Sterilization Methods

Sterilization Methods

• 2 types
• Physical methods
• Heat
• Filtration
• Radiation
• Chemicals methods

Sterilization vs Disinfection

• Sterilization
• Complete killing (includes spore form)

Materials	Method
Surgical instruments (except sharps)	Autoclave > H₂O₂ > ETO
Plastic & rubber materials	Autoclave > H₂O₂ > ETO
Glass & Sharps	Autoclave > Hot air oven
All culture media (CM) except	Autoclave
↳ Serum CM (Loeffler’s serum slope) ↳ Egg CM (Lowenstein-Jensen medium)	Inspissation > Tyndallization
Oily & powdery materials	Hot air oven
Bacteriological loop	Heating turns red hot
Slides, cover slip	Pass over flames 3 times

• Mnemonic: EFGHAPPPT
• E - Ethylene oxide
• F - Formaldehyde
• G - Glutaraldehyde
• H - H2O2, Hot air oven, 1% Hypochlorite
• A - Autoclave
• P - Per Acetic acid
• P - Plasma sterilization
• P - o-phthalic acid
• T - Tyndallization

• Disinfection
• Excludes spore form

Level	Examples	Uses
High level (HLD)	Aldehyde ↳ Better → kills spores	• Cidex → Gluteraldehyde 2% • Formalin • Duckering → Formaldehye 2%
Intermediate level (ILD)	1% Na hypochlorite ()	• Blood spill
Low level (LLD)	Alcohol	• Sanitiser

• Bleaching powder is disinfectant, not sanitizer

Heat

Physical methods

A. Heat

1. Dry Heat

a. Hot Air Oven

• Temperature and duration
• 160°C for 2 hr

• Uses
• Glassware
• Cotton swabs
• Dusting powder
• Oil
• Greasy material
• Liquid paraffin

• Dusty, oily, greasy and liquid material stored

• Control
• Biological:
• Spore forming organisms
• Bacillus subtilis
• Bacillus atrophaeus
• Clostridium tetani
• Chemical control:
• Browne's Tube (green spot)
• If we get green spot then sterilization is complete
• Brown hot girl with subtle tits ⇒ Spore forming ⇒ did for 2 hrs
• Dusty oily greasy liquidy

b. Incineration

• All hospital waste and human body parts

• There 2 chambers:
• 700° - 800°C
• 1000° - 1100°C

• Uses
• Hospital waste
• Human anatomical waste

2. Moist Heat

• Pasteur in water batch

• Flashing only for 20 seconds

• Holding for 30 mins

• Autoclave
• Auto 15 mins odich → 121 Rs
• 1.5 hrs odich → 134 Rs

Uses of Autoclave

• Instruments

• Aprons

• Sutures,
• except Catgut sutures (heat sensitive) → γ Radiation

• Media
• except LJ, LSS → Inspissation
• Because LJ and LSS are in <100°C

• Sputum
• Prior to discard it is autoclaved

B. Filtration

• Seitz filter
• Contains - Asbestos (carcinogenic)
• Pore size - 0.22 μ

Uses of filtration:

• Heat sensitive substances
• Vaccines
• Antibiotics
• Serum
• Toxins
• Sugar solutions

• Air purifiers
• HEPA: High Efficiency Particulate Air filter
• ULPA: Ultra Low particulate Air filter

• Control:
• Brevundimonas diminuta
• Serratia
• Minute serrations in filter

Radiation

• Types:
• Ionizing radiation
• Non-Ionizing radiation

Ionizing Radiation	Non-ionizing radiation (Hot radiation)
Examples ◦ X rays ◦ Gamma rays ◦ Cosmic rays	Examples ◦ UV rays ◦ Infrared rays
Ion → Single term ↳ X, γ, Cosmic	Non-Ion → 2 terms ↳ IR, UV
Cold radiation	Hot radiation
Does not increase temp of surface	Microbiologist works
High penetrating power	Low penetrating power
Sporicidal	Bactericidal (not sporicidal)
Uses ◦ Catgut sutures ◦ Grafts	Uses ◦ OT Fumigation ◦ Biosafety cabinet
ㅤ	Control: Hot Pamela ◦ Bacillus Pumilus ◦ P – R

Chemical Methods of Sterilization

1. Alcohols

• Ethyl alcohols (70%): Spirit swabs

• Isopropyl Alcohol: (70-80%)
• Stethoscope
• Thermometer

2. Formaldehyde

• Gas - OT fumigation

• Formalin (liquid) - All human specimens stored

• Duckering - killing bacillus anthracis spores from animal wool
• Process where animal wool is treated with 2% formaldehyde

• Duck (Duckering) From (Formalin) Anthra ()

3. Glutaraldehyde

• Glutaraldehyde 2%
• CIDEX

• Activated by alkalinisation - active for 14 days
• Bronchoscope
• Laryngoscope
• Endoscope
• Except: Arthroscope and urethroscope sterilized by plasma sterilization

4. Phenol

• Antiseptics
• Phenol (5%)
• Cresol (1-3%)
• Lysol (2-5%)
• Modified phenol
• Chlorhexidine + Cetrimide = Savlon
• (Old name for savlon: Hibitane and Citavlon)
• Chloroxylenol = Dettol

5. Halogen/ Iodine / Chlorine

• Skin antiseptic

• Betadine (povidone iodine)

• Tincture iodine (2% iodine) for skin antiseptic

• 1% sodium hypochlorite for blood spill

6. Plasma Sterilization

• Plasma: 4th state of matter

• Process
• UV photons used
• Vacuum
• Low temperature
• H₂O₂ chemical present

• Advantage
• No toxicity
• Shorter time duration

• Use
• Surgical instruments
• Arthroscopes
• Ureteroscopes

• Control: Bacillus Stearothermophilus (autoclave, Plasma sterilization)

7. Gas Sterilization

• Ethylene oxide (ETO)
• Never use 100% ETO
• 3-10% ETO is enough
• Mix with inert gas because its inflammable

• Side effects
• Highly inflammable
• Highly irritant
• Highly explosive

• Uses: Cardiopulmonary machines

• Control: Bacillus globigii
• Global Gas

Sterilization Controls Summary

Testing of Disinfectant

Spaulding Classification