Bacterial human infectious diseases

Question 1

What is a commensal?

Answer 1

organism that benefits from interaction with host
-host neither benefitted or harmed

Question 1

What is a pathogen?

Answer 1

Organism which causes harm by its actions

Question 2

What is an opportunistic pathogen?

Answer 2

organism that causes disease in host under the right set of circumstances
-in other circumstances, is a commensal
-require additional factor to compromise normal host defence, eg. barrier breach, immunocompromisation, etc

eg. C.difficile (colonises when large intestine has inflammation)

Question 3

What is a zoonotic pathogen?

Answer 3

organism with an animal reservoir that can be transmitted to and cause disease in humans
-in its reservoir it could be a commensal or a pathogen

Question 4

How do bacteria colonise hosts?

Answer 4

using virulence factors
-adhesins (adhere to host)
-invasins (penetrate tissues)
-nutrient acquisistion
-motility
-chemotaxis (sensing)

Question 5

How do bacteria cause damage?

Answer 5

using virulence factors
-exo and endo -toxins
-proteases (degrade prots)
-DNase (break down DNA)
-lipase (dissolve membranes)
-haemolysins (make pores in cell membranes to steal contents)

Question 6

What are Koch’s postulates?

Answer 6

-microorganism abundant in organisms with disease and not in those without
-microorganism isolated and grown in pure culture
-cultured microorganism can cause disease when introduced to healthy individual
-microorganism re-isolated from this host and still identical to before

Question 7

When do Koch’s postulates not work?

Answer 7

-pathogen secretes something that causes disease, so does not need to be present for disease to occur (eg. botulinum prods toxins)
-organism can’t be grown in pure culture
-lab growth causes loss of virulence
-no available model organisms

Question 8

What are strict pathogens?

Answer 8

pathogens that require pathogenesis to live inside host (ie. only way to survive in host, unlike opportunists)
-limited survival outside of host (can’t grow outside host)
-v. adapted to host, oft unique niche with little competition
-small genomes
-generally transmit easily between hosts

eg. Heliobacter pylori

Question 9

What are facultative pathogens?

Answer 9

pathogens adapted to multiple lifestyles
-equally adapted for environmental niches and causing disease
-large genomes
-most pathogens

eg. E.coli -lives in gut, causes infections in UT

Question 10

How does strain variation affect pathogenicity?

Answer 10

not all strains of pathogen will be equally pathogenic

eg. most E.coli strains are harmless commensals, some have virulence factors so cause disease in humans