General microbiology-3 Flashcards
Physical methods of sterilization
- Heat
- Filtration
- Radiation
Types of dry heat sterilization
Sunlight
Hot air oven
Incinerator
Flame burners
Candle
Mechanism of dry heat sterilization
‘CODE’
Charring
Oxidative damage
Denaturation of protein
Electrolytes increased
Moist heat sterilization example
Boiling water, Pressure cookers
Moist heat > Dry heat
Mechanism of moist heat sterilization
Coagulation and denaturation of proteins
What is a hot air oven?
A dry heat sterilization device that uses hot air (160°C) to kill microorganisms by oxidation.
What are the standard temperature and time settings for a hot air oven?
160°C – 2 hours
170°C – 1 hour
180°C – 30 minutes
What items can be sterilized using a hot air oven?
✅ Glassware (flasks, test tubes, Petri dishes)
✅ Metal instruments (forceps, scalpels)
✅ Powders (talc, zinc oxide)
✅ Oily substances and fats
What items cannot be sterilized in a hot air oven?
❌ Plastic materials (melts at high temperatures)
❌ Rubber items (gets damaged)
❌ Culture media (heat-sensitive)
What is the biological indicator used to check sterilization efficiency in a hot air oven?
Bacillus atrophaeus spores
Bacillus subtilis spores
C. tetani spores
What is the chemical indicator used to check sterilization efficiency in a hot air oven?
Browne’s tube (green spot means sterilization complete)
What is the temperature range used in incineration?
There are 2 chambers-
700-800 C
1000-1100 C
Uses of Incineration
Human anatomical waste
Animal carcasses
Hospital waste
Soiled bedding, dressings
Expired cytotoxic drugs
Types of moist heat sterilization
Below 100 C-
-Pasteurisation
-Inspissation
-Vaccine water bath
100C
- Boiling
- Tyndallization
Above 100C
- Autoclave
Types of pasteurization
Holder method «_space;Flash method (kills Coxiella)
Holder- boil at 63 C for 30 mins
Flash- boil at 72 C for 20 secs, cool to <13 C
Inspissation
80 C for 20-30 mins for 3 consecutive days
Used for Loeffler’s serum slope, LJ media for TB
Vaccine water bath
60 C for 60 mins
Boiling vs Tyndallisation
Boiling- at 100 C for 15 mins
Didnt kill spores
Tyndallisation- at 100 C for 20 mins for 3 days
Spores dead
Autoclave settings
125 C for 15 mins at 15 psi
To kill prions-
134 C for 1.5 hrs
Uses of autoclave
Surgical instruments
Culture media (except LJ and LSS)
Laboratory glassware
Dressings and bandages
Sutures (except catgut)
Sputum (prior to discard)
What biological indicator is used to check autoclave efficiency?
Geobacillus stearothermophilus spores (heat-resistant bacteria).
Filtration is done by
Seitz filter
Sietz filter contains
Asbestos (carcinogenic)
Pore size: 0.22 Mc
Uses of Sietz filter
Heat sensitive substances such as vaccines, antibiotics, serum, toxins, sugar solutions
Another method of filtration
Air purifiers-
HEPA- High Efficiency Particulate Air Filter
ULPA- Ultra Low Particulate Air Filter
Control of filtration
Brevundimonas diminuta
Serratia
Ionizing radiation
Cold radiation
Eg; X rays, Gamma rays, Cosmic rays
High penetrating power
Sporicidal
Uses- Catgut sutures, grafts
Non ionizing radiation
Hot radiation
Eg. UV rays, Infrared rays
Used for OT fumigation, Biosafety cabinet
Low penetrating power
Bactericidal but not sporicidal
Control for radiation
Bacillus pumilus
Types of chemical sterilization
Alcohol
Aldehyde
Halogens
Phenols
Plasma sterilization
Gas sterilization
Alcohol as chemical sterilizing agent
Ethyl alcohol- 70%
Isopropyl alcohol- 70 to 80%
Used to clean thermometers, stethoscope
Formaldehyde for chemical sterilization
Gas- OT fumigation
Formalin- store human specimens
Duckering- killing B. anthracis spores from animal wool with formaldehyde
Glutaraldehyde as chemical sterilization agent
Commercial name- CIDEX
To clean bronchoscope, endoscope, laryngoscope
Except arthroscope- by plasma sterilization
Phenol for sterilisation
Used as antiseptics
Phenol (5%)
Cresol (1-3%)
Lysol (2-5%)
Modified phenol:
- Chlorhexidine + Cetrimide= Savlon
- Chloroxylenol= Dettol
Halogens used as chemical sterilization
- Chlorine- 1% sodium hypochlorite for blood spills
- Iodine- betadine (povidone iodine), tincture iodine (2% iodine)
Plasma sterilization
A low-temperature sterilization method using hydrogen peroxide vapor and plasma to kill microorganisms.
How does plasma sterilization kill microorganisms?
By generating free radicals (hydroxyl & superoxide ions) that disrupt cell membranes, DNA, and proteins.
What materials can be sterilized using plasma sterilization?
Plastics
Arthroscopes, Ureteroscopes
Biological Indicator for Plasma Sterilization
Geobacillus stearothermophilus spores (same as for autoclave).
Which gas is commonly used in gas sterilization?
Ethylene Oxide (EtO) is the most commonly used gas for sterilization.
MOA of Ethylene oxide (ETO)
Microbicidal and sporicidal
Side effects of ETO
Highly irritant
Highly inflammable
Highly explosive
so, never use 100% ETO, 3-10% is enough
Mix with inert gas to prevent inflammation
Uses of ETO
Cardiopulmonary machines
Pre packed syringes
Control for ETO
Bacillus globigii
Tests of Disinfectants
- Rideal Walker test/ Phenol coefficient test
Compared with phenol.
Disadv: we don’t know the efficacy of organic matter - Modified Rideal Walker test/ Chick Martin test
Compared in presence of Yeast, soil (organic matter) - Kelsey-Sykes test/ capacity test: to check capacity of disinfectant
- Kelsey- Maurer test/ in use test: to check usage of disinfectant
Sporicidal agents
APT EFGH
Autoclave
Plasma sterilization
Tyndallisation
ETO
Formaldehyde
Glutaraldehyde
H2O2, Hot air oven, 1% Hypochlorite
Spaulding classification
Critical device- penetrates sterile sites
Use High level disinfectant (HLD)
Semi critical device- in contact with mucous membranes- Use HLD
Non critical device- in contact with skin- Intermediate/ Low level disinfectant
Non critical surfaces/ Medical equipments- computers, desks, tables- LLD
