8 - Microbes as Agents of Infectious Disease

Question 1

Pathogen Definition

Answer 1

A pathogen is an organism or molecule that causes disease

Question 2

Types of pathogens

Answer 2

Bacteria, viruses, fungi, protozoa, worms

Question 3

How do pathogens cause disease (4)

Answer 3

Invade a host
Evade hosts defences
Cause disease
Spread to new hosts

Question 4

Invade host

Answer 4

Adheres to host cells using pili/fimbriae, invades using surface components

Question 5

Evade host defences

Answer 5

Capsules protect against phagocytosis

Question 6

Cause disease

Answer 6

Produces toxins (exotoxins/endotoxins) or triggers damaging immune responses

Question 7

Spread to new host

Answer 7

Through direct (e.g., droplets) or indirect (e.g., contaminated water) transmission

Question 8

Koch’s Postulates

Answer 8

Microbe must be present in all cases of disease

Microbe must be isolated and grown in pure culture

It must cause disease in a healthy host

It must be re-isolated and identical to the original

Question 9

Exceptions to Koch’s Postulates (4)

Answer 9

Asymptomatic carriers (e.g., cholera)

Microbes that can’t be cultured (e.g., Treponema pallidum)

Multi-pathogen diseases

Ethical issues with infecting humans

Question 10

Falkow’s Molecular Postulates

Answer 10

Focus on genetic tools to identify virulence genes

Explain how harmless microbes can become pathogenic when they acquire new genes

Question 11

Transmission Types (2)

Answer 11

Vertical

Horizontal

Question 12

Vertical Transmission

Answer 12

From mother to child (e.g., rubella)

Question 13

Horizontal Transmission

Answer 13

Person-to-person via

Direct Contact: STIs
Airborne: TB
Indirect Contact: Fomites, contaminated food/water
Animal Vectors: Malaria via mosquitoes

Question 14

Control Methods - Infectious Disease (6)

Answer 14

Vaccination
Quarantine
Hygiene and sanitation
Vector control
Safe food and water practices
Surveillance and outbreak tracking

Question 15

Morbidity

Answer 15

The state of being diseased

Question 16

Mortality rate

Answer 16

The frequency of death

Question 17

Prevalence

Answer 17

Proportion of cases in a population at a specific time

Question 18

Incidence

Answer 18

Number of new cases in a given period

Question 19

Endemic

Answer 19

Always present in a population

Question 20

Epidemic

Answer 20

Sudden increase in cases in a population

Question 21

Pandemic

Answer 21

Disease spreading across countries or continents

Question 22

R Number

Answer 22

The average number of people one infected person will spread the disease to

Question 23

Case Study

Answer 23

John Snow’s 1854 cholera outbreak mapping → identified contaminated water as the source

Question 24

What disease is caused by Vibrio cholerae

Answer 24

Cholera

Question 25

How is Vibrio cholerae transmitted

Answer 25

Via contaminated water (faecal-oral route)

Question 26

Key features of Vibrio cholerae infection

Answer 26

Severe diarrhoea and dehydration. Can cause large-scale outbreaks, especially where clean water access is limited

Question 27

What disease is caused by Borrelia burgdorferi

Answer 27

Lyme disease

Question 28

How is Borrelia burgdorferi transmitted

Answer 28

Through tick bites — vector-borne transmission

Question 29

Through tick bites — vector-borne transmission

Answer 29

Causes a rash (often bullseye-shaped), joint inflammation (arthritis), and neurological symptoms Common in woodland or grassy areas

Question 30

What diseases are caused by Helicobacter pylori

Answer 30

Gastritis, peptic ulcers, and stomach cancer

Question 31

How is H. pylori transmitted

Answer 31

Person-to-person, possibly oral-oral or faecal-oral

Question 32

Key features of H. pylori

Answer 32

Barry Marshall proved causation by self-infection Common but often asymptomatic Antibiotic resistance is a growing issue

Question 33

What diseases can be caused by Staphylococcus aureus

Answer 33

Sepsis, pneumonia, toxic shock syndrome

Question 34

How is S. aureus transmitted or acquired

Answer 34

Part of normal skin/respiratory flora; infection occurs when skin/mucosal barriers are breached

Question 35

Key features of S. aureus

Answer 35

Produces Protein A (which binds antibodies to evade immune response), toxins, and enzymes. MRSA strains are resistant to many antibiotics

Question 36

What disease is caused by Neisseria gonorrhoeae

Answer 36

Gonorrhoea

Question 37

How is N. gonorrhoeae transmitted

Answer 37

Sexually transmitted (human-exclusive pathogen)

Question 38

Key features of N. gonorrhoeae

Answer 38

Survives inside neutrophils; causes inflammation and tissue damage. Resistance is rising — some strains are untreatable with standard antibiotics (‘super gonorrhoea’)

Question 39

Antibiotics Definition

Answer 39

Antibiotics kill or inhibit the growth of bacteria

Question 40

Antibiotics Modes of Action (6)

Answer 40

Cell wall synthesis inhibition Protein synthesis inhibition DNA replication inhibition RNA synthesis inhibition Folate metabolism inhibition Cell membrane disruption

Question 41

Cell Wall Synthesis Inhibition

Answer 41

beta-lactams (penicillin)

Question 42

beta-lactams (penicillin)

Answer 42

macrolides (erythromycin)

Question 43

DNA Replication Inhibition:

Answer 43

ciprofloxacin

Question 44

RNA Synthesis Inhibition

Answer 44

rifampin

Question 45

Folate Metabolism Inhibition

Answer 45

sulfonamides

Question 46

Cell Membrane Disruption

Answer 46

polymyxin B

Question 47

What is the difference between bacteriostatic and bactericidal antibiotics

Answer 47

Bacteriostatic: Stops bacterial growth Bactericidal: Kills bacteria

Question 48

Broad-Spectrum

Answer 48

Effective against many types of bacteria

Question 49

Narrow-Spectrum

Answer 49

Targets specific bacteria.

Question 50

Prophylaxis

Answer 50

Prevents infection

Question 51

Metaphylaxis

Answer 51

Treats a group at risk before symptoms appear

Question 52

Empiric Therapy

Answer 52

Given before the pathogen is identified

Question 53

Definitive Therapy

Answer 53

Targeted treatment after identifying the pathogen

Question 54

Why Antibiotic Resistance Develops

Answer 54

Overuse/misuse of antibiotics Poor infection control Use in agriculture Lack of new antibiotics

Question 55

Mechanisms of Resistance (5)

Answer 55

Decreased uptake Effigy’s pumps Enzymatic inactivation Target modification Alternative enzymes

Question 56

Decreased Uptake

Answer 56

Altered bacterial membranes

Question 57

Efflux Pumps

Answer 57

Bacteria pump out antibiotics

Question 58

Enzymatic Inactivation

Answer 58

beta-lactamase breaks down penicillin

Question 59

Target Modification

Answer 59

Changes in antibiotic binding sites

Question 60

Alternative Enzymes

Answer 60

Bypass the inhibited metabolic pathway

Question 61

Horizontal Gene Transfer

Answer 61

Plasmids and phages spread resistance genes

Question 62

Future Approaches to Combat Resistance (4)

Answer 62

Better diagnostics Narrow-spectrum antibiotics Genomic targeting Development of new antimicrobials, vaccines, and immunotherapies