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3rd yr- IWB- Microbiology > How bacteria cause disease > Flashcards

How bacteria cause disease Flashcards

1
Q

Define pathogen

A

A microbe capable fo causing host damage/ disease

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2
Q

Define opportunistic pathogen

A

An organism that is a member of the resident microbiota or normally inhabiting the external environment that causes infection under certain circumstances

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3
Q

What does commensal refer to when describing micro organisms

A

Refers to a symbiotic relationship between a microorganism and its host where the micro organism befits from the host and the host is not harmed in the process

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4
Q

Define symbiont

A

A member of the resident microbiota that confers benefit to the host

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5
Q

Define pathbiont

A

A member of the resident microbiota that causes disease when loss of the normal balance between the host and resident microbiota (dysbiosis) occurs

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6
Q

Define dysbiosis

A

Imbalances in the resident human microbiota or our responses to them

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7
Q

Define pathogenicity

A

Capacity of a microbe to cause damage in a host

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8
Q

Define virulence

A

Relative capacity of an organism to cause damage in a host “degree of pathogenicity”

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9
Q

Define virulence determinant/ factor

A

Component of pathogens that damages the host/ allows pathogen to cause disease

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10
Q

How do we write lethal/infectious doses down?

A

LD50/ ID50

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11
Q

What does LD50 refer to?

A

Stands for 50% lethal dose

Number of organisms needed to kill half the host

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12
Q

What does ID50 refer to?

A

Stands for 50% infectious dose

Number of organism needed to cause infection in half the host

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13
Q

List the 4 major steps of the bacterial virulence mechanism

A
  1. Transmission
  2. Adherence to host surface
  3. Invasiveness
  4. Toxigenicity
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14
Q

How can infections be transmitted?

A

Externally or internally

Exogenously or endogenously

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15
Q

What are endogenous infections caused by?

A

Caused by the human microbiota behaving as a opportunistic pathogen

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16
Q

How can endogenous infections be transmitted?

A
  1. Ingestion
  2. Fecal contamination of food and water
  3. Inhalation
  4. Sexually
  5. Contaminated needles
  6. Insect bites
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17
Q

Name the 4 portals of entry for pathogens to get into out body

A
  1. Skin
  2. Respiratory tract
  3. Gastro intestinal tract
  4. Genito urinary tract
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18
Q

Following transmission what is the first step for infections to cause problems in a host?

A

Adherence to host surface

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19
Q

How can microorganism adhere to cell surface?

A
  1. Some have structural adaptations

2. Some produce chemicals to help them adhere to certain surfaces

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20
Q

How does e coli adhere to its host?

A

It has hair like pili that allow it to attach itself directly to the epithelium

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21
Q

How does neisseria gonorrhoea adhere to its host?

A

It has hair like pili that allow it to attach itself directly to the epithelium

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22
Q

How do s mutans adhere to its host?

A

Their extracellular polysaccharide structure help them to adhere to the enamel surface

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23
Q

What are 60% of human infections associated with?

A

The formation of a biofilm

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24
Q

How do bacteria in biofilms maintain their population levels

A

By releasing small amounts of chemicals called form sensing molecules

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25
What are the benefits to bacteria of being in a biofilm
1. Protection from host immune mechanisms 2. Poor penetration of antimicrobials into deeper layers of the biofilm 3. Degradation of antimicrobials 4. Gene expression leading to more virulent or resistant organisms
26
What is invasiveness dependent on?
Depends on secreted bacterial enzymes
27
Give examples of bacterial enzymes that affect invasiveness
1. Collagenase 2. Hyaluronidase 3. Coagulase 4. Kinase
28
Where is Hyaluronidase found?
Is present in staphylococcus aureus (skin infections) and streptococcus progenes (sore throat)
29
Where is Collagenase found?
Is present in clostridium perfringens (gas gangrene)
30
What does coagulase do?
It aids in the conversion of fibrologin into fibrin this protects the bacteria from phagocytosis as it clots the micro organism in a fibrin layer
31
What does kinase do?
It removes the fibrin layer that coagulase made and helps inject microorganisms into the tissues
32
What does immunoglobulin A (IgA) protease do?
Degrades IgA on the mucosal surfaces allowing bacteria to adhere to mucous membranes
33
What does leukocidins
Can destroy key classes of host immune cells such as neutrophilic leukocytes and macrophages
34
Give an example of a bacteria that produces leukocidins
Aggregatibacter actinomycetemcomitans.
35
Give an example of a bacteria that produces Immunoglobulin A (IgA) protease
N. gonorrhoeae, Haemophillus influenza Streptocccus pneumonia
36
What does toxigenicity refer to?
Refers to toxin production
37
Name the 2 types of toxins
Endotoxins | Exotoxins
38
What are endotoxins
The lipid portions of lipopolysaccharides in the cell walls gram negative bacteria
39
When are endotoxins liberated
When the bacteria die and their cell wall breaks down
40
Which bacteria are Endo toxins NOT found in?
gram positive
41
List some of the biological effects of endotoxins
1. Fever 2. Hypotension and shock 3. Activation of the alternative pathway of compliment cascade 4. Generalised activation of the coagulation system 5. Increased phagocytic activity of macrophages and polycolonal B cell activation 6. Increased antibody production
42
How do endotoxins cause biological side effects
They lead to the proaction of host factors such as IL1, TNF from macrophages
43
How do endotoxins lead to the development of fever
As it leads to the release of IR1 from macrophages which effects the thermoregulatory centre of the hypothalamus and resets the body temperature to a higher temperature
44
Why is the activation of the coagulation system bad ?
As it leads to inflammation and tissue ischaemia
45
Describe e coli
It is a gut commensal bacteria | It is gram negative
46
What are exo toxins
They are protein produced by both gram positive and negative bacteria
47
Which type of bacteria more commonly produces exotoxins
Gram positive
48
Give an example of an exotoxin
Tentanus toxin Diptheria Botulinum
49
What does the tetanus toxin do?
It presents the release of the inhabitory neurotransmitter glycine causing muscle spams
50
Name the most toxic compound known
Botulinum toxin
51
What does Botulinum toxin do?
It blocks the release of acetylene choking at the synapse leading to paralysis of the muscle
52
What is Botulinum toxin
It is an obligate anaerobe | Endospore former
53
How can you get infected by Botulinum toxin?
1. Ingesting pre formed toxin in contaminated food 2. Ingesting the spores 3. Infection of dirty wounds
54
iWhen we describe a bacteria as being an Endospore former what do we mean?
Means the bacteria protects itself by forming a spore which is a lot harder to remove through sterilisation procedures
55
Describe the clinical presentation of botulism
``` Presents 1-2 days after infection Patient can present with: 1. Diplopia 2. Dysphagia (difficulty swallowing) and speech problems 3. Dry mouth 4, Respiratory failure 5. Death ```
56
List some examples of Endo toxin mediated disease
1. Cholera 2. Diphtheria 3. Diarrhoea, pseudomembranous colitis - 4. Haemorrhagic colitis 5. Whooping cough 6. Scarlet fever 7. Scalded-skin syndrome
57
What is cholera caused by?
Vibrio cholerae (enterotoxin)
58
What is Diphtheria caused by?
Corynebacterium diphtheriae
59
What is Diarrhoea, pseudomembranous colitis caused by?
Clostridium difficile
60
What is Haemorrhagic colitis caused by?
E. coli O157 (verotoxin)
61
What is Whooping cough caused by
Bordetella pertussis (pertussis toxin)
62
What is Scarlet fever caused by?
Streptococcus pyogenes (exotoxins)
63
What is scalded skin syndrome caused by?
S. aureus (epidermolysin)
64
List the 5 bacterial virulence factors
1. Adhesin 2. Invasin 3. Impedin 4. Aggressin 5. Modulin
65
What does Adhesin enable?
Enables binding to host tissues
66
What does invasin enable
Enables invasion of host cell/ tissues
67
What does impedin enable?
Enables avoidance of host cell defence mechanisms
68
What does aggression cause
Causes direct damage to the host
69
What does modulin induce
Indices indirect damage by perturbing regulation of host defences

3rd yr- IWB- Microbiology (12 decks)

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