Sterilization and Asepsis (Control of Microbes)

Control of Microorganisms (sterilization and asepsis)

• Terminology:
• Asepsis:
• Without infection
• Free of infectious agents

• Sterilization:
• Destruction or removal of all life
• Removal includes spores, viruses
• Sterile: free of all life

• Disinfection:
• Removal of pathogens from nonliving surfaces or objects
• Some organisms may survive
• Disinfectant: agent used to disinfect nonliving surfaces
• Example: Lysol

• Antiseptic:
• Agent used on living tissue to prevent infection
• Example: hand-sanitizer, mouthwash
• Sanitization:
• Removal of 99.9% of vegetative pathogens

Cidal and Static Action

• –cide refers to killing
• Example: germicide

• –stasis refers to stopping or to inhibit without killing
• Example: bacteriostatic 

Control Methods: Physical

• Heat: heat kills microbes through denaturation of enzymes
• Moist heat
• Boiling: 100 degrees C at sea level
• Kills most vegetative bacteria, viruses, fungi
• Endospores and some viruses may survive
• Autoclaving
• Higher temperature under pressure
• Pressure is used to increase the boiling point of water
• 0 psi: 100 degrees C
• 15 psi: 121 degrees C
• 30 psi: 135 degrees C
• This is the preferred method of sterilization
• Autoclaving should kill endospores and viruses

Physical Methods: Dry Heat

• Dry heat requires longer times because it carries less heat for the same temperature.
• Sterilization
• Incineration
• Hot air oven

Physical Methods: Cold

• Static for most organisms
• Refrigeration
• Freezing

Physical Methods: Drying

• Static for most organisms
• Lyophilization: freeze-vacuum drying

Physical Methods: Osmotic Pressure

• Salt or sugar are used to preserve food
• Static for most organisms

Physical Methods: Radiation (sterilization)

• Ionizing radiation:
• Gamma rays, X rays or high energy electron beams with wavelength shorter than non-ionizing radiation
• Have penetrating ability

• Non-ionizing radiation
• Ultraviolet (UV) light
• UV light damages the DNA of exposed cells
• Not very penetrating

Physical Methods: Filtrations

• Physical removal of organisms from liquids
• Does not generally harm the organisms
• Filtration is important for water treatment

Types of Disinfectants

Disk-Diffusion Method

• Used to determine microbial susceptibility to disinfectants and/or antibiotics
• Measure the zone of inhibition

Pasteurization of Milk

• Milk may have potential pathogens
• Milk is a superb fluid medium for the growth of microbes
• Several possible sources of pathogens:
• Present in the udder
• Example:
• Staphylococcus
• Brucella spp. (brucellosis)
• From fecal contamination
• Example:
• Salmonella spp
• Campylobacter sp
• E. coli
• From personnel
• Mainly a problem in hand washing

Milk

• Pasteurization
• Minimum 72 degrees Celsius for 15 seconds
• Higher temperature often used
• Should remove all pathogens
• Allowing only organisms that can withstand heart to survive
• Streptococcus lactis
• Lactobacillus spp.
• Some bacillus spp.
• Considered static

Homogenized milk

• A technique used to mix the water soluble portion of milk with milk fat
• Fat droplets are broken down from very large to very fine
• Does not change the bacterial count

Asepsis - Back to Microbiology
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