disinfection and sterilization Flashcards
what is sterilization?
killing of all microorganisms (bacteria, fungi, viral).
what is a germicide?
agent used to kill bacteria
what is antisepsis?
application of chemical agents to the surface of the human body to kill of inhibit pathogenic bacteria
what does it mean for something to be septic?
characterized by the presence of pathogenic bacteria in living tissue
what does it mean for something to be aseptic?
without pathogenic bacteria
what does it mean to sanitize something?
lower bacterial content of food utensils or similar objects wtihout necessarily killing all bacteria (ie dishes washed in hot water and soap)
what is a preservative?
agent used in small (non-toxic) concentrations to inhibit the growth of organisms in, for example, food or vaccines
what is the phenol coefficient?
measure of the killing capacity of an agent, compared with phenol
ration of the minimal killing concentration of phenol to that of the agent
agent that works at concentrations lower than the killing concentration of phenol has a coefficient much greater than one
what are the three main physical agents used for sterilization, etc.?
in order of importance:
1: heat (wet or dry)
2: filtration
3: radiation (UV, gamma rays)
what types of heat are most effective?
wet heat (such as steam) is much more effective than dry heat because water molecules speed the denaturation of bacterial proteins by providing H bonds to replace those normally in the proteins - heated water molecules disrupt the H bonds
with dry heat, need greater time and temp for sterilization
what does an autoclave do?
provides standard conditions for complete killing of all bacteria (including spores)
live steam under pressure
what are the advantages and disadvantages of autoclaves?
advantages: assurance of complete sterilization
disadvantages: requires complicated equipment, unsuitable for heat-sensitive materials
what are the advantages and disadvantages of using dry heat?
takes longer and need higher temps
good for materials that would be damaged by water such as powders or surgical dressings
what are the advantages and disadvantages of using boiling water to sterilize?
kills most bacteria but not spores
but fast - five to ten minutes
simple equipment and is convenient
what is pasteurization?
heating of milk or other liquids to sterilize - reduces total bacterial count to 1-3% of initial level
63 degrees for 30 minutes
does not kill spores
what is high temperature short time? when is it used?
HTST - flash pasteurization
higher temps than normal pasteurization but much shorter (15-17 seconds)
used in juices and in milk sometimes in the US, method of choice for milk in europe and asia
how do you determine if milk has been sufficiently pasteurized?
if it tests negative for alkaline phosphatase - enzyme denatures under conditions similar to those that kill C. burnetii (which was what was originally tested for)
when would you use filtration?
when the liquid material to be sterilized is sensitive to heat (so can’t heat sterilize)
what are the advantages and disadvantages of filtration?
nondestructive but inconvenient, esp. for large volumes
where is filtration commonly used?
pharmaceutical industries have automated it
can also use presterilized, disposable filters that attach to a syringe in hospital and lab settings
what is commonly sterilized via filtration?
many vaccines, drugs,
kept in sealed, rubber-capped vials
how does filtration work?
run liquid through filter - bacteria too big to get through filter
what determines flow rate in filtration?
pore size
pressure applied
whether bacteria or other solids have begun to clog pores
what can not be removed via filtration?
a few types of bacteria can get through pores of .45 microns
none can get through .22 micron pores, but viruses can
how is radiation most commonly applied?
with a UV light emitted by mercury vapor lamps = nonionizing radation
when is radiation used?
to decrease bacterial content of air in ORs, barracks, nurseries, restaurants, hospital wards, and animal rooms
how does radiation sterilize (mechanism)?
nucleic acids and proteins absorb UV wavelengths
produces cross-linked thymine dimers in DNA
interferes with DNA replication
also causes toxic intracellular peroxide formation
what is the advantage of the UV? disadvantage?
simple to set up
can be left on for a long time
need little attention
poor capacity to penetrate anything but air and the thinnest layers of solids and liquids (won’t penetrate glass)
can irritate and damage human tissues
when are X-rays used for sterilization?
more energetic - have been used in food sterilization, but results questionable
how would drying lower bacterial levels?
water needed for bacterial growth
how would high osmotic pressure reduce bacterial levels?
high salt can dry out microbes
high sugar acts as a preservative
what do chemical sterilization methods do (generally)?
interact with lipids, proteins, or DNA
what determines the rate of killing of chemical methods of sterilization?
for most, rate increases with concentration and length of exposure
what is gaseous sterilization? what is it used for?
ethylene oxide = alkylating agent
used to sterilize heat-sensitive materials (esp plastics)
what are the advantages and disadvantages of gaseous sterilization?
reliable
suitable only for dry materials
toxic to humans
needs special equipment
explosive if pure so used only in presence of high CO2
when in gaseous sterilization used?
plasticware
surgical equiptment
hospital bedding
materials handled by patients
what is the widest used chemical sterilization method?
ethanol
what is the optimum concentration of ethanol for sterilization?
60-70%
how does ethanol sterilize?
denatures proteins
what are the advantages of ethanol versus isopropyl alcohol?
ethanol has legal restrictions on use
isopropyl alcohol doesn’t have those, slightly more potent, less volatile, but more expensive
when is ethanol used?
commonly on skin before infections
in tinctures of antiseptics and germicides
in jars where thermometers are stored
what does ethanol kill?
does not kill spores
what halogens are used for sterilization?
iodine
chlorine
what does tincture of iodine consist of?
iodine in water-ethanol solution
contains iodine and KI
how does tincture of iodine sterilize?
oxidizes the hydroxyl group of reactive tyrosine residues
when is tincture of iodine used?
reliable skin antiseptic
used for minor wounds (but hurts)
with detergents, used to prepare skin before surgery
when is chlorine used?
as a gas in water supplies and swimming pools as hypochlorite solutions by food and dairy industries to clean surfaces
what is the advantage of chlorine?
in the food industry, traces rapidly lost or destroyed, leaving no odor or flavor
how does chlorine sterilize?
oxidizes cysteine sulfydryl groups
what bacteria are cationic detergents effective against?
all kinds of bacteria
how do cationic detergents work?
disrupt cell membranes and dissolve lipid films that may protect bacteria
what are the most effective cationic detergents?
quaternary ammonium salts
have three short chain alkyl grous and a long chain alkyl group
why don’t anionic detergents work well?
the molecules are repelled by the negative charge of the bacterial surface
what are the advantages of cationic detergents?
leave a bacteriocidal film
work at low concentrations
usually non-irritating
what do cationic detergents not work against?
not active against pseudomonas
poorly active against mycobacterium tuberculosis
what oxidizing agents are used for sterilization?
hydrogen peroxide
potassium permanganate
when is hydrogen peroxide used?
as a 3% solution, infrequently used to treat wound infections, esp. deep ones that may contain anaerobes
to control growth of the plethora of anaerobic bacteria that grow in gingivial crevices of the gums
what antagonizes hydrogen peroxide action?
catalase
all staphylococci are catalase positive
when is potassium permanganate used?
as a urethral antiseptic
what is the mechanism of action of phenols?
denature proteins
when are phenols used?
to spray surgical operating rooms
what are the advantages and disadvantages of phenols?
kills wide variety of bacteria
but needs high concentrations
when are substituted phenols used?
as skin antiseptics
in antibacterial soaps
as a textile preservative
what do soaps effectively do?
remove bacteria and dirt from skin surfaces - only weakly bacteriocidal
what can make soaps antibacterial?
triclosan = antibacterial agent
how does triclosan work? what are the disadvantages?
inhibits specific step in lipid biosynthesis
resistant mutants can be isolated
how are heavy metals used to sterilize?
example = silver salts = 1% solution of silver nitrate - put in eyes of newborns to kill gonococcal organisms
mercurial compounds in organic form can be used on minor skin wounds
how do heavy metals sterilize?
bind to SH groups in proteins
how are dyes used to sterilize?
genetian violet = antifungal agent
used for candida and tinea (athletes foot)
what aldehydes are used to sterilize?
formaldehyde
glutaraldehyde
what is formaldehyde used for?
in vaccines
what is glutaraldehyde used for?
to treat areas wehre blood samples and used syringes are present - kills hepatits
what can be used to preserve food?
short chain FA and organic acids
eg. lactic acid in pickles and sauerkraut
acetic acid in pickles and relishes
propionic acid in bread (prevents mold growth)
benzoic acid in pharmaceuticals and food
natural phenolics (tymol; eugenol) as mild antiseptics and preservatives
smoked foods covered and partially penetrated by phenolic compounds from wood smoke
