Physical Control

Time required to kill all the target microbes at a specific temperature

The temperature at which an organism is killed in 10 minutes

Direct flame; loop in Bunsen burner; disposable materials

Care should be taken to be sure pathogens do not escape the flame before they are killed

Hot air oven at 160 C for 1.5 to 2 hours

Powders, glassware; used on materials that cannot withstand moisture

Penetrates more rapidly than dry heat

100 C for 10 minutes will kill vegetative forms

Viruses & spores: 2 hours; not a very reliable method

Most dependable method; steam under pressure; 121 C at 15 psi for 15 mins

Limitations: plastic ware melts, sharp instruments become dull, some chemicals break down; Bacillus stearothermophilus used as a control

Fractional sterilization; steam at 100 C for 3 minutes on 3 successive days

Used for liquids and heat- sensitive materials

Not a method of sterilization; destroys pathogens and organisms that cause spoilage and reduces bacterial count

Pasteurization is aimed at destroying

Device for removing microbes from a solution

Pad of porcelain or ground glass

Use diatomaceous earth (remains of marine algae); swimming pool, aquarium filters

Pad of cellulose

Valuable because colonies will form on pad and can be counted

265 nm is most destructive to bacteria (visible light: 400- 800 nm)

Cannot penetrate solids or liquids; reduces airborne or surface contamination

Ionizing (high energy) radiation used to sterilize vitamins, hormones, and antibiotics; break chemical bonds

No specific activity against microbes other than heat generation

Sound waves with frequencies beyond the range of human hearing are passed through a fluid; used for fluids

High frequency sound waves cause formation of bubbles or cavities. The cavities collapse and send out shock waves which destroy microbes

Few practical applications; geneticists split cells to study organelles, dentists use sonicare