Micro Chapter 15

Microbial mechanisms of pathogenicity

Pathogenicity

the ability to cause disease

more pathogenic = more dangerous

Virulence

the degree of pathogenicity

Portals of entry

most pathogens have a preferred portal of entry/invasion

mucous membranes(most bacteria)

skin

parenteral route

Parenteral route

deposited directly into tissues when barriers are penetrated (punctures, injections, bites, cuts, wounds and surgery)

ID 50

infectious dose for 50% of a sample population

What does ID 50 measure

virulence of a microbe

LD 50

lethal dose for 50% of a sample population

what does LD 50 measure

potency of a toxin

Which does a lower LD 50 or ID 50 mean?

microbe is more virulent/toxic, might not detect the bug in a sample, so give whole population vaccines

Ex. Bacillus anthracis- skin is easier to acquire bc only 10-50 ID

Adherence(Adhesion)

process where pathogens attach to host tissues

higher adherence = bugs will stay, not get coughed out and be more virulent

Adhesins (ligands)

bind to receptors on the host cells

Glycocalyx

type of adhesins, capsules and slime layer (IN SUGARS)

Fimbriae

hair like adhesins,

Pilli

bigger hair like structure

Biofilms

communities that share nutrients

happens more in nature (community of obligate aerobes on top, anaerobes most deep, etc. sharing nutrients based on oxygen)

Capsules

help cell penetrate host defenses

glycocalyx around the cell wall

help bug survive, bc they impair phagocytosis

Ex. streptococcus pneumoniae

M protein

resists phagocytosis

not only in bacteria → can go to heart. makes our immune system confused and causes autoimmune disorders

Famous m protein bug?

Streptococcus pyogenes!!!!!!!

Another name for streptococcus pyogenes?

Group A strep, GAS

Opa protein

allows attachment to host cells

Ex. neisseria gonorrhoeae

Waxy lipid(mycolic acid)

resists digestion, acid fast staining

Waxy lipid bug?

Mycobacterium tuberculosis!! KNOW THIS!

Different enzymes

coagulates, kinases, hyaluronidase, collagen's, IgA proteases

What bacteria produces enzymes

strepto and stapho bacteria

Coagulases

isolates the bug

coagulate fibrinogen

Kinases

digest fibrin clots, once bug is built they can now spread

Hyaluronidase

digest polysaccharides that hold cells together, so cells fall apart

Collagenase

breaks down collagen, skin gets fragile

Hyaluronidase and collagenase are?

very big vigilance factors, because it helps bacteria swim deeper into tissue

IgA proteases

destroys IgA antibodies

IgA antibodies

present in mucus, to help protect us

Antigenic variation

pathogens alter their surface antigens (and antibodies are rendered ineffective)

change shape to prevent antibodies from blocking their receptor

Invasins

helps them get into the host cell cytoskeleton

surface proteins produced by bacteria that rearrange actin filaments of the cytoskeleton, causes membrane ruffling

Actin and Invasins

use actin to move from one cell to the next (shigella and listeria)

cells can never reach bacteria, because they jump to another cell before lysosomes comes

Siderophores

uses host nutrients (they need iron- part of chemical formula)

proteins secreted by pathogens that bind iron more tightly than host cells

used if RBCS are ruptured

Direct damage

disrupts host cell function

uses host cell nutrients

produces waste products

multiples in host cells and causes ruptures

Toxins

poisonous substances produced by microorganisms

produce fever, cardiovascular problems, diarrhea, and shock

Toxigenicity

ability of a microorganism to produce a toxin

Toxemia

emia= in the blood

presence of toxin in the host’s blood

Intoxications

presence of toxin without microbial growth

bacteria died, but produced toxins during its time, making someone sick

Exotoxins

made in cytoplasm and then released OUTSIDE of the cell

proteins produced and secreted by bacteria

grow fast by ribosomes = more toxins grow

Solubility and exotoxins

its soluble in bodily fluids, destroy host cells and inhibit metabolic functions

Antitoxins

antibodies against specific exotoxins

Toxoids

inactivated exotoxins used in vaccines/chemical treatment

they look similar to toxin, but through heat they are inactive

What type of bacteria have exotoxins?

mostly gram positive, but both gram negative and positive produce them!

A-B toxins

contain an enzyme component (A PART)

and binding component (B PART)

Ex. T dap

A-B Toxin action

1. bacterium produces and releases the A-B toxin

2. B (binding) component of exotoxin attaches to host cell receptor

3. 3. the plasm membrane of the host cell invaginates (FOLDS INWARD), and the exotoxin enters the cell

4. A-B receptor are enclosed in pinched of portion of plasma membrane during PINOCYTOSIS

5. A-B components separate, and B component is released

A component

alters host cell function by inhibiting protein synthesis

it kills the host

B component

finds the host, blocks the receptor and then is released

How does endotoxin enter the cell

receptor-mediated endocytosis

Membrane-disrupting toxins

lyse host cells by disrupting plasma membranes

MD exotoxin- Leukocidins

kill phagocytic leukocytes

MD exotoxin- Hemolysins

kill erythrocytes by forming protein channels

MD exotoxin- streptolysins

hemolysis produced by streptococci (kills RBCS by GAS)

Superantigens

causes an intense immune response due to release of cytokines from host cells (T cells)

Superantigens symptoms

fever, nausea, vomiting, diarrhea, shock, and death

Genotoxins

damage DNA

Genotoxins symptoms

causes mutations, disrupting cell division, and leading to cancer

Endotoxins

intracellular, don’t get from gram positive (bc no LPS)

What does gram negative have?

endotoxins and exotoxins

Endotoxins in bacteria?

lipid A portion of lipopolysaccharides of gram negative bacteria

released during bacterial multiplication and when g negative bacteria die

Endotoxins causes?

causes disseminated intravascular coagulation

Macrophage endotoxin steps?

1. a macrophage ingests a gram-negative bacterium

2. the bacterium is degraded in a vacuole, releasing endotoxins, that induce the macrophage to produce cytokines