Lecture 21 - Controlling Microbes

Type and number of microbes, environmental conditions, risk of infection (bio lab safety levels), composition of fomite

The selection of an effective procedure depends on the _______

Sterilization

killing/removal of ALL living organisms (pathogens) from inanimate objects (endospores)

Disinfection

killing/removal of most/all organisms (pathogens) from inanimate objects (not endospores)

Antisepsis

killing/removal of most/all pathogens from the surface of living tissues (not endospores)

Sanitation

reducing the microbial population to safe levels

Physical Control - Heat

Dry heat: high heat incinerates microbes

Moist heat (most effective)

Boiling does no sterilize

Autoclave sterilizes

Pasteurization

Pasteurization

Heating at high temps for short times. Not all organisms killed

Not general sterilization

Boiling water, steam canning, use for high-acid foods

physical control - canning

not general sterilization

• boiling water

• steam canning

• use of high-acid foods

Sterilization

• pressure canning

• not automated

autoclave

• destroys endospores

• temperature higher than boiling point

• Sterilization typically 121°C and 15 psi in
  20min

• Flash sterilization at higher temperature
  can be used

Physical control - freezing

Low temperature

• refrigeration slows growth

• freezing stops microbial growth

• microbial cells can grow once thawed

Physical control - filtration

Filtration of fluid (membrane filters)

• small pore size (0.2 um)

• thin

Filtration of air

• High efficiency particulate air (HEPA) filters

• remove nearly all microbes from air (0.3 µm)

Physical control - radiation

Ionizing (high energy)

• Gamma rays, x-ways

• Produces reactive oxygen species

Ultraviolet

• damages DNA (disinfect)

• Poor penetration power (glass and plastic will block)

Chemical methods of microbial growth

disinfectants, antiseptics, sterilants, and antibiotics

main mechanisms of action

• Disruption of cell membranes

• Protein denaturation

• Nucleic acid damage

Sterilants/sporicides

Destroy all microorganisms and endospores

• peracetic acid = acetic acid + hydrogen peroxide

• oxidizes primary metabolites

• destroys cell walls and spores

• penetrates biofilms

High level disinfectants

can’t destroy endospores, struggling;e with biofilms

• denatures proteins through oxidation

• oxidizes lipids

• needs high concentration to penetrate biofilms

intermediate disinfectants

can’t destroy some non-enveloped viruses and all endospores (70% isopropyl alcohol)

• 70% isopropyl alcohol (IPA) = 70% isopropanol + 30% water

• denatures proteins by dehydration

• dissolves lipids, causing membrane rupture

• not effective against biofilms

Low level disinfectants

can’t destroy all viruses, bacteria, fungi, or endospores

ex. Lysol

• disrupts and dissolves cell membranes

• alters some membrane proteins

• not biofilm effective

• not effective against some gram negatives

Chemical agents

alcohol, halogens, phenolics, aldehydes

Alcohol

Examples: ethanol, isopropanol

Level: intermediate

Use: skin antiseptic, surface disinfectant

Mode of action: oxidizes cellular components, denaturing enzymes, and disrupting membranes

Halogens

examples: iodine, chlorine

level: high (concentration matters)

Use: water treatment, wound antiseptics

Mode of Action: Oxidizes cellular components,
denaturing enzymes & disrupting membranes

Phenolics

Examples: Triclosan, lysol

Lvele: intermediate

Use: household disinfectants

Mode of action: denatures proteins disrupting lipid membranes

aldehydes

examples: formaldehyde, glutaraldehyde

level: high level (sterilants)

Use: sterilization of medical instruments

Mode of action: crosslinks proteins and DNA, making them inactive