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BDS 2: FHHD > M1: How bacteria cause disease > Flashcards

M1: How bacteria cause disease Flashcards

1
Q

What are commensals

A

Bacteria colonised on a healthy host that do not cause disease

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2
Q

What are opportunistic pathogens?

A

Pathogens that arises caused by disturbance in the homeostasis between host and commensal

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3
Q

Define carriage

A

When a person asymptomatically carries a pathogenic microorganism which can be transmitted to other people

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4
Q

How does normal flora help prevent infection?

A

By competing with pathogens for colonisation sites

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5
Q

What is virulence

A

The quantitative ability of a pathogenic microorganism to cause disease

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6
Q

The virulence/pathogenicity of a microbe depends on what?

A

Depends on microbial and host factors

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7
Q

What microbial factors affect virulence? (4)

A
  • Transmissibility
  • Infectivity
  • Invasiveness/toxicity
  • Ability to evade host defences
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8
Q

What host factors affect virulence? (4)

A
  • Age
  • Genetic factors
  • General and local host defences
  • Immunodeficiency
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9
Q

What are 3 exogenous sources of infections?

A
  • Other humans
  • Animals
  • Environment (water)
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10
Q

What is an endemic infection?

A

Always present in a population at a more or less constant level, although the level may be cyclic

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11
Q

What is an epidemic infection?

A

A higher than normal level in the population, usually much higher than the endemic level

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12
Q

What is an outbreak infection?

A

Localised increase in incidence of a disease

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13
Q

What is a pandemic infection?

A

An epidemic spreading between continents

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14
Q

How can congenital infections spread? (2)

A
  • Via mother’s blood stream and by crossing the placenta

- Acquired shortly before or during delivery

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15
Q

What are fomites?

A

Inanimate object that can carry and transmit microorganism

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16
Q

How does skin to skin transfer normally occur?

A

Transfer usually occurs through abrasion in the epidermis

17
Q

What is cellulitis?

How is it caused?

A
  • A spreading infection of the soft tissues

- Streptococcus progenies getting into a small abrasion of skin

18
Q

How is herpes simplex spread?

A

Transferred directly by contact with infected secretions (salivary spread)

19
Q

What is respiratory spread dependant on? (3)

A
  • The amount of infective discharge
  • Size of aerosol droplets
  • The resistance of the infectious agent to drying (or inactivation by UV)
20
Q

How can blood borne transmission occur? (2)

A
  • Use of blood products (dirty needles)

- Through insect host

21
Q

How is congenital syphilis spread?

A

Spread can occur to the infant via birth canal

22
Q

What are the most common types of nosocomial infections? (3)

A
  • Urinary tract infections
  • Wound/skin and soft tissue infections
  • Respiratory tract infections
23
Q

How can infection spread in a hospital setting be minimised? (3)

A
  • Isolating patients
  • Adhere to infection control
  • Hand washing between patients
24
Q

How easily the infection spreads depends on its? (6)

A
  • Ability to survive
  • Ability to find alternative host
  • Shedding capacity
  • Infectivity
  • Virulence
  • Ability to evade immune response
25
Q

What is the degree of infectivity?

A

Ability to enter, multiply and survive in host

26
Q

How do invading organisms colonise the body?

A

Invading organisms must attach themselves to host tissues to colonise the body

27
Q

What does neisseria gonorrhoea adhere to?

A

Genital mucosa by fimbriae

28
Q

How does the influenza virus attach to host cells?

A

By its hemagglutinin antigen

29
Q

How do respiratory bacteria evade the immune response?

A

Respiratory bacteria secrete an IgA protease which degrades host immunoglobulin.

30
Q

How does Streptococcus pyogenes evade the immune response?

A

Expresses protein A which binds to host immunoglobulin preventing opsonisation and complement activation

31
Q

How does Streptococcus pneumoniae evade the immune response?

A

Has a polysaccharide capsule which inhibits uptake by polymorphs

32
Q

How does Mycobacterium tuberculosis evade the immune response?

A

Mycobacterium tuberculosis can survive inside host macrophages

33
Q

Exotoxins are excreted by?

Produced from organism

A

Gram positive bacteria

34
Q

Endotoxin are excreted by?

Produced within organism

A

Gram negative bacteria

35
Q

List some features of exotoxins (4)

A
  • Highly toxic
  • Act at specific target sites
  • Neutralised by antitoxin.
  • Often destroyed by heat
36
Q

What is the mechanism of action for endotoxins?

A

Causes host cell to produce IL-1 and tumour necrosis factor causing fever and shock

37
Q

How can IgM levels help diagnose an infection?

A

IgM is the first antibody to appear in response to initial exposure to antigen

BDS 2: FHHD (34 decks)

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