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PA20351 > Determinants of infectious disease I > Flashcards

Determinants of infectious disease I Flashcards

1
Q

What are the key stages (in order) through infection?

A

Colonisation, invasion, proliferation and transmission.

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2
Q

What are the key determinants of infectious disease?

A

Pathogenicity and virulence, transmission, adhesion and colonisation and invasion.

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3
Q

What is pathogenicity?

A

The ability of an organism to cause disease.

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4
Q

What is virulence?

A

The degree of harm caused by a microorganism.

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5
Q

What does virulence depend on?

A

Infectivity, invasiveness and degree of damage.

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6
Q

What are factors that are involved in virulence?

A

Adhesion, invasion, evasion of host defence, obtaining nutrients from the host and toxicity.

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7
Q

What is the infectious dose?

A

ID50 - the dose to infect 50% of hosts.

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8
Q

What is the lethal dose?

A

LD50 - the dose to kill 50% of hosts.

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9
Q

What determines whether an infection leads to a disease or not?

A

Virulence, number of bacteria and host resistance.

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10
Q

How does survival of caterpillars change with different concentrations of MRSA?

A

With increasing concentrations, fewer numbers survive - low concentrations result in very minimal death.

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11
Q

What happens if the immune system is compromised of the caterpillar species upon infection of samonella enterica?

A

The concentration needed for the LD50 is significantly reduced - this shows the immune system plays an important role.

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12
Q

What are the two key types of transmission?

A

Direct - host to host transmission and indirection host to host transmission, which is facilitated by living or inanimate objects.

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13
Q

What are some direct transmission routes?

A

The respiratory route, routes through body contact, faecal-oral route, body fluids and vertical transmission.

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14
Q

What bacteria can travel through the respiratory route?

A

Mycobacterium tuberculosis.

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15
Q

What are the different routes of tramission through body contact?

A

STDs, skin infections e.g. ring worms, warts and through damaged skin.

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16
Q

What bacteria can transmit through damaged skin?

A

Staphylococcus aureus.

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17
Q

What are is involved in the faecal-oral route of transmission?

A

Transmission of faecal matter to the mouth through contact such as indirectly through food or through GIT pathogens.

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18
Q

What is an example of a pathogen that can be transmitted through the faecal-oral route?

A

Salmonella enterica.

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19
Q

What are some diseases that can be transmitted by body fluids?

A

Hepatitis, HIV

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20
Q

What is vertical transmission?

A

Transmission from mother to child - can be prenatal/perinatal/postnatal.

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21
Q

What is germline transmission?

A

Transmission through viral DNA such as certain types of leukemia.

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22
Q

What are vehicles?

A

Animate or inanimate objects involved in indirect transmission.

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23
Q

What are some examples of vehicles?

A

Soil, contaminated water, contaminated food and fomites.

24
Q

What is a bacteria transmitted through water?

A

Vibrio cholerae.

25
Q

What is a bacteria transmitted through fomites?

A

Clostridium difficile.

26
Q

What are fomites?

A

Inanimate objects such as bedding, toys, surgical instruments.

27
Q

What are some vectors for indirect transmission?

A

Warm-blooded animals, rat fleas.

28
Q

What are commensal organisms?

A

When an organism derives food or nutrients from another organism without hurting it.

29
Q

What must bacteria do in order to enter an organ system?

A

Must compete with commensals, evade host defences and obtain nutrients.

30
Q

Why are mucosal surfaces more favourable for entry of bacteria than through the skin?

A

They are warm, moist environments with more nutrients, whereas the skin has an acidic pH.

31
Q

What is the idea of adhesion?

A

In order for the bacteria to colonise, it must adhere to host cells or tissues. It must also be able to survive in the host environment and compete with the natural microbiota.

32
Q

What is adherence to surfaces dependent on?

A

Adhesins.

33
Q

What are the two categories of bacterial adhesins?

A

Proteins and polysaccharides.

34
Q

What are some of the protein adhesins?

A

Fimbrial and afimbrial surface proteins.

35
Q

What are fimbrials?

A

Short hairs on bacteria.

36
Q

What are polysaccharides key in bacterial adhesins?

A

They make up components of capsules - some bacteria make capsules around themselves to help them to adhere to surfaces.

37
Q

What are the bacterial copolymers involved in adhesins?

A

Teichoic/lipoteichoic acid.

38
Q

What is the difference between teichoic/lipoteichoic acids?

A

Teichoic acids are covalently bound to peptidoglycan (wall acids) whereas lipoteichoic acids are bound to the plasma membrane.

39
Q

What do adhesins interact with?

A

Receptors on the cell surface of the host.

40
Q

What kind of interactions can adhesins have?

A

Protein-protein interactions and protein-carbohydrate interactions.

41
Q

What are some of the adhesin receptors that may be found on the host?

A

Membrane proteins, glycolipids, extracellilar matrix proteins (such as collagen and fibronectin).

42
Q

What is a bacteria that frequently causes UTIs?

A

Escherichia coli.

43
Q

How can E.coli cause UTIs?

A

Certain strains are good at binding to the urinary tract via P-pili or type I pili binding to sugar molecules of glycolipids on the epithelial cells lining the tract.

44
Q

What are the two types of invasion pathogens can have?

A

Extracellular invasion and intracellular invasion.

45
Q

What is extracellular invasion?

A

When barriers of tissues are broken down.

46
Q

What is intracellular invasion?

A

Microbes penetrate cells and survive intracellularly.

47
Q

What are the features of extracellular invasion?

A

It allows access to niches in tissue that aid in proliferation and spreading. It is achieved through production of enzymes that attack the extracellular matrix, degrade the carbohydrate-protein complexes between the cells and disrupt the cell surface.

48
Q

What are examples of enzymes involved in extracellular invasion?

A

Hyaluronidase, collagenase, haemolysin and streptokinase.

49
Q

What is hyaluron?

A

An important polymer in the body.

50
Q

What is streptokinase involved in?

A

Digestion of the fibrin clots.

51
Q

What are the features of intracellular invasion?

A

Some pathogens penetrate cells and survive extracellularly. Some are obligate intracellular - needed to survive - whereas others use it as a method of proliferation.

52
Q

What are the ways in which pathogens can intracellularly invade?

A

Phagocytic cells can invade through phagocytosis whereas non-phagocytic cells can invade using systems that induce a phagocytosis-like process.

53
Q

What are the basic steps in phagocytosis?

A

A bacterium binds to the cell membrane, and the phagocyte pushes its cell membrane around the bacterium using the cytoskeleton. A phagosome is created (a large vesicle) which then separates from the cell membrane and moves into the cytoplasm. The phagosome then fuses with lysosomes (forms phagolysosome) that contain digestives enzymes and the bacteria is killed and digested within the vesicle.

54
Q

How can pathogens survive phagocytosis?

A

They can reside in the phagolysosome, reside in the unfused phagosome or destroy or escape from the phagosome and live in the cytosol.

55
Q

How can pathogens invade non-phagocytic cells?

A

Proteins on the bacteria recruit host proteins that induce phagocytosis. The bacteria then injects invasion proteins into the cytosol which causes rearrangement and polymerisation of the cytoskeleton - actin is recruited.

PA20351 (11 decks)

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