Microbial Control

Question 1

What is the difference between sanitation and sterilisation?

Answer 1

Sanitation destroys microorganisms by reducing the viable numbers present on clean surfaces, however, is not usually effective in the present of organic residue or detergent. It is used to meet product quality and health standards, and is achieved with moist heat (steam) or chemical (chlorine/bleach). Sterilisation on the other hand, refers to the complete removal of all microbes, including bacterial spores.

Question 2

What is the difference between disinfectant and an antiseptic?

Answer 2

A disinfectant removes or causes the destruction of harmful microbes (not usually spores), for inanimate objects, where as antiseptics are disinfectants for animate areas.

Question 3

What is Pasteurisation?

Answer 3

Pasteurisation is a process in which packaged and non-packaged foods are treated with mild heat to eliminate pathogens and extend shelf life. This process is intended to reduce spoilage and eliminate vegetative bacteria, however not bacterial spores.

Question 4

What are the temperatures and times for LTLT and HTST, is regards to pasteurisation?

Answer 4

LTLT = 63 degrees Celsius for 30 minutes

HTST = 72 degrees Celsius for 15 seconds

Question 5

List 3 modes of action for disinfectants.

Answer 5

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

Question 6

What is the optimum % of alcohol for disinfection?

Answer 6

60-70% (ethanol/propyl)

Question 7

List the advantages and disadvantages of Betadine when used as a skin disinfectant in pre-surgical operations.

Answer 7

ADVANTAGES:

• Antiseptic for wounds
• Good residue effect
• Effective of a wide range of microbes

DISADVANTAGES:
- Skin discolouration 
- Hypersensitivity 
- Pseudomonas are able to grow (bacteria is resistant; 
  found in water)

Question 8

What is the mechanism of QUATS against bacteria?

Answer 8

Due to the positive charge of Quaternary Ammonium Compounds (QUATS), they are able to adhere to negatively charged microorganisms while dissolving their cell walls. This is believed to increase the microorganisms permeability and the loss of K+ ions from it.

Question 9

Why are QUATS no longer used in hospitals?

Answer 9

• They are not effective against non-enveloped viruses,
  fungi and bacteria spore.
• Many bacteria have become resistant to QUATS.
• High water hardness; materials such as cotton and
  gauze make them less microbial as they absorb the
  active ingredient.
• Have been associated with causing asthma and other
  respiratory illnesses.
• Linked to eczema and skin irritation.

Question 10

What are three ways the presence of organic matter interfere with the action of disinfectants?

Answer 10

• Forms a precipitate.
• Reacts with the disinfectant to produce non-bacterial
  agents.
• Coats bacteria; protecting it 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

UV radiation does not penetrate liquids or go around corners. In addition to this, its low penetrating power means that longer exposure times are necessary to disinfect.

Question 12

What is the “Decimal Reduction Time”?

Answer 12

The decimal reduction time (‘D’ value), refers tot he time that it takes, at a given condition, or a set of conditions, to kill 90% of the exposed microorganisms.

Question 13

What is sterilisation?

Answer 13

Sterilisation refers to the removal of all microbes including bacterial spores.

Question 14

Why are endospores difficult to kill?

Answer 14

Bacterial spores are the most heat resistant and difficult to kill microbial structure, due to their thick spore coat. This protects them from radiation and chemical.

Question 15

Why is moist heat better than dry heat?

Answer 15

Moist heat (achieved in an autoclave), is more effective than dry heat (hot oven air), as moisture is a more efficient conductor of heat, and allows for better penetration.

Question 16

In what circumstances would you use a dry heat oven instead of an autoclave?

Answer 16

When sterilising metal instruments that are likely to rust. Dry heat is also used for the sterilisation of fats, oils and powders.

Question 17

What methods are used to make sure and autoclave is working properly?

Answer 17

• Autoclave printouts/monitoring
• Biological spore strips (done once a week)
• Autoclave tape (Bowie-Dick test)

Question 18

Name two chemicals for cold sterilisation.

Answer 18

• Formaldehyde

- Ethylene oxide

Question 19

How does ionising radiation affect microbes and kill them?

Answer 19

By damaging the DNA through disrupting the chemical bonds in cells.

Question 20

State the filtration pore size needed to filter out bacteria and viruses.

Answer 20

• Filters out bacteria 0.45 microns and less.
• Filters out bacteria and viral particles 0.01 microns in
  size.

Question 21

What is the difference between bacteriostatic and bactericidal agents?

Answer 21

Bacteriostatic agents are compound that inhibit the growth of microorganisms (they remain viable), whereas bactericidal agents are compounds that kill microorganisms.

Question 22

List the six modes of action for anti-bacterial agents.

Answer 22

• 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 23

Describe the action of B-lactam antibiotics.

Answer 23

B-lactam is a strain of antibiotics characterised by its B-lactam ring structure. These antibiotics work by targeting the penicillin binding proteins (PBP’s), which are a group of enzymes involved in the cross linking of the bacterial cell wall. They are made unable to perform their role in cell wall synthesis, which results in the death of the bacterial cell, due to its osmotic instability or autolysis.

Question 24

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

Answer 24

If patients fail to complete a course of antibiotics, the infection causing agent may well possibly survive and grow resistance to that particular strain of antibiotic, as they were not exposed to it for a long enough period of time to be killed off. This is a unnatural form of natural selection and will result in the bacterial population in the afflicted patient having a higher resistance to the antibiotic than normal. As it continues to replicate and is transmitted from person to person, the resistance is passed on, and the infection will no longer be able to be treated by that antibiotic.

Question 25

Why are antibiotics of no use to treat the common cold?

Answer 25

The common cold is a viral infection. Antibiotics work only to treat bacterial infections, and would therefore be ineffective against the common cold.

Question 26

Define antibiotic.

Answer 26

Antibiotic is a drug used to treat bacterial infections, via inhibiting the growth of or destroying microorganisms.

Question 27

What is the antibiotic creed?

Answer 27

• Microbiology guides therapy wherever possible.
• Indications should be evidence based.
• Narrowest spectrum required.
• Dosage appropriate to the site and type of infection.
• Minimise duration of the therapy.
  Ensure mono-therapy in most cases.

Question 28

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

Answer 28

Due to human cells being eukaryotes, they do not have a cell wall (only a plasma membrane), and therefore have no peptidogylcon. They work well as they are able to kill bacteria without damaging the cells of the host, and for that reason they are commonly referred to as magic bullets.

Question 29

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

Answer 29

Treatment can be toxic, as human cells are fungal infections are both eukaryotes, and therefore have a similar structure. Treatment can often result in damage to the patients healthy cells and can lead to toxicity in the kidneys, liver and bone marrow. For this reason, treatment is often applied in small amounts over a prolonged period of time.

Question 30

List two modes of action for anti-vial drugs.

Answer 30

• Inhibit viral replication.

- Interfere with viral release.