Establishment of Infectious Disease: Pathogenicity

Question 1

What are commensals?

Answer 1

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

Question 2

What is the normal flora/human microbiome?

Answer 2

The collective name for all the commensals in the body

Question 3

What are pathogens?

Answer 3

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

Question 4

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

Answer 4

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

Question 5

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

Answer 5

The host will remain healthy

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

Question 6

Under what circumstances does a host become a carrier?

Answer 6

Is the pathogen assumes a benign relationship with the host

Question 7

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

Answer 7

The host loses the competition

An infectious disease develops

Question 8

What types of organisms make up the microbiome?

Answer 8

Mostly bacteria but some fungi

Question 9

How do commensals enter a new born?

Answer 9

Through food or the environment (including other humans)

Question 10

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

Answer 10

Gastrointestinal tract

Oral cavity

Urogenital tract

Skin

Question 11

Name a bacteria found in the GIT

Answer 11

Escherichia coli

Question 12

Name the most common bacteria found in the oral cavity.

Answer 12

Streptococcus mutans

Question 13

Name the most common bacteria found in the urogenital tract.

Answer 13

Lactobacillus sp

Question 14

Name the most common bacteria found on the skin.

Answer 14

S. epidermis

Question 15

Give three symbiotic benefits of the human microbiome.

Answer 15

Competitive inhibition - inhibits other pathogens

Immune system stimulus

Aids digestion

Important nutrients (Vit K)

Question 16

What are the four harmful effects of the human microbiome?

Answer 16

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

Question 17

What do bacteria have that increase their pathogenicity?

3

Answer 17

Cell wall proteins

Extracellular enzymes

Toxins

Question 18

What is virulence?

Answer 18

The degree of pathogenicity of an organism

Question 19

What are the five stages of pathogenesis?

Answer 19

Exposure/entry

Adherence and local invasion

Colonisation

Invasion and growth

Evasion of the host immune defenses

Question 20

In what four places can pathogens enter the body?

Answer 20

Skin that has been penetrated

Respiratory tract (inhalation)

Gastrointestinal tract (ingestion)

Urogenital tract (sexual contact)

Question 21

What is the infective dose?

Answer 21

The number of pathogens required to successfully infect a host

Question 22

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

Answer 22

Shigella (10-100)

Question 23

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

Answer 23

Staphylococcus aureus (10^3 - 10^8)

Question 24

How does a bacteria adhere to a cell?

Answer 24

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

Question 25

Give an example of a bacteria that have fimbriae.

Answer 25

Oral streptococci

Question 26

What are adhesins?

Answer 26

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

Question 27

Give an example of a bacteria that has adhesins.

Answer 27

N. gonorrhoeae

Question 28

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

Answer 28

Capsules - adhere to target cell Biofilm

Question 29

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

Answer 29

E.coli

Question 30

What is colonisation?

Answer 30

The process by which pathogens may multiply in an area

Question 31

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

Answer 31

Siderophores

Question 32

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

Answer 32

Staphylococcus aureus - boil

Question 33

What are invasive bacteria?

Answer 33

Bacteria that can spread from the initial site of infection

Question 34

What facilitates bacterial infection?

Answer 34

Degradative enzymes Toxins

Question 35

How do degradative enzymes work?

Answer 35

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

Question 36

Give some examples of degradative enzymes. | 4

Answer 36

Hyaluronidase Collagenase Coagulase Streptokinase

Question 37

Give an example of a bacteria that produces hyaluronidase.

Answer 37

Staphylococcus aureus

Question 38

How does hyaluronidase work? | 2

Answer 38

It breaks down the hyaluronic acid matrix between the cells This allows bacteria to penetrate into deep layers of the skin

Question 39

Give an example of a bacteria that produces collagenase.

Answer 39

Clostridium perfringens

Question 40

How does collagenase work?

Answer 40

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

Question 41

Give an example of a bacteria that produces coagulase.

Answer 41

Staphylococcus aureus

Question 42

What does coagulase do? | 2

Answer 42

It causes the formation of fibrin clots in the site of infection This provides protection for the organisms

Question 43

What species of bacteria produce streptokinase?

Answer 43

Streptococci

Question 44

What does streptokinase do?

Answer 44

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

Question 45

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

Answer 45

Exotoxins Endotoxins

Question 46

What type of bacteria secrete exotoxins?

Answer 46

Primarily gram-positive bacteria

Question 47

What type of bacteria secrete endotoxins?

Answer 47

Gram negative bacteria (component of their outer membrane)

Question 48

How are exotoxins released?

Answer 48

They are released from pathogens as they grow

Question 49

How many types of exotoxins are there?

Answer 49

Three

Question 50

What are the three types of exotoxins?

Answer 50

Cytolytic AB toxins Superantigen toxins

Question 51

What are cytolytic toxins?

Answer 51

They degrade integrity of cytoplasmic membranes causing cell lysis

Question 52

Give an example of a cytolytic toxin.

Answer 52

Alpha toxin (lecithinase)

Question 53

Name a bacteria that uses alpha toxin (lecithinase).

Answer 53

Clostridium perfringens

Question 54

What are AB toxins? | 3

Answer 54

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

Question 55

Give an example of an AB toxin.

Answer 55

Tetanus toxin

Question 56

What bacteria produces tetanus toxin?

Answer 56

Clostridium tetani

Question 57

What is tetanus toxin?

Answer 57

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

Question 58

What are superantigen toxins? | 2

Answer 58

Toxins that over-stimulate the immune system Cause extensive inflammation and tissue damage

Question 59

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

Answer 59

Streptococcus pyogenes

Question 60

What does streptococcus pyogenes do? | 4

Answer 60

Implicated in streptococcal Toxic-Shock Syndrome Bloodstream infection Necrotising Organ failure + amputation

Question 61

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

Answer 61

Lipid A component

Question 62

How are endotoxins released?

Answer 62

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

Question 63

What does Lipid A do when released? | 6

Answer 63

Fever Shock Hypotension Thrombosis (formation of blood clots) Septic shock Death from organ failure

Question 64

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

Answer 64

Capsules Intracellular pathogens

Question 65

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

Answer 65

Antigenic switching

Question 66

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

Answer 66

They prevent the cells from being phagocytosed

Question 67

Give an example of a bacteria that forms a capsule. | 3

Answer 67

Streptococcus pneumoniae Nesseria meningitidis Encapsulated strains of Haemophilus influenzae type b

Question 68

What are intracellular pathogens?

Answer 68

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

Question 69

Give an example of an intracellular pathogen.

Answer 69

Mycobacterium tuberculosis

Question 70

What is antigenic switching?

Answer 70

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

Question 71

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

Answer 71

Salmonella

Question 72

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

Answer 72

The virulence of the particular organism The immune status of the host being colonized

Question 73

What does it mean to be a compromised host?

Answer 73

One or more defence mechanisms are inactive