Tissue tropisms in group A Streptococcus: what virulence factors distinguish pharyngitis from impetigo strains?Bessen, Debra E.Current Opinion in Infectious Diseases: June 2016 - Volume 29 - Issue 3 - p 295–303 doi: 10.1097/QCO.0000000000000262 PATHOGENESIS AND IMMUNE RESPONSE: Edited by Dennis L. Stevens Abstract Author Information Purpose of review: Group A streptococci (GAS) are a common cause of pharyngitis and impetigo, and distinct throat strains and skin strains have been long recognized. This review aims to describe recent advances in molecular differences between throat and skin strains, and the pathogenic mechanisms used by virulence factors that may distinguish between these two groups. Recent findings: Recent findings include a new typing scheme for GAS strains based on sequence clusters of genes encoding the entire surface-exposed portion of M protein; correlations between emm-based typing schemes, clinical disease and surface adhesins; covalent bond formation mediated by GAS pili and other adhesins in binding to host ligands; a key role for superantigens in oropharyngeal infection via binding major histocompatibility complex class II antigen; and migration of GAS-specific Th17 cells from the upper respiratory tract to the brain, which may be relevant to autoimmune sequelae. Summary: The gap between molecular markers of disease (correlation) and virulence mechanisms (causation) in the establishment of tissue tropisms for GAS infection currently remains wide, but the gap also continues to narrow. Whole genome sequencing combined with mutant construction and improvements in animal models for oropharyngeal infection by GAS may help pave the way for new discoveries. Department of Microbiology and Immunology, New York Medical College, New York, USA Correspondence to Debra E. Bessen, PhD, Department of Microbiology and Immunology, New York Medical College, Valhalla, NY 10595, USA. Tel: +1 914 594 4175; e-mail: email@example.com Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved.