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4细菌的感染,诊断,防治,消毒,灭菌.pptx
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时间:2023-01-04

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细菌 感染 诊断 防治 消毒 灭菌
Bacterial Infection Normal flora Opportunistic pathogen Pathogenic bacteria(virulent bacteria)Dysbacteriosis Exotoxins Endotoxins Separation&Culture of bacteria Bacteriemia Septicemia Pyemia Toxemia Endotoxemia Carrier Colony Toxoids Antitoxin Key Words Not all bacteria cause disease Normal flora The normal flora are bacteria which are found in or on our bodies on a semi-permanent basis without causing disease.There are more bacteria living in or on our bodies,than we have cells of our own.A human body contains around 1013 cells.The human body is home to around 1014 bacteria.One fourth of fecal weight is made of bacteria!The normal flora are particularly important in the large intestine.Normal flora are also found in the nose,mouth,throat,skin.Opportunistic bacteria can be part of the normal flora but not pathogenic for normal persons,cause disease only in immunocompromised persons,or under specific conditions.Pathogenic bacteria(virulent bacteria)Normally not members of the normal flora,have mechanisms to promote their own growth in the expense of hosts tissue or organs function The normal flora protect us from disease by:1.Competing with invaders for space and nutrients.2.Producing compounds(bacteriocins)which kill other bacteria.3.Lowering the pH so that other bacteria cant grow.In addition to the above ways of protecting us from disease our normal flora help us in other ways.Of course,there is a down side as well.The Good Side Produce vitamins we are unable to produce such as vitamin B12.Boost our immune system Germ free animals(born and raised in a germ free plastic tent)are very susceptible to disease when removed from the germ free environment because their immune system is underdeveloped.Help digest food.The Bad Side If the normal flora escape from their normal location,they can cause disease.For example,Escherichia coli,commonly found in the intestine,can cause urinary tract infections if introduced into the bladder.Immunosuppression can allow otherwise harmless bacteria to cause disease.AIDS,some cancer treatments and transplant rejection drugs all suppress the immune system and allow the normal flora to cause occasionally serious disease.Three conditions correlate with opportunistic infection:1.Immune System Compromise 2.Dysbacteriosis 3.Change of Inhabiting Places:Pathogenesis is a multi-factorial process which depends on the nature of the species or strain(virulence factors),the Pathway of Bacterial Entrance(gateway)and the immune status of the host,as well as the number of organisms in the initial exposure and the Environmental conditions.Bacterial Pathogenesis BACTERIAL VIRULENCE FACTORS 1.Adherence Factors Surface hydrophobicity,pili,Capsule&glycocalyx Bacterial Biofilms 2.Invasion of Host Cells&Tissues:Enzymes 3.immune evasion:Capsule&glycocalyx,IgA1 Proteases,Antigenic variation,Interference of complement activity Intracellular pathogenicity.Bacterial Virulence Factors 4.Toxins Exotoxins Endotoxins Exotoxins proteins usually enzymes destroy cellular structures destroy extracellular matrix Antibodies(anti-toxins)neutralize -vaccination Active Binding A Cell surface B A-B toxins Cholera toxin and E.coli labile toxin ADP-ribosylation of regulator adenylate cyclase activation cyclic AMP active ion and water secretion diarrhea Tetanus toxin inhibits glycine release inactivates inhibitory neurons muscles over-active rigid paralysis Normal condition Rigid paralysis Botulinum toxin inhibits acetylcholine release inhibits nerve impulses muscles inactive flacid paralysis(Acetylcholine)15 Exotoxins Antibodies(anti-toxins)neutralize vaccination Endotoxins Lipopolysaccharide(LPS):a toxic lipid A a core polysaccharide O antigen polysaccharide side chains Cell wall lysis required Formaldehyde and heat resistant Poor antigen as free molecule Endotoxin effects Endotoxin effects Fever-pyrogen 1 microgram/kg Leukopenia and leukocytosis necrosis Endotoxemia and shock Disseminated intravascular coagulation(DIC).Non-specific inflammation.Cytokine release Complement activation B cell mitogens Polyclonal B cell activators Adjuvants Exotoxins Toxins produced by bacteria and secreted to the outside of the bacteria cell(different from the endotoxin)acting on cell surface By binding to certain receptors Possess some degree of host cell specificity denatured by formaldehyde treatment to generate toxoids which lack toxic activity but still induce protective immunity when used as vaccines.Many exotoxins have an A-B subunit structure A subunit-provides the toxic activity B subunit-mediates adherence of the toxin complex to a host cell Summary Endotoxins(LPS)derived from Gcell walls and are often liberated when the bacteria lyse.heat-stable,three main regions a toxic lipid A a core polysaccharide O antigen polysaccharide side chains The pathophysiologic effects of LPS are similar.Pathway of Bacterial Entrance Contact:direct or indirect(Sexual contact)Inhalation:transmitted by the respiratory route(Airborne droplets)Ingest

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