Microbial Mechanisms of Pathogenicity

Question 1

What are the Immune System’s three lines of defense?

Answer 1

• 1st Line of Defense:
  
  • PREVENT ENTRY
• 2nd Line of Defense
  
  • LIMIT THE SPREAD
• 3rd Line of Defense
  
  • IDENTIFY, LOCATE, REMOVE
    *

Question 2

What is Normal Microbiota?

Answer 2

Generally considered harmless if their numbers remain within “normal” range or they remain in are of the body in which they normally function.

• May become opportunistic pathogens
• Can help limit the spread of other microbes due to microbial antagonism

Question 3

What are Opportunistic Pathogens?

Answer 3

A microorganism that can become pathogenic under certain circumstances.

Question 4

What are True Pathogenic Bateria?

Answer 4

• Bacteria that WILL cause disease upon succeful entry into a host.
• They contain Virulance Factors

Question 5

What are some non-bacterial pathogens?

Answer 5

• Protozoa
• Viruses
• Worms
• Fungi

Question 6

What are some abilities that a pathogenic trait may exhibit in order to allow the microbe to infect host cells.

Answer 6

1. Enter host.
2. Attach to host
   
   • allows for migration and replicate.
3. Hide from host immune systems
4. Spread and gain access to host resources.
   
   • may cause tissue damage
5. Exit.
   
   • Pathogens need acess to new hosts.

Question 7

Define Infection.

Answer 7

Growth of microorganisms in body

Question 8

Define Disease

Answer 8

• An abnormal stat in which part or the whole body is incapable of performing normal functions.
• “A change in state of health”

Question 9

How can microbes enter a host?

Answer 9

Microbes enter cells through portals of entry.

• Mucous membranes
  
  • lining the respiratory tract, gastrointestinal tract, genitourinary tract, and conjunctiva, a delicate membrane that covers the eyeballs and lines the eyelids
• Skin
  
  • broken skin, follicles and sweat gland ducts.
• Parenternal Route
  
  • Punctures, injections, bites, cuts, wounds, surgery, and splitting of the ski

Question 10

Are all microbes equally pathogenic?

Answer 10

NO. There are different Virulence rates

Question 11

Does the amount of invading microbes matter?

Does it matter depending on the invading microbe?

Answer 11

• YES! A few can be overcome by the immune system, however too many can cause a disease.
  
  • The likelihood of disease increases as the number of pathogens increases.
• ​The number also matters depending on the invading microbe and the portal of entry which it is envading.

Question 12

Explain LD50 and ID50

Answer 12

• LD50: The potency of toxin
  
  • lethal dose of 50% of the sample population
• ID50: The virulence of microbe
  
  • Infectious dose of 50% of the sample population.

Question 13

How do pathogenic microbes adhere to cells?

Answer 13

• Surface molecules on a receptor such as adhesions and ligands (glycoproteins & lipoproteins) bind to complementary surface receptors on host cells (sugars like mannose)
• Fimbriae, capsules, flagella, pili
• Microbial cooperation
  
  • ex. Dental cavity: Streptococcus mutans is involved in the production of Dextran which is used by actinomyces as an adherance receptor.
• Biofilm
  
  • ​microbes adhere to a particular surface that is typically moist and contains organic matter. the first set of microbes typically produces glycocalyx which allows other microbes to adhere.
    
    • Resist disifectants and antibiotics

Question 14

How do baterial pathogens penetrate host cells with capsules?

Answer 14

Capsules are a virulence factor because they resists a host’s defenses by imparing phagocytosis.

• Glycocalyx composed capsules
• polysaccharide composition

Strains with capsules are virulent, but strains without capsules are avirulent because they are susceptible to phagocytosis.

Presense of a capsule typically avoids the first line of defense.

Question 15

How does the cell wall composition increase virulence

Answer 15

• M Protein
  
  • heat & acid resistant
  • mediates attachment to epithelium cells
  • resists phagocytosis by white blood cells
  • Avoids 2nd line of defense
• OPA
  
  • an outermembrane protein that, along with fimbrae attaches to inside human epithelial cells and leukocytes
• Mycolic Acid
  
  • Waxy Lipid that allows the resistance of digestion by phagocytes
  • Allows for the multiplication within phagocytes.
  • Avoids 2nd line of defense

Question 16

What are exoenzymes and how do they contribute to virulence?

Answer 16

Extracellular enzymes

• contribute to pathogenicity at early stages

Examples:

• Coagulases
  
  • forms clots in blood. Fibrin protects baterium form phagocytosis & isolates from other defenses
• Kinases
  
  • Break down fibrin & digest clot used to prevent the spread of microbes
• Hyaluronidase
  
  • ​Hydrolyzes Hyaluronic acid, which binds connective tissue, & helps spread of infection
• Collagenase
  
  • ​Breaks down collegen which holds connective tissue together
• IgA Proteases
  
  • ​Destroys IgA antibodies

Question 17

How does Antigenic Variation contribute to virulence?

Answer 17

Pathogens disguse themselves by altering surface antigens. This allows them to avoid the third line of defense because once the body recognizes the antigen and produces the appropriate antibody, the pathogen has disguised itself with different antigens and now the antibodies are useless.

Question 18

How does a pathogen penetrate a host cell cytoskeleton?

Answer 18

• Invasins rearrange actin which allows penetration of cell wall.
• Membrane Ruffling distruption of cytoplasm
  
  • cell-cell movement of bacteria.

Question 19

How do siderophores of some baterial pathogens damage host cells?

Answer 19

• Siderophores are released into the medium, where they take the iron away from iron- transport proteins by binding the iron even more tightly.
• Once the iron-siderophore complex is formed, it is taken up by siderophore receptors on the bacterial surface.
• Then the iron is brought into the bacterium.

OBTAIN IRON

Question 20

How do pathogens inflict direct damage to host cell?

Answer 20

• Use host cells nutrients and produce waste products, which can lead into the rupture of the host cell.
• Following the rupture, pathogens can spread and damage other host cells
• Enzymes released by pathogens and even pathogen’s motility can damage cell.

Question 21

Define Toxins and Toxigenicity

Answer 21

• Toxin: a poisionous factor; virulence factor
• Toxigenicity: The ability to produce toxins

Question 22

What are exotoxins and how do they work?

What are types of exotoxins.

Answer 22

• Exotoxins are proteins produced inside pathogenic bacteria
  
  • Most commonly gram-positive bacteria.
  • Act OUTSIDE of the bacterium
  • Bacteria does not have to be present for damage to occur
  • May be longlasting even in low amounts
  • Water soulable so transport easily.
  • TARGET SPECIFIC
• Types:
  
  • A-B Toxins
    
    • A- Active enzyme that alters host cell once B causes host cell to invaginate and allows AB complex to enter cell.
  • Membrane-disrupting Toxins
    
    • ​Cause lysis by disrupting membrane
      
      • ex. Hemolysis, leukocidin, enterotoxin, cytotoxin
  • Supertoxins
    
    • ​Cytoxins, too many equal death

Question 23

What are endotoxins and how do they affect host cell?

Answer 23

• Found in outer membrane of Gram Negative bateria.
• Intact cells do not release endotoxins until cell is compromised or upon cell death.
  
  • LPS
  • Lipid A
    
    • Stimulates macrophages to release cytokines which triggers series of events in the body.
      
      • increases vasular permeability, decreases blood pressure which can cause Septic Shock/Endotoxic Shock
• Symptoms: Chills, fever, weakness, aches, shock maybe death.

Question 24

How asre plasmids and lysogeny involve in pathogenicity?

Answer 24

1. Plasmids may carry genes for virulence factors and can be passed to other bateria
2. Latent virally infected cells may have virulence factor genes from a previously infected bacterial cells.
   
   • when virus entered they lytic cycle to exit the host, the viral genome may have picked up genes from the hose. There are then passed to other bacteria via viruses.

Question 25

What are Portals of Exit?

Answer 25

• Ex. Secretions, excretions, discharges, or tissue that has been shed
• a microbe uses the same portal for entry and exit.
• Respiratory tract and gastrointestinal tract are the most common.