Bacterial pathogenesis

Question 1

What are generally harmless bacteria found naturally in the environment called?

Answer 1

• commensals

Question 2

What is the definition of pathogenicity?

Answer 2

• the ability of an infectious agent to cause disease

Question 3

What is the definition of virulence?

Answer 3

• the measure of ability to cause disease

Question 4

What is the definition of pathogenesis?

Answer 4

• the process of disease progression

Question 5

What is a commensal?

Answer 5

• a microorganism which naturally resides harmlessly on the body
• in balance with the body’s immune defences

Question 6

What is another word for microflora?

Answer 6

• microbiome

Question 7

What is an opportunistic pathogen?

Answer 7

• a pathogen only capable of causing disease when allowed to do so through particular circumstances of the host

Question 8

What is a nosocomial infection?

Answer 8

• healthcare associated infection
• acquired in a place of health care caused by you or the circumstances in which you are working

Question 9

What are the 5 steps to pathogenicity?

Answer 9

1. gain access to the host
2. bacterial adhesion
3. acquisition of nutrients
4. evading host defences
5. damage to the host

Question 10

If we can block these 5 steps what can we prevent?

Answer 10

• severe disease

Question 11

When is harm acquired to the animals during the 5 steps?

Answer 11

• while bacteria is trying to gain access to nutrients

Question 12

How are endogenous infections caused?

Answer 12

• caused by commensal bacteria becoming opportunistic pathogens

Question 13

What are examples of bacteria in endogenous infections?

Answer 13

• E.coli
• Bordetella bronchiseptica

Question 14

How are exogenous infections acquired?

Answer 14

• infections are acquired from an external source:
  . Environment = clostridium tetani
  . Animal source = streptococcus equi

Question 15

How can harmless bacteria be removed from the site of infection?

Answer 15

• can be easily removed from the site of infections by the flushing action of body’s fluids and the muco-ciliary escalator

Question 16

Why a pathogens harder to removed from the body?

Answer 16

• as they can stay attached

Question 17

What can bacteria use as an adhesion factor to stay attached and increase their SA?

Answer 17

• fimbriae

Question 18

How can E.coli persist to cause a UTI?

Answer 18

• P-fimbriae cause adherence to the uroepithelium and so E.coli can resist flushing action of urine

Question 19

Fimbriae can should species specificity - what does E.coli expressing K88 fimbriae have a specificity for?

Answer 19

• calf gastrointestinal epithelium (mucosal surface)

Question 20

How can Bordetella bronchiseptica (kennel cough) avoid removal by the mucociliary escalator?

Answer 20

• they have filamentous haemagglutinin which causes adherence to canine ciliated tracheal epithelium

Question 21

How can fimbriae play a role in dichelobacter nodoses (ovine footrot)

Answer 21

• fimbriae cause adherence of D nodosus to keratinised tissues in the hoof of sheep, leading to footrot
• if fimbriae are removed there is no disease

Question 22

What does initial bacterial survival in the body depend on?

Answer 22

• depends in multiplication of the organism inside the host tissues, when key nutrients may be severely restricted

Question 23

What nutrients are ready available in the body for bacteria?

Answer 23

• amnio acids and sugars

Question 24

What properties are needed for bacteria to survive?

Answer 24

• iron acquisitional properties are needed

Question 25

Where can iron be acquired from?

Answer 25

- haemoglobin - transferrin - lactoferrin

Question 26

Why do non-pathogens fail to grow in vivo?

Answer 26

- as they are starved of iron

Question 27

What is hemochromatosis?

Answer 27

- a condition were there is a lot of free iron in the blood

Question 28

How can iron be collected from sources in the body?

Answer 28

- it can be scavenged or harvested - siderophores = iron carriers - transferrin-binding proteins

Question 29

What do neutrophils do to non-pathogenic bacteria?

Answer 29

- easily phagocytose non-pathogenic bacteria through surface phagocytosis

Question 30

How can pathogens evade host defences?

Answer 30

- evade phagocytosis - resisting complement and lysozyme - hiding from defences

Question 31

How can pathogens avoid phagocytosis?

Answer 31

- may pathogens produce a capsule or LPS - phagocytosis avoided by this hydrophilic surface

Question 32

What does the complement system use? What can it enhance?

Answer 32

- opsonisation with C3b - can be enhance uptake by neutrophils

Question 33

How can pathogens prevent being opsonised?

Answer 33

- some pathogens produce a capsule or LPS that is non-stabilising for complement

Question 34

In response to a evading pathogen the body makes Ab what does this activate?

Answer 34

- classical pathways complement activation - Ab-mediated opsonophagocytosis

Question 35

How can some bacteria avoid provoking Ab production?

Answer 35

- through molecular mimicry (look like host cells so wont be recognised as a threat) - Ab is not produced and so the bacteria are not cleared

Question 36

What is the K1 antigen of E.coli used in mimicry?

Answer 36

- sialic acid

Question 37

What is used for mimicry of B-haemolytic streptococci?

Answer 37

- hyaluronic acid capsule

Question 38

What is the K5 antigen of E.coli used in mimicry?

Answer 38

- desulfoheparin

Question 39

Ab-mediated opsonophagocytosis is also avoided by the use of other bacterial components - what are these?

Answer 39

- Protein A - leucocidins - antichemotaxins - M-protein

Question 40

What are 2 examples of obligate intracellular pathogens?

Answer 40

- chlamydia - lawsonia

Question 41

What are some examples of facultative intracellular pathogens?

Answer 41

- brucella abortus - mycobacterium bovis - salmonella enterica

Question 42

What are facultative intracellular pathogens?

Answer 42

- they can survive outside but like to be in phagocytes

Question 43

What are the three main mechanisms of surviving and growing inside host cells?

Answer 43

1. inhibit phagosome/lysosome fusion 2. lyse phagosome membrane and escape into the cytoplasm 3. resist killing by lysosomal killing mechanisms

Question 44

How can bacteria damage the host?

Answer 44

- bacterial toxins - immune-mediated injury

Question 45

What are the two types of bacterial toxins?

Answer 45

- exotoxin - endotoxin

Question 46

What are exotoxins produced by?

Answer 46

- produced by gram-positive and gram-negative bacteria

Question 47

Where are exotoxins produced?

Answer 47

- produced by bacterial cell and pushed out into the host

Question 48

What do gram positive bacteria produce?

Answer 48

- enzymes that digest their surroundings such as . phospholipase . protease . collagenase . hyaluronidase

Question 49

What is an example of an endotoxin from gram-negative bacteria?

Answer 49

- lipopolysaccharide lipid A from the outer membrane of gram negative bacteria which is released when they die

Question 50

What does LPS stimulate in endotoxic shock?

Answer 50

- stimulates a massive innate immune response and cytokine storm - activates clotting cascade - induces fever - systemic vasodilation - catastrophic fall in BP - death

Question 51

What happens during immune-mediated injury?

Answer 51

- immunopathological tissue destruction

Question 52

How does immunopathological tissue destruction occur during immune-mediated injury?

Answer 52

- cytokine damage occurs as the body response to infection and tries to rid itself of foreign invading organisms

Question 53

How can bacteria from commensals enter the body to become opportunistic?

Answer 53

- skin/ears - conjunctiva - naso-oropharynx - biliary duct - urinary tract - repro tract - GIT

Question 54

Why is pathogenesis of bacteria important in animal welfare and health?

Answer 54

- contributes to prevention of disease though treatment and vaccination

Question 55

What is pathogenesis of bacteria important in public health?

Answer 55

- zoonotic infection - allows prevention and treatment of important human disease

Question 56

Is pathogenies of bacteria important in ecosystem health?

Answer 56

- no immediate significance of microbial pathogenicity in ecosystem health