Control of Microbial Growth Sterilization and Disinfection.

Control of Microbial Control of Microbial GrowthGrowth

Sterilization and Sterilization and DisinfectionDisinfection

SterilizationSterilization

COMPLETECOMPLETE destruction of all destruction of all microbial lifemicrobial life

All or nothing process – something All or nothing process – something cancan’’t be almost sterile, just like you t be almost sterile, just like you cancan’’t be almost pregnant!t be almost pregnant!

Heat is the most common method for Heat is the most common method for sterilizationsterilization

Disinfection and AntisepsisDisinfection and Antisepsis

DisinfectionDisinfection Removal of harmful Removal of harmful

organisms from organisms from surfacessurfaces

NOT sterileNOT sterile Generally involves Generally involves

the use of the use of chemicalschemicals

Example - VespeneExample - Vespene

AntisepsisAntisepsis Removal of harmful Removal of harmful

organisms from the organisms from the skinskin

NOT sterileNOT sterile Use of a less harsh Use of a less harsh

chemical chemical substancesubstance

Antibacterial Antibacterial washeswashes

-cidal -cidal or or -static-static

-cidal means to kill-cidal means to kill BacterioBacteriocidalcidal agent kills bacteria agent kills bacteria -static means to inhibit or prevent-static means to inhibit or prevent BacterioBacteriostaticstatic agent will only inhibit agent will only inhibit

or prevent bacterial growthor prevent bacterial growth Growth will resume after the agent is Growth will resume after the agent is

removedremoved

Physical Methods to Control Physical Methods to Control Microbial GrowthMicrobial Growth

Heat – moist or dryHeat – moist or dry FiltrationFiltration Low temperatureLow temperature DesiccationDesiccation Osmotic pressureOsmotic pressure Radiation - Radiation -

AutoclaveAutoclave

Steam under pressureSteam under pressure Achieves temperatures above 100°CAchieves temperatures above 100°C Very high penetrating powerVery high penetrating power Kills bacteria and spores by denaturing Kills bacteria and spores by denaturing

proteinsproteins Typical cycle is 30 min, 18psi, 122°CTypical cycle is 30 min, 18psi, 122°C Items to be sterilized must be heat stableItems to be sterilized must be heat stable Examples : media, glassware, lab coats, Examples : media, glassware, lab coats,

surgical instrumentssurgical instruments

Dry Heat SterilizationDry Heat Sterilization

Kills by oxidation – incinerationKills by oxidation – incineration Flaming your inoculating loop is an Flaming your inoculating loop is an

exampleexample Hot air sterilization – ovenHot air sterilization – oven Temperature required is 170°C Temperature required is 170°C

(312°F) for 2 hrs(312°F) for 2 hrs Oven sterilization also requires that Oven sterilization also requires that

the items be heat stablethe items be heat stable

PasteurizationPasteurization

Method for treating milk to eliminate Method for treating milk to eliminate pathogenic microbespathogenic microbes

Low temperature pasteurization: 72°C for Low temperature pasteurization: 72°C for 15 sec15 sec

Kills pathogens but the milk is Kills pathogens but the milk is NOTNOT sterile sterile Ultra high temperature pasteurization: Ultra high temperature pasteurization:

74°C to 140°C for 5 sec and back to 74°C 74°C to 140°C for 5 sec and back to 74°C does achieve sterilitydoes achieve sterility

FiltrationFiltration Method used to Method used to

sterilize heat sensitive sterilize heat sensitive liquidsliquids

Culture media, Culture media, antibiotics, vaccines, antibiotics, vaccines, enzymesenzymes

Solution is passed Solution is passed through a membrane through a membrane with pours so small with pours so small that bacteria cannot that bacteria cannot pass throughpass through

Resultant solution is Resultant solution is STERILE!STERILE!

FreezingFreezing

Bacteriostatic effect onlyBacteriostatic effect only Slows down bacterial growth but Slows down bacterial growth but

does not kill the bacteriadoes not kill the bacteria Some bacteria may be killed on the Some bacteria may be killed on the

freeze-thaw but many survivefreeze-thaw but many survive NO STERILITY from freezingNO STERILITY from freezing

DesiccationDesiccation

Drying out; removal of waterDrying out; removal of water Bacteriostatic Bacteriostatic Bacteria will grow once water is Bacteria will grow once water is

addedadded Bacterial cultures are often Bacterial cultures are often

preserved in a freeze dried state; preserved in a freeze dried state; Add media and presto, live bacteria!Add media and presto, live bacteria!

NO STERILITY from desiccationNO STERILITY from desiccation

Osmotic PressureOsmotic Pressure

High salt or sugar content can High salt or sugar content can ““preservepreserve”” foods by preventing foods by preventing bacterial growthbacterial growth

BacteriostaticBacteriostatic Honey, jelly, salted meats resist Honey, jelly, salted meats resist

bacterial growth because of osmotic bacterial growth because of osmotic pressure exerted by the sugar or saltpressure exerted by the sugar or salt

Molds and yeast often still growMolds and yeast often still grow

Radiant Energy SpectrumRadiant Energy Spectrum

Types of RadiationTypes of Radiation Ionizing radiationIonizing radiation Gamma rays, X rays, Gamma rays, X rays,

high energy electron high energy electron beamsbeams

Short wavelength, Short wavelength, high energyhigh energy

Continuous exposure Continuous exposure to ionizing radiation to ionizing radiation does achieve sterilitydoes achieve sterility

Sterilizing plastics, Sterilizing plastics, medical supplies, medical supplies, gloves, syringes, heat gloves, syringes, heat sensitive itemssensitive items

Non-ionizing radiationNon-ionizing radiation Longer wavelengthLonger wavelength UV lightUV light Damages DNADamages DNA Germicidal lampsGermicidal lamps Disadvantage is the Disadvantage is the

very low penetrating very low penetrating power of UV radiationpower of UV radiation

Sterilization of Sterilization of surfaces, heat surfaces, heat sensitive itemssensitive items

Phenols and PhenolicsPhenols and Phenolics

Derivatives of carbolic acidDerivatives of carbolic acid Found in throat lozenges and soapsFound in throat lozenges and soaps Primary activity is injury to bacterial Primary activity is injury to bacterial

plasma membraneplasma membrane Well known products that contain Well known products that contain

these chemicals are Lysol, pHisohex these chemicals are Lysol, pHisohex soap, chlorhexidine soaps used in soap, chlorhexidine soaps used in surgical scrubssurgical scrubs

Phenol and phenolic compoundsPhenol and phenolic compounds

HalogensHalogens

Iodine and Chlorine compoundsIodine and Chlorine compounds Very reactive molecules that kill Very reactive molecules that kill

microbesmicrobes Betadine – iodine compound used to Betadine – iodine compound used to

clean surgical sites and woundsclean surgical sites and wounds Chlorine is used to disinfect waterChlorine is used to disinfect water Household bleach is chlorine and can Household bleach is chlorine and can

be used to disinfect home surfacesbe used to disinfect home surfaces

Oligodynamic ActionOligodynamic Action

Action of certain heavy metals to kill Action of certain heavy metals to kill bacteriabacteria

Metals such as silver, copper, zinc, Metals such as silver, copper, zinc, and mercury can prevent bacterial and mercury can prevent bacterial growthgrowth

Metal ions combine with proteins to Metal ions combine with proteins to cause denaturation (loss of protein cause denaturation (loss of protein function)function)

Oligodynamic ActionOligodynamic Action

AlcoholsAlcohols

Effective agent to kill bacteriaEffective agent to kill bacteria Denatures proteinsDenatures proteins Ethanol and isopropanol are the most Ethanol and isopropanol are the most

commonly used alcoholscommonly used alcohols Need to clean a wound in the wild? Need to clean a wound in the wild?

Use that Tequila youUse that Tequila you’’re carrying, re carrying, then drink the rest!then drink the rest!

Quaternary Ammonium Quaternary Ammonium CompoundsCompounds

Widely used surface active agentsWidely used surface active agents Positive charged ammonium group is Positive charged ammonium group is

responsible for anti-microbial actionresponsible for anti-microbial action Quats are bacteriocidal (G+), Quats are bacteriocidal (G+),

fungicidal, amoebicidal, and virucidalfungicidal, amoebicidal, and virucidal Two best known quats areTwo best known quats are

– Zephiran (benzalkonium chloride)Zephiran (benzalkonium chloride)– Cepacol (cetylpyridinium chloride)Cepacol (cetylpyridinium chloride)

Quaternary Ammonium Quaternary Ammonium CompoundsCompounds

AldehydesAldehydes

FormaldehydeFormaldehyde GlutaraldehydeGlutaraldehyde Both are strong bacterial killersBoth are strong bacterial killers Cause protein inactivationCause protein inactivation Glutaraldehyde is often used to Glutaraldehyde is often used to

sterilize hospital instruments (Cidex)sterilize hospital instruments (Cidex)

Gaseous sterilizersGaseous sterilizers

Ethylene oxideEthylene oxide Denatures proteinsDenatures proteins Used in closed areas such as roomsUsed in closed areas such as rooms High penetrating power, but High penetrating power, but

dangerously explosive in pure formdangerously explosive in pure form Used to sterilize heat sensitive items Used to sterilize heat sensitive items

or large spaces such as roomsor large spaces such as rooms