B2: sterilization/disinfection to physical methods

what is sterilization?

the removal of ALL microbial life, including endospores, from an object/surface

what is disinfection?

the removal of common harmful bacteria (but not endospores)

• lowering the number of harmful microbes to an acceptable level

• disinfectant = chemical agent used

what is antisepsis?

disinfection of living tissue (antiseptic)

are all disinfectants antiseptics?

no! not all disinfectants are antiseptics → some disinfectants are harmful to living tissue

what is sanitization?

cleaning to remove debris, soil, microbes, and other materials to reduce risk of infection

whats the difference between a microbicidal and a microbistatic antimicrobial agent?

microbicidal = kill the microbes; make it so they cannot reproduce anymore

microbistatic = stop the microbes from growing; focuses on shutting down their metabolism

examples of microbicidal antimicrobial agents?

bacteriocide

fungicide

algicide

viricide

if you remove the microbicidal antimicrobial agent, what happens to the bacterium?

stays dead

examples of microbistatic antimicrobial agents

bacteriostatic

fungistatic

if you remove the microbistatic antimicrobial agent, what happens to the bacterium?

they’ll grow again

what does moist heat do?

denatures proteins and degrades DNA

how effective is boiling water?

good technique for disinfecting

most bacteria, parasites, and viruses are killed quickly by boiling water

a few are not and can survive for hours in boiling water → DOES NOT get hot enough to kill endospores

what does using autoclave achieve?

sterilization

autoclaving increases the temperature to 121°C

even endospores will be killed in 15 minutes

what is an autoclave?

a pressurized tank that increases the pressure of a liquid solution to heat it up

uses high pressure to get the water hot → pressure does not kill, the heat does

what is thermal death time (TDT)?

the shortest time required to kill all test microbes at a given temperature

what is thermal death point (TDP)?

lowest temperature required to kill all test microbes in 10 minutes

what does dry heat do?

oxidizes (or incinerates) microbes

• applying heat through the air → causes reactions with oxygen in the air to burn things

what is the difference between wet (moist) heat than dry heat?

dry heat has to work longer since heat is transferred slower by air than it is by moisture (steam/boiling water)

what are the methods of dry heat?

sterilizing oven = 2-3 hours at 160°C

• speed of delivery of heat through the air is slower

bunsen burners or bacti-cinerators = ~1500-2500°C

what do cold methods do?

slow or stop growth by lowering the temperature

what are examples of cold methods?

freezing

refrigeration

freezing

-20°C or lower

stops growth, no liquid water

• microbes can’t grow without liquid water

some cell death from ice crystals disrupting membranes

microbistatic approach (not a reliable disinfectant)

refrigeration

4°C

greatly slows growth of most organisms → microbistatic approach

food keeps much longer

what is the problem with refrigeration?

some pathogens (Listeria) are psychrophiles and continue growing

what is dessication?

the removal of all liquid water

bacteriostatic

what microbes get killed from dessication?

Gram negative

what usually happens to most microbes when dessicated?

preserved and live longer

what is lyophilization?

rapid drying and freezing of a bacterial sample

• commonly used to preserve bacteria for long-term storage

what is filtration?

separates microbes from a solution or from air

how does filtration reduce or eliminate microbes in a liquid or in air?

air or water is sucked through a filter with very small holes

microbes are too big to pass through

how do filters disinfect? sterilize?

disinfect: if pores are large

sterilize: if pores are small

what is pasteurization?

heating at a moderately high temperature, or for a short time, so the food isn’t destroyed

is pasteurization a sterilizing or disinfecting process?

disinfecting technique

• just kills or reduces the bacterial population of a particular microbe

• want to reduce microbial numbers to a manageable level, not necessarily achieve complete sterility

• prolongs the lifespan of a food product…but it isn’t sterile

what is classic pasteurization?

60° for 30 minutes

what is high temperature short term (HTST)?

72°C for 15 seconds

what is ultrahigh temperature (UHT)?

138°C for 1-3 seconds

examples of ionizing radiation?

x-rays, gamma rays

what does ionizing radiation do?

damages DNA (severe)

some can pass right through most substances

possible to sterilize items inside and out

what is ionizing radiation effective against? not effective against?

endospores

not always effective against viruses

what are the challenges of using ionizing radiation?

hard to implement → need equipment and high risk to people who are handling it

what does ultraviolet (UV) radiation do?

damages DNA (less severe)

little penetrating power

• can’t UV radiate in and out of the cell

• BUT using it safely is quite easy

what is UV radiation effective against?

endospores

when is UV radiation useful?

disinfecting the air or outer surfaces

can reduce microbes in water

is moist heat a bactericidal or bacteriostatic approach?

bactericidal

• boiling water

• autoclave

is dry heat a bactericidal or bacteriostatic approach?

bactericidal

• sterilizing oven

• bunsen burners/bacti-cinerators

is pasteurization a bactericidal or bacteriostatic approach?

bacteriostatic

is cold a bactericidal or bacteriostatic approach?

bacteriostatic

• freezing

• refrigeration

• dessication

• lyophilization

is ionizing and UV radiation a bactericidal or bacteriostatic approach?

bactericidal

is filtration a bactericidal or bacteriostatic approach?

not bactericidal or bacteriostatic → mechanical separation