Microbiology Week 2

Question 1

What is the purpose of Koch’s postulate?

Answer 1

to identify the organism causing an infectious disease

identifies cause

Question 2

Tenets of Koch’s postulate

Answer 2

1. The organism is found in diseased animal but not healthy
2. The organism can be isolated and grown alone
3. The organism isolated in pure culture causes the same disease when re-inoculated into suspectible animals
4. The organism can be re-isolated

Question 3

Limitations to Koch’s

Answer 3

Some organisms can’t be grown away from host

Some diseases can be caused by multiple organisms

Carrier states

Question 4

What is a carrier state?

Answer 4

some animals/humans can be colonized by a pathogen without developing disease

Question 5

Virulence factors

Answer 5

a factor produced by a pathogen that is important for causing disease

Question 6

Examples of virulence factors

Answer 6

toxins, adhesins, capsules, etc.

Question 7

What determines the type of disease a pathogen causes?

Answer 7

Its virulence factors

Question 8

What is virulence?

Answer 8

the number of organisms it takes to start an infection

the disease producing power of an organism / potency

Question 9

What should happen with inactivation of the virulence gene?

Answer 9

a measurable loss of virulence

Question 10

What should happen when wild-type genes are added to an inactive virulence gene?

Answer 10

should restore virulence

Question 11

Example of virulence factor and pathogen

Answer 11

Cholera toxin is a virulence factor for the bacterium, Vibrio cholerae

Question 12

What 2 things do successful pathogens need to overcome?

Answer 12

the host defense

the normal flora / microorganisms

Question 13

infection vs. intoxication

Answer 13

infection is when we introduce actual microorganisms into our bodies

intoxication is when we eat foods containing the toxins of bacteria

in intoxications, we do not consume the actual pathogen. we consume the virulence factors

Question 14

How does disease actually occur? (2)

Answer 14

damage by directly from pathogen factors or damage from the immune response

Question 15

Steps of the infectious cycle (6)

Answer 15

1. Pathogen enters body
2. Pathogen adherence and colonization
3. Pathogen invasion through epithelium (sometimes)
4. Pathogen evasion of host defenses
5. Cell tissue / damage (toxins or immune)
6. Dissemination of pathogen so it can infect a new host

Question 16

Advantages of intracellular pathogen growth

Answer 16

Nutrients are supplies

the pathogen is initially protected from immune system and some antibiotics

Question 17

Disadvantages of intracellular pathogen growth

Answer 17

Mammalian cells are good at killing invaders

Takes a lot of energy to stay alive intracellularly

Question 18

2 types of intracellular pathogens

Answer 18

Facultative

Obligate

Question 19

What are all viruses?

Answer 19

obligate intracellular pathogens

Question 20

What are most fungi?

Answer 20

Facultative intracellular pathogens

With exception of cryptococcus which is extracellular

Question 21

What are most protozoa ?

Answer 21

facultative intracellular pathogens

Question 22

what is another word for protoza?

Answer 22

parasite

Question 23

What is true of most gram-positive bacteria?

Answer 23

they are extracellular

except for: listeria monocytogenes

Question 24

Vibrio cholerae

Answer 24

extracellular pathogen

Question 25

Colonizers

Answer 25

they are good microorganisms

commonly found in the gut and skin

protect against harmful bacteria

Question 26

Opportunists

Answer 26

organisms normally do not cause harm

at the wrong place and wrong time, can cause disease

Question 27

example of an opportunist

Answer 27

when inserting a catheter through the skin, staph might be able to get into the bloodstream

Question 28

Pathogens

Answer 28

organisms that are always harmful to us

Question 29

Do you italicize viruses?

Answer 29

No

Question 30

PCR

Answer 30

primer recognition of known viral or bacterial genetic sequences

Question 31

If a differential diagnosis is infectious, what is the next step to identify?

Answer 31

bacterial, viral, fungal or parasitic

Question 32

When should you collect a specimen?

Answer 32

ideally before starting antimicrobials

Question 33

What can cause a false positive when examining microorganisms?

Answer 33

not taking into account the resident microflora

Question 34

What can cause a false negative when examining microorganisms?

Answer 34

prior antimicrobial use

Question 35

How do viruses and prions violate Koch’s postulate?

Answer 35

they cannot be cultured on cell-free media

Question 36

qualitative culture

Answer 36

use for sterile body sites (CSF and blood)

false positives from contamination are common

Question 37

semi-qualitative culture

Answer 37

helps decide whether the isolated organisms is colonizing or contaminating only

helps to decide if the organism is the cause

Question 38

Words for infection of bloodstream

Answer 38

Bacteremia or fungemia

Question 39

What is a common problem with blood cultures?

Answer 39

improperly collected cultures can be contaminated by organisms from the skin’s microbiome

Question 40

How should blood cultures be collected?

Answer 40

2 sets from 2 different sites

Question 41

How can you help rule out contamination from the GI tract in urine samples?

Answer 41

absence of epithelial cells (their prescence would indicate contimination)

prescence of white blood cells (indicates infection)

high concentration of organisms

only one kind of bacteria

Question 42

What can CSF help diagnosis?

Answer 42

meningitis

since CSF bathes the meninges

Question 43

Meninges

Answer 43

3 layers that surround the CNS

Question 44

Sputum

Answer 44

a substance spat out from the lower airways (different than saliva)

Question 45

What can stool help identify?

Answer 45

parasites infecting the gut / gastroenteritis