医学微生物学资料：Pathogenic elements of bacteria and defense of host

1、Pathogenic elements of bacteria and defense of host Pathogenic elements (1)Invasion of bacteria cell into host tissue through: fimbrea (pilli) of bacteria cell help bacteria adhere to mucous membrane of host microcapsule of bacteria cell helps bacteria adhere to host tissues with hard and smooth sur

2、faceDefense factors against adherenceAntibody of IgG, IgA (especially SIgA)Biological mechanisms of antiboy neutrolize binding of bacteria to mucus membraneExplanation in the view of clinical performanceAdaptive defense mechanism and potential risk factors of infectionClinical performance like hygie

3、ne and nursing proceduresDevelopment of vaccine inducing surface protection and the safety assessmentPathogenic elements (2)Flagellum and “diving capacity” of the bacteria through penetration into the biofilm of gutImportant warning molecules as an outcome of long-term evolution，which are recognized

4、 by toll-like receptors of host(TLR 5) Mucus membrane of gut Mucus as a barrier against invasion of bacteriaantigenmucusepithiliacellGut Toll-like receptor Martin Proc Am Thor Soc 2005Clinical significance Bed-side diagnosis based on microscopyFast orientation to the potential source of infectionBio

5、logical benefits to the development of specific immunity (adjuvant molecules)Pathogenic elements (3)Protein enzymes like hyaluronidase targeting at hyaluronic acid, which helps bacteria penetrate into and spread in host tissue Some enzymes like streptokinase and streptodonase to stop blood coagulati

6、on and dilute pus Pathogenic elements (4)Cell structure protects bacteria from phagocytosis of host immune system like capsuleSpore and the challenge to disinfectionSome toxins like leukocidine from G+ cocciAgglutinins from bacteria cell surface to cause haemo-agglutination. Endospores (spores)Patho

7、genic elements (5)Exo-toxins which explain a variety of clinical symptomsEndotoxins (LPS) which stimulate clinical responses like fever, headache, vomiting and DIC through IL-1 system of hostImmune response ( type II, III and IV response) which result in tissue damage or function failure of host Enz

8、ymens and toxins from StaphylococcusCatalaseCoagulaseLeukocidinExfoliative ToxinToxic Shock Syndrome Toxin (super antigen)EnterotoxinsProtein AimmunoglobulinFc receptorBACTERIUM PHAGOCYTE剥脱性皮炎Pathogenic mechanism of diphtheria toxinCholera toxinEnterotoxin-cholera toxin-CtxABEncoded by a prophageMol

9、ecular mass of 84,000 daltonsA subunit-ADP-ribosylating toxinB subunit-bind GM1-gangliosides on enterocytesA subunit ADP ribosylates Gs-alpha which regulates activation of adenlyate cyclaseResult is persistent increase in cAMP levelsHyper secretion of Na, Cl, K, bicarbonate and H20Pathogenesis of NE

10、CPotential strategy to protect host against toxins and/or enzymesAnti-toxin antibodyToxoid as vaccine to evoke immunity against toxinClinical management of LPS diseases control of germ infection steroid treatment based on clinical evaluation potential medicine like osmotic bactericidal protein from

11、leucocytes (professor 安云庆 from CMU)Pathogenic elements (6)Cell factors which are not well identified yet may interfere physiological functions of host and auto-immune diseases ( e.g. Crohns disease of newborns)Secretion system of bacteriaClinical responseEncourage of vaginal delivering babySupport c

12、olonization of gut floraMinimize bacterial infections especially in low birth weight babiesOperation finding of NECDefense elements of host (1)Mechanical barrier of skin and derma-secretions like salts and fatty acidsMechanical barrier of mucus membrane and ciliated transportation systemEM picture o

13、f human skinHunter et al Pediatr Res 2008Altered defense mechanisms in the premature gutDefense elements of host (2)Cells to engulf bacteria like neutrophils and macrophagesComplements components mediate phagocytosis like C3a and C5aComplement activation cascade with the outcome product of MAC ( mem

14、brane attacking component) to lyses cell membrane of bacteria Defense elements of host (3) Inhibition of invading bacteria by normal flora through competition of nutrients that are essential for bacteria growth. For example sidophore moleculespH environment created by multiplication of normal floraDefense elements of host (4) Acquired immunity including antibody and activated cytotoxic T cells ( CD8+ T cells), cytokines which stimulate immune response of hostA special type of im