Microbial Control (W3) Flashcards
what are the 4 controls of microbial growth
- cleaning
- sanitisation
- disinfection
- sterilisation
what is achieved by disinfection
removal of pathogens only
what is achieved by sterilisation
removal of all microbes, including bacterial spores
what is achieved by cleaning
removal of visible soils and microorganisms are removed but not killed
what is achieved by sanitisation
destroys enough microorganisms to meet safety guidelines, not effective in presense of organic matter
define germicide
an agent that kills pathogenic organisms
what are the 2 types of germicide disinfection and what are they both used for
Disinfectant- inanimate objects
Antiseptic - animate areas
what are 4 methods of disinfection
- pasteurisation
- radiation
- heat (boiling)
- Chemical solutions
describe pasteurisation generally
- takes place at 60 - 80 deg for a few mins
- kills pathogens and most other bacteria
- it reduces spoilage bacteria
- Extends shelf life
what are the 2 ways pasteurisation can be conducted and their conditions
- Low Temp + Long Time = 63 deg for 30 mins
- High Temp Short Time = 72 deg for 15 secs
what 3 radiations can be used for disinfection
- ultra-violet
- non ionising radiation
- ionising radiation (electron beam, gamma rays and X rays
how does ultraviolet radiation kill bacteria and how is it used
- it kills bacteria by damaging proteins and nucleic acid
- it has a low penetration power, and is used for a moderate exposure time (3 hours)
what are the 3 modes of action of chemical disinfection and give an example of each
- protein coagulation and denaturation
eg. Alcohols and aldehydes - disruption of cell membrane
eg. Surface Active Antigens - inactivation of enzymes ( chemical antagonism )
eg. Metals
How (3) does organic matter inhibit disinfection
- Forms a precipitate
- reacts to produce non-bactericidal agents
- Coats bacteria
why are endospores difficult to kill
they are covered in thick spore coat that protects from chemicals and radiation
Why is moist heat better than dry heat?
moist heat is better because moisture is a good conductor of heat, therefore it has better heat penetration
What are the typical conditions used for moist heat sterilisation?
15 mins at 121deg and 15 psi
when would you use a dry heat oven instead of autoclaving
dry heat is used for oils, powders, sharp objects and glassware
what are the 3 methods we can use to ensure the autoclave is working properly
- autoclave printout
- Bowie-dick tape
- spore strips
how does ionising radiation kill microbes
by disrupting chemical bonds that damages DNA
what are 2 chemicals used for cold sterilisation
- formaldehyde
- ethylene oxide
what filtration pore size is needed to filter out bacteria and what size for viruses
bacteria = 0.45um
viruses = 0.01um (or 10nm)
what is a bacteriostatic agent and what is a bactericidal agent
bacteriostatic prevent reproduction
bactericidal kill cell (by damaging cell wall)
what are the 6 modes of action for antibacterial agents
- cell wall synthesis inhibitors
- inhibit DNA replication
- inhibit RNA synthesis
- inhibit ribosome function / protein synthesis
- metabolic inhibitors
- membrane active antimicrobial agents
