Microbial infection

Question 1

What does the innate immune system consist of

Answer 1

notmal microbiota
physicals barriers
chemical barriers
phagocytic cells

Question 2

How do normal microbiota contribute to the immune response

Answer 2

• offer competition when pathogens are looking for colonisation sites
• produce antibiotic substances which suppress growth of competing organisms (bacteriocins)
• may produce toxic metabolic products to inhibit other microorganisms
• may alter pH (lactobacilli)

Question 3

Physical barriers

Answer 3

skin:
-secrets sebum and fatty acids to inhibit growth
mucomuciliary clearance
-particles settle on sticky mucus of respiratory epithelium
-debris transported by cilia to oropharynx where its swallowed
Flushing:
-urinary tract
peristalsis:
-GI

Question 4

Chemical barriers

Answer 4

-Mucus
-Antimicrobial proteins
lysosome
lactoferrin (antioxidant)
defensins (defence peptides)
-gastric acid
-plasma proteins
complement
CRP
MBL
Transferrin

Question 5

Phagocytic cells

Answer 5

Process by which the body destroys dead or foreign cells

Question 6

Describe the infection process

Answer 6

An infection occurs when a microorganism causes ill health
2 ways:
-invading host tissues
-exerting effects from mucosal surfaces

Question 7

commensal

Answer 7

microorganism which forms part of the normal host microbiota

Question 8

pathogenicity

Answer 8

the capacity to cause disease

Question 9

virulence

Answer 9

the measure of capacity to cause disease

Question 10

obligate pathogen

Answer 10

almost always associated with disease e.g. HIV

Question 11

Conditional pathogen

Answer 11

may cause disease if certain conditions are met e.g. bactericides fragilis, Straphylococcus aures

Question 12

opportunistic pathogen

Answer 12

usually only infects immunocompromised host

phneumocystis jiroveci

Question 13

What are the steps of infection

Answer 13

• recognition
• attachment and entry
• multiplication
• evasion of host defences
• shedding
• damage

Question 14

What are the four methods of establishing infection

Answer 14

1. specific attachment and penetration mechanisms of host body surface
2. introduced via biting arthropods
3. skin wounds or animal bites
4. only able to infect when host defences are impaired

Question 15

What is tissue tropism

Answer 15

affinity for a specific tissue (supports growth of a particular microbe)
influencing factors:
pH
Temperature 
physical barriers
transcription factors 
presence of cell receptors

Question 16

common examples

Answer 16

Helicobacter pylori = gastric mucosa
chicken pox = nerve cells
rhino virus = upper respiratory tract

Question 17

virulence factors

Answer 17

-toxin secretion (toxigenesis) bacteria and fungi
-antibiotic resistance
-pilus formation
-capsule
iron transport systems
-adhesion factors
-enzymes (proteases, DNAses, lipases)

Question 18

what are bacterial endotoxins

Answer 18

low toxicity
part of cell wall of gram negative bacteria
lipopolysacchride
low specificity

Question 19

what are bacterial exotoxins

Answer 19

highly toxic
secreted from bacterial cells
produced by both gram positive and negative bacteria
can be converted into toxoids for vaccine use
tetanus toxin, cholera toxin etc.

Question 20

Tell me about antibiotic resistance

Answer 20

genees on plasmids 
production of enzymes (β-lactamase)
impermeability
efflux mechanisms (move stuff out of cells)
alteration of target site
- HIV
- MALARIA 
- TB
- MRSA
- VRSA

Question 21

What three factors does transmission depend upon

Answer 21

• the number of microorganisms shed
• the number of microorganisms required to infection a fresh host (its efficiency)
• the microorganisms stability in the environment

Question 22

Zoonoses vectors

Answer 22

invertebrate
-arthropods(malaria, yellow fever) and shellfish (Hep A, cholera)
vertebrate
-mammals (rabies, tapeworm) and birds (salmonella)