MICR 201 Microbiology for Health Related Sciences

1. Lecture 8: Microbial mechanisms of pathogenicity Edith Porter, M.D. MICR 201 Microbiology for Health Related Sciences

2. Lecture outline • Important definitions • The infection cycle • Bacterial pathogenesis • How bacteria enter and invade a host • How bacteria circumvent host defenses • How bacteria damage host cells • Pathogenic properties of viruses • Pathogenic properties of fungi, protozoa, and helminths

3. Important definitions • Pathogenicity • The ability to cause disease • Virulence • The extent or degree of pathogenicity • Obligate pathogen (pathogen) • Causes disease in the healthy adult by means of specific pathogenic factors • Typically not part of the normal microbiota • Opportunist • Causes disease only in individuals with locally or systemically compromised immune function • Often part of the normal microbiota

4. Virulence • ID50: Infectious dose for 50% of the test population • LD50: Lethal dose for 50% of the test population

5.  Health Disease  Disease Health Disease Health Opportunists and pathogens  

6. The infection cycle

7. Portals of entry • Mucous membranes • Parenteral route • Skin Penetration through intact skin Schistosomamansoni Trematode (Fluke), with male and female worms, live in blood vessels

8. Port of entry and dose matter

9. Exit route • Respiratory tract • Coughing, sneezing • Gastrointestinal tract • Feces, saliva • Genitourinary tract • Urine, semen, vaginal secretions • Skin • Blood • Biting arthropods, needles/syringes Exit route is typically the same as entry route

10. Main pathogenicity factors • Entry • Adherence • Penetration • Enzyme and toxin production • Direct damage to host • Evasion of host defense • Resistance to uptake by phagocytes • Change of surface molecule expression • Latency (hiding in host cells) • Degradation of host defense molecules

11. Adherence factors • Adhesinsbind to specific receptors on host cells

12. Penetration/Invasion • Neisseriagonorrhoeae initiates receptor mediated uptake by urethral or cervical epithelial cells • Salmonella typhimurium invades intestinal epithelial cells using their cell surface protein invasin (rearranges the cytoskeleton)

13. Bacterial pathogenic enzymes • Coagulase • Coagulates blood (S. aureus, thick pus) • Kinases • Streptokinase* • Digest fibrin clots • Hyaluronidase* • Hydrolyses hyaluronic acid • Collagenase • Hydrolyzes collagen Facilitate tissue degradation and spreading * Therapeutic use!

14. Toxin Poisonous substance Molecule that contributes to pathogenicity Toxigenicity Capacity of a microbe to produce toxin Toxigenic strains: strains producing toxins Toxicity Ability to induce toxic reactions in host Toxemia Presence of toxin the host's blood Toxoid Inactivated toxin used in a vaccine Antitoxin Neutralizing antibodies against a specific toxin Bacterial toxins

15. Exotoxin versus Endotoxin

16. Exotoxins • Secreted by the microbe • Act locally and in a distance • Typically proteins • AB toxins: inactivate essential cell functions • Membrane disrupting toxins • Toxins overstimulating immune system

17. The action of AB toxins

18. AB-Toxins: Inactivate Essential Cell Functions C. diphteriae • Toxins with 2 sub units: • A: Active component, mediates toxicity • B: Binding component, guides toxin to the target cell • Example: Diptheria toxin • Inhibits elongation factor II in ribosomes, inhibits protein synthesis • 0.01 mg can kill a 200 lb person

19. Animation • http://www.sumanasinc.com/webcontent/animations/content/diphtheria.html

20. Diphteria toxin inhibits protein synthesis Diphteria Membrane

21. Membrane disrupting toxins • Disrupt host cell plasma membrane • Depending on target: • Hemolysins: erythrocytes • Leukocidins: phagocytes • Some destroy also other cell types • Examples: • Pore forming • S. aureus alpha toxin • S. pyogenesstreptolysin -O and -S • Enzymatic • C. perfringensphospholipase C SLO-Pores (Bhakdi et al) Gas Gangrene

22. Selected bacterial toxins *phage coded

23. Endotoxin • LPS (lipopolysaccharide) • Component of outer membrane of gram-negative bacteria • Triggers fever! • Pyrogen

24. Endotoxins and the Fever Response

25. Evasion by preventing phagocytic uptake/killing • Capsules • M-protein in Streptococci • Intracellular survival • Escape into cytoplasma • Rickettsia • Resistance against antimicrobial factors • M. tuberculosis with lipids

26. Evasion by changing surface molecules (antigenic variation) • Trypanosoma • Vary surface glycoprotein • 1 of 1000 genes expressed at a time • Genes randomly switched on and off • Schistosoma • Assume host molecules • Shedding of surface • N. gonorrhoeae • Vary outer membrane protein (opa) • Influenza virus • Changes in spikes Undulating Membrane Trypanosome cruzi

27. Evasionthrough latency • Microbial agent (virus) retreats in host cells • HIV in Lymphocytes • Herpes viridae in Nerve cells • Herpes simplex • Fever blister • Varizella Zoster Virus • Chicken pox • Latency in dorsal root ganglion • Recurrence: zoster in skin cells

28. Evasion by degrading host defense molecules • Many mucosal pathogens produce IgA-proteases • Degrade antibody type A

29. Cytopathiceffects of viruses Negri bodies in rabies • Inclusion bodies • Cell rounding • Cell aggregation • Syncytium: multinucleated cells • Inactivation of host defense cells (HIV) • Down regulation of host defense • Transformation: loss of contact inhibition, uninhibited growth • Cancerogenic • oncogens Transformed cells in culture

30. Pathogenic properties of fungi • Chronic infections provoke an allergic response • Toxins • Ergot toxin: Claviceps, Hallucinations, LSD like, abortions • Aflatoxin: Primary liver cancer • Mycotoxin: amanitin, neurotoxin, death

31. Pathogenic properties of protozoa • Presence of protozoa • Protozoan waste products and products released from damaged tissue may cause symptoms • Avoid host defenses by • Growing in phagocytes • Antigenic variation

32. Pathogenic properties of helminths • Helminth body mass can block host liquid movement • Ileuswith Ascaris infection • Elephantiasis (Filaria infection blockage of lymph vessels) Elephantiasis Filaria Adult Can survive for 5 – 10 y

33. Summary of microbial pathogenicity

34. Important to Remember • Virulence determined by invading microorganism and host defense • Entry route is typically same as exit route • Main pathogenic factors: • Promote entry • Damage host • Enzyme and toxin production • Toxins often phage coded • Evasion of host defense • Disease is a combination of direct cell damage and host defense response

35. Additional resources • http://www.doctorfungus.com/thefungi/Cryptococcus.htm • http://www.geo.ucalgary.ca/~macrae/palynology/dinoflagellates/dinoflagellates.html • http://www.mikrobiologie.medizin.uni-mainz.de/de/index.html • Primary Literature available on request