sterilisation and disinfection

susceptibility

• varies with killing agent

• vegetative bacteria are killed at 60-70 for 5 min by denaturation of proteins and disruption of lipi membrane

• some baceria are adpatd for survival

• prions can survive dry heat at 200 for 1-2 hours

why

medicine

• intrument

• dressing

• clothing

• inject

microbiology

• protection of personnel

• purity of cultures

food

• canning and bottling

physical sterilisation- autoclave

• moist heat

• 15 min 121 degrees

• only way to get rid of endospores effectively

how can you test if the autoclave worked

• autoclave tape- line turns black. this detects steam

• brownes tubes are glass tubes containing red heat sensitive dye. changes colour to green after a defind period of time at a certain temp. and indicator strips- detecting heat and time

• detecting sterilisation- spore strips contain non pathogenic spore which are transferred asepticaly to culture medium to germinate

factors affecting autoclaving

• steam penetrating- moist heat required

• time to reach temp- large vol of liquid

physical sterilosayion- dry heat

• hot air oven- 45 min at 160degrees

• glass, metal istrumentcotnainers

• bunsen flame- microbiological loop

physical tyndallisation

• heat to boiling point and hold 15 min, 3 days in succession

• rest in between in a moist warm env

  • allow any surviving spores to germinate then be killed

• day 1- vegetative organissm killed, spores activated

• day 2- germinated spors killed

• day 3- just to be sure

not reliable- some endospores may survive

• things that cannot withstand pressurised heating eg plant seed

other heat method

• boiling at 100

• pasteurisation

  • slow 63-66 × 30 min

  • rapid 73 × 15min

  • kills m bovis and b abortus and many other zoonotic pathogens

• endospores not killed

• acts as amean of disinfection/ decontaminaiton

physical- radiation

uv

• poor penetration

• small scale

• clean surface

gamma

• good penetration

• industrial scale

• 60 Co

• wont ermove endospore

physical- filtration

• membrane filter- not sterilising

• often used for drug for injection

• pore size determines what passses through- 0.22 um viruses pass through

chemical

10 percent formalin

• formaldehyde solution HCHO 43 percent w/v

• tissue fixation- spores killed

20ppm hydrochlorite- bleach

• undissociated hypochlorous acid is powerufl oxidising agent

10 percent ethyleen oxide gas , liquid boils at 10 degrees

CH2.O.CH2

• industrial sterilisation of plastic disposables

• explosive, carcinogenic, requires special apparatus

disinfection

• removes most infective organisms

  • endospores and some virses may survive

• disinfectant destroys or inhiits growht of microorganism on inanimate

• antiseptic- on living tissue

what is needed for effective disinfection

organic material will inactivate many disinfectants

so cleaning needed

how do disinfectants work

examples of harsh

• hypochlorous acid eg domestos

• phenols eg dettol