Sterilization and Disinfection
Method | Principle | Time/Temp. | Utility | ||
Heat | Moist Heat: Spores of Bacillus stereothermophilus are used for sterilization control | Autoclave | - Denaturation and coagulation of protein - More heat at low temp. due to latent heat of vapourization | 5 psi- 109 oC - 60 min | - Graduated cylinder - Biological waste - Culture Media - Linens - Gloves - Plastic wares - Culture plates |
10 psi- 115 oC - 30-40min | |||||
15 psi- 121oC -15-20min | |||||
20 psi- 126 oC -10 min | |||||
25 psi- 131 oC -5 min | |||||
30 psi- 135 oC -3 min | |||||
Tyndallisation | Denaturation and coagulation of protein | 100 oC for 15-20 min x 3 days | - For canned food items | ||
Inspissation | Denaturation and coagulation of protein | 70-80 oC for 15 min x 3 days | - Dorset Egg media, LJ Media | ||
Pasteurization | Denaturation and coagulation of protein | Holder's method: 63 oC for 30 min | - To destroy the vegetative form of pathogenic bacteria found in milk Esp. M. tuberculosis, Brucella spp, Salmonella and Coxiella brunetti (only by flash method) | ||
Flash Method: 72 oC/15sec | |||||
Ultra high temp:132 oC/2sec | |||||
Vaccine Bath | Denaturation and coagulation of protein | 60 oC for 60 min | For Vaccines | ||
Dry Heat | Red Heat | Burning | Keeping over flame until red hot | - Wireloops, straight wire | |
Incineration | Burning | Burning down to ashes | - All surgical and laboratory infected wastes that cannot be recycled | ||
Hot air oven | Denaturation of protein and enzymes & altered ion concentration | 180 oC for 20 min | - Cotton, ungraduated glasswares, - Powder, oil, - scissors and blades | ||
170 oC for 30 min | |||||
160 oC for 60 min | |||||
150 oC for 150 min | |||||
Flaming | Denaturation of protein and enzymes & altered ion concentration | Passing over flame 2-3 times | Mouth of Glass wares e.g. Glass tube, conical flask , round bottle , measuring cylinder |
Method | Principle | Utility | ||
Rdiation | Ionizing radiation | Gamma rays X-rays Cosmic ray | Have high frequency and low wavelength Damage DNA. Cause ionization of the atoms in cells | Sterilization of plastics, syringes, swab, catheter etc |
Non-ionizing radiation | UV ray Infra red rays | Damage DNA by inducing mutations by formation of thymine-thymine dimer. Cannot kill spores. Cannot cause ionization of the atoms in cells | Cleaning biosafety cabinet, safety hood, Microbiology room etc | |
Filtration | - Sintered glass filter - Membrane filter - Seitz filter - Asbestos | Serritia marcescence is used as control organism | - antibiotic solutions - sera - carbohydrate solution | |
Vibration | - Ultra sonic - Sonic vibration | High frequency waves destroy the bacteria by agitation and rupture of cell wall | - For certain heat and chemical sensitive liquids | |
Chemical Method | Alcohol | Ethanol Isopropanol | Protein Denaturation, cannot destroy spores | Cleaning Working bench, hand sanitizing, |
Aldehyde | Gluteraldehyde | Acts on amino acid of proteins | For sterilization of plastic tubings, catheters, endoscope and metal instruments | |
Formalin | Acts on amino acid of proteins, bactericidal, sporicidal, viricidal | Preserving anatomical specimen, killing anthrax spores in wool, cleaning metal surfaces, fumigation of rooms | ||
Dyes | Aniline Dye: - Malachite green - brilliant green - crystal violet | More active against Gram Positive Bacteria. Active at high dilutions. Destroy by acting upon acid component of bacteria | - Used as antiseptics for wounds on skin - Used as selective agents in culture media | |
Acridine Dye: - Proflavin - Acriflavin | Destruction of DNA complexes and thus reproduction | - Antiseptics | ||
Halogen | Hypochloride | Bactericidal, viricidal | Disinfectant | |
Iodine | Bactericidal, viricidal | Skin antiseptics | ||
Phenol | Damage to cell membrane | Disinfectant for floor, work bench | ||
Surface active agents | Cationin and anionic detergents | Bactericidal | For floor and surfaces | |
Metallic salts | HgCl2 and AgNO3 This action is due to affinity of certain protein for metallic ions. | Bactericidal in concentration less than 1 part per million. | ||
Gases | Ethylene Oxide, Formaldehyde, betapropeolactone | Rooms , chambers, microbiology labs, Operation theater | ||
Sterilization control
Autoclave
- Spores of Bacillus stearothermophilus
- Browne’s tube
- Autoclave tapes
- Thermocouples
Hot Air Oven
- The spores of non-toxigenous strain of Clostridium tetani
- Browne’s tube: A green color is produced after 60 minutes at 160°C
- Thermocouples