Microbial Control

Sterilization

Removing and destroying all microbial life.

Commercial Sterilization

Killing microbes/endospores in canned goods without damaging food quality.

Sterilant

Agent for sterilizing (ex.heat)

Disinfection

Destroying harmful microorganism on inanimate surfaces/objects

Antisepsis

Destroying harmful microorganisms from living tissue.

Degerming

Mechanical removal of microbes from limited area (ex. handwashing)

Sanitization

Lowering microbial counts to safe levels (ex. dishwasher)

Biocide/Germicide

Treatment that kills microbes

Biostasis

Inhibiting, not killing, microbes

Effectiveness of antimicrobials depends on :

• Number of microbes

• Environment (organic matter, temp., biofilms)

• Time

• Microbial characteristics

Actions of microbial agents :

• Damages plasma membrane

• Damages proteins/enzymes

• Damages nucleic acids

Thermal Death Point (TDP)

Lowest temp at which all cells in a liquid culture dies in 10 minutes

Thermal Death Time (TDT)

Minimum time for all bacteria in liquid culture to be killed at particular temp.

Decimal Reduction Time (DRT) / D value

Amount of minutes it takes to kill 90% of a specific population of bacteria at given temp.

Dry Heat

Kills by oxidation (ex. flaming, incineration, hot air)

Types of Moist Heat

• Boiling

• Autoclave

• Pasteurization

Boiling

Disinfection, water penetrates material quicker than dry heat; kills most vegetative cells.

Autoclave

Sterilization, steam under pressure; 121 C at 15 psi for 15 minutes will kill all except prions.

Pasteurization

Reduce spoilage organisms and pathogens in milk/juice

High-temp short time pasteurization (HTST)

72 C for 15 seconds ; heat resistant organisms survive, but unlikely to cause disease

Ultra-high temp pasteurization (UHT)

140 C for 4 seconds ; sterilize milk, creamer, and juice to make them shelf stable

High-efficiency particulate air filter (HEPA)

Remove microbes >0.3 micrometer in diameter

Membrane filter

Removes microbes >0.05-0.22 micrometer ; can filter viruses and large proteins

Types of cold bacterial controls :

• Refrigeration

• Deep-freezing

• lyophilization (freeze-dry)

Desiccation

Removal of water ; microorganisms cannot grow or reproduce until water resumes

Osmotic Pressure Microbial Control

Creates hypertonic environment that cause plasmolysis (cell shrinking)

Ionizing Radiation

Ionizes water to create reactive hydroxyl radicals ; high energy, shorter wavelength, more penetration. Damages DNA

What is ionizing radiation used for?

Sterilization of medical and lab equipment and preservation of food.

Gamma Rays

Type of ionizing radiation ; penetrates deeply, but takes hours to sterilize

High Energy Electron Beams

Type of ionizing radiation ; less penetration, but takes seconds to sterilize

Nonionizing Radiation

Damages DNA by making thymine dimers ; good for surfaces.

Thymine Dimers

Inhibit correct replication of DNA during cell replication.

Disk-diffusion Method

Disk of filter paper gets soaked with chemical and then placed on agar plate; clear halo shows inhibition

Effectiveness of chemical microbial controls depends on :

• Concentration of disinfectant

• Organic matter present

• pH

• Temp

• Time

Phenol and Phenolics

Injure lipids of plasma membrane and cause cell leakage ; remain active in presence of organic matter. Ex. lysol

Biguanides

Disrupts plasma membrane ; effective against gram neg/pos bacteria and envelopes viruses. Ex. Chlorhexidine used in surgical hand scrubs and pre-op skin prep.

Halogen Types

Iodine : most effective antiseptic

Chlorine : disinfectant that shuts down cellular enzyme systems (ex. bleach)

Alcohol

Denatures proteins and dissolve lipids ; no effect of endospores or enveloped viruses.

Heavy Metals

Denatures proteins ; effective in small amounts. Ex. zinc chloride in toothpaste

Oligodynamic Action

Ability to exert antimicrobial activity in small amounts

Soap

Cause microbial destruction due to sudden alkalinity on skin surface.

Aldehydes

Inactivate proteins by cross-linking with functional groups

Formalin

Used for preserving tissue specimen ; type of aldehydes

Glutaraldehyde

Liquid chemical sterilizing agent ; used on equipment that can’t be autoclaved

Alkylation

Replace hydrogen atoms of a chemical group with a free radical ; gas used for heat sensitive materials

Ethylene Oxide

Gas used to sterilize large pieces of equipment ; needs sealed chamber

Chlorine Dioxide

Used for fumigation and surface disinfection

Peroxygen

Oxidizing agents