Bacteria release membrane-derived vesicles (MVs), which are small particles that can transport virulence factors to neighbouring bacteria or to the cells of a mammalian host. This special MV-based system for delivering toxic proteins and nucleic acids in a protected manner to the target cells may have different specific functions depending on whether the bacterium acts as an extracellular or intracellular pathogen. This is according to a doctoral thesis from Umeå University in Sweden.