Microbiology Lecture 8

Question 1

Define sterilisation.

Answer 1

Kills all viable organisms including endospores

Question 2

Define disinfection.

Answer 2

Kills all vegetative organisms, but not endospores

Question 3

Does everything need to be sterilised?

Answer 3

No, items like cutlery, thermometers, plates etc

Question 4

Why arent thermometers sterilised?

Answer 4

Doesnt penetrate the body, just mouth. Swallowed endospores typically not a problem.

Question 5

What does an antiseptic chemical do?

Answer 5

Kills or inhibits microbial growth, but nontoxic enough to be used on living tissue.

Question 6

What is the difference between an antiseptic and disinfectant?

Answer 6

Antiseptic is non-toxic.

Question 7

What affects sterilisation/disinfection efficacy? How is this prevented?

Answer 7

Affected by presence of fat/protein on the item. Important to preclean beforehand.

Question 8

How do biofilms affect disinfection/sterilisation?

Answer 8

Less penetration of chemicals

Question 9

Order the following from most resistant to least resistant.
Lipid/medium viruses
Mycobacteria
Non-lipid/small viruses
Vegetative bacteria
Fungi
Bacterial spores

Answer 9

Bacterial spores
Mycobacteria
Nonlipid/small viruses
Fungi
Lipid/medium viruses
Vegetative bacteria

Question 10

Are hypochlorites effective when dilute or concentrated? What are they particularly effective against?

Answer 10

Must be diluted to be effective (1/10 dilution needed).

Excellent against viruses

Question 11

What are hypochlorites inactivated by? How can this be a problem during cleanup?

Answer 11

Organic matter. ie. a blood spill must be visibly removed first before disinfection.

Question 12

Is alcohol well suited for use on skin, or is it an irritant? Is pure alcohol more effective than a lower ww%? Why is this so?

Answer 12

Suitable for skin, less irritating than soap.

70% is better than 100%. This is because pores close at 100%, better entry at 70%.

Question 13

What are 3 properties of a good handwash? Name one.

Answer 13

Good wetting properties
Rinses well
Has residual activity
Chlorhexidine

Question 14

When is soap usually used?

Answer 14

When hands are visibly soiled.

Question 15

Describe the handwashing process in 5 steps.

Answer 15

Wet hands
Add handwash
Rub hands
Scratch palms to reach fingernails
Rinse well, and pat dry

Question 16

Why must hands be wet first before adding handwash?

Answer 16

Prevents skin irritation.

Question 17

Name 3 advantages of alcohol handrub. Name one disadvantage.

Answer 17

Convenient, dries quick, less irritating than handwashing

No good if hands are visibly soiled.

Question 18

Name 2 properties of a good antimicrobial.

Answer 18

Must be effective at low concentrations, and selectively toxic.

Question 19

What is a therapeutic index, and what is it in penicillin vs gentamycin?

Answer 19

Therapeutic index describes suitability of antimicrobial.
Penicillin has high selective toxicity - high index.
Gentamycin has toxicity to both host and target pathogen - lower index.

Question 20

Gentamycin is used on resistant bacteria. How is it usually administerd given all its side effects?

Answer 20

Blood levels rise quickly and can kill auditory nerves.

Typically given in 8h periods, and levels in blood monitored before the next dose is administered.

Question 21

Define microbiostatic agent.

Answer 21

Inhibits microbe growth.

Question 22

Define broad spectrum antibiotic.

Answer 22

Effective against many groups of microbes, but disrupts natural flora

Question 23

Define narrow spectrum antibiotic.

Answer 23

Effective against a specific target microbe. Leaves more natural flora intact.

Question 24

How are penicillin resistant gram positive bacteria killed?

Answer 24

Vancomycin.

Question 25

Where are antibiotics made naturally, and why? If there are so many antibiotics in nature, why do we have a shortage clinically?

Answer 25

Made by fungi and bacteria in nature, for competition.

Less than 1% of these are clinically useful as they are typically too toxic to be used in vivo.

Question 26

Which antibiotic group accounts for more than 50% of the worlds use? Name 3 examples.

Answer 26

Beta lactam antibiotics, including penicillins, cephalosporins, and cephamycins.

Question 27

What bond links cell wall units together? What about cell wall interlinks?

Answer 27

Unit links - glycosidic bonds

Interlinks peptide bonds

Question 28

What is the mechanism of action for aminoglycoside antibiotics? Which bacteria is it effective against, and what are two side effects?

Answer 28

Inhibits protein synthesis by targeting small ribosomal subunits.
Effective against gram negative bacteria
Is neutotoxic and nephrotoxic.

Question 29

What is the mechanism of action for macrolide antibiotics?

Answer 29

Inhibits protein synthesis by targeting large ribosomal subunits.

Question 30

What is tetracycline made by, and what is it effective against?

Answer 30

Made by streptomyces, broad spectrum, effective against almost all gram positive and negative bacteria.

Question 31

Name 6 mechanisms of action for antibiotics.

Answer 31

Injury to membrane
Inhibit synthesis of essential metabolites
Inhibit transcription
Inhibit DNA replication
Inhibit cell wall synthesis
Inhibit protein synthesis

Question 32

How can antibiotic resistance be spread?

Answer 32

Bacteria that make antibiotic resistance have mechanisms to resist their own antibiotics.
Can be transferred to other microbes via transformation.

Question 33

Name 2 ways resistance to penicillin can be achieved.

Answer 33

B lactam ring in penicillin cleaved by B lactamase

Can make pumps to pump it out.