Bacterial membrane vesicles: Biogenesis, immune regulation and pathogenesis

Outer membrane vesicles were first described approximately 50 years ago and for many years were considered to be an artifact of bacterial growth. Since that initial discovery, it has become evident that outer membrane vesicles are produced by almost all Gram-negative bacteria as part of their normal growth in addition to driving pathogenesis within the host. More recently, the identification of membrane vesicle (MV) production by some Gram-positive bacteria, parasites, fungi, mycobacteria and infected host cells has significantly broadened the field of MV research and emphasized their importance to pathogenesis. In this review, we will focus on discussing recent advances in the field of bacterial MV biogenesis and the mechanisms whereby they modulate immunity and contribute to pathogenesis. We will highlight findings identifying the contribution of extracellular vesicles produced by Gram-positive bacteria, fungi, parasites, and infected host cells in mediating pathogenesis in addition to the functions of MVs produced by commensal bacteria. Finally, we will discuss recent progress in the development of bacterial MVs as novel vaccines capable of mediating cellular and humoral immune responses.