Chapter 7 Control of Microbial Growth

Sepsis

Microbial contamination

Asepsis

A sense of significant contamination

Aseptic surgery techniques prevent

Microbial contamination of wounds

Sterilization

Removing all microbial life

Commercial sterilization

Killing clostridium botulinum endospores

Disinfection

Removing pathogens

Antisepsis

Removing pathogens from living tissue

Degerming

Removing microbes from a limited area

Sanitization

Lowering microbial counts on eating utensils

Biocide/germicide

Kills microbes

Bacteriostasis

Inhibiting, not killing, microbes

Population death rate is

Constant

Effectiveness of treatment depends on

• # of microbes

• Environment

  • Organic matter

  • Temperature

  • Biofilms

• Time of exposure

• Microbial characteristics

Actions of a microbial control agent

• alteration of membrane permeability

• Damage to proteins

• Damage to nucleic acids

Physical methods of microbial growth

• heat

• Filtration

• Low temperature

• High pressure

• Desiccation

• Osmotic pressure

• Radiation

Thermal death point

Lowest temperature at which all cells in a culture are killed in 10 minutes

Thermal death time

Time at which all cells in a culture are killed

Decimal reduction time

Time to kill 90% of cells at a given temperature

Autoclave

Steam under pressure

Autoclave conditions

• 121 Celsius

• 15 psi

• 15 minutes

• Kills all organisms and endospores

Pasteurization

Reduces spoilage organisms and pathogens

Pasteurization rules

63 celsius for 30 minutes

High temperature short time

72 C for 15 seconds

Ultra high temperature

140 C for <1 second

What organisms survive during pasteurization

Thermoduric (heat resistant bacteria in milk)

Dry heat sterilization

Kills by oxidation

Filtration

Used to sterilize heat-sensitive materials such as

• enzymes

• Vaccines

Desiccation prevents

Metabolism

Radiation

Damages DNA

Ionizing radiation

• Ionizes water to create reactive hydroxyl radicals

• Damages DNA by causing lethal mutations

Nonionizing radiation

Damages DNA by creating thymine dimers

Microwaves

Kill by heat, not especially antimicrobial

Chemical methods

Effective disinfection

• concentration of disinfectant

• Organic matter

• PH

• Time

Disk-diffusion method

• Evaluates the efficacy of chemical agents

• Look for zone of inhibition around disks

Phenol and phenolic

Disrupt plasma membranes and causes leaks

Halogens

• iodine

  • Tinctures

  • Iodophors

• Chlorine

  • Bleach

  • Chlorine gas

Alcohols

• ethanols

• Isopropanol

What does alcohol do

• denature proteins

• Dissolve lipids

What do heavy metals do

Denature enzyme and proteins

Soap

Degerming

Acid alcohol anionic detergents

Sanitizing

Sulfur dioxide prevents

Wine spoilage

Nitrite prevents

• Endospores germination

• Used in ham, bacon, hot dogs

Chemical food preservatives

• sulfur dioxide

• Organic acids

• Nitrite

• Antibiotics

Use of aldehyde

Medical equipment

Gaseous sterilants

• denatures proteins

• Damages DNA

Gaseous sterilants use

Heat sensitive material

Peroxygens def

Oxidizing agents

Peroxygens use

Contaminated surfaces (hydrogen peroxide)