1. Microbiology- a clinical approach by Anthony Strelkauskas et al. 2010 Chapter 5: Requirements for infection

2.  Intoduction to the mechanisms in the infectious disease process. © Professor P. M. Motta et al / Science Photo Library

3. Exit covered in Chapter 6 * *

4.  Entry – getting in  Establishment – staying in  Defeat the host defenses  Damage the host  Exit the host -getting out  and be transmitted to another host Covered in chapter 6

5.  Any point at which pathogens can enter is called a portal of entry.  There are three categories of portals of entry: ◦ Mucous membranes (in humans in total 400 m 2, ~3600 sf)  Cover all internal body surfaces  Respiratory tract  Gastrointestinal tract  Genitourinary tract ◦ Skin  Covers external body surfaces ◦ Parenteral routes  Blood  Lymphatics  Placenta ◦ Typically, a pathogen has one preferred entry site  Exception: Yersinia pestis

8. Portal of entryPathogenDisease Respiratory tractMycobacterium tuberculosis Bordetella pertussis Influenza virus Tuberculosis Whooping cough Flu Gastrointestinal tractEscherichia coli Listeria monocytogenes Vibrio cholerae Helicobater pylori Hemolytic uremic syndrome Listeriosis, still birth Cholera Gastric ulcer, cancer Genitourinary tractNeisseria gonorrhoeae Chlamydia trachomatis HIV virus Gonorrhea Nongonococcal urethritis AIDS SkinClostridium perfringens Staphylococcus aureus Gas gangrene Abscess ParenteralHepatitis B and C virus Plasmodium species Hepatitis, liver cancer Malaria

9.  Requires attachment followed by increasing the number of pathogens

10.  After entry into the host, pathogens must find a way to stay in the body. ◦ Attachment and adherence  Pathogens use physical structures, to attach to the surface of cells or tissues. ◦ Fimbriae or pili (proteins) ◦ Glycocalyx (carbohydrates)  Pathogens can use molecules called adhesins to adhere to tissue. ◦ Glycolipids ◦ Glycoproteins ◦ Lipoproteins

11. Colon epithelial cells Bacteria

12. ◦ Plaque forms on teeth when a pellicle coats the tooth and bacteria subsequently adhere to it. ◦ As many as 300 to 400 different types of bacteria will adhere to each other building a biofilm on the tooth. This is the plaque.

13. Spirochetes like Treponema pallidum (the causative agent of syphilis) first adhere to epithelial cells and then corkscrew into tissues. © CDC/ Dr. David Cox

14.  Increasing the number of pathogens can establish the infection in the host.  Rapid growth leading to increased numbers of pathogens can happen very quickly. ◦ Some pathogens can double their numbers in as short a period as twenty minutes. ◦ An organism that doubles every twenty minutes will become 1 x 10 21 organisms in just 24 hours if not inhibited.

15.  Some pathogens are more virulent than others– more pathogens are needed for a successful infection.  We use the terms ID 50 and LD 50 to characterize these differences between pathogens. ◦ ID50: infectious dose 50: the number of organisms required for 50% of the population to show signs of an infection. ◦ LD50: lethal dose 50: the number of organisms required to kill 50% of the hosts.  As lower the ID50 or LD50 number as more virulent is the organism.

17. A. 10 B. 100 C. 1000 D. 5000 E. 10000

18. A.Strain A: ID50: 10 5 B.Strain B: LD50: 10 C.Strain C: ID50: 10 7 D.Strain D: LD50: 10 4 E.Strain E: LD50: 100

20.  The body possesses powerful defense mechanisms.  Pathogens must avoid, evade, or compromise these defenses in order to survive and thrive.  Pathogens can defeat host defenses by evasion: ◦ Capsules (carbohydrate) ◦ Incomplete phagocytosis ◦ Antibody binding and inactivation ◦ Hiding ◦ Attacking defense cells Prevents normal phagocytosis

21.  Phagocytes are specialized leukocytes (white blood cells).  They engulf pathogens and normally quickly kill and degrade them. phagolysosome

22.  The main passive defense mechanism is the bacterial capsule which inhibits phagocytosis by host.

23.  Some pathogens can block their degradation and remain alive inside the phagocyte.

24.  Staphylococcus aureus can secrete the enzyme coagulase, which initiates blood clotting, and uses this to form an abscess. Some pathogens release kinases that can lyse blood clots and thereby are able to spread better.

25.  There are five requirements for a successful infection: entry, establishment, evasion of host defense, damage to the host, exit and transmission.  Places at which pathogens enter are called portals of entry  The major portals of entry are mucous membranes, skin, and parenteral.  Important mucus membrane portals of entry are the respiratory, digestive, genitourinary tract.  Establishment of infection can be accomplished by adhesins (molecules), fimbriae and pili (physical structures).  Criteria for virulence of a given pathogen can be gauged by the ID50 and LD50 of that organism.  Pathogens can defeat the host by evading or inhibiting phagocytosis, inactivating defense cells, binding off antibodies, forming blood clots, or hiding inside of host cells.

27.  Most of the damage to a host can be divided into two causes: ◦ Damage that occurs because pathogens are present, alive and active.  Pathogens release substances that harm the host ◦ Damage that occurs because of host defense mechanisms.  For example host cells can release proteins (cytokines) that induce fever or kill host cells, or degrade host tissue (proteases)

28.  Enzymes  Toxins ◦ Exotoxins ◦ Endotoxin

29.  Examples are hyaluronidase and collagenase  Break down connective tissue and collagen

30.  Leukocidins – destroy white blood cells  Hemolysins – attack red and white blood cells ◦ Some of them form structural holes in host cells Streptolysin O pores

32.  Bacterial toxins are: ◦ Very harmful ◦ Easily diffusible into blood and lymph which causes distal pathology.  Bacterial toxins can produce fatal outcomes in patients.  They produce common symptoms such as fever, shock, diarrhea, cardiac and neurological trauma, and the destruction of blood vessels.  There are 2 types of toxins: ◦ Exotoxins ◦ Endotoxins

33. can be fatal

35.  Exotoxins are produced by and exported from certain pathogens and then enter host cells.  Often encoded in plasmids.  They are among the most lethal substances known. ◦ 1 g of botulinum toxin kills 10 6 people. ◦ For comparison, 1 g of strychnine kills 10 people

36.  Three are main types exotoxins: ◦ Cytotoxins – kill cells (e.g., diphteria toxin) ◦ Neurotoxins – interfere with neurological signaling (e.g., botulinum toxin) ◦ Enterotoxins – affect the cells lining the digestive system (e.g., cholera toxin)

38.  Diphtheria toxin is a cytotoxin.  It is produced by Corynebacterium diphtheriae.  It inhibits protein synthesis in the host.  A single molecule can kill a host cell.

39.  Botulinum toxin is a neurotoxin.  It is produced by Clostridium botulinum.  The toxin inhibits the release of the neurotransmitter acetylcholine. ◦ This disrupts neurological signaling of the skeletal muscle. ◦ This disruption causes paralysis.

40.  Cholera toxin (also known as vibrio toxin) is an enterotoxin.  It is produced by Vibrio cholerae.  It has a 2 chain polypeptide structure ◦ One chain binds to the target cell ◦ One chain causes cells to release large amounts of electrolytes. ◦ The cell remains intact and does not die.  The release of large amounts of electrolytes causes potentially lethal diarrhea and vomiting.

41.  The damage to the host caused by endotoxins is very different from the damage caused by exotoxins.  Endotoxins are part of Gram-negative cell walls and are released on the death of the host. ◦ Endotoxin is lipopolysaccharide (LPS). ◦ The toxic moiety of LPS is Lipid A.  LPS binds to macrophages which in turn release cytokines that induce the typical symptoms.

42.  The effect are mediated by the host derived cytokines.  Nanograms are sufficient to induce severe symptoms. ◦ 1 ng = 0.000000001 g  Endotoxins cause the following symptoms: ◦ Chills ◦ Fever (“pyrogen”) ◦ Aches ◦ Muscle weakness ◦ Large amounts of endotoxins can cause disseminated intravascular clotting (DIC) and death.

43.  Endotoxins can contaminate materials and equipment. ◦ “pyrogen-free” label on pipettes, lines etc.  There are tests for endotoxin contamination.

44.  Viral host cell damage is referred to as a cytopathogenic effect (CPE).  The cytopathogenic effect of viruses occurs in three ways: ◦ From viral overload  Host cell is filled with viruses and infected cell lyses. ◦ From cytocidal effects (killing of host cells)  Host detects virus infected cells and kills these. ◦ From noncytocidal effects (damage caused by host defense)  Virus instructs the cell to produce virus only and the normal cell function can no longer be maintained.

45.  Viral cytopathology can be seen microscopically. ◦ Cell lysis ◦ Viral inclusions such as Negri bodies can be seen in rabies infections. ◦ Cell rounding ◦ The presence of syncytia (giant cells) Cell lysis Syncytium Negri body

46.  The requirements for infection include entry, establishment, avoiding host defenses, damaging the host, and exiting from the host.  Portals of entry for pathogens, including skin, parenteral routes, and the mucous membranes of the respiratory, gastrointestinal, and genitourinary tracts.  Pathogens use virulence factors such as adhesins to establish themselves in the host.  Pathogens avoid being killed by the host’s defenses by using virulence factors including capsules, coagulase.

47.  Pathogens cause damage to host cells by releasing enzymes like hyaluronidase and collagenase, poreforming toxins like leukocidins and hemolysin, as well as exotoxins, including specific types such as cytotoxins, neurotoxins, and enterotoxins.  Endotoxins on the cell wall of Gram-negative bacteria cause damage to the host and are released and disseminated when the bacterial cell dies.  Viruses can also damage the host causing microscopic cytopathic effects such as cell rounding, inclusion bodies, syncytium formation.

48. A. Using fimbriae to attach to cell receptors B. Releasing several exotoxins to destroy host cells C. Using adhesins to attach to tissues D. Creating a biofilm on a body surface E. Releasing endotoxin that will cause clotting

49. Advertisement: MICR 420 Emerging and Re-Emerging Diseases offered in Spring 2013

50.  11:40am – 12:10pm  Chapters 1 thru 6: Lecture, Reading, Chapter End Self Study Questions  Twenty-five Multiple Choice Questions = 50 points  Please bring: ◦ Scantron (form No. 882-E for the Quiz – available at no cost at the Student Bookstore) ◦ No. 2 pencil only