Microbiology Lecture 6

Question 1

Define commenalism.

Answer 1

Host has no benefit, microbe benefits.

Question 2

Define muutalism.

Answer 2

Both benefit.

Question 3

Define neutralism.

Answer 3

Neither are benefited nor harmed.

Question 4

What type of interaction do our normal flora have with us?

Answer 4

Commensalism.

Question 5

Are all our floral bacteria commenals?

Answer 5

Not entirely, E. coli provides benefits by providing B vitamins, competition, and taking up attachment sites.

Question 6

Describe the morphology of staphylcoccus epidermidis, where it grows, what it feeds on, and its effect on us.

Answer 6

Gram positive, round in clusters.
Grows on the skin surface, feeding on sebum.
No harm to humans.

Question 7

Describe the morphology of staphylcoccus aureus, where it grows, what it feeds on, and its effect on us.

Answer 7

Like epidermidis, but lives in moist skin.

It can invade through broken skin, and is an opportunistic commensal.

Question 8

What does golden staph typically refer to?

Answer 8

Staphylococcus aureus, but usually the antibiotic resistant form.

Question 9

What effect does contact with broken skin have on staphylococcus aureus?

Answer 9

Activates genes encouraging tissue spread and toxin production.

Question 10

Which gram type bacteria does better on dry surfaces like skin? Why is this so?

Answer 10

Gram positive, as they have a thicker cell wall, and more adapted to desiccation.
Gram negative can still grow in dry conditions, just better when moist.

Question 11

Name 4 bacteria that grow at the conjunctiva of the eye.

Answer 11

Staphylococcus epidermidis
Staphylococcus aureus
Propionibacterium
Diphtheroids

Question 12

Name 2 bacteria that grow within the nose and throat.

Answer 12

Staphylococcus epidermidis

Staphylococcus aureus

Question 13

Name 2 bacteria that grow within the mouth. How do these populations grow?

Answer 13

Streptococcus
Anaerobes
Streptococcus grows in a layer at night when there is no salivary movement, and dries out. Underneath the layer becomes anoxic, encouraging anaerobe growth.

Question 14

Name 4 bacteria that grow within the large intestines.

Answer 14

E. coli
Bacteroides (anaerobes)
Lactobacillus
Enterococcus

Question 15

What is the bacterial population of the urogenital tract like?

Answer 15

Lower urethra has a resident bacterial population.

The bladder is sterile. Infection caused when resident population reaches it.

Question 16

Name 3 instances of mutualism.

Answer 16

Rumen and cellulose digesting bacteria
Legumes and rhizobacteria
Lichen

Question 17

Define the effect of competition.

Answer 17

Harmful to both parties.

Question 18

Define amensalism

Answer 18

No effect on host, negative on bacteria.

Question 19

Define parasitism.

Answer 19

Negativ effect on host, positive to bacteria.

Question 20

What is the harm of staphylcoccus epidermidis? What about another bacteria similar to it?

Answer 20

When it grows on plastics to form a biofilm. Aureus also does this.

Question 21

Does pseudomonas aeruginosa do well in low moisture? Does it grow on plastic?

Answer 21

No, does very well in high moisture. Grows on plastic.

Question 22

How is pathogenicity measured?

Answer 22

By virulence

Question 23

Define infection.

Define disease.

Answer 23

Infection - microbe is growing in a host, with or without host damage.
Disease - damage that impairs host function.

Question 24

What are two ways microbes cause disease?

Answer 24

Invasion

Toxin production

Question 25

Define the incubation period.

Answer 25

The beginning of infection - no signs or symptoms

Question 26

Define the prodromal period.

Answer 26

Mild signs and symptoms.

Question 27

Define the illness period.

Answer 27

Most severe signs and symptoms - microbe numbers peak.

Question 28

Define the decline period.

Answer 28

Signs and symptoms begin to disappear. This period begins as the peak number of microbes begins to decrease.

Question 29

Define the convalescence period.

Answer 29

Period of recovery. May continue to be a source of infection however.

Question 30

Define direct contact transmission.

Answer 30

Direct contact with the microbial population.

Question 31

Define indirect contact transmission.

Answer 31

The microbial population is spread to a secondary surface first.

Question 32

Define droplet transmission.

Answer 32

Aerosolisation - sneezing

Question 33

Define vehicle transmission.

Answer 33

Foodborne, airborne, waterborne etc.

Question 34

Name an airborne bacteria.

Answer 34

Legionella - causing legionnaires disease.

Question 35

Name 3 disease vectors.

Answer 35

Fleas, mosquitoes, ticks.

Question 36

Define koch’s postulates (3).

Answer 36

• Microorganism must be isolated from the host, grown in pure culture, and identified.
• Isolated organism is injected into a healthy host to cause the same disease.
• Same bacteria must be isolated from the new host, cultured, and identified as the same organism.

Question 37

What are kochs postulates used for? Can they always be used?

Answer 37

To define the causative organism of a disease. No, when the organism cannot be cultured in the lab or when they grow as a co-culture.

Question 38

When cant kochs postulates be used (3)?

Answer 38

When the organism cannot be cultured, or if it requires a co-culture (viruses in a host cell), or when the disease requires more than one organism to be present.

Question 39

Define kochs molecular postulates (6).

Answer 39

• Causative organism is identified by analysing genes.
• Trait should be more associated with pathogens than non-pathogens.
• Gene inactivation should reduce virulence.
• Replacement with a wild-type gene should restore virulence.
• Gene should be expressed at some point in the disease.
• Antibodies directed against the gene products should confer host protection.