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module 102: T4 infection and immunity > professional pathogens > Flashcards

professional pathogens Flashcards

1
Q

Define infection

A

when an organism enters the body, increases in number and damages the host in the process

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2
Q

Define colonisation

A

when an organism lies on us but doesn’t cause infection

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3
Q

Define a pathogen

A

an organism which can evade the immune defences of the normal host to cause infection

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4
Q

Define a commensal

A

an organism which lives on us but doesn’t cause infection

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5
Q

Define symbiosis

A

mutual benefit

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6
Q

Define parasite

A

unequal benefit, used colloquially for eukaryotic infections

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7
Q

What are the two types of pathogens and what do they do?

A
  • PROFESSIONAL: cause disease in any susceptible host
  • OPPORTUNISTIC: only cause disease in immunocompromised patients
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8
Q

Define virulence

A

fundamental properties of the organism which determine how it causes the disease it does

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9
Q

Describe the appearance of staphylococcus aureus on agar?

A

golden colonies

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10
Q

Describe the appearance of Staphylococcus aureus down a microscope?

A

gram positive cocci in clusters which look like bunches of grapes

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11
Q

Which types of protein exotoxins can S. aureus secrete?

A
  • cytotoxins
  • exfoliative toxins
  • enterotoxins (superantigens)
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12
Q

What are cytotoxins?

A

pore-forming toxins, which lyse host cells

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13
Q

What are exfoliative toxins?

A

proteases which target epidermal structural proteins

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14
Q

What are enterotoxins (superantigens)?

A

stimulate massive T cell activation, leading to immune evasion

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15
Q

Describe S. aureus coagulase?

A
  • cell wall-bound enzyme
  • stimulates clotting
  • plays a role in immune evasion
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16
Q

What can the S. aureus coagulase be used for?

A

can be used as a test to distinguish S. aureus from other less virulent staphylococci

17
Q

What is the role of the S. aureus capsule?

A

masks cell surface features from recognition by the immune system

18
Q

Describe the S. aureus capsule

A
  • polysaccharide capsule
  • compared with other bacterial species, this one is thin (microcapsule) but helps avoid phagocytosis by neutrophils
19
Q

What does the S. aureus cell wall contain to help it?

A
  • adhesins
  • adherence to nasal mucosa and deep body tissues
20
Q

How exactly do adhesins on the S.aureus cell wall help?

A
  • TISSUE ADHERENCE: for colonisation or deep infections
  • IMMUNE EVASION: ‘cloaking’, e.g protein A
21
Q

How does S. aureus use gene regulation to aid itself?

A

can survive and adapt to different conditions by sensing environmental cues and altering production of virulence factors needed to survive

22
Q

Which gene cluster encodes the peptide quorum-sensing system in S. aureus ?

A

the accessory gene regulator (agr)

23
Q

Which kind of skin infections can S. aureus cause?

A
  • furunculosis
  • impetigo
  • staphylococcal abscess
24
Q

How can S. aureus cause food poisoning?

A

by ingestion of staphylococcal enterotoxins in contaminated food

25
Q

List the common S. aureus infections

A
  • normal commensal
  • soft tissue infections
  • surgical site infections
  • vascular line-related infections
  • bacteraemia
26
Q

Where is s. aureus often found?

A

a normal commensal of anterior nares is found in 20-60% of healthy adults

27
Q

What does protein A in the cell wall of S. aureus do?

A

it binds to the Fc portion of immunoglobins, holding them out like umbrellas

28
Q

Why is it so dangerous when the lipopolysaccharide gets disseminated in the blood?

A
  • there is a SYSTEMATIC activation of immune response
  • can manifest as sepsis
29
Q

What does Neisseria meningitidis like to adhere to?

A
  • nasopharyngeal epithelium
  • endothelial cells
  • meninges
30
Q

What are common streptococcus pneumoniae diseases?

A
  • commonest form of penumonia (40%)
  • upper respiratory tract infections
  • bacteraemia
  • meningitis
  • endocarditis (infection of heart valves)
31
Q

What does the IgA protease released by S. pneumoniae do?

A

breaks down secreted immunoglobulin A, preventing mucosal clearance

32
Q

What does pneumococcal surface protein A (PspA) in S. pneumoniae do?

A
  • inhabits complement deposition and hence activation of cascade and clearance of bacteria
  • neutralises lactoferrin’s bactericidal activity
33
Q

How does the S. pneumoniae capsule help?

A
  • polysaccharide coat prevents complement-mediated phagocytosis
  • specific antobodies to capsule required
34
Q
A

module 102: T4 infection and immunity (2 decks)

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