1. Microbial Mechanisms of Pathogenicity

2. LEARNING OBJECTIVES Identify the principal portals of entry and exit.
Using examples, explain how microbes adhere to host cells.
Explain how capsules and cell wall components contribute to pathogenicity.
Compare the effects of coagulases, kinases, hyaluronidase, and collagenase.
Describe the function of siderophores.
Provide an example of direct damage, and compare this to toxin production.
Contrast the nature and effects of exotoxins and endotoxins.
Outline the mechanisms of action of A-B toxins, membrane-disrupting toxins, and superantigens
Classify diphtheria toxin, erythrogenic toxin, botulinum toxin, tetanus toxin, Vibrio enterotoxin, and staphylococcal enterotoxin

3. Vocabulary Attachment is step 1: Bacteria use ___________ ___________
Pathogenicity: Ability of a pathogen to cause disease by overcoming the host defenses
Virulence: Degree of pathogenicity.
Attachment is step 1:
Bacteria use ___________
___________
Viruses use ___________

4. (Preferred) Portals of Entry
Mucous membranes
Conjunctiva
Respiratory tract: Droplet inhalation of moisture and dust particles. Most common portal of entry.
GI tract: food, water, contaminated fingers
Genitourinary tract
Skin
Impenetrable for most microorganisms; can enter through hair follicles and sweat ducts.
Parenteral Route
Trauma (S. aureus, C. tetani)
Arthropods (Y. pestis)
Injections

5. Numbers of Invading Microbes
ID50: Infectious dose for 50% of the test population
LD50: Lethal dose (of a toxin) for 50% of the test population
Bacillus anthracis
Portal of Entry
ID50
Skin
10–50 endospores
Inhalation
10,000–20,000 endospores
Ingestion
250,000–1,000,000 endospores
Clinical and Epidemiologic Principles of Anthrax at

6. Adherence
Adhesins: surface projections on pathogen, mostly made of glycoproteins or lipoproteins. Adhere to complementary receptors on the host cells. Adhesins can be part of:
Glycocalyx: e.g.Streptococcus mutans
Fimbriae (also pili and flagella): e.g.E. coli
Host cell receptors are most commonly sugars (e.g. mannose for E. coli
Biofilms provide attachment and resistance to antimicrobial agents.

7. Overcoming Host Defenses
Capsules: inhibition or prevention of _____________
Cell Wall Proteins: e.g. M protein of S. pyogenes
Antigenic Variation: Avoidance of IS, e.g. Trypanosoma Neisseria
Penetration into the Host Cell Cytoskeleton: Salmonella and E. coli produce invasins, proteins that cause the actin of the host cell’s cytoskeleton to form a basket that carries the bacteria into the cell.
ANIMATION Virulence Factors: Hiding from Host Defenses

8. Penetration into the Host Cell Cytoskeleton
Invasins
Salmonella alters host actin to enter a host cell
Use actin to move from one cell to the next
Listeria
Fig 15.2

9. Enzymes
Coagulase: Blood clot formation. Protection from phagocytosis (virulent S. aureus)
Kinase: blood clot dissolve (e.g.: streptokinase)
Hyaluronidase: (Spreading factor) Digestion of “intercellular cement”  tissue penetration
Collagenase: Collagen hydrolysis
IgA protease: IgA destruction

10. Enzymes Used for Penetration

11. How Pathogens Damage Host Cells
Use host’s nutrients; e.g.: Iron
Cause direct damage
Produce toxins
Induce hypersensitivity reaction
ANIMATION Virulence Factors: Penetrating Host Tissues
ANIMATION Virulence Factors: Enteric Pathogens

12. Toxins Exotoxins: proteins (Gram- and + bacteria can produce)
Endotoxins: Gram- bacteria only. LPS, Lipid A part  released upon cell death. Symptoms due to vigorous inflammation. Massive release  endotoxic shock
Foundation Fig 15.4
ANIMATION Virulence Factors: Exotoxins

13. Vocabulary related to Toxin Production
Toxin: Substances that contribute to pathogenicity.
Toxigenicity: Ability to produce a toxin.
Toxemia:
Toxoid:
Antitoxin:
Antitoxin: Antibodies against a specific toxin.

14. By-products of growing cell
Exotoxins Summary
Source:
Gram + and Gram -
Relation to microbe:
By-products of growing cell
Chemistry:
Protein
Fever? No
Neutralized by antitoxin?
Yes
LD50:
Small
Circulate to site of activity. Affect body before immune response possible.
Exotoxins with special action sites: Neuro-, and enterotoxins

15. Toxin Examples Portal of Entry ID50 Botulinum (in mice) 0.03 ng/kg
Shiga toxin
250 ng/kg
Staphylococcal enterotoxin
1350 ng/kg
Which is the least potent toxin?
Botulinum
Shiga
Staph

16. Type of Exotoxins: A-B Exotoxins
Fig 15.5
Fig 15.5

17. Membrane-Disrupting Toxins
Lyse host’s cells by
Making protein channels into the plasma membrane, e.g. S. aureus
Disrupting phospholipid bilayer, e.g. C. perfringens
Examples:
Leukocidin: PMN and M destruction
Hemolysin (e.g.: Streptolysin) : RBCs lysis  get at?

18. Superantigens Special type of Exotoxin
Nonspecifically stimulate T-cells.
Cause intense immune response due to release of cytokines from host cells.
Fever, nausea, vomiting, diarrhea, shock, and death.

19. Representative Examples of Exotoxins
Bacterial Species
Exotoxin
Lysogeny
C. diphtheriae
A-B toxin +
S. pyogenes
Membrane-disrupting erythrogenic toxin
C. botulinum
A-B toxin; neurotoxin
C. tetani
V. cholerae
A-B toxin; enterotoxin
S. aureus
Superantigen

20. Endotoxins
Bacterial cell death, antibiotics, and antibodies may cause the release of endotoxins.
Endotoxins cause fever (by inducing the release of interleukin-1) and shock (because of a TNF-induced decrease in blood pressure).
TNF release also allows bacteria to cross BBB.
The LAL assay (Limulus amoebocyte lysate) is used to detect endotoxins in drugs and on medical devices.
Fig 15.6

21. Endotoxin Summary Source: Gram – Relation to microbe:
Present in LPS of outer membrane
Chemistry:
Lipid A component of LPS
Fever?
Yes
Neutralized by antitoxin? No
LD50:
Relatively large

22. Inflammation Following Eye Surgery
Patient did not have an infection
The LAL assay of solution used in eye surgery
What was the cause of the eye inflammation?
What was the source?
Clinical Focus, p. 440

23. Pathogenic Properties of Viruses
Evasion of IS by
Growing inside cells
Rabies virus spikes mimic Ach
HIV hides attachment site  CD4 long and slender
Visible effects of viral infection = Cytopathic Effects
cytocidal (cell death)
noncytocidal effects (damage but not death).

24. Pathogenic Properties of Fungi
Fungal waste products may cause symptoms
Chronic infections provoke allergic responses
Proteases
Candida, Trichophyton
Capsule prevents phagocytosis
Cryptococcus
Fungal Toxins
Ergot toxin
Claviceps purpurea
Aflatoxin
Aspergillus flavus
This month's fungus is a plant parasite, commonly found on grains of rye (as shown here) or sometimes on other grasses such as quackgrass. The fungus infects the flowers when they're young and cause the growths you see. It induces the cells to divide (hyperplasia) and to enlarge (hypertrophy), creating the relatively large brown sclerotia to the left. These sclerotia are hard resting structures that allow the fungus to survive adverse conditions, such as winter and desiccation. In the life cycle of this organism, the sclerotia fall to the ground and overwinter, germinating in the spring to produce a stroma that contains perithecia, which produces spores to. Someday I'll have a good picture of this to put online-- the stroma are fragile and don't photograph well so far.
It's really not a devastating parasite to the plant. You might think its main detriment is that is replaces one of the grains of the plant, thus reducing yield. However it also draws nutrients away from the other uninfected grains so that they become stunted, thus reducing yield quite a bit more. But its worst problem is when the sclerotia inadvertently get mixed in with the grains and are incorporated into foods, thus causing a devastating and sometimes deadly syndrome called ergotism in humans and other animals.
Ergotism is caused by the chemicals in the fungus called ergot (pronounced AIR-got). Consumption of foods contaminated with ergot and ergot derivatives may cause vomiting, diarrhea, hallucinations, and may lead to gangrene in serious cases. Historically the fungus has been implicated in epidemics causing thousands of fatalities, but due to increased knowledge of this fungus and a more varied modern diet such epidemics no longer occur in humans. However, chronic exposure through consumption of contaminated foods can lead to health complications.
However as recently as 1951, in Pont-St. Esprit, a small town in France, there was an outbreak of the disease. First a bit of background-- in Europe it is the custom to buy fresh bread nearly every day. Much more civilized than our American custom of buying bread with preservatives in it that allow it to last several weeks. In this small town there was only one bakery and everyone bought bread from it. Strange things started happening. People developed a burning sensation in their limbs, began to hallucinate that they could fly, did strange things to their dogs with forks and in general acted weirdly. This outbreak is chronicled in a marvelous (but out of print) book called "The day of St Anthony's Fire" by John Grant Fuller. St. Anthony is the patron saint of lost causes (incidentally I went to St. Anthony's church until I was about 18). When all of the other saints have failed, St. Anthony is the one you are supposed to pray to. And St. Anthony's fire was rampant in the town that day. Similar outbreaks probably occurred throughout the world wherever the conditions were right for the growth of Claviceps purpurea. The chemical responsible for the hallucinations is actually LSD! lysergic acid. There was even an outbreak of egotism on the television show "Quincy" starring Jack Klugman, who played a coroner. He was aboard a cruise ship and people were acting very strangely. Quincy finally traced the behavior to contamination of the flour tortillas that had been served aboard ship. I haven't seen this episode for 15 years, but I still remember it because I figured it out before Quincy did!

25. Pathogenic Properties of Protozoa & Helminths
Presence of protozoa
Protozoan waste products may cause symptoms
Avoid host defenses by
Growing in phagocytes
Antigenic variation
Presence of helminths interferes with host function
Helminths metabolic waste can cause symptoms
Wuchereria bancrofti

26. Portals of Exit Respiratory tract: Coughing and sneezing
Gastrointestinal tract: Feces and saliva
Genitourinary tract: Urine and vaginal secretions
Skin
Blood: Biting arthropods and needles or syringes

27. Microbial Mechanisms of Pathogenicity - Overview
Foundation Fig 15.9
The End