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1. Microbiology > Establishment of Infectious Disease: Pathogenicity > Flashcards

Establishment of Infectious Disease: Pathogenicity Flashcards

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Biology 101 flashcards
1
Q

What are commensals?

A

Non-pathogenic organisms that grow on the skin and in the mucous membrane

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2
Q

What is the normal flora/human microbiome?

A

The collective name for all the commensals in the body

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3
Q

What are pathogens?

A

Anything that tried to invade the human body by direct or indirect means

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4
Q

What does the outcome of the host-pathogen relationship depend on?

A

It depends on the pathogenicity of the pathogen and the resistance of the host

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5
Q

What will happen if a pathogen attacks a host with a strong resistance?
(2)

A

The host will remain healthy

The pathogen is either eliminated or assumes a benign relationship with the host (host = carrier)

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6
Q

Under what circumstances does a host become a carrier?

A

Is the pathogen assumes a benign relationship with the host

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7
Q

What will happen if a pathogen attacks a host with a weak resistance?
(2)

A

The host loses the competition

An infectious disease develops

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8
Q

What types of organisms make up the microbiome?

A

Mostly bacteria but some fungi

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9
Q

How do commensals enter a new born?

A

Through food or the environment (including other humans)

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10
Q

What four environments on the human body are the most densely populated with microorganisms?

A

Gastrointestinal tract

Oral cavity

Urogenital tract

Skin

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11
Q

Name a bacteria found in the GIT

A

Escherichia coli

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12
Q

Name the most common bacteria found in the oral cavity.

A

Streptococcus mutans

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13
Q

Name the most common bacteria found in the urogenital tract.

A

Lactobacillus sp

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14
Q

Name the most common bacteria found on the skin.

A

S. epidermis

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15
Q

Give three symbiotic benefits of the human microbiome.

A

Competitive inhibition - inhibits other pathogens

Immune system stimulus

Aids digestion

Important nutrients (Vit K)

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16
Q

What are the four harmful effects of the human microbiome?

A

Dysbiosis (disturbance) of gut microbiome may cause diseases such as coeliac disease

Displaced microbiome can cause blood stream infections - skin flora in bloodstream

Diminished microbiome - e.g. after antibiotics - pathogens such as Candida albicans can become established

Overgrowth - establishes infection when host becomes compromised

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17
Q

What do bacteria have that increase their pathogenicity?

3

A

Cell wall proteins

Extracellular enzymes

Toxins

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18
Q

What is virulence?

A

The degree of pathogenicity of an organism

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19
Q

What are the five stages of pathogenesis?

A

Exposure/entry

Adherence and local invasion

Colonisation

Invasion and growth

Evasion of the host immune defenses

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20
Q

In what four places can pathogens enter the body?

A

Skin that has been penetrated

Respiratory tract (inhalation)

Gastrointestinal tract (ingestion)

Urogenital tract (sexual contact)

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21
Q

What is the infective dose?

A

The number of pathogens required to successfully infect a host

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22
Q

Give an example of a bacteria that has a very low infective dose.

A

Shigella (10-100)

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23
Q

Give an example of a bacteria with a very high infective dose.

A

Staphylococcus aureus (10^3 - 10^8)

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24
Q

How does a bacteria adhere to a cell?

A

They deploy specific adherence mechanisms such as fimbriae/pili or adhesins

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25
Q

Give an example of a bacteria that have fimbriae.

A

Oral streptococci

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26
Q

What are adhesins?

A

Surface proteins that bind to specific receptors on the surface of host cells

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27
Q

Give an example of a bacteria that has adhesins.

A

N. gonorrhoeae

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28
Q

Other than pili or adhesins, how can bacteria stay close to target cells.

A

Capsules - adhere to target cell

Biofilm

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29
Q

Give an example of a bacteria that attaches using a capsule.

A

E.coli

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30
Q

What is colonisation?

A

The process by which pathogens may multiply in an area

31
Q

What can be produced by some bacteria to help them obtain iron?

A

Siderophores

32
Q

Give an example of a bacteria that stays localised after colonisation.

A

Staphylococcus aureus - boil

33
Q

What are invasive bacteria?

A

Bacteria that can spread from the initial site of infection

34
Q

What facilitates bacterial infection?

A

Degradative enzymes

Toxins

35
Q

How do degradative enzymes work?

A

They degrade components of the extracellular matrix providing bacteria with easier access to the host cell surfaces

36
Q

Give some examples of degradative enzymes.

4

A

Hyaluronidase

Collagenase

Coagulase

Streptokinase

37
Q

Give an example of a bacteria that produces hyaluronidase.

A

Staphylococcus aureus

38
Q

How does hyaluronidase work?

2

A

It breaks down the hyaluronic acid matrix between the cells

This allows bacteria to penetrate into deep layers of the skin

39
Q

Give an example of a bacteria that produces collagenase.

A

Clostridium perfringens

40
Q

How does collagenase work?

A

It breaks down tissue collagen network enabling bacterial spread through the body

41
Q

Give an example of a bacteria that produces coagulase.

A

Staphylococcus aureus

42
Q

What does coagulase do?

2

A

It causes the formation of fibrin clots in the site of infection

This provides protection for the organisms

43
Q

What species of bacteria produce streptokinase?

A

Streptococci

44
Q

What does streptokinase do?

A

It dissolves fibrin clots used by the body to restrict an infected area

45
Q

What are the two main types of toxins that can be produced by bacteria?

A

Exotoxins

Endotoxins

46
Q

What type of bacteria secrete exotoxins?

A

Primarily gram-positive bacteria

47
Q

What type of bacteria secrete endotoxins?

A

Gram negative bacteria (component of their outer membrane)

48
Q

How are exotoxins released?

A

They are released from pathogens as they grow

49
Q

How many types of exotoxins are there?

A

Three

50
Q

What are the three types of exotoxins?

A

Cytolytic

AB toxins

Superantigen toxins

51
Q

What are cytolytic toxins?

A

They degrade integrity of cytoplasmic membranes causing cell lysis

52
Q

Give an example of a cytolytic toxin.

A

Alpha toxin (lecithinase)

53
Q

Name a bacteria that uses alpha toxin (lecithinase).

A

Clostridium perfringens

54
Q

What are AB toxins?

3

A

Toxins that consists of two sub-units, A and B

B is responsible for the binding of the toxin to the host cell

A is responsible for the toxic affect

55
Q

Give an example of an AB toxin.

A

Tetanus toxin

56
Q

What bacteria produces tetanus toxin?

A

Clostridium tetani

57
Q

What is tetanus toxin?

A

A neurotoxin that blocks the release of neuro-transmitters involved in muscle control - results in twitching paralysis and affected muscles are constantly contracted

58
Q

What are superantigen toxins?

2

A

Toxins that over-stimulate the immune system

Cause extensive inflammation and tissue damage

59
Q

Give an example of a bacteria that produced a superantigen toxin.

A

Streptococcus pyogenes

60
Q

What does streptococcus pyogenes do?

4

A

Implicated in streptococcal Toxic-Shock Syndrome

Bloodstream infection

Necrotising

Organ failure + amputation

61
Q

What part of the lipo-polysaccharide (LPS) is the endotoxin?

A

Lipid A component

62
Q

How are endotoxins released?

A

They are released in large amounts into the host following bacterial cell lysis

63
Q

What does Lipid A do when released?

6

A

Fever

Shock

Hypotension

Thrombosis (formation of blood clots)

Septic shock

Death from organ failure

64
Q

What mechanisms do bacteria use to evade the innate immune system?
(2)

A

Capsules

Intracellular pathogens

65
Q

What mechanism do bacteria use to avoid the adaptive immune system?

A

Antigenic switching

66
Q

How do capsules help bacterial cells avoid the innate immune system?

A

They prevent the cells from being phagocytosed

67
Q

Give an example of a bacteria that forms a capsule.

3

A

Streptococcus pneumoniae

Nesseria meningitidis

Encapsulated strains of Haemophilus influenzae type b

68
Q

What are intracellular pathogens?

A

Bacteria that can resist killing and survive or multiply inside of phagocytes or other cells

69
Q

Give an example of an intracellular pathogen.

A

Mycobacterium tuberculosis

70
Q

What is antigenic switching?

A

This is where pathogens can periodically change their surface antigens to prevent host antibody-mediated activity

This can be used to change their surface proteins

This will prevent antibodies already made from fitting anymore

71
Q

Give an example of a bacteria that can undergo antigenic switching.

A

Salmonella

72
Q

What does the outcome of a host microbe interaction depend on?

A

The virulence of the particular organism

The immune status of the host being colonized

73
Q

What does it mean to be a compromised host?

A

One or more defence mechanisms are inactive

1. Microbiology (12 decks)

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