tailieunhanh - Chapter 114. Molecular Mechanisms of Microbial Pathogenesis

Over the past three decades, molecular studies of the pathogenesis of microorganisms have yielded an explosion of information about the various microbial and host molecules that contribute to the processes of infection and disease. These processes can be classified into several stages: microbial encounter with and entry into the host; microbial growth after entry; avoidance of innate host defenses; tissue invasion and tropism; tissue damage; and transmission to new hosts. Virulence is the measure of an organism's capacity to cause disease and is a function of the pathogenic factors elaborated by microbes. . | Chapter 114. Molecular Mechanisms of Microbial Pathogenesis Over the past three decades molecular studies of the pathogenesis of microorganisms have yielded an explosion of information about the various microbial and host molecules that contribute to the processes of infection and disease. These processes can be classified into several stages microbial encounter with and entry into the host microbial growth after entry avoidance of innate host defenses tissue invasion and tropism tissue damage and transmission to new hosts. Virulence is the measure of an organism s capacity to cause disease and is a function of the pathogenic factors elaborated by microbes. These factors promote colonization the simple presence of potentially pathogenic microbes in or on a host infection attachment and growth of pathogens and avoidance of host defenses and disease often but not always the result of activities of secreted toxins or toxic metabolites . In addition the host s inflammatory response to infection greatly contributes to disease and its attendant clinical signs and symptoms. Microbial Entry and Adherence Entry Sites A microbial pathogen can potentially enter any part of a host organism. In general the type of disease produced by a particular microbe is often a direct consequence of its route of entry into the body. The most common sites of entry are mucosal surfaces the respiratory alimentary and urogenital tracts and the skin. Ingestion inhalation and sexual contact are typical routes of microbial entry. Other portals of entry include sites of skin injury cuts bites burns trauma along with injection via natural . vector-borne or artificial . needlestick routes. A few pathogens such as Schistosoma spp. can penetrate unbroken skin. The conjunctiva can serve as an entry point for pathogens of the eye. Microbial entry usually relies on the presence of specific microbial factors needed for persistence and growth in a tissue. Fecal-oral spread via the alimentary tract .