Sterilization methods

 

APPLICATION OF DIFFERENT STERILISATION METHODS

Objectives:- To know about different sterilization methods used in the laboratory for tools, glassware, or other equipment to eliminate or reduce microbial contamination.

 Theory:

Sterilization is the process of eliminating or killing all forms of microbial life, including bacteria, viruses, fungi, and spores. It describes a process that destroys or eliminates all forms of microbial life. Sterilization is an absolute term, i.e., the article must be sterile, meaning the absence of all microorganisms. No relative terms like half sterile or semi-sterile can be used.

Various sterilization methods are used in hospitals, clinics, and laboratories to ensure the complete elimination of microorganisms from equipment, surfaces, or materials. There are some common sterilization methods like

1.     Red Heat 

Application: Red heat is commonly used in microbiology laboratories for sterilizing inoculating loops, needles, and other small metal instruments.

Process: The metal instrument is heated in a flame until it glows red, effectively killing any microorganisms present.

Use Cases: Used for routine sterilization of tools before and after use in microbiological procedures like streaking plates or inoculating cultures.

2.     Flaming:

Application:
Flaming is widely used in microbiology laboratories to sterilize the mouths of test tubes, culture tubes, flasks, and bottles, particularly during the transfer of microorganisms to prevent contamination.

Process:
The opening of the glass container (e.g., test tube or flask) is passed quickly through the flame of a Bunsen burner. The brief exposure to high temperature kills airborne or surface contaminants present around the mouth of the container.

Use Cases:

• Sterilizing the necks of culture tubes before and after taking or introducing inoculum.
• Commonly performed during aseptic techniques to maintain sterile conditions.
• Helps create an upward air current to prevent airborne microbes from entering the container.
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3.     Hot Air Oven:

Application: Hot air ovens are used for sterilizing glassware, metal instruments, and other heat-resistant materials that are not affected by high temperatures.

Process: Items are placed inside the oven and exposed to dry heat at temperatures typically ranging from 160°C to 180°C for a set period, usually 1 to 2 hours.

Use Cases: Commonly used in laboratories, pharmaceutical industries, and healthcare facilities for sterilizing equipment and glassware, as well as for decontaminating certain types of medical waste.

4.     Autoclave:

Application: Autoclaves are widely used in healthcare facilities, laboratories, and industrial settings for sterilizing a variety of materials, including glassware, surgical instruments, clothing, media, and equipment.

Process: The autoclave uses steam under pressure to achieve sterilization. Items are placed inside the autoclave chamber, and steam is introduced at high pressure 15 lb/in² and temperature (usually 121°C) for a specified duration, typically 15 minutes.

Use Cases: Essential for sterilizing heat-resistant materials that can withstand high temperatures and moisture. It is a crucial tool in medical and laboratory settings where absolute sterility is required.

Result and Discussion

Sterilization Method	Time	Temperature	Uses
Red Heat	A few seconds (until red hot)	~700–1000°C (flame)	Sterilizing inoculating loops, needles, and forceps tips
Flaming	2–3 seconds (brief exposure)	Flame temperature	Sterilizing the mouths of test tubes, flasks, and bottle openings
Hot Air Oven	1–2 hours	160–180°C	Sterilizing glassware, powders, oils, and metal instruments
Autoclave	15–20 minutes (standard)	121°C at 15 psi	Sterilizing culture media, surgical instruments, and laboratory waste

 

Bottom of Form

 

Dry heat sterilization is an effective method for achieving sterility in materials that can withstand high temperatures and do not require exposure to moisture. It is commonly used for sterilizing glassware, metal instruments, and heat-stable plastics in laboratory, healthcare, and industrial settings. While dry heat sterilization requires longer exposure times and higher temperatures compared to moist heat methods such as autoclaving, it offers advantages such as compatibility with heat-sensitive materials and ease of operation.

Moist heat sterilization, particularly through autoclaving, is a highly effective and widely used method for achieving sterility in various materials. By subjecting materials to high temperatures and steam under pressure, autoclaving rapidly and efficiently eliminates a wide range of microorganisms, including heat-resistant spores. This method is indispensable in laboratory, medical, and industrial settings for sterilizing equipment, media, glassware, surgical instruments, and other materials.

 

Conclusion: Hence, dry heat and moist heat methods were studied, that is employed in laboratory settings for the elimination of microorganisms.

 

Precautions:

Red heat

1. Allow the loop or needle to become red hot to ensure complete sterilization.
2. Cool the instrument before touching the culture to prevent killing the inoculum.
3. Hold the instrument at an angle to avoid splatter or aerosol formation.
4. Avoid heating near flammable materials or alcohol-based disinfectants.

Flaming

1. Pass the mouth of tubes or flasks briefly through the flame (2–3 seconds).
2. Do not overheat glassware—it may crack or explode.
3. Hold the tube at a 45-degree angle to reduce the risk of airborne contamination.
4. Ensure hands and clothing are away from the flame.

Hot Air Oven

1. Ensure the temperature and time are set properly (e.g., 160°C for 2 hrs).
2. Do not overload the oven; allow air circulation for even heating.
3. Use heat-resistant glassware and metal only.
4. Do not open the door immediately after the cycle ends—let it cool gradually to avoid breakage.

Autoclave

1. Ensure water level in the chamber is sufficient before use.
2. Do not seal containers tightly—steam must enter to sterilize properly.
3. Use autoclave tape or indicators to confirm sterilization.
4. Do not open until pressure is released completely and internal temperature drops.
5. Wear heat-resistant gloves and safety goggles while unloading.

Reference:

• Pelczar, M.J., Chan, E.C.S., & Krieg, N.R. Microbiology: Concepts and Applications, McGraw-Hill.
• WHO Laboratory Biosafety Manual, 3rd Edition.
• Cappuccino, J.G. & Sherman, N. Microbiology: A Laboratory Manual. Pearson Education.