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BMS2052 Microbes in Health and Disease > Bacterial Pathogenesis > Flashcards

Bacterial Pathogenesis Flashcards

1
Q

How does normal flora protect the host from disease?

A

Competing with pathogenic bacteria
Producing compounds that kill other bacteria (e.g. lowering pH)
Keeping balance of other bacteria

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2
Q

What are the functions of normal flora?

A

Protect from disease, aid digestion, produce vitamin (B12 and K), regulate body weight, immunity

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3
Q

What is the normal site of Staphylococcus aureus?

A

Eye conjunctiva

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4
Q

What is the normal site of Streptococcus spp. and Pseudomonas spp.?

A

Outer ear

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5
Q

What are some normal skin flora?

A

Bacillus spp., S. aureus, Propionibacterium acnes, Candida spp.

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6
Q

What are some normal flora of the respiratory tract?

A

Streptococcus spp.

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7
Q

What are opportunistic infections?

A

Infections due to normal flora being out of balance or not in their normal site.

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8
Q

What types of infections are hospital patients are susceptible to? (HAI)?

A

To opportunistic infections

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9
Q

What is the major difference between Salmonella typhi and Salmonella typhimurium in terms of infections?

A

Typhi causes disease in humans but not mice, while typhimurium causes severe disease in mice but not humans.

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10
Q

What are the four Koch’s postulates?

A
  1. Microorganism must be present in all organisms suffering from the disease but not affected organisms
  2. The organism must be isolated from a disease organism and grown in pure culture
  3. The cultured organism should cause the disease when introduced into a healthy organism. The animal should get sick.
  4. The microorganism must be isolated from the inoculated, diseased experiment host and identified as being identical to the original causative agent.
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11
Q

What are the 5 limitations of Koch’s postulates?

A

Host factors are not taken into account
Not all organisms can be cultured
Organisms can loose/gain virulence during lab culture
The organism may not be required to cause the disease if the toxin alone is sufficient
Need a suitable model.

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12
Q

What are the Molecular Koch’s postulates?

A
  1. The virulence gene should be present in all pathogenic strains but not in non-pathogenic strains.
  2. The gene should be expressed in a host.
  3. Inactivation of the gene should lead to a measurable loss in virulence
  4. Reversion of the mutated gene should restore of pathogenicity
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13
Q

What are the 5 steps of pathogenicity?

A 
Entry into the body
Colonisation of host
Evade host defences
Multiply and disseminate
Cause damage to the host
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14
Q

How does the Helicobacter pylori achieve colonisation in such a hostile environment?

A

Cleaves urea in the stomach to produce ammonia and neutralise surrounding environment.

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15
Q

Describe the process of bacterial adhesion through use of pili.

A

The tip of the pilus has the protein pilin, which acts as a receptor for host glycoproteins, glycolipids, collagen or fibronectin. Creates loose adhesion.

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16
Q

What are afimbrial adhesins?

A

Adhesins with no ordered structure.

17
Q

What are capsules?

A

Polymeric network surrounding the bacterial cell membrane, usually made of polysaccharide.

18
Q

What is the function of a capsule?

A

Avoid desiccation, mask antigens, create a sticky surface.

19
Q

What is the difference between invasion and transcytosis?

A

Invasion is entering the target cell while transcytosis is going through a cell to enter the target cell through the basal lamina.

20
Q

What is the trigger mechanism of invasion?

A

Bacteria injects type III secretion systems into the cell to let the bacteria in.

21
Q

What is the zipper mechanism of invasion by bacteria?

A

Bacteria enter the cell through interaction between surface ligand interaction.

22
Q

What are two examples of bacteria that use the trigger mechanism?

A

Salmonella spp, Shigella spp, enteropathogenic (only!) E. coli.

23
Q

What is the shared mechanism of the zipper and tripper mechanisms?

A

Rearrangement of actin, formation of pseudopods and membrane ruffles.

24
Q

How does the enteropathogenic E. coli (T3SS) invade host cells?

A

Injects Tir- receptor for the E. coli.

25
Q

What are two examples of bacteria that use the Zipper mechanism for invasion?

A

Listeria sp. and Yersinia sp.

26
Q

Where are IgG and IgM found in the body?

A

blood and tissue.

27
Q

Where is IgA found in the body?

A

Mucosal surfaces and is most abundant.

28
Q

Describe the structure of IgG, IgA and IgM

A

IgG- monomer
IgA- @ monomers covalently linked by a J chain protein.
IgM- pentamer made of monomers attached in Fc region.

29
Q

What is the complement system?

A

Complex series of proteins that are activated by pathogens to either enhance phagocytosis or form pores in the bacteria by a MAC complex.

30
Q

What are serum sensitive bacteria?

A

Bacteria susceptible to the MAC complex.

31
Q

How can bacteria protect themselves from antibodies and complement factors?

A

Capsulation, production of protein A to find to Fc region of antibody and hide it from macrophages, cleavage of IgA to reduce viscosity of mucus by proteases cleaving J chain.

32
Q

How can bacteria avoid eliciting antibodies?

A

Not producing antigens (bacteria do not use this)
Host mimicry, e.g. Nisseria spp., Campylobacter jejuni- LPS, H. pylori- O antigen. Coat with host antibodies, colonise privileged sites.
Change antigens throughout infection.

33
Q

How can bacteria evade phagocytes?

A

Avoid recognition.
Kill phagocyte/induce apoptosis
inhibit digestion processes in the phagocytes, e.g. prevent fusion of lysosomes (Salmonella).

34
Q

What are some methods of inhibition of phagosome maturation?

A

Block vacuole fusion, escape into membrane, block acidification, block assembly of NADPH oxidase, produce SOD, make acid resistant proteins.

35
Q

How do bacteria acquire iron in a host?

A

Secrete iron-chelators to capture iron
iron-binding membrane proteins
receptors for host iron-binding proteins
express toxins to release host Fe.

BMS2052 Microbes in Health and Disease (2 decks)

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