The Adhesion and Invasion Mechanisms of Streptococci

Streptococci are common human pathogens, colonizing multiple parts of the human body such as the upper respiratory tract, urethra, gastrointestinal tract, and oral cavity. Since they cause a variety of serious infections including heart diseases, meningitis, and oral diseases, streptococci are considered to play an important role in human diseases. Two critical steps in the pathogenesis of streptococcal infection are the adhesion to and invasion of host cells. This invasion is a strategy of streptococci to evade the host immune response and antibiotic therapy, as well as to penetrate to deeper tissues. To establish interaction between bacteria and host cells, adhesion is the initial step. To effectively adhere to host cells, streptococci express multiple adhesins, and the expression of different adhesins may lead to distinct mechanisms of subsequent invasion. The binding of streptococcal molecules to host proteins triggers downstream signal transduction in the host cells, leading to the uptake of bacteria. In this review, we present the adhesion and invasion mechanisms of different streptococci and the interaction with host cells leading to internalization.