第五章细菌感染与免疫(七年制).pptVIP

Chapter5 Bacterial InfectionandImmunity ; Section 1 Normal flora and Opportunistic pathogen ;?normal flora the microorganism that parasitize on the body surface or tracts connecting with external, don’t harm the host in ordinary condition.;I.?Distribution of normal flora skin oral cavity: anaerobes intestinal tract: anaerobes: aerobes=1000:1 vagina: Lactobacillus. respiratory ;;II. Role of normal flora 1. biological barrier: antagonism 2.?nutrient synthesize : amino acid, VB, Vk 3.?immunity: enhance and develop and maturation of immune system 4. removal of harmful substances 5. anti-aging 6. anti-tumor;Opportunistic pathogen some bacteria are unable to cause infection in ordinary condition , but can initiate infection under some certain condition.;opportunistic pathogen If: (1) host immunity reduce (2) dysbacteriosis balance of normal flora was broken (3) translocation normal flora leave their ordinary habitant and gain access to other part ;Section 2 Bacterial Pathogenesis Mechanism;?virulence: refers to extent (the degree) of pathogenicity ?median lethal dose(LD50): The number of pathogens required to cause lethal disease in half of the exposed hosts is called an LD50. ?median infective dose(ID50 ): The number of pathogens required to cause disease (or, at least, infection) in half of the exposed hosts is called the ID50.;Infection and Disease ;;(I)Invasiveness： The ability of bacteria to resist host defence, colonize, multiply and spread. ; 1.adherence factors ------surface structure ? bacteria to host cell: pili (/flagella) capsule lipoteichoic acid colonization factor ?bacteria to bacteria: