Lecture 4: Inhibition

Question 1

How susceptible are viruses to destruction?
Difference between enveloped and non enveloped viruses and their ability to be destructed.
How are most killed?

Answer 1

• huge variability in survival rate outside of host
• enveloped viruses are more susceptible as their envelope is easily destroyed
• non enveloped viruses are more resilient
• most killed by heating to 60 deg for 30 min
• some can last days at 4 degrees

Question 2

How are viruses inactivated?

Iw what kind of conditions would have this effect?

Answer 2

• stable at pH 5-0
• Destroyed by alkaline conditions
• required to alcohols, iodine and ammonium salts
• require higher dose of bleach than bacteria
• more susceptible with greater contact time

Question 3

What chemical can inactivate them and how?

Answer 3

Detergents:

• denature proteins
• alters lipoprotein envelope

Alcohols:
-best at 70% as water required for denaturation. Not ideal

Bleach:
-not very effective, requires more bacteria

Halogens:
-idodine, chlorine, bromine, fluorine, can have effect on many viruses, used in operating theatres

Acids and Alkalines: most don’t like a higher pH. Some can withstand low pH (GIT infections)

Formaldehyde (very effective against all viruses. Can be toxic)

Phenolics:
-more active enveloped than non enveloped viruses e.g. detol

Chlorhexadine:
-Effective against a number of viruses

Question 4

How would you physically inactivate viruses?

Answer 4

1. Heat:
   - depends on contact time and temp
   - >60 deg for 30 min
   - pasteurisation won’t kill viruses (pasteurisation - partial sterilization of foods at a temperature that destroys harmful microorganisms without major changes in the chemistry of the food.)- coz contact time is important
   - best methods involve heat, water and pressure (autoclave)
2. Sterilisation: removal of all living organisms
3. Autoclaving- 121deg, C15 psi for 15 min

Question 5

How can you inhibit viruses

Answer 5

1. Filtration:
   - some filters are capable of filtering out viruses
2. Radiation:
   - denatures DNA
   - use cobalt-60 source
   - radiation enters package of can be sterilised after packaging
   - dangerous to use

Question 6

Check out the Methods of sterilisation on slide 15- should know this i think

Answer 6

cheh

Question 7

What is the function of Nucleotide analogues?

Answer 7

Nucleoside analogues are molecules that act like nucleosides in DNA synthesis. They include a range of antiviral products used to prevent viral replication in infected cells.

They alter shape of DNA making it unworkable