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Infection (Semester 4) > 1.1 Intro to infection > Flashcards

1.1 Intro to infection Flashcards

1
Q

Name the 7 types of microorganisms

A

Bacteria, fungi, viruses, protozoa, algae, archaea, multicellular animal parasites

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2
Q

What classification system exists for viruses?

How does replication differ between the classes (1 +2 and 3-7)

A

The Baltimore system:
Class 1 + 2 DNA viruses replicate within the nucleus
Class 3-7 RNA viruses replicates in the cytoplasm

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3
Q

Explain the process of gram staining

A

1) apply crystal violet to bacteria on dish
2) apply iodine to bind crystal violet and trap it in cell
3) add acetone or methanol to wash away the stain
- gram (+) fixes crystal violet
- gram (-) turn colourless (thin PGN)
4) add pink counterstain (safranin) leaving:
- gram (-) pink
- gram (+) purple

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4
Q

What are the structural differences between gram (-) and (+) bacteria

A

Gram (-) has a thin peptidoglycan layer and a lipopolysaccharide layer which holds antibodies

Gram (+) has a thick peptidoglycan layer and no lipopolysaccharide layer

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5
Q

What stain would you use to identify mycobacterium and why?

A

Ziel Neilson stain because the mycolic acid prevents the crystal violet stain from washing away

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6
Q

Compare the terms pathogenicity and virulence

What determines these factors?

A

Pathogenicity is the ability of a microorganism to cause disease and damage

Virulence is the degree of pathogenicity.

They are both determined by the composition of the genome (virulence can also depend on how the bacteria entered the host)

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7
Q

Compare the terms parasite and pathogen

A

A parasite is an organism that can live on or within a secondary organism/’host’

A pathogen is an organism that can cause damage to the host, cause disease

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8
Q

What is a plasmid?

A

An extra piece of DNA often carrying the bacteria’s virulent factors

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9
Q

Define attenuation

A

When a pathogen’s virulence is reduced

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10
Q

What 5 key steps do virulence factors help bacteria to do? (ACTII)

A
  1. Attach to the host (Via adhesins)
  2. Colonization (and enzymes)
  3. Invade
  4. Toxins (and enzymes) aid deeper penetration to avoid host defences
  5. Inhibit phagocytosis
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11
Q

Define the following terms:

a) Toxin
b) Toxigenicity
c) Toxemia
d) Toxoid
e) Anti-toxin

A

Toxin: substances produced by pathogens that contribute to pathogenicity

Toxigenicity: ability to produce a toxin

Toxemia: Presence of toxin in the host’s blood

Toxoid: inactivated toxin used in a vaccine

Anti-toxin: antibodies against a specific toxin

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12
Q

What are the 2 types of toxins and what is their key difference?

A

Exotoxins: toxins produced/secreted extracellularly as the organism grows
Endotoxins: lipopolysaccharides present on part of the outer layer of gram negative bacteria

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13
Q

Where are endotoxins released from and describe how they are released into the blood stream

Why are they so damaging?

A

Endotoxins are released from the lipid portion of the outer membrane from gram (-) bacteria

Process:

1) gram (-) bacteria is engulfed by a phagocyte and ingested by lyososmes
2) the dead debris is released into the bloodstream
3) once detected by the immune systems ➞ triggers an immune response

Endotoxins are highly antigenic and provoke a strong immune response, quickly causing heightened inflammation, fever and possible shock

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14
Q

What are exotoxins released from?

A

Both gram-positive and negative bacteria BUT all major gram-positive will produce it

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15
Q

Name the 3 types of exotoxins and their method of causing damage/dysfunction

A

Type I: Signalling at the host cell

Type II: Damaging the membrane/phospholipid bilayer by making protein channels in it

Type III: Entering the target cell and directly altering the function

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16
Q

Name the 3 classes of toxins

A

1) Neurotoxin (acts on nervous system)
2) Enterotoxin (acts on gut)
3) Superantigen

17
Q

What type of exotoxins are superantigens?

Give the MoA?

Name 4 symptoms associated

A

Type I exotoxin

Causes an intense response due to release of cytokines from host cell. They are unspecific and bind to any T cell causing a heightened intense immune response

Symptoms = nausea, vomiting, fever, shock and death

18
Q

Which Superantigen causes Toxic shock syndrome?

Name 3 major signs

A

Toxic shock syndrome toxin is caused by TSST-1 superantigen.

Causes hypotension, organ dysfunction and desquamative (peeling) skin lesions

19
Q

What bacterium causes Staphlococcal scalded skin syndrome?

What toxin is released?

List 5 symptoms

A

Caused by staphylococcus aureus which produces an “exfoliating toxin” causing the outer layers of skin to blister and peel

Symptoms: fever, redness, skin exfoliation, skin wrinkles and blisters/lesions

20
Q

What type of exotoxin does clostridium produce?

How can it lead to gas gangrene?

A

Clostridium are type II exotoxins -> they cause membrane damage and disruption which leads to:

increased permeability of blood vessels ➞ disrupts blood flow ➞ allows gas to enter tissues

21
Q

How is spore-forming advantageous to Clostridum

A

Because they’re anaerobic and particular about where they grow, they create spores as a protective mechanism so they can withstand environments they can’t grow in (aerobic)

22
Q

Describe the size, shape, (-) or (+), environmental niche and protective features of a clostridia

A
  • Large
  • bacilli
  • gram (+)
  • anaerobic
  • spore forming
23
Q

Explain the ‘A’ and ‘B’ segment of an A-B enterotoxin

A

1) The B portion binds to the surface receptors of the host cell
2) The entire A-B protein is taken into the cell by endocytosis
3) Once inside the cell the vacuole becomes extremely acidic causing dissociation of A and B portions
4) The A part is active and enters the cytoplasm and can then be incorporated into the host cell.
5) The B part is then recycled out by exocytosis, while A stays and infects

24
Q

What type of exotoxin does Vibrio Cholera produce?

Give its shape, type (-) or (+), environmental niche and protective features

What part of the body does it commonly affect and why?

A

It produces a type III A-B enterotoxin

  • Bacilli
  • gram (-)
  • lives in warm water pH >7, salty
  • has flagella which allows it to propel forwards

Attaches to the intestinal epithelia and reproduces due to the acidic environment of the gut

25
Q

What bacteria causes Tetanus?

What type of exotoxin does this produce + incl the specific name of the toxin?

A

Clostridum tetani

Type III A-B neurotoxin

Toxin = Tetanospasmin

26
Q

Name one feature of pili

A

They are antigenic and provoke an immune response

27
Q

What bacteria causes Botulism and where is it found?

What type of exotoxin does it produce + specific name of toxin?

How does this cause Botulism?

A

Clostridium botulinum, found in soil and intestinal tract of humans and animals

Produces a Type III A-B neurotoxin ➞ ‘metalloprotease toxin’

Toxin enters PNS, causing proteolysis of key proteins resulting in Inhibition of ACh release

28
Q

What are the 3 forms of Botulism disease?

A

1) Food borne
2) Infant borne
3) Wound botulism

29
Q

What are the main symptoms of Botulism?

A

Flacid paralysis leading to muscle weakness and respiratory arrest

30
Q

How do type II exotoxins cause damage

A

These are membrane disrupting toxins

They lyse the host cells by making protein channels in the plasma membrane (eg. leukocidins, hemolysins) which disrupt the phospholipid bilayer

31
Q

Give the MoA of how the cholera toxin causes damage (A-B mechanism)

A

1) One of the B subunits bind to a glycoprotein receptor on the cytoplasmic membrane
2) This results in cleavage of the A subunit which then enters the cytoplasm
3) Once in the cytoplasm it activates adenyl cyclase
4) adenyl cyclase converts ATP into cAMP
5) cAMP stimulates active secretion of electrolytes from cell into intestinal lumen
6) water flows to area with high electrolytes ➞ into intestinal lumen
7) Results in very water diarrhoea

32
Q

How are the stools in a patient infected with cholera described? (Hint: hallmark of cholera)

A

Watery diarrhoea with flecks of mucus -> “rice-water stool”

33
Q

List 4 important signs of cholera infection

A

1) dehydration
2) thirst
3) tachycardia
4) sunken eyes and flacid skin

34
Q

Describe the electrolyte/ acid-base imbalances in cholera

A

Metabolic acidosis ➞ loss of HCO3-

Hypokalemia ➞ loss of K+ (causes muscle cramps)

35
Q

What type of exotoxin does Clostridium Tetani produce?

Give its shape, type (-) or (+) and environmental niche

A

Type III A-B neurotoxin

  • bacilli
  • gram (+)
  • anaerobic, found in soil or GI tract of animals
36
Q

Describe the mechanism of how clostridium tetani causes damage?

A

1) spores become activated and develop into gram (+) bacteria that produce the toxin tetanospasm
2) this bind motor neurons that control muscles
3) it enters axons, migrates into the synapse of motor nerves and binds to the nerve terminals
4) this inhibits the release of inhibitory neurotransmitters (GABA and glycine)
5) This process intensifies results in severe muscle tightening and spasm

Infection (Semester 4) (19 decks)

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