UnravelingHaemophilus influenzaevirulence mechanisms enable discovery of new targets for antimicrobials and vaccines

Purpose of review The human upper respiratory tract is colonized with a variety of bacterial microorganisms includingHaemophilus influenzae. The speciesH. influenzaeconsists of typeable and nontypeableH. influenzae(NTHi) variants. TypeableH. influenzaeare subdivided into types a through f, based on the polysaccharide capsule, whereas the NTHi strains do not express a polysaccharide capsule. In this review, we highlight the current advances in the field ofH. influenzae, with the focus on bacterial virulence mechanisms that facilitate bacterial colonization and disease, particularly for NTHi. Recent findings In the past decade, it has become apparent that NTHi has the ability to cause invasive infections. Recently, a number of adhesins have been shown to be crucial for bacterial colonization and invasion and these proteins were investigated as vaccine antigens. Although NTHi lacks a polysaccharide capsule, it expresses lipooligosaccharide that contribute to adhesion and evasion of complement-mediated killing, both contributing to bacterial virulence, which could potentially be targeted by novel antimicrobial drugs or vaccines. The unraveling ofH. influenzaevirulence mechanisms resulted in the identification of promising targets for novel antimicrobials and vaccine antigens aiming to prevent or treat both typeable and nontypeableH. influenzaeinfections.