Microbial Control

Question 1

What is the difference between sterilisation and sanitisation?

Answer 1

Sterilisation: the destruction of all microbes
Sanitisation: the destruction of many microorganisms to reduce viable numbers

Question 2

What is the difference between a disinfectant and an antiseptic?

Answer 2

Disinfectant: destroys microbes on inanimate objects
Antiseptic: a disinfectant for animate areas

Question 3

What is pasteurisation?

Answer 3

A process developed by Louis Pastuer that reduces spoilage bacteria and increases the shelf life of food

Question 4

What are the temperatures and times for LTLT and HTST relating to pasteurisation?

Answer 4

LTLT: 63 degress, 30 min
HTST: 72 degrees, 15 sec

Question 5

List the 3 modes of action for disinfectants?

Answer 5

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

Question 6

What is the optimal percentage of alcohol for disinfection?

Answer 6

70%

Question 7

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

Answer 7

Advantages:
- good treatment for small wounds and infections
- effective on a wide range of microbes
- can be a pre-operation skin disinfectant
Disadvantages:
- can cause discolouration of skin 
- can lead to hypersensitivity of skin
- psuedonomas are able to grow from it

Question 8

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

Answer 8

• They are surface active agents

Question 9

Why are QUATS no longer used in some hospital settings?

Answer 9

• Can be inactivated by soaps, low level disinfectants

Question 10

What is the “decimal reduction time (D)”?

Answer 10

The ‘decimal reduction time’ (D) is the time (minutes) for the survivors to be destroyed by one log cycle which represents 90% of the initial population

Question 11

What is Sterilisation?

Answer 11

The destruction of all microbes

Question 12

Why are endospores difficult to kill?

Answer 12

• They are the most heat resistant and difficult to kill microbial structure
• The thick spore coat protects from radiation and chemicals

Question 13

Why is moist heat better than dry heat?

Answer 13

• Moist heat (autoclave) is more effective than dry heat (hot air oven)
• Moisture is a better conductor of heat and has better heat penetration

Question 14

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

Answer 14

• When sterilising glassware, oils and powders (it doesn’t make sharps blunt)

Question 15

What methods are used to ensure an autoclave is working?

Answer 15

• Autoclave prinouts/monitoring
• Spore strips: endospores put on paper strip inside envelope, placed inside autoclave, transferred to broth and incubated at 55 degrees for 5 days, if there is growth then the autoclave is successful, if not, then it is not
• Autoclave tape: Stripes on a strip of tape are white before sterilisation, tape is placed inside the autoclave, if there are neat lines on the tape then autoclave is successful, if they are faded out then it is unsuccessful, the brings an immediate result but does not indicate the time held

Question 16

Name two chemicals used for “cold sterilisation”. How does ionizing radiation affect microbes and kill them?

Answer 16

• Cold sterilisation works to denature proteins

- Formaldehyde and ethylene oxide can be used for cold sterilisation

Question 17

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

Answer 17

• Bacteria: 0.45 micrometres or less

- Virus: 0.01 mircrometre or less

Question 18

What is the difference between Bacteriostatic and Bactericidal agents?

Answer 18

• Bacteriostatic: inhibit growth of bacteria

- Bactericidal: kill bacteria

Question 19

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

Answer 19

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

Question 20

Describe the action of the β-lactam antibiotics.

Answer 20

• 𝛃- lactams inhibit the last stage of the cell wall production process
• Not effective against resting bacteria
• These agents binds to proteins at the cell wall/cell membrane interface (PBPs) that are involved in the cross linking of the peptidoglycan strands – results in cell lysis (all are bactericidal)

Question 21

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

Answer 21

• Not completing a course of antibiotics (that work) = selecting resistant mutants

Question 22

Why are antibiotics of no use against the common cold?

Answer 22

• The common cold is a virus, antibiotics work on bacterial infections

Question 23

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

Answer 23

• Antibiotic: natural compounds produced by microorganisms that kill or inhibit other microorganisms
• Antibiotic Creed: the guidelines doctors go by in order to determine how much of an antibiotic to prescribe to a patient

Question 24

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

Answer 24

• Because eukaryote cells (including humans) do not have a cell wall (only a plasma membrane) and no peptidoglycan, the β-lactams work well in that they kill bacteria without damaging cells of the host

Question 25

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

Answer 25

• Fungi are difficult to treat because they are eukaryotic and so have similar structures to human cells
• Can kill human cells along with fungal cells

Question 26

List two modes of action for anti-viral drugs.

Answer 26

• Prevention of uncoating of virus (e.g. Amantadine for Influenza)
• Inhibit viral replication (e.g. Aciclovir for Herpes)