence of a sic negative serotype M1 mutant and of non-Sic-producing GAS strains to human epithelial cells. Sic was rapidly internalized by human epithelial cells, inducing cell flattening and loss of microvilli. Ezrin and moesin, human proteins that functionally link the cytoskeleton to the plasma membrane, were identified as Sic-binding proteins by affinity chromatography and matrix-assisted laser desorption͞ionization time-of-flight mass spectrometry analysis. Sic colocalized with ezrin inside epithelial cells and bound to the F-actin-binding site region located in the carboxyl terminus of ezrin and moesin. Synthetic peptides corresponding to two regions of Sic had GAS adherence-inhibitory activity equivalent to mature Sic and inhibited binding of Sic to ezrin. In addition, the sic mutant was phagocytosed and killed by human polymorphonuclear leukocytes significantly better than the wild-type strain, and Sic colocalized with ezrin in discrete regions of polymorphonuclear leukocytes. The data suggest that binding of Sic to ezrin alters cellular processes critical for efficient GAS contact, internalization, and killing. Sic enhances bacterial survival by enabling the pathogen to avoid the intracellular environment. This process contributes to the abundance of M1 GAS in human infections and their ability to cause epidemics. microbiology ͉ Serotype M1 ͉ epidemic waves ͉ ezrin F or most bacterial pathogens, there is relatively little understanding of why certain clonally related isolates cause abundant infections, whereas others do not. Molecular explanation of these phenomena is critical to development of rational methods to limit pathogen emergence, resurgence, and dissemination.Group A Streptococcus (GAS) is an important human pathogen that causes infections ranging from pharyngitis to necrotizing fasciitis and the postinfectious sequelae acute rheumatic fever and acute glomerulonephritis. GAS are genetically highly heterogeneous. For example, more than 150 distinct M-types have been identified on the basis of antigenic differences in the M protein, an antiphagocytic surface molecule that is an important virulence factor (1). However, GAS expressing relatively few M types cause the majority of human invasive infections. In particular, M1 strains are the most common serotype recovered from invasive disease episodes and also have a propensity to cause epidemics (2).Streptococcal inhibitor of complement (Sic) is a secreted protein produced by serotype M1 GAS that inhibits the formation of the membrane attack complex (MAC) of complement in vitro by binding to the C5b-C7 complex (3, 4). Sic production is necessary for per...

“…Serotype M1 GAS strain MGAS5005 was used because it is genetically representative of serotype M1 strains causing abundant disease in North America and Western Europe (7). Serotype M6 GAS strains JRS4 and isogenic irr Ϫ mutant, JRS550, have been described (8).…”

Section: Methodsmentioning

confidence: 99%

Genome-wide protective response used by group AStreptococcusto evade destruction by human polymorphonuclear leukocytes

Voyich

Sturdevant

Braughton

et al. 2003

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146

Group A Streptococcus (GAS) evades polymorphonuclear leukocyte (PMN) phagocytosis and killing to cause human disease, including pharyngitis and necrotizing fasciitis (flesh-eating syndrome). We show that GAS genes differentially regulated during phagocytic interaction with human PMNs comprise a global pathogen-protective response to innate immunity. GAS prophage genes and genes involved in virulence, oxidative stress, cell wall biosynthesis, and gene regulation were up-regulated during PMN phagocytosis. Genes encoding novel secreted proteins were upregulated, and the proteins were produced during human GAS infections. We discovered an essential role for the Ihk-Irr twocomponent regulatory system in evading PMN-mediated killing and promoting host-cell lysis, processes that would facilitate GAS pathogenesis. Importantly, the irr gene was highly expressed during human GAS pharyngitis. We conclude that a complex pathogen genetic program circumvents human innate immunity to promote disease. The gene regulatory program revealed by our studies identifies previously undescribed potential vaccine antigens and targets for therapeutic interventions designed to control GAS infections.