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MICR 341 > FIRST LINE OF HOST DEFENSE > Flashcards

FIRST LINE OF HOST DEFENSE Flashcards

1
Q

What is the first step of a bacterial infection?

A

Contact/exposure.

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2
Q

What is an example of a secondary party mediating the invasion of a host?

A

Fleas allow for bacteria to enter the host by biting the host and allowing a mode of transmission.

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3
Q

What are two ways a pathogen colonizes the tissue and causes damage?

A
  1. Release of toxins
  2. Establishing itself/replication of the pathogen in the host
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4
Q

What are two examples of toxins released during the growth of pathogens in an infection?

A
  • Collagenase can be released to degrade tissue
  • Hemolysin can be used to disrupt the membrane of blood cells.
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5
Q

What is arguably the most important step for the bacteria’s survival during an infection?

A

Exiting the host to continue transmission. The bacteria must leave the host in order to live, because if it kills the host while it is still inside, the bacteria dies with the host.

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6
Q

Salmonella typhi interacts with what cells during infection of the intestinal tract?

A

M Cells

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6
Q

What is the function of M Cells?

A

M Cells present pathogens and foreign bodies to cells of the immune system (macrophages and dendritic cells) to initiate an immune response.

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7
Q

How does Salmonella hijack the host defense system during the early stages of infection?

A

Salmonella is presented to a macrophage by M Cells and overtakes the macrophage.

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7
Q

How is hijacking a macrophage beneficial to Salmonella Typhi during infection?

A

Macrophages transport the bacteria to areas that are heavily populated with other macrophages (ie. Spleen, bone marrow, liver) and infects more parts of the body.

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7
Q

What is a systematic infection?

A

An infection that has targeted many areas and systems of the body.

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7
Q

How does Salmonella Typhi exit the host after it has caused damage?

A

It reinserts itself into the intestinal tract through the gall bladder and is excreted through the waste of the host.

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7
Q

Differentiate between epithelial and endothelial cells

A
  • Epithelial cells are the outer most layer of cells and are tightly bound to protect areas from invasion. Epithelial cells surround the intestinal tract, respiratory tract, skin, vaginal tract etc.
  • Endothelial cells cover blood vessels and are loosely attached to allow immune system cells to leave the blood and enter the tissue (during an immune response).
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8
Q

The upper respiratory tract contains cells that have Cilia. What are Cilia and what are its function?

A

Cilia are finger like projections present on epithelial cells of the intestinal and respiratory tract that move mucus from the lungs/intestine. They help remove bacteria that had been trapped in mucus.

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8
Q

What are the three layers of the intestinal tract?

A
  1. epithelial cells covered in mucus
  2. basal lamina - a network of connective tissue holding the epithelial cells together.
  3. looser connective endothelial tissue that contain intracellular matrix, proteins and blood capillaries.
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8
Q

How might pathogens take advantage of endothelial cells?

A
  • Endothelial cells are loosely connected and allow material to pass through it easily.
  • The cells do not differentiate between immune system cells and pathogen, so the pathogen can cross endothelial tissue.
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9
Q

What are the two poles present in some epithelial cells? What part of the cells are they closer to?

A
  1. basolateral surfaces are closer to the basal lamina (bottom) of the cell
  2. apical surfaces are closer to the cilia of the cell (top_
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10
Q

What tracts are the basolateral and apical surfaces present in?

A

Intestinal and Respiratory tracts - any cells that contain cilia.

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11
Q

What are tight junctions?

A

Protein networks that keep intestinal cells tightly attached.

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12
Q

What is the importance of tight junctions in intestinal cells?

A

Prevents pathogens from entering the spaces between epithelial intestinal cells.

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13
Q

What protein do intestinal pathogens target in order to weaken tight junctions?

A

Occludin

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14
Q

An experiment sampling Wild Type E.Coli and 3 other mutant E.Coli found that only the Wild Type strain actively degraded occludin. What does this say about the pathogenic tendencies of the species examined?

A
  • Wild Type E. Coli is the only strain that displayed pathogenic defense, therefore we can assume this strain has developed virulence factors to infect the host.
  • The other mutants do not have the type 3 secretion system needed to break down occludin and are non-pathogenic.
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15
Q

The epidermis of the skin contains two cell layers. They are:

A
  1. A layer of dead skin cells that are highly keratinized and hard
  2. A layer of live, dividing cells
16
Q

What defense mechanism is highlighted by the structure of the epidermis of skin?

A
  • Dead cells above the living cells are easily shed. If bacteria colonize those dead cells, they are easily removed when the host cleans himself/wipes off the dead cells.
17
Q

The dermis of the skin contains what kind of cells?

A

SALTs - skin associated lymphoid tissues are a sequence of macrophages and DC cells

They patrol the dermis and notify the immune system when there is a pathogen present.

18
Q

What defense mechanism is highlighted by SALTs?

A

SALTs notify the immune system and trigger adaptive or passive immunity.

They are an alert to the host that the system has been breeched.

19
Q

What are 3 ways your skin microbiota fight against pathogens?

A
  1. They occupy the space that pathogens would want to target
  2. They secrete antimicrobial compounds to ward off pathogens
  3. They use up nutrients from the host, leaving nothing from the pathogen to feed on.
20
Q

What feature of the skin do Leprosy causing bacteria target?

A
  • The skin usually runs at temperature lower than inside the body.
  • Leprosy-causing bacteria only colonize areas that are below 37 degrees - ie. your skin
  • Leprosy patients will have infected extremities.
21
Q

How is temperature and pH considered a defense mechanism of the skin?

A

Low temperatures and high pH limits the growth of microbes ie. pathogen growth.

22
Q

What makes the pH of the skin acidic?

A

Sweat and fluid secretion changes the pH of skin

23
Q

How does the human microbiota survive the defense mechanisms intended for pathogens?

A

The microbiota have adapted to conditions of human skin. They can survive low pH, colder temperatures, and ward off pathogens in favor of the host.

24
Q

What cells secrete mucus in the intestinal and respiratory tract?

A

Goblet cells

25
Q

What are MALTs or GALTs?

A

Mucus-Associated Lymphoid Tissues and Gut-Associated Lymphoid Tissues

They are a series of macrophages and dendritic cells that notify the immune system of pathogens present.

26
Q

Where are MALTs and GALTs found?

A

Below the epithelial cells in the respiratory and intestinal tract respectively

27
Q

IGA is an antibody secreted by Mucosa. What is its function?

A

The antibodies bind to pathogens and anchor the pathogen in mucus. This traps the pathogen and once the mucus is expelled from the intestinal tract, the bacteria moves with it.

28
Q

What physical characteristic of mucus makes it difficult for bacteria to degrade it?

A

Mucus is a network of proteins that are highly glycosylated - surrounded by sugars

29
Q

What other protective molecules do mucus secrete to fight against pathogens?

A

lysozymes and antimicrobial peptides

30
Q

What protein makes up mucus?

A

MUC-2 protein

31
Q

Goblet cells are positioned sparsely across the epithelial cells of the intestinal tract. What about this is problematic in the host’s defense?

A

Goblet cells that secrete mucus will not create an even layer of mucus. Areas that are closer to the goblet cells will have more mucus than others. The areas that have thin mucus layers will be targeted by pathogens because there is a lower chance of them getting stuck.

32
Q

What does lysozyme target?

A

Lysozymes target the peptidoglycan of bacteria

33
Q

What bonds in peptidoglycan do lysozymes target?

A

N-acetylglucosamine (NAG) and N-acetlymuramic acid (NAM) bonds

34
Q

Why are gram negative bacteria resistant to lysozymes?

A

They have an outer membrane containing LPS which protects their peptidoglycan.

35
Q

What are antimicrobial peptides? How long are they?

A

Short peptides (20-30 amino acids long) that are secreted to harm pathogens.

35
Q

What are two other ways gram positive AND gram negative bacteria protect itself from lysozymes?

A
  1. creating capsules to shield themselves
  2. secreting proteases that degrade lysozyme proteins
36
Q

What allows antimicrobial peptides to harm pathogens?

A

The peptides are positively charged and are attracted to the negatively charged membranes of gram +/- bacteria. When they attach to the bacteria they destabilize the membrane and destroy it.

37
Q

What portions of gram negative and gram positive bacteria make their membranes negatively charged?

A
  • LPS of gram negative bacteria is negatively charged.
  • Lipoteichoic acid of gram positive cells is negatively charged.
38
Q

Presumably, antimicrobial peptides are most effective in gram negative cells. What about gram positive cells still makes the peptides effective at destabilizing the membrane?

A

The gram positive membrane is not rigid, it is permeable. Small peptide chains can still pass through the membrane.

39
Q

How doe antimicrobial peptides avoid eukaryotic cells (your own cells) and only attack bacterial cells?

A

Eukaryotic cell membranes are neutrally charged - peptides are not attracted.

40
Q

How do pathogens resist antimicrobial peptides?

A

By changing their surface charge.

41
Q

What two positive compounds can be added to Staphylococcus Aureus to neutralize its membrane?

A
  1. D-alanine added to the lipoteichoic acid of gram + membrane.
  2. D- lysinea added to the phospholipids of gram + membrane.
42
Q

What positive compound is added to Salmonella Typhi to neutralize the membrane?

A

Aminoarabinose is added to Lipid A to neutralize the gram - membrane

43
Q

What is an additional benefit of adding compounds to the pathogen membranes as a defense against the host’s immune system?

A

It adds rigidity to the membrane further preventing peptides from entering it.

44
Q

What are two other mechanisms used by pathogens to resist antimicrobial peptide defense?

A
  1. peptidase production to degrade the peptide chain.
  2. capsules to protect the bacteria
45
Q

How can fimbriae be a commensal and a virulence factor?

A
  • In commensal bacteria, fimbriae allow the bacteria to attach to the host permanently - occupying the space that may be targeted by pathogens.
  • In pathogenic bacteria fimbriae are used to interact with the host’s cells and penetrate its defense system.

MICR 341 (4 decks)

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