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VMS 2009 > The pathogenesis of bacterial infections > Flashcards

The pathogenesis of bacterial infections Flashcards

1
Q

What is pathogenesis?

A

Pathogenesis involves all the cellular events leading to the development of disease

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2
Q

What is the definition of a pathogen?

A

an organism that has the ability to cause disease

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3
Q

What causes peptic-ulcer disease?

A

Stress/Environmental factors

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4
Q

What bacteria causes peptic ulcers?

A

H.Pylori

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5
Q

What are three reasons why infections are not in all hosts in the population?

A
  • Infection depends on host factors as well as bacterial factors
  • Differences in hosts range (wide vs limited)
  • Even among the host range some can be resistant whilst others are susceptible
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6
Q

What is pathogenicity?

A

An ability to cause disease (damage the host)

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7
Q

What is Virulence?

A

The degree of pathology caused by the organism/ infection

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8
Q

What is infectivity?

A

The capacity for transmission and spreading to new hosts

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9
Q

What can effect infectivity?

A
  • Type of pathogen
  • Dosage/ Inoculum
  • Host factors
  • Environmental factors
  • Virulence: Species, Strain
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10
Q

What is transmissibility?

A
  • Capacity to grow in parts of the body
  • Capacity to readily exit an infected host
  • Capacity to survive in transition between hosts
    (sporulation, environment and arthropod-borne infections)
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11
Q

What are the two different sources of infection?

A

Exogenous and Endogenous

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12
Q

What are exogenous sources of infections?

A

Mainly true pathogens

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13
Q

What are endogenous sources of infections?

A

Opportunistic pathogens and persistent true pathogens

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14
Q

What is the first step of a succesful bacteria pathogen?

A

Attachment to and entry into the host body
The movement through fluids is mediated by the flagella

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15
Q

What are the helical structures that extend from the bacteria made up from?

A

They are long helical structures that extend outward from the surface of the cell
composed of polymerisation of flagellin protein
evolutionarily conserved

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16
Q

What are some routes of entry for bacteria?

A

Skin and extended mucosa (direct contact)
Body orifices e.g eye/ear reproductive/urinary tract
Direct injection into the blood stream (arthropod-borne infections)

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17
Q

What is the second step for a succesful bacterial pathogen?

A

Bacterial pathogens often bind to a niche to gain entry into tissue and have to evade host defences

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18
Q

Why can it be a struggle for bacteria to enter into a host cell?

A

Many parts of the body are protected by mucin which acts as a lubricant and also traps bacteria (prevents microbes from gaining access/ binding to the first layer of cells)

mucin= mesh of proteins and polysaccharides

19
Q

What are some strategies bacteria can use to evade host defences?

A
  • molecular mimicry
  • switching off “irritants”
  • hiding inside epithelial/ immune cells
  • prevention of activity immune response
20
Q

What is the third step for a succesful bacteria pathogen?

A

Multiplication and Spread
Once the bacteria have entered/ passed the dermal and mucin layers they can either become an extracellular or intracellular pathogen

21
Q

What is the 4th step in being a succesful bacterial pathogen?

A

Damage to the host and therefore inducing disease

22
Q

What are some of the mechanisms that can be used to induce disease?

A
  • lysis of host cells/tissues via toxins or invasion
  • disruption of the immune system
  • disruption of the barrier function
  • disruption of the local mciroflora
23
Q

What is the fifth step of a succesful bacterial infection

A

Transmission to a new susceptible host

24
Q

What are some ways the immune system can respond after damage through secretion of toxins?

A
  • Creates pus (proteins, dead cells, host cells)
  • Spreading factors, proteins like DNases and proteases facilitate spread into neighbouring tissue
25
Q

What are some common mechanisms of transmission?

A
  • TB- coughing/sneezing
  • Anthrax- air inhalation of spores
  • Contaminated water- E.coli in fecal material
    Vectors: Insects
26
Q

What are four major issues for bacteria in the “outside world”?

A
  1. availability of essential nutrients
  2. lack of adherence sites
  3. exposure to noxious chemicals/ predators
  4. Exposure to sunlight and extreme weather
27
Q

What are some survival mechanisms of bacteria in the ‘outside world’?

A
  • Form endospores
  • “Hibernation”/ changes into metabolism/ slow down or go into the dormant stage
  • Genome plasticity
  • Parasitize another host
  • Form a collective= biofilm
28
Q

What are four different types of colonisation factors?

A
  • Adhesins
  • Bacterial mobility/ Chemotaxis
  • Production of enzymes that breakdown mucin or other host tissues
  • Metabolism
29
Q

What are adhesins?

A

Best mechanism of adhering to host surfaces through specialist attachment proteins known as pilli/ fimbriae

30
Q

How is metabolism a colonisation factor?

A

The ability to use specific nutrients to contribute to succesful colonisation

31
Q

What are four different virulence strategies?

A
  • Colonisation factors
  • Invasiveness
  • Toxigenicity
  • Aggressins
32
Q

How is ‘invasiveness’ a virulence strategy?

A

Several species of pathogenic bacteria are capsulated which assists invasion by neutralising, escaping or withstanding phagocytosis

33
Q

What is an exotoxin?

A

Exotoxins are proteins produced inside pathogenic bacteria
They are then secreted or released into the surrounding medium following lysis

34
Q

What is an endotoxin?

A

The lipid portion of lipopolysaccharides that are part of the outer membrane of the cell wall of gram negative bacteria

35
Q

What are the key points of exotoxins?

A
  • Mainly produced by Gram + positive bacteria
  • They are proteins in nature and a few are enzymes
  • fatal in small doses
  • thermolabile
  • Can cause cytopathic effects
36
Q

What are the key points about endotoxins?

A
  • Often released after natural autolysis or artificial disruption
  • thermostable
  • integral part or the outer layer of the bacterial cell wall
  • Mainly associated with gram-negative bacteria
  • Can cause TSS
37
Q

How do aggressins work?

A

They contribute to the ability of capsulate or non-capsulate bacteria to invade and multiply in the hosts tissues
They then enhance the permeability of tissues and facilitate the spread of bacteria

38
Q

What percentage of peptic ulcers are caused by H.pylori?

A

85-95%

39
Q

What cancer is H.pylori linked with?

A

Gastric cancer

bacterial class I carcinogen

40
Q

What are some of the weaknesses of kochs postulates?

A
  • Not all infections can be isolated
  • Some agents present in both healthy and sick hosts
  • may be no animal model for the experimental infection
  • may be no characteristic lesions
41
Q

What is the difference between exogenous and endogenous pathogens?

A

Endogenous pathogens originate from the hosts own body whereas exogenous pathogens come from outside the hosts body

42
Q

What can only gram positive bacteria do as a survival mechanism?

A

Create endopsores

43
Q

How may some succesful bacteria resist phagocytosis?

A
  • Inhibit opsonisation
  • Kill phagocytes
  • Inhibit fusion of lysosomes
  • escape from phagocytes
  • survive the acid environment

VMS 2009 (45 decks)

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