Sterilization Methods

Explain difference between sterilization and disinfection

  • Sterilization - completely destroy/remove microbial life + spores (heat resistant)

  • Disinfection - removal of harmful microorganisms, but may not include spores, organisms aren’t all killed but reduced to a safe level

  • Disinfectant - products to kill microorganisms, may be sporostatic (inhibiting growth)

  • Antiseptic - killing growth of microorganisms on living tissue

  • Aseptic - absence of pathogenic microbes



Understand modes of action for various physical + chemical agents

  • Physical sterilization: sunlight, heat (moist - boiling, steaming, autoclave (moist heat), dry - incineration, hot oven), UV, ionizing radiation (X-ray, gamma), filtration

  • Chemical: alcohol (hand sanitizer), phenols, dyes, oxidizing agents



Recognize methods like autoclave, filtration, heat, radiation for sterilization + disinfection

  • Disrupt cell wall

  • Disrupt lipid structures/proteins

  • Modify DNA

Dry Heat - incineration, heating a loop until red

Hot air oven - much longer exposure, 1/2 hours at 160C, or 30 min at 180C

Autoclave - 15-20 min at 121C, kills very high heat resistant spores

Pasteurization - for liquids/dairy, LTH, HTST  (high temperature short time), UHT - 138C + 3 sec

Filtration - removes bacteria from heat labile liquids, like sera, antibiotics

  • Membrane: pores that trap microbial organisms, water purification, made of cellulose esters for solutions, 0.2 mm

** even if bacteria are filtered, viruses are smaller and might pass through

Radiation - used in DNA



Alcohol - most common, ethanol, disinfection of the skin + hands, objects

Detergents - dish washing, clothing wash

Phenols - first disinfectant

Chlorine - water purification, swimming pool purification

Iodine - skin antiseptic

Heavy metals - treatment (ie. eyedrops)

Hydrogen peroxide - cleaning wounds, contact lenses

Formaldehyde - plastic/rubber disinfectant

Ethylene oxide - sterilization of heat sensitive hospital equipment (i.e. surgical instruments, plastics)

acids/alkalis - food preservatives 

Nucleic acid - dyes for staining and inhibiting growth



Sterilization control - applied to instruments prior to being autoclaved, changes to black to pass properly (Bowie Dick tape)



Apply knowledge to hospital scenarios

  • Hot air ovens are used in glassware, metallic instruments, swabs, oils, and pharm. products

  • Autoclaves for sterilization (surgical tools, linen), research labs (glass wear, nutrition, biohazardous waste, food manufacturing)

  • UV rays are used to disinfect smooth surfaces to lower airborne viruses

  • X-rays and gamma are used to sterilize hospital plastics like syringes, catheters 

  • Easy to kill: viruses with lipid envelopes, alcohol can kill the membrane

  • Extremely hard to kill: prions (abnormal proteins) that cause diseases