Sterilization and Disinfection Overview

Study Notes

Sterilization: Process of removing all microorganisms, including spores.
Disinfection: Reduces the number of harmful microorganisms to a level where they no longer cause disease.
Sepsis: Indicates bacterial contamination.
Asepsis: Absence of significant contamination.
Bacteriostatic: An agent that inhibits bacterial growth.
Bactericide: An agent that kills bacteria.
Antiseptics: Chemicals safe for use on skin and mucous membranes (e.g., ethyl alcohol), not suitable for systemic use.

Microbial Control Methods: Broad category encompassing physical, chemical, and mechanical removal methods.
Physical Agents: Methods include heat (dry and moist), radiation (ionizing and non-ionizing), and mechanical removal (filtration).
- Dry Heat: Used for items not harmed by heat, using techniques like incineration or dry ovens (e.g., 160°C for 2 hours or 170°C for 1 hour).
- Moist Heat: Effective against microorganisms, using steam under pressure (autoclave) at 121°C for 20 minutes or 134°C for 3-6 minutes under pressure. Boiling water and pasteurization are also methods of moist heat but do not always result in sterilization.
- Radiation: Kills microorganisms using ionizing X-rays, gamma rays, or non-ionizing UV rays.
  - Ionizing radiation is used for items such as plastics, syringes, and some medical equipment.
- Mechanical Removal: Use of filtration techniques for heat-sensitive materials such as sera, hormones, vitamins, plasma, and vitamin C.
Chemical Agents: Disinfectants can be gaseous or liquid, and target animate (living organisms) or inanimate (non-living) objects and surfaces. - Gaseous: Used for sterilization. - Liquid (Animate): Chemotherapy. - Liquid (Inanimate): Antiseptics and other disinfecting solutions.

Hot Air Oven: Uses dry heat to sterilize items, relying on oxidation to kill microorganisms. Controlling temperature with a thermostat is important. Double-walled insulation conserves energy by keeping heat in. Effective for metal, glass, oil, and powders.
Flaming: Used to sterilize inoculating loops or wires by heating them in a Bunsen burner flame until red hot.
Incineration: Destruction of materials like contaminated cloths and animal carcasses.
Pasteurization: Process to kill pathogens, but not necessarily sterilize, typically used for milk when heated to 63°C for 30 mins (Holder Method) or 72°C for 15-20 seconds (Flash Process).
Inspissator: Sterilization by heating at 80–85°C for three successive days for half an hour. Used to sterilize media such as Lowenstein-Jensen and Loeffller's.
Chemical Agents: Include alcohols (e.g., ethanol), aldehydes (e.g., formaldehyde, glutaraldehyde), halogens (e.g., iodine, chlorine), and phenols.
Filtration: Eliminates microorganisms by passing solutions or air through a filter, effective for heat-sensitive materials.
Radiation: Non-ionizing radiation such as UV is used to reduce bacteria, suitable for sterilization of surfaces. Ionizing radiation, like X-rays and gamma rays, is used to sterilize equipment like plastics and metal.

High-level disinfection: Kills most organisms, including bacteria (excluding spores), viruses, and fungi. Hydrogen peroxide is an example.
Intermediate-level disinfection: Kills vegetative bacteria but not spores, and some viruses and fungi. Ethanol is an example.
Low-level disinfection: Kills most vegetative bacteria but not spores, some viruses and fungi. Quaternary ammonium compounds are an example.