7-1 - BacterialInfectionandImmunity...

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Bacterial Infection and Immunity Bacterial Infection and Immunity Xiao-Kui GUO
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Symbioses Symbioses Commensalism: one partner benefits and the other is neither harmed nor benefited. Mutualism: both partners benefit. Parasitism: one partner benefits at the expense of the other.
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Role of the resident flora Role of the resident flora Members of the resident flora in the intestinal tract synthesize vitamin K and aid in the absorption of nutrients. Members of the resident flora on mucous membranes and skin may prevent colonization by pathogens and possible disease through “bacterial interference”. The normal flora may antagonize other bacteria through the production of substances which inhibit or kill nonindigenous species. The normal flora stimulates the development of certain tissues , i.e., the caecum and certain lymphatic tissues (Peyer's patches) in the GI tract The normal flora stimulate the production of cross- reactive antibodies .
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Hospital acquired infection: Infections acquired during hospital stays. Pathgen: A microorganism capable of causing sisease. Nonpathogen: A microorganism that does not cause disease; may be part of the normal flora . Opportunistic pathogen: An agent capable of causing disease only when the host’s resistance is impaired (ie, when the patient is “immunocompromised”). Pathogenicity: The ability of an infectious agent to cause disease Virulence: The quantitative ability of an agent to cause disease. Virulent agents cause disease when introduced into the host in small numbers. Virulence involves invasion and toxigenicity. LD 50 (age /sex /health /route of entry, etc ) LD50: The number of pathogens required to cause lethal disease in half of the exposed hosts is called an LD 50 . ID50: The number of pathogens required to cause disease (or, at least, infection) in half of the exposed hosts is called the ID 50 Adherence (adhesion, attachment): the process by which bacteria stick to the surfaces of host cells. Once bacteria have entered the body, adherence is a major initial step in the infection process. The terms adherence, adhesion, and attachment are often used interchangeably. Invasion: The process whereby bacteria, animal parasites, fungi, and viruses enter host cells or tissues and spread in the body. Toxigenicity: The ability of a microorganism to produce a toxin that contributes to the development of disease.
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Koch’s Postulates Molecular Koch’s Postulates Molecular Guidelines for Establishing Microbial Disease Causation Koch's postulates I I solated solated diseased not healthy diseased not healthy people people G G rowth rowth pure culture pure culture I I nduce disease nduce disease susceptible animals susceptible animals R R e-isolated e-isolated susceptible animals susceptible animals
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Pathogenesis Pathogenesis is a multi-factorial process which depends on the immune status
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7-1 - BacterialInfectionandImmunity...

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