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Fundamentals of Microbiology (Y2,S1) > Bacteria & Disease > Flashcards

Bacteria & Disease Flashcards

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Biology 101 flashcards
1
Q

Pathogenicity

A

The ability of a pathogen to inflict damage on host

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2
Q

Infection

A

Microorganism (not a member of local microbiota) is established & growing in host

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3
Q

Pathogen

A

Organism that causes disease or tissue damage in a host

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4
Q

Virulence

A

The relative ability of a pathogen to cause disease

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5
Q

How can virulence be estimated

A

By experimental studies of the LD50 (lethal dose 50 - the amount of an agent that kills 50% of animals in the test group)

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6
Q

Roles of virulence factors (7)

A
  • adherence to host cell
  • invasiveness
  • nutrient acquisition from host
  • immune evasion - inhibition of phagocytosis
  • toxins
  • superantigens
  • antibiotic resistance
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7
Q

Steps of infection process

A
  1. Exposure to pathogens
  2. Adherence to skin or mucosa
  3. Invasion through epithelium
  4. Multiplication - growth & production of virulence factors and toxins
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8
Q

Compromised physical defences examples

A
  • Broken skin
  • Injections/surgery
  • In-dwelling medical devices
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9
Q

Swimming motility in bacteria is controlled by what

A

Flagella

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10
Q

Why is adherance of the bacteria necessary

A

To avoid innate host defense mechanisms - peristalsis in gut, flushing action of mucous/saliva/urine

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11
Q

What are the receptors on bacteria called

A

Adhesins
They extend from bacterial surface.

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12
Q

What are adhesins often

A
  • Glycoproteins
  • Lipoproteins
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13
Q

What 2 functions do glycocalyx play in bacterial pathogenicity

A
  1. They contain specific receptors to enable adhesion to host cells
  2. Protect bacteria from ingestion by wbcs
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14
Q

Fimbriae & Pili functions

A
  • Gene transfer by conjugation
  • Attachment to human tissue
  • Motility
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15
Q

Colonisation

A

The growth of microorganisms after they’ve gained access to host tissues

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16
Q

Why do bacteria show tissue specificity

A

Different bacteria have different nutritional & environmental needs

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17
Q

Which bact adapted to survival in gastrointestinal tract

A

Salmonella & Shigella
Good at surviving in low pH

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18
Q

Invasion

A

Penetration of host cells & tissues beyond skin & mucous surfaces

19
Q

What is invasion mediated by

A

Molecules called invasins

20
Q

Example of enzymes as virulence factors (2)

A
  1. Hyaluronidase breaks down hyaluronic acid which holds cells together, enabling bacteria to invade deeper tissues
  2. Collagenase breaks down collagen which surrounds endothelial cells, allows bacteria enter bloodstream
21
Q

Bacteraemia

A

The presence of bacteria in the bloodstream

22
Q

Septicaemia

A

Bloodborne systemic infection

23
Q

What protects bacteria from phagocytosis by immune cells in the bloodstream

A

Formation of a fibrin clot protects bacteria from phagocytosis by immune cells

24
Q

Benefit to bacteria of travelling inside host cells

A
  1. Protects from parts of immune response
  2. Enables them to avoid clearance by shear stress/secretions
  3. Gives access to nutrients
25
Q

Example of opportunistic intracellular pathogen

A

E. coli

26
Q

Example of obligate (needs oxygen) intracellular pathogen

A

Chlamydia

27
Q

How do bacteria get inside host cells (2)

A
  1. Engulfed by immune cell (phagocyte)
  2. Force a non phagocyte (epithelial/endothelial cell) to engulf it
28
Q

How does Salmonella force its way into human cells

A
  • Needle like structure injects proteins into host cell
  • Causes reorganisation of actin cytoskeleton leading to uptake of bacterium
  • Salmonella enclosed in vacuole - survives & proliferates
29
Q

What nutrient is required for most bacteria

A

Iron

30
Q

How do bacteria get iron

A
  • Secrete proteins called siderophores that bind iron more tightly than host cells
  • (If cell loses too much iron it can die, this on a wide scale causes anaemia)
31
Q

Toxicity

A

Ability of an organism to cause disease by means of a toxin that inhibits host cell function or kills host cells

32
Q

What kind of bacteria have endotoxins

A
  • Gram neg bacteria
  • Lipid A portion of LPS responsible for toxic properties
  • Only pathogenic bacteria have toxic LPS
33
Q

What assay detects endotoxins

A

Limulus amebocyte lysate (LAL) assay.
Amebocytes lyse in presence of endotoxin, producing a clot.

34
Q

What are AB exotoxins composed of

A
  • An active (A) domain
  • Binding (B) domain
35
Q

4 examples of AB exotoxins

A
  1. Diphtheria toxin
  2. Tetanus toxin
  3. Botulinum toxin
  4. Cholera toxin
36
Q

What is happening to acetylcholine in botulism vs in tetanus

A
  • Acetylcholine inhibited in botulism, results in flaccid paralysis
  • Acetylcholine constantly being released in tetanus, muscle constantly contracts resulting in spastic paralysis
37
Q

Enterotoxin

A

An exotoxin whose activity affects small intestine

38
Q

What does cholera toxin cause

A

Massive secretion of fluid into intestinal lumen, resulting in vomiting & diarrhoea

39
Q

What do cytolytic toxins do

A

degrade cytoplasmic membrane integrity, causing cell lysis & death

40
Q

What do superantigen exotoxins do

A
  • Cause a non specific overstimulation of immune cells
  • Strong inflammatory response, can lead to high fevers, low bp, multi organ failure, shock, death
41
Q

What is the process where pathogens lose their virulence called

A

Attenuation
(Due to mutation)

42
Q

What can attenuated strains be used as

A

Vaccines e.g: TB vaccine

43
Q

Endotoxin vs exotoxin: LD50

A
  • Endotoxin have a high LD50
  • Exotoxins have low LD50 (so only a small amount is needed to see effects - more dangerous)

Fundamentals of Microbiology (Y2,S1) (9 decks)

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