Bacterial Pathogenesis

1. Bacterial Pathogenesis

2. The term infection describes the process that pathogenic microorganisms multiply,release toxin within the body and produce a change in the normal physiology of the body.

3. Section 1 Normal flora and opportunistic pathogens • Definition: microorganisms that live on or in human bodies, and ordinarily do not cause human diseases but under certain condition can cause disease

4. pathogen

5. The distribution of normal flora

6. Normal flora Skin Staphylococcus epidermidis Diphtheroids Streptococci Peptococcus

7. The significance of normal flora • constitute a protective host defense mechanism: Competition of nutrients and receptors Metabolic substances by normal flora: e.g., bacteriocins, antibiotics, etc. • serve a nutritional function:several B vitamins and vitamin K • keep our immune systems in tune normal flora share many antigenic determinants with pathogenic organisms

8. Opportunistic pathogens • Definition: normally nonpathogenic microorganisms capable of causing infection disease in an immunosuppressed host. • Conditions of causing diseases by opportunistic pathogens: • Alteration of colonization sites • Declination of host immune system function

9. Dysbacteriosis Definition: the state in which the proportion of bacterial species and the number of the normal flora colonizing in certain site of a host present large-scale alteration.

10. Nosocomial infections • Infectious diseases acquired as a result of a hospital stay are known as nosocomial infections. • Surgical procedures and lower defenses permit resident flora • Indwelling devices • Fomites ,medical equipment,other patients

11. toxins Cause disease 细菌 bacteria bacteria 细菌 bacteria bacteria Section 2 Bacterial pathogenesis bacteria 细菌 inbody outerbody Immune status of the host

12. Why do Animal get infectious diseases? From the organism’s perspectives The number of organisms The virulence of these organisms From the host’s perspective Innate immunity acquired immunity Antibody-mediated cell-mediated

13. Pathogenicity of bacteria • Pathogenicity and virulence: refer to an organism's ability to cause disease. • LD50 (median lethal dose) or ID50 (median infectious dose):refers to the number of bacteria or amount of bacterial products, such as toxins, that cause death or bacterial disease in 50% of animals in a defined period after the bacteria are administrated by a designated route.

14. Pathogenicity of bacteria • pathogenicity（determined by): • virulence factors of the bacterium • the number of infecting bacteria • route of entry into the body

15. Virulence factors • Invasiveness • Definition: the ability of a microorganism to invade human cells or tissues,and to multiply on or within them.

16. Capsules and slime layers: e.g., pneumococci • Interfere with the ability of phagocytic blood cells to engulf and destroy bacteria and protect bacteria against some antimicrobial substance

17. 2.Adhesins • Bacterial infections are usually initiated by adherence of the microbe to a specific epithelial surface of the host,otherwise the organism is removed • Peristalsis and defecation ciliary action,coughing and sneezing or urination • A specific “stickiness”

18. (1)Finbrial adhesins involved in mediating attachment of some bacteria to mammalian cell surfaces

19. (2)Non-fimbrial adhesin Including the filamentous haemagglutinin of Bordetella pertussia,a mannose-resistant haemagglutinin from Salmonella serotype Typhimurium and a fibrillar haemagglutinin from helecobacte pylori Pili: e.g., Neisseria gonorrhoeae Other surface structures of bacteria: LTA

20. Other extracelluar aggressins • Invasive enzymes: e.g.Coagulase:working in conjunction with serum factors to coagulate plasma.contributes to the formation of fibrin walls around staphylococcal lesions.

21. Toxins • Exotoxin • Definition:a soluble protein toxin usually secreted from a living bacterium.

22. Origin and release:produced by Gram-positive bacteria as well as Gram-negative cells • Physical and chemical properties:proteins and usually heat-labile.

23. Virulence factors • Toxins • Exotoxin • Immunity: excellent antigens that elicit specific antibodies called antitoxins.

24. Antitoxin: Definition: a specific antibody capable of neutralizing the exotoxin that stimulates its production. Toxoid: Definition: a modified exotoxin that has been treated to destroy its toxicity and remains immunogenicity.

25. Virulence factors Exotoxin • Component characteristics: most exotoxins consist of two parts, an A (active) component and a B (binding) component. Toxicity: high and even fatal; highly tissue specificity

26. Categories: Cytotoxins: exotoxins that destroy the target cells directly by various mechanisms. Neurotoxins: exotoxins that affect nerve transmission of the nerve system. Enterotoxins: exotoxins that stimulate hypersecretion of water and electrolytes from the intestinal epithelium and produce watery diarrhea.

27. Exotoxin Neurotoxin Tetanus toxin ,clostridium tetani glycine spastic paralysis Botulinum toxin, clostridium botulinum acetylcholine flaccid paralysis Cytotoxin diphtheria toxin inhibits protein synthesis Enterotoxins v. cholerae perturb the processes that regulate ion and water exchange across the intestinal epithelium

28. Virulence factors Endotoxins • Origin and release: produced only by Gram-negative bacteria and released only when bacteria lyze. • Chemical and physical properties: lipopolysaccharide of the outer membrane of Gram-negative bacteria; heat-stable

29. Endotoxins • Immunity: weakly immunogenic • Biologic activity: lipid A is the primary toxic component all endotoxins present similar biologic effects. Pyrogenicity Leukocyte reaction Endotoxemia and endotoxin shock DIC (dissemiated intravascular coagulation)

30. Endotoxin (especially lipid A)) Activates Hageman fatcor Activates complement Activates macrophages C3a Hypotension Edema TNF Fever and hypotension C5a Neutrophil chemotaxis Coagulation cascade DIC IL-1 Fever Nitric oxide hypotension

31. Endotoxins • Detection of endotoxin: The Limulus lysate test

32. The different between indotoxin and exotoxin

33. Virulence of pathogenic bacterial

34. Ⅱ.Portals of Entry and the size of the inoculum • If certain pathogen enter the wrong portal,they will not be infectious. • Occasionally,an infective agent can enter by more than one portal.e.g.mycobacterium tuberculosis.

35. Portals of entry • skin • respiratory system • ingestion system • genitourinary system C. tetani

36. The size of the inoculum • The quantity of microbes in the inoculating dose.

37. Ⅲ.the originate and progress of infection • A.The source of the infection • B.routes of pathogen transmission • C.Patterns of infection

38. A.The source of the infection • Living reservoirs Persons or animals with frank symptomatic infection are obvious sources of infection • Nonliving reservoirs

39. Sources of infectious diseases • Exogenous infections: • Patients • Carriers: those in whom pathogens are present and may be multiplying, but who shows no clinical response to their presence. • Contaminated animals • Endogenous infections

40. Carrier state • Definition of carriers: those in whom pathogens are present and may be multiplying, but who shows no clinical response to their presence • Definition of carrier state: a type of infections causing no signs of symptoms, in which pathogens multiply and may be transmitted to other individuals

41. two major types of carrier: Convalescent carriers: those who recover from infectious disease and in whom the pathogens remain and multiply without causing overt symptoms. Healthy carriers: those who do not have the clinical symptoms but carry pathogens indeed. Typhoid Mary (Mary Mallon)

42. B.routes of pathogen transmission • 1.respiratory infections the tiny particles of liquid released into the air form aerosols or droplets • 2.wound infectons:in soil and feces of human and animal • 3.intestinal infections: contaminate drinking water and food or when used to fertilize crops

43. 4.contact infection:directly contact between the skin and mucous membranes of the infected person or animal and that of healthy person • 5.animal bites infections:the majority of animal vectors are arthropods such as fleas,mosquitos,flies,and ticks

44. acute infection chronic infection C.Patterns of infection Apparent infection 1.apparent infection When an infection causes pathological changes leading to disease,it is often accompanied by a variety of signs and symptoms Infectons that come on rapidly,with severe but short-lived effects,are called acute infections The infection persists several months to several years called chronic infection

45. Inapparent infection:also called subclinical infection that has no detectable clinical symptoms

46. local infection generalized/systemic infection Localized infection stands for the case that the microbe enters the body and remains confined to a specific tissue

47. Generalized infection • Bacteremia • Definition: a transitory disease in which bacteria present in the blood are usually cleared from the vascular system with no harmful effects. • Septicemia • Definition: a disease in which the blood serves as a site of bacterial multiplication as well as a means of transfer of the infectious agent from one site to another.

48. Toxemia • Definition: the presence of microbial toxins in the blood • Pyemia • Definition: the presence of pyogenic bacteria in the blood as they are being spread from one site to another in the body

49. Local lesion 毒素 毒素 毒素 毒素 毒素 毒素 toxin 血液 局部病灶 局部病灶 toxin 毒素 毒素 Defense function↓↓ toxin special toxic symptom pathogenic bacterium can grow in blood Organism is seriously dadamaged, toxic symptom all over the body。 Toxemia Bacteremia Septicemia e.g.tetanus

50. 毒素 toxin blood 局部病灶 局部病灶 toxin 毒素 毒素 When Pyosis bacteria cause Septicemia，multiple pyosis focus of infection will happen.e.g. staphylococci aureus New pyosis focus of infection Pyosepticemia