Ch 13: Sterilization, Disinfection, and Antibiotic Therapy

commercial sterilization

killing Clostridium botulinum (spores) without altering quality of food

NOT considered actual sterilization

sterilization

destruction of all living cells, spores, and or viruses

disinfection

removal of disease causing microorganisms from inanimate surfaces

doesn’t always result in sterilization

antisepsis

removal of disease causing microorganisms from living tissue

doesn’t always result in sterilization

asepsis

absence of significant contamination

ex) aseptic surgery techniques prevent microbial contamination of wounds

biocide

lethal effects (kills targeted organism)

bacteriostasis

slows or stops metabolism or reproduction

not necessarily lethal

d value

time it takes to reduce microbial population by 90%

tdt thermal death time

minimal time for all bacteria in a liquid culture to be killed at a particular temperature

thermal death point tdp

lowest temperature at which all cells in a liquid culture are killed in ten minutes

autoclave sterilization

high temp and high pressure method

pasteurization

only moderately high temps

kills bacteria that causes spoilage in fermenting beer and wine without affecting texture, color, or taste

12D method

amount of time to kill 10^12 endospores (otherwise known as reducing population size by 12 logs)

lyophilization

freeze drying

cultures are quickly frozen at very low temperatures in a vacuum

freezing

stalls growth

mix cultures in 1:1 with glycerol for long term storage

filtration

removes/separates microorganisms from solution

cannot filter viruses

pore size 0.2 um

uv light (x penetrate liquids or solids well, useful for surface sterilization)

type(s) of non ionizing radiation

gamma rays, electron beams, x rays

type(s) of ionizing radiation

presence of organic matter, type of microbe present, corrosiveness

usefulness of a chemical agent depends on

resistant organism examples

endospore

gram negative because of outer membrane

microbacterium because they have mycolic acid

non enveloped viruses with protein capsid

high disinfection

kills everything

ex) ethylene oxide, glutaraldehyde, formaldehyde

intermediate disinfection

not able to kill endospores

ex) phenolics and halogens aka lysol and clorox

low disinfection

cannot kill mycobacteria or endospores

ex) alcohols

autoclave, filtration (with certain pore size), ionizing radiation, aldehydes, ethylene oxide

sterilization methods

selective toxicity

antibiotics are harmful to specific bacteria without harming eukaryotic organisms

can be used in non immunocompromised individuals that have a strong enough system

why would a bacteriostatic antibiotic that only inhibits growth of a pathogenic bacterium be useful for treating an infection?

bacteriocidal antibiotic

completely kills bacteria

used in immunocompromised individuals whose immune system is not strong enough to fight

minimum inhibitory concentration (mic)

minimum antibiotic concentration to inhibit bacterial growth

minimal bactericidal concentration (mbc)

minimum antibiotic concentration to kill all bacteria

requires further plating to determine if any cells survived

zone of inhibition

clear zone around disk that shows effectiveness of an antibiotic

bigger zone means more effective treatment

chemotherapeutic index

toxic dose/therapeutic dose

higher

the blank the chemotherapeutic index, the safer the drug