Microbial Control

Question 1

What is the difference between sterilisation and sanitisation?

Answer 1

Sterilisation- the removal of all microbes including bacterial spores

Sanitisation- the destruction of various microorganisms to reduce viable numbers on clean surfaces to meet product quality and public health standards

Question 2

What is the difference between a disinfectant and an antiseptic?

Answer 2

Disinfectant- substance that removes or destroys pathogens from inanimate areas

Antiseptic- disinfectant for animate areas

Question 3

What is pasteurisation

Answer 3

A process developed by Louis Pasteur that reduces spoilage bacteria and increases the shelf life

Question 4

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

Answer 4

Low temp - long time : 63 degrees for 30 mins

High temp - short time : 72 degrees for 15 sec

Question 5

List 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 iodophors 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

Advantage - good residual effect, effective on a wide range of microbes, good for treatment on small wounds, surgical scrub, pre-operative skin disinfection

Disadvantage - skin discolouration, hypersensitivity, pseudomonas able to grow

Question 8

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

Answer 8

They are surface active agents; they can disrupt the cell membrane of the target microorganism

Question 9

Why are QUATs no longer used in some hospital settings

Answer 9

Skin/ respiratory irritation

Pseudomonas can grow in QUATs

Question 10

How could the presence of organic matter interfere with the action of disinfectants

Answer 10

Forms precipitate - removes disinfectant from contact with bacteria

Reacts with the disinfectant to produce a non-bacterial agent

Coats bacteria - protects bacteria from the disinfectant

Question 11

UV radiation damages proteins and nucleus acid if bacteria. What is the main disadvantage of UV radiation as a disinfectant

Answer 11

The radiation is not very penetrative, so for the organism to be killed must be directly exposed to the rays

Question 12

What is the ‘decimal reduction time (D)’

Answer 12

The time in minutes for the survivors to be destroyed by one log cycle which represents 90% of the initial population

Question 13

What is sterilisation

Answer 13

A process in which all microbes including endpapers are destroyed

Question 14

Why are endoscopes difficult to kill

Answer 14

Most heat resistant and difficult to kill microbial structure
Thick spore coat protects from radiation and chemicals

Question 15

Why is moist heat better than dry heat

Answer 15

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

Question 16

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

Answer 16

Dry heat ovens are used to sterilise items that might be damaged by moist heat or might be susceptible to corrosion

Good for glassware, oils, powders - that you don’t want to get wet

Question 17

What methods are used to ensure an autoclave is working

Answer 17

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 autoclave is not successful

Autoclave tape - stripes on a strip of tape are white before sterilisation, tape is placed inside the autoclave, if there are best lines on the tape then autoclave is successful, if they are faded out then it is unsuccessful, this brings an immediate result but does not indicate the time held

Question 18

Name two chemicals used for ‘cold sterilisation’

Answer 18

Cold sterilisation works to denature proteins

Formaldehyde and ethylene oxide can be used for cold sterilisation

Question 19

How does ionising radiation affect microbes and kill them

Answer 19

Has the energy to liberate an electron from an atom

Question 20

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

Answer 20

Bacteria - 0.45 micrometer um

Viruses - 0.01 micrometer um

Question 21

What is the difference between bacteriostatic and bactericidal agents

Answer 21

Bacteriostatic - inhibit growth of bacteria

Bactericidal - kill bacteria

Question 22

List the 6 modes of actions for antibacterial agents

Answer 22

1 - inhibitors of cell wall synthesis
2 - membrane-active antimicrobial agents
3 - inhibitors of DNA replication
4 - inhibitors of RNA synthesis
5 - inhibitors of ribosome function - protein synthesis
6 - metabolic inhibitors

Question 23

Describe the action of the B-lactam antibiotics

Answer 23

B-lactams inhibit the last stage of the cell wall production processes 
Eukaryotic cells (including humans) do not have a cell wall (only plasma membrane) and no peptidoglycan, the B-lactams work well in that they kill bacteria without damaging cells if the host. 

• the ring must be intact for antibacterial activity, inactivated by beta lactamase enzymes of bacteria
• these agents bond 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 B-lactams are bactericidal)
• not effective against eating bacteria

B-lactams inhibit the last stage of the cell wall production processes
Not effective against resting bacteria
These agents bind to proteins at the cell wall/ cell membrane interface (PBPs) that are involved in the cross linking of peptidoglycan strands - results in cell lysis

Question 24

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

Answer 24

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

Question 25

Why are antibiotics of no use against the common cold

Answer 25

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

Question 26

Define antibiotic

Answer 26

Natural compounds produced by microorganisms that kill or inhibit other microorganisms

Question 27

Antibiotic creed

Answer 27

The guidelines doctors go by to determine how much of an antibiotic to prescribe to a patient

Question 28

Why are B-lactam agents good for treating susceptible bacterial infections in humans

Answer 28

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

Question 29

Why are many treatments for fungal infections often toxic to humans

Answer 29

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 30

List two modes of action for antiviral drugs

Answer 30

• Prevention of uncoating of virus (e.g. Amantadine for influenza)
• inhibit viral replication (e.g. Aciclovit for Herpes)