Mob. DNA III

The majority of species in the genus Neisseria are commensal bacteria that colonize mucosal surfaces. The two pathogenic species, Neisseria gonorrhoeae (the gonococcus) and Neisseria meningitidis (the meningococcus), are the causative agent of gonorrhea and the primary cause of bacterial meningitis in young adults, respectively. Both organisms are strict human pathogens with no known environmental reservoirs that have evolved from commensal organisms within the human population (1). The study of the Neisseria is important for public health reasons, but also provides a defined system to study evolution of two highly related organisms that cause distinct diseases. One unique aspect of the pathogenic Neisseria is the presence of sophisticated genetic systems that contribute to pathogenesis. The processes of DNA transformation and pilin antigenic variation will be discussed in this chapter.