Lecture 2: Microbial Pathogenesis

Question 1

Define symbiosis

Answer 1

organisms that live together in close association

Question 2

What are the 4 types of symbiosis and define them

Answer 2

mutualism (beneficial to both symbionts)
neutralism (neither symbiont is affected by relationship)
commensalism (beneficial to only one symbiont)
parasitism (harmful to one symbiont, host, beneficial to the other, parasite)

Question 3

define synergism

Answer 3

two or more microorganisms “team up” to cause disease. AKA polymicribial infection

Question 4

Define a pathogen

Answer 4

microorganism that cases disease

less thazt 3% of microorganisms

Question 5

What is an opportunistic pathogen

Answer 5

microorganism that has the potential to cause disease

carry disease, it can become pathogenic in the right environment

Question 6

What are the main sites of indigenous microflora in humans? give some examples

Answer 6

• bacteria on skin (1 trillion, staph and strep feed of sweat and produce BO)
• oral streptococci (biofilm, strep)
• gut flora (>500 species, make nutrients lie vitamins K and B12, crowd out harmful bacteria)
• vaginal flora (beneficial bacteria, lactic acid against yeast)

Question 7

What is the difference between microbial intoxication and infection disease?

Answer 7

Infectious disease - a pathogen colonises the body and causes the diseases
microbial intoxication - a pathogen produces a toxin in vitro, toxin causes the disease, dont need the bactria itself to cause disease

Question 8

Describe Kochs postulates

Answer 8

1. microoganism must always be found in similariy diseases animmals but not in healthy ones (same symptoms)
2. microorganism must be isolated from a diseases animal and grown in pure culture
3. the isolated microogranism must cause the original disease when inoculated in a susceptibel host
4. the microorganism must be re-isolated from the experimentally infected animals - get same bacteria

Question 9

explain the steps by which microogranisms cause disease

Answer 9

1. entry: “portal of entry”
2. attachment: binding to host tissue (colonisation) –> if they cannot colonise they cannot cause an infection
3. multiplication: at infection site (localised infection) –> proliferation, harder for immune system to get rid of the bacteria
4. invasion or spread (system disease)
5. evasion of host defenses (immune evasion) –> overcome immune responses, become symptomatic
6. damage to host tissue: symptoms, disability, death

Question 10

the the types of virulence mechanisms of microorganisms

Answer 10

1. promote attachment to host cells (adhesins, biofilms)
2. help bacterium enter host cell (invasins)
3. damage host cell or tisse (cytolysins)
4. help bacteria to spread from local infection (spreading factors)
5. over-stimulate immune response (immunopathogenic factors)
6. mediate immune evasion

Question 11

Describe how adhesins work

Answer 11

allow for the attachment to host tissue and thus colonisation

Question 12

Describe how Biofilms work

Answer 12

thick layer of secreted polysaccharides, immune systen has trouble reaching the bacteria in thick biofilm, same thing for antibiotics –> hard to get to bacteria trapped in biofilm

Question 13

Describe how invasins work

Answer 13

bacteria binds to invasin and allows it to enter the cell resulting in intracellular growth, resistance to antibiotics because it cant get to the bacteria and protection from the immune system

Question 14

Describe how cell and tissue destruction works (cytolysins)

Answer 14

destroy cells, results in access to nutrients, immune evasion (destroy WBC) and bacterial spreading

Question 15

Define immune evasion factors

Answer 15

mechanism by which a pathogens can evade the immunoge response of a host’s cells and continue proliferating and causing disease

Question 16

Give examples of immune evasion factors

Answer 16

• capsules (prevent opsonisation and phagocytosis)
• destruction of phagocytes (like macrophages, neutrophils)
• inhibition of phagocyte chemotaxis
• inhibition of pjhagocytosis
• destruction of complement factros
• destruction of immunoglobulins (IgG and igA etc)
• intracellular replication

Question 17

List the sites of microbial infection and shedding

Answer 17

1. mouth to respiratory tract or anus
2. urogenital tract
3. skin/scratch or injury
4. anthropod to capillary