Lecture 8 Flashcards
what is sterilisation?
Killing/removal of all viable organisms, including endospores
what is disinfection?
Killing/removal of all vegetative forms, not including endospores. we dont sterilise if its something that isnt gonna penetrate the skin. disinfectants are used on surfaces as they do not kill endospores. some examples are ethanol, cationic detergents, bleach.
What are the chemical sterilants?
Ther are used in hospitals on thermometers and this will kill endospores. this happens inside enclosed chambers with added gas such as formaldehyde or hydrogen peroxide
what are antiseptics?
they kill/inhibit the growth of microorganisms but are non-toxic enough to be used on living tissue
what are sanitisers?
sanitisers reduce microbial numbers to “safe” levels
explain disinfectant efficiency?
get rid of anything biological. if an organism is making a biofilm or crusts which is hard to disinfect.
Action of disinfectants affected by material surrounding the microorganisms
Presence of proteins, fats etc in the surrounding area will protect microorganisms, many disinfectants are neutralised by organic materials
Some microorganisms form biofilms
Penetration of chemicals reduced
Major problem in hospitals, biofilm formation on catheters etc
organise the most resistant bacteria to the least resistant in terms of biocides?
bacteria spores > mycobacteria > nonlipid or small viruses > vegetative bacteria
how to do dilutions?
Hypochlorite can be used at 5000 parts per million as a very strong solution
You have a bottle of White King that is 5%
How much White King do you mix with water?
5% = 5 parts per 100 Or 5000 parts per 100,000 But we want 5000 parts per 1,000,000 i.e. we want it diluted 10 times So take 1 ml and add to 9 ml of water, total 10 ml and 1/10 of this is hypochlorite (1:10 dilution)
C1 V1 = C2 V2 5 per 100 x V1 = 5000/1000000 x 10 ml Solve for V1 V1 = 5000/1000000 x 10 x 100/5 V1 = 1 ml So take 1 ml of white king and make up to 10 ml i.e., add 9ml of water
why is 70% of alcohol better than 100%?
because at 100% bacteria close their pores but if 30% is water the bacteria open their pores allowing the solution to flow through
what is therapeutic index? TI
This lecture will discuss antimicrobial agents used in vivo
These agents must be effective at low concentrations, and must be selectively toxic - must be more toxic to the pathogen than the host
Can derive a Therapeutic Index (TI), the higher the TI, the better the drug
Penicillin has a high TI, is selectively toxic by inhibiting bacterial cell wall synthesis, however some people are allergic
Gentamicin and streptomycin are toxic to host as well as to pathogen - lower TI, still used eg on bacteria resistant to other antimicrobials
Naturally produced antibiotics by fungi and bacteria (Why?)
Inhibit or kill other cellular microorganisms
Less than 1% of naturally-occurring antibiotics are clinically useful
Many are too toxic to be used in vivo in humans or animals
Many antibiotics are structurally modified in the lab to enhance efficacy – semisynthetic antibiotics
