Pathogenic microbes breach the body's barriers

The 2010-2011 lectures ran from late November to late January. The title of this session was: "Breach of the organism's "barriers" by pathogens". The concept was to consider the development of infectious diseases from the angle of the subversion by the pathogens responsible of one or more integrated barriers supposed to stop them in the course of their spread. I illustrated this series with a quotation from Mao Tse-tung, which seemed to me to sum up the main idea perfectly, albeit in an entirely different context: Without destruction no construction; without barrier no current; without stop no advance.. The idea was to attempt to define, in molecular, cellular and immunological terms, the integrated anatomical, histological and physiological aspects of barrier-forming surfaces/structures and organs (intestinal, cutaneous, blood-brain, respiratory, genitourinary barriers), and how this complex integrated process could be subverted or even destroyed by a microorganism, enabling it to disseminate further into its host, possibly to the next barrier to be subverted again. On several occasions, where relevant, the basis of the transition from commensalism to pathogenicity was also addressed: how can a microorganism saprophytic of a mucosal surface, for example, suddenly "decide" to cross this mucosal barrier and become invasive? A number of cofactors were considered, including viral co-infections that facilitate the development of bacterial infection.