Lecture 3

Question 1

What is the difference between sterilisation and sanitisation?

Answer 1

Sanitation is the process that destroys various microorganisms to meet quality and health standards
Sterilization is the removal of all microbes including bacterial spores

Question 2

What is the difference between a disinfectant and an antiseptic?

Answer 2

Disinfectant is on inanimate areas

Antiseptic is on animate areas

Question 3

What is the purpose of pasteurisation in the food industry?

Answer 3

It was originally invented to prevent the spoilage of wine, however, its mostly used for milk products.
It kills key pathogens, reduces spoilage bacteria and extends the shelf life of products

Question 4

What are the temperatures and times for Low Temperature Long Time (LTLT) and High Temperature Short Time (HTST) relating to pasteurisation?

Answer 4

LTLT – 63 degrees, 30 mins

HTST – 72 degrees, 15 secs

Question 5

List the 3 modes of action of chemical disinfectants?

Answer 5

Proetin coagulation / denaturation
Disruption of cell membrane
Chemical antagonism (inactivation of enzymes)

Question 6

What is the optimal percentage of alcohol for disinfection?

Answer 6

Optimal is 70%

Question 7

Betadine is a combination of iodophor and detergent which is used as a skin disinfectant in pre-surgical operations. List the advantages and disadvantages of Betadine for this use.

Answer 7

Advantages
		Good residual effect
		Effective of a wide range of microbes
	Disadvantages
		Skin discolouration
		Hypersensitivity
Pseudomonas able to grow

Question 8

What is the mechanism of action for Quaternary Ammonium Compounds (QUATs) against bacteria?

Answer 8

Disruption of the cell membrane

Question 9

Why are QUATS no longer used in some hospital settings?

Answer 9

There are more effective agents that replaced it

Question 10

How could the presence of organic matter interfere with the action of disinfectants? (3 ways)

Answer 10

Form a precipitate with disinfectant – removes disinfectant from contact with bacteria
Reacts with the disinfect and to produce a non-bactericidal agent
Coats bacteria – protects the bacteria from the disinfectant

Question 11

UV radiation damages proteins and nucleic acids of bacteria. What is the main disadvantage of UV radiation as a disinfectant?

Answer 11

Low penetrating power

Moderate exposure time

Question 12

What size particles are N95 masks rated to remove?

Answer 12

0.3 micrometers or µm

Question 13

What is Sterilisation?

Answer 13

The removal of all microbes

Question 14

Why are endospores difficult to kill?

Answer 14

They have a thick protective outer shell that shields them from radiation and chemicals

Question 15

Why is moist heat better than dry heat? What are the typical conditions used for moist heat sterilisation?

Answer 15

Moist heat is a better conductor of heat and better heat penetrator

15 minutes @ 121 degrees at 15 psi above atmospheric pressure

Question 16

In what circumstance would you probably use a dry heat oven instead of autoclaving?

Answer 16

To prevent sharp instruments becoming blunt

Glassware, oils and powders

Question 17

What methods are used to ensure an autoclave is working?

Answer 17

Biological – spore strips
Autoclave tape (Bowie-dick test)

Question 18

Name two chemicals used for “cold sterilisation”.

Answer 18

Formaldehyde
Glutaraldehyde
Ethylene oxide
Plasma Sterilisation (hydrogen peroxide gas)

Question 19

How does ionizing radiation affect microbes and kill them?

Answer 19

Damages DNA by disrupting chemical bonds in cells

Question 20

State the filtration pore size needed to filter out a) bacteria, b) viruses.

Answer 20

Bacteria – 0.01 micrometers

Viruses – 10 nanometers

Question 21

What is the difference between Bacteriostatic and Bactericidal agents?

Answer 21

Bacteriostatic stops the microorganisms from growing but does not kill them
Bactericidal agents kill microorganisms

Question 22

List the 6 modes of action for anti-bacterial agents (i.e. 6 target sites).

Answer 22

Inhibitors of cell wall synthesis
	Membrane active antimicrobial agents
	Inhibitors of DNA replication
	Inhibitors of RNA synthesis
	Inhibitors of ribosome synthesis – protein synthesis
Metabolic inhibitors

Question 23

Describe the action of the β-lactam antibiotics.

Answer 23

Inhibits cell wall synthesis
Stops the last stage of cell wall production which results in cell lysis (disintegration of a cell by rupture of the cell wall or membrane)

Question 24

How could incompletion of a prescribed course of antibiotics lead to bacterial resistance?

Answer 24

Should there be a small proportion of bacteria with antibiotic resistance, normally the antibiotics would kill the bacteria and the resistant bacteria would be taken care of by the immune system. If the course is incomplete, it leaves the susceptible bacteria alive for the resistant bacteria to then transfer their resistant genes. This results in the bacteria multiplying and the majority can become resistant.

Question 25

Why are antibiotics of no use against the common cold?

Answer 25

Antibiotics only fight against bacteria and not viruses

Question 26

Define “antibiotic”. Define the ‘Antibiotic Creed’.

Answer 26

Antibiotic Definition
Natural compounds produced by microorganisms that kill or inhibit other microorganisms
Antibiotic Creed
Microbiology guides therapy wherever possible
Indications should be evidence based
Narrowest spectrum required
Dosage appropriate to the site an type of infection
Minimize duration of therapy
Ensure monotherapy in most cases

Question 27

Why are the β-lactam agents good choice for treating susceptible bacterial infections in humans?

Answer 27

Beta-Lactam agents work via inhibiting cell wall synthesis. Humans do not have cells with cell walls, therefore they do not become affected by the agents.

Question 28

Why are many treatments for fungal infections often toxic to humans?

Answer 28

Fungi are Eukaryotic like human cells and therefore as the treatment kills the fungi, it can also have negative effects upon the human cells.

Question 29

List two modes of action for anti-viral drugs.

Answer 29

Inhibit viral replication

Interfere with viral release