Nature and Pathogenicity of Micro-organisms

• Micro-organisms and higher organisms have evolved together and interact in complex ways. Only a small percentage of microbes are inherently pathogenic. • Pathogenicity, the ability of infectious agents to cause disease, must be interpreted in the context of the properties of both transmissible agent and host. • Understanding this interplay is important to developing methods to prevent infection and reduce the severity of disease. • The initial step in infection is usually adherence, mediated by the interaction of surface structures on the pathogen with host cell membrane proteins or carbohydrates. This often presents excellent targets for immunity. • Intracellular pathogens have evolved methods to neutralize the cellular defenses that can destroy invaders.