Streptococcus pyogenes

Abstract

Group A Streptococcus ( GAS) has long been recognized as a human pathogen causing an exceptionally broad range of infections. In order to successfully colonize or invade to a host, microorganisms need mechanisms to escape recognition by the immune system or to modulate the responses directed against the infecting agent . Streptococcus pyogenes produces a variety of protein toxins and enzymes that are capable of killing host cells and breaking down cell constituents, presumably to provide nutrients for the bacteria and/or to promote their spread. Some of these secreted products are hemolysins, streptokinases, hyaluronidases, exotoxins and proteases. In some cases, they play an important role in resistance to the host immune system, acting alone or in combination with cell-associated virulence factors (such as the capsule and surface proteins). These enzymes either directly or indirectly modulate the activity of immune defense molecules such as immunoglobulins, complement factors, or other inflammatory mediators. However, the immunity following a natural infection and evidence of vaccine-induced protection in animals and humans support the feasibility of developing a GAS vaccine. Our review presents an update on virulence factors and antigenic determinants which may be considered as options for S. pyogenes vaccine.