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FHHD > How Bacteria Causes Disease and How Infections Spread > Flashcards

How Bacteria Causes Disease and How Infections Spread Flashcards

1
Q

What are commensals

A

These are bacteria that are colonised in a healthy host and do not cause disease

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2
Q

What are opportunistic pathogens

A

Pathogens that tend to cause disease when the opportunity arises caused by disturbance in the homeostasis between host and commensal

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3
Q

Give examples of opportunities for infection that opportunistic bacteria might take advantage of

A
  • In immunocompromised hosts
  • When they get to sites where they don’t normally live
  • Antibiotics and other therapies
  • Dietary imbalances
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4
Q

Give examples of pathogenic bacteria that can be spread due to asymptomatic carriage

A
  • Staphylococcus Aureus in the nose
  • Streptococcus Pneumoniae in the respiratory tract
  • Salmonella typhi in the gut or the gall bladder
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5
Q

How can the normal flora help prevent infection

A

The bacteria competes with pathogens for colonisation and invasion by undesirable, exogenous organisms

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6
Q

What is Virulence

A

This is the quantitative ability of a pathogenic microorganism to cause disease

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7
Q

What microbial factors influence virulence

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

What host factors influence virulence

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

What are some exogenous sources of infection

A
  • Person to person
  • Animal pathogens may spread to humans - zoonosis
  • Human can be infected by organisms in the environment
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10
Q

Define an endemic infection

A

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

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11
Q

Define an epidemic infection

A

Higher than normal level in the population usually much higher than the endemic level and usually short term

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12
Q

Define an outbreak infection

A

Localised increase in incidence of a disease e.g. e.coli food poisoning

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13
Q

Define a pandemic infection

A

An epidemic spreading between continents

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14
Q

What is horizontal and vertical infection transmission

A

Horizontal - Transmission or organism between individuals

Vertical - Transmission from mother to offspring in utero/around birth

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15
Q

How can vertical spread of congenital infections occur and give examples of infections that can be spread by each pathway

A
  • From mother’s bloodstream and by crossing the placenta e.g. syphilis, rubella, toxoplasmosis
  • May be acquired shortly before or during delivery e.g. Herpes simplex, hepatitis B virus
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16
Q

Name some modes of transmission for infections

A
  • Respiratory spread
  • Faecal-oral spread
  • Via the skin or mucous membranes
  • Blood
  • Fomites - inanimate object that can carry and transmit microorganisms
  • Zoonoses
  • Sexual transmission
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17
Q

What is cellulitis and what is it often caused by

A

A spreading infection of the soft tissues, most commonly caused by streptococcus pyogenes, getting into a small abrasion of the skin

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18
Q

What is erythema and oedema

A

Erythema - reddening

Oedema - swelling

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19
Q

What are some infections that can spread by faecal-oral spread

A

Salmonella spp.
Shigella spp.
Hepatitis A

20
Q

How can blood borne transmission occur

A
  • Needles
  • Direct transmission
  • Insects like mosquitos and fleas
21
Q

What is a Nosocomial infection

A

Hospital Acquired infection

22
Q

What are the most common types of nosocomial infection

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

How can spread of infection in hospitals be minimised

A
  • Isolating patients with known resistant organisms if at all possible
  • Sensible adherence to sensible infection control policies - isolating patients in side rooms if required
  • Handwashing between patients
24
Q

What affects how easily an infection can spread

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

What respiratory infections can be spread by shedding

A
  • Influenza
  • Measles
  • M. tuberculosis
26
Q

What skin-contact infections can be spread by shedding

A
  • Herpes Simplex

- Staphylococcus aureus

27
Q

What facial-oral infections can be spread by shedding

A
  • Salmonella typhimurium

- Hepatitis A

28
Q

What is infectivity

A

This is the ability of an infection to enter, multiply and survive in host

29
Q

What factors do infections need to be able to resist outside the host

A
  • Drying
  • UV
  • Water
  • Soil
30
Q

What are some ways that invading organisms can attach themselves to host tissues to colonise the body

A
  • Neisseria gonorrhoea adheres to the genital mucosa by fimbriae
  • Giardia laamblia attaches to the jejunal mucosa by a special sucking disc
  • Influenza virus attaches to host cells by its hemagglutinin antigen
31
Q

How do respiratory bacteria overcome host immune defences

A

They secrete an IgA protease which degrades host immunoglobulin

32
Q

How does streptococcus pyogenes

A

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

33
Q

How can organisms avoid destruction by host phagocytes

A
  • Streptococcus pneumonia has a polysaccharide capsule which inhibits uptake by polymorphs
  • Some organisms e.g. mycobacterium tuberculosis can survive inside host macrophages
34
Q

What kinds of enzymes can pathogens express to damage the host

A 
Coagulase (s.aureus)
Proteases 
Lipases
Nucleases
Glycosidases
35
Q

What kind of bacteria release exotoxins

A

Gram positive bacteria

36
Q

What kind of bacteria release endotoxins

A

Gram negative bacteria

37
Q

Name some properties of exotoxins

A
  • Highly toxic, acts at specific target sites
  • Neutralised by antitoxin
  • Often destroyed by heat
38
Q

Name some types exotoxin

A

Streptococccal erythrogenic toxin - can lead to scarlet fever
S. Aureus enterotoxin = diarrhoea
Vibrio cholera enterotoxin = stimulates adenyl cyclase = watery diarrhoea

39
Q

Describe the morphology of vibrio cholerae

A
  • Curved bacterium rod-shaped
  • Gram-negative
  • Motile
40
Q

How do endotoxins damage the host

A

They cause the host cells to produce IL-1 and TNF causing fever and shock

41
Q

Where are endotoxins found

A

Found int he outer later of gram negative bacteria cell walls

42
Q

What steps should you go through in the diagnosis process

A
  • History
  • Clinical examination
  • Laboratory investigations
  • Others as needed - x rays an dat
43
Q

What general questions should you ask when asking for patient history

A
  • Travel
  • Contact with animals and infected people
  • Food
  • Drugs
  • Symptoms and duration
44
Q

What ways can pathogens be detected for certain

A

Culture - gold standard

  • Microscopy
  • Immunofluorescence
  • Colorimetric
  • Nucleic acid extraction/pCR amplification/ sequencing tech.
45
Q

What do you need to look for in a general serological diagnosis

A

at least 4x rise in antibody titre in acute infection or presence of IgM

46
Q

Why do you look for IgM in general serological diagnosis

A

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

47
Q

When is serology particularly useful in diagnosis

A

In viral infections or when it is hard to grow the presumptive bacteria

FHHD (21 decks)

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