Bacterial infection 1

Question 1

Infection

Answer 1

Microbe is established in a host

May not involve disease or any symptoms
Can lead to disease

Question 2

Nosocomial infections

Answer 2

Acquired in hospital

Question 3

Disease

Answer 3

Infection causes damage or pathology to host

Question 4

Pathogenesis

Answer 4

Sequence of events + mechanisms + processes that cause disease

Question 5

Catheter associated UTI

Answer 5

Often nosocomial

Often asymptomatic + infected unless serious complications arise

Encrustation + blockage issues

Question 6

Latent TB

Answer 6

TB lives but doesn’t grow in body
Asymptomatic
Can’t spread between people
Can advance to TB disease

Question 7

TB disease

Answer 7

Active + grows in body
Symptomatic
Can spread between people
Fatal if untreated

Question 8

Dynamic balance between health + disease

- disease factors

Answer 8

Pathogen exposure
Routes of transmission
Pathogen load
Site of pathogen exposure

Question 9

Dynamic balance between health + disease

- health factors

Answer 9

Immune status 
Nutrition 
Vaccination 
Sanitation 
Injury 
Ageing 
Medical devices

Question 10

Parasite

Answer 10

Org that colonises host + causes harm

Question 11

Primary pathogens

Answer 11

Breach defences + cause disease in a healthy host

Question 12

Opportunistic pathogen

Answer 12

Cause disease in compromised host

Question 13

Pathogenicity

Answer 13

Ability to cause disease

• combines infectivity + virulence

Question 14

Virulence

Answer 14

Measure indicating severity of a disease

e.g. LD50 for lethal pathogens

Question 15

LD50

Answer 15

= Lethal dose 50%

No. of orgs (cells/virions) required to kill 50% of hosts in a test group

Question 16

How do infections begin?

Answer 16

Exposure to a pathogen

Question 17

Route of transmission

Answer 17

1. Exposure
2. Adherence
3. Invasion
4. Infection
   (can lead to further exposure at local sites)
5. Toxicity or Invasiveness (can lead to further exposure)
6. Tissue damage + disease

Question 18

Transmission

Answer 18

Horizontal - indirect or direct
Vertical
Vehicle
Insect vectors

Question 19

Horizontal indirect transmission

Answer 19

Inanimate objects (fomites), vehicle transmission or an insect vector

Question 20

Horizontal direct transmission

Answer 20

By direct contact or aerosolisation e.g. sneeze

Question 21

Vertical transmission

Answer 21

An insect can transmit an infectious agent to its offspring

Question 22

Vehicle transmission

Answer 22

Inanimate objects

- e.g. fomites, food, water, air

Question 23

Virulence factors

Answer 23

Bacterial traits that facilitate infection

e.g. toxins, effector proteins , biofilm formation, adhesion

Question 24

Molecular Koch’s postulates

Answer 24

= set of criteria that must be met to show a gene in a pathogen encodes a product that will contribute to disease

Question 25

Molecular Koch's postulates | - trait should be associated w/ a pathogenic strain

Answer 25

Inactivation of suspected virulence gene -> should lead to measurable loss in virulence Replacement of inactive gene w/ function copy should restore virulence (measure using LD50)

Question 26

After exposure

Answer 26

Pathogen finds site of colonisation | - stays there via attachment mechanisms

Question 27

Innate defences role

Answer 27

Try to exclude + clear bacteria before they can cause disease

Question 28

Innate defences | e.g.s

Answer 28

Mucociliary escalator + microflora All mucosal sites have fluid flow + resident microflora Peristalsis in intestine Stomach acid

Question 29

Adhesion

Answer 29

To avoid clearance mechanisms | - stick to hosts (often mucosal surfaces)

Question 30

Adherence molecules

Answer 30

Pili = specific specialised structures Adhesions = range of proteins + molecules

Question 31

Pili

Answer 31

Repeating subunits assembled on cell surface Proteins at top vary to recognise different host cell receptors Adhesin at tip

Question 32

Pili | - common e.g.s produced by pathogenic bacteria

Answer 32

Type 1 + Type 4 Type 4 can retract - pull bacteria closer to host - twitching motility - disrupt tight junctions between cells

Question 33

Pili | - interactions

Answer 33

Doesn't provide close cell-cell contact

Question 34

Pili | + adhesins

Answer 34

Bind to components present on host cells - via hydrophobic or charge interactions, or receptor-ligand interactions (specific binding)

Question 35

E.coli EPEC - name - virulence factors

Answer 35

= Enteropathogenic E. coli Attaching lesions Pedestal formation

Question 36

Pathovars

Answer 36

Pathogenic strains grouped based on their disease characteristics

Question 37

E.coli EPEC - route of transmission - reservoirs - colonisation

Answer 37

Faecal-oral route of transmission - via contaminated food/surfaces Animals Colonise intestinal tissues facilitated by type 4 pili + systems to promote close contact w/ epithelial cells

Question 38

E.coli pathovars

Answer 38

Virulence capabilities of pathovars largely determined by acquisition of PAIs

Question 39

PAIs

Answer 39

Pathogenicity Islands = clusters of genes that encode for various virulence factors Can be transferred between strains or species

Question 40

Pili affects...

Answer 40

Host range | Sites of infection within hosts

Question 41

EPEC features

Answer 41

35kb PAI = LEE adhere to gut epithelia tissue form micro colonies + attaching lesions LEE encodes Initimin/TIR proteins

Question 42

EPEC adhesion to epithelial cells in intestine

Answer 42

Pili interact w/ N-acteyl-lactosamine- containing receptors on host cells Pili also important for EPEC self-interactions -> micro colonies Retraction of Type 4 pili - > cells closer - > LEE system can work effectively

Question 43

Intimin

Answer 43

OM protein made by EPEC strains BUT no natural receptor in host cells so EPEC produces + injects Tir via T3SS

Question 44

Tir

Answer 44

= Translocated intimin receptor Localises to membrane + provides receptor for Initmin -> pedestal formation triggered