Bacterial Pathogenesis

Question 1

Define pathogen

Answer 1

a microbe that harms the host/causes disease

Question 2

Define commensal

Answer 2

: a microbe that does not cause harm and that is typically considered part of the normal flora

Question 3

Define Saprophyte

Answer 3

feeds on and decomposes dead organic material

Question 4

Define Infection

Answer 4

the colonisation of host by micro-organisms that have the potential to cause disease (& associated disease?)

Question 5

Define Infectious disease

Answer 5

damage to host by micro-organisms that impair host function

Question 6

Define Pathogenesis

Answer 6

PATHOGENESIS of a disease = the biological mechanism(s) that lead to the diseased state.

Question 7

Define Virulence

Define virulence factors

Answer 7

1. the relative ability of a pathogen to cause disease in the host
2. are mechanisms/products of pathogens that promote their ability to cause infection and disease. considered to be 2 major types: 1) Factors promoting colonisation/invasion of host
   2) Factors causing damage to host

Question 8

Define opportunistic pathogen

Answer 8

can be part of the normal flora BUT may be harmful if they move from one part of the body to another

Question 9

Define strict pathogen

Answer 9

always associated with disease

Question 10

Colonisation and infection?

Answer 10

COLONISATION is not the same as INFECTION

Question 11

BActeria and pathogenesis

Answer 11

1. Few bacteria are ALWAYS pathogenic and this is dependent on the host species
2. Some bacteria are potentially pathogenic e.g. E coli
3. Most bacteria are never pathogenic

Question 12

what 2 major components are considered as part of abcteria pathogenesis

Answer 12

1. The bacterial virulence factors that damage or alter the host cells & tissues e.g. toxins, secretion systems, adhesins
2. The host response: especially including the immune and/or inflammatory response that may lead to damage

Question 13

What are the steps to bacteria pathogensis?

Answer 13

EAICoVID
Eat apples in covid
1. Exposure to pathogen
2. Adhere to skin or mucosa
3. Invasion through epithelium
4. Colonisation and growth. Production of virulence factors
THEN both/ either or:
5. Additional virulence factor interaction with host e.g. toxins
5. Invasiveness = further growth at original and distant sites
6. Tissue damage, disease

Question 14

What are examples of pathogen determinants

Answer 14

Virulence
Environmental stability
Route of entry
Infective dose
Tissue tropism
Susceptibility to host defense

Question 15

Examples of host determinants

Answer 15

Species
Breed
Age
Sex
Genetic factors
Physiological factors
Immune competence

Question 16

Examples of bacterial virulence factors

Answer 16

1. exotoxins
2. Proteases
3. Capsule
4. Pilli
5. Adhesins
6. Flagellum
7. Plasmid
8. Bacteriophage

Question 17

What did Koch’s prostulates help discover?

Answer 17

1. Bacillus anthracis was the first bacterium proven to be the causative (AETIOLOGICAL) agent for a disease, anthrax (Anthrax is a serious infectious disease caused by gram-positive, rod-shaped bacteria known as Bacillus anthracis.)
2. Agents of cholera and tuberculosis

Question 18

list 4 of Koch’s prostulates

Answer 18

1) The microbe should be found in all cases and at all sites of the disease.
2) The microbe should be isolated from the infected persons and maintained in pure culture.
3) The pure cultured microbe should cause symptoms of the disease on inoculation into a susceptible individual.
4) The microbe should be reisolated from the intentionally infected host.

Question 19

Limitations of Koch’s Prostulates

Answer 19

1) Viruses/some bacteria/parasites cannot grow independent of host
2) Asymptomatic carriers
3) Opportunistic pathogens
4) Polymicrobial diseases

Question 20

Describe Falkow’s adaptation of Koch’s postulates for identification of virulence factors

Answer 20

1) Phenotype under investigation should be associated with pathogenic members of a Genus or pathogenic strains of a species.
2) Specific inactivation of genes associated with a suspected virulence trait should lead to a measurable loss in pathogenicity or virulence.
3) Reactivation of the mutated gene should lead to restoration of pathogenicity

Question 21

Colonisation and growth

Answer 21

Pathogen must find relevant environment for growth
Some organisms often remain localised, producing small focus of infection (eg. Boils)
Generalised infections occur due to bacteraemia – pathogen in bloodstream
Some pathogens multiply in blood plasma producing toxic waste products e.g. endotoxin causing – septicaemia

Question 22

What are examples of secreted virulence factors. What do they aid? What do they often break down?

Answer 22

1. AID: secreted extracellular proteins can aid establishment & maintenance of pathogens
2. often break down host tissues:
   EXAMPLES:
   Coagulase- clots plasma, protecting against host defences
   Proteases- degrade protein
   Nucleases- degrade nucleic acids
   Leukocidins- kill leukocytes
   Haemolysins- lyse erythrocytes, causing anaemia & releasing iron for microbial growth

Question 23

What is an exotoxin?

Answer 23

protein released by an organism as it grows that has toxic effects

Question 24

How are exotoxins defined?

Answer 24

1. enterotoxins - intestinal mucosa
2. neurotoxins - nerve tissue
3. cytotoxins - general tissue

Question 25

How do bacteria become pathogenic?

Answer 25

Horizontal gene transfer:

1. Uptake of naked DNA from the environment
2. Direct transfer of plasmid DNA between bacteria
3. DNA transfer mediated by bacteriophages

Question 26

What are plasmids

Answer 26

Circular double-stranded DNA molecules that replicate independently of the chromosome.
2. can carry virulence genes e.g. toxins