Sterilization Equipment

Study of Sterilization Equipment in the Microbiology Laboratory

Objectives

• To study the working principle and applications of sterilization equipment (Hot Air Oven, Autoclave, Bunsen Burner, Laminar Air Flow).
• To understand their role in achieving aseptic conditions in microbiology laboratories.

Theory
Sterilization is the process of destroying or removing all forms of microorganisms, including bacterial spores. It can be achieved by different physical and chemical methods. In laboratories, the following physical methods are most common:

 
1. Dry Heat Sterilization- Works by oxidation and protein denaturation at high temperature.

Methods:
Hot Air Oven: Sterilizes at 160–170°C for 2–3 hours. Suitable for glassware, metal instruments, oils, powders.
Bunsen Burner: Direct flame incinerates and sterilizes inoculating loops/needles; also creates an aseptic zone around the flame.

 2. Moist Heat Sterilization

Works by coagulation and denaturation of proteins. More effective than dry heat at lower temperature.
Method:
Autoclave: Steam under pressure (121°C, 15 psi, 15–20 minutes) sterilizes culture media, instruments, and dressings.

 3. Radiation Sterilization

Uses high-energy rays or UV light to damage microbial DNA.
Method:
Laminar Air Flow (LAF): Equipped with UV lamp to sterilize the work area before operations. UV causes thymine dimer formation in DNA, preventing microbial growth.

4. Filtration Sterilization
Removes microorganisms by passing liquids or air through filters with pore size <0.22 μm.
Method:
In Laminar Air Flow, sterile air is maintained by HEPA (High Efficiency Particulate Air) filters, preventing entry of microbes during aseptic work.


Requirements

• Hot Air Oven
• Autoclave
• Bunsen Burner
• Laminar Air Flow cabinet
• Glassware (test tubes, Petri plates, pipettes)
• Culture media
• Heat-resistant gloves, cotton, distilled water

Procedure
a) Hot Air Oven

• Clean and dry the glassware.
• Wrap in paper or aluminum foil.
• Place inside the oven.
• Set temperature to 160–170°C for 2–3 hours.
• Switch off and allow to cool before removal.

b) Autoclave

• Add sufficient water to the chamber.
• Load materials like culture media in conical flask in autoclavable containers.
• Close lid, set pressure to 15 psi.
• Run for 15–20 minutes at 121°C.
• Allow pressure to fall naturally before opening.

c) Bunsen Burner

• Connect burner to gas source.
• Light carefully with matchstick.
• Sterilize inoculating loop/needle until red hot.
• Use aseptic zone around flame for transfers.

d) Laminar Air Flow

1. Clean the working area with disinfectant.
2. Switch on blower and UV light (15–20 minutes before work).
3. Turn off UV, keep fluorescent light and airflow on.
4. Perform aseptic manipulations inside the sterile cabinet.

Observation

Equipment	Principle/Working	Material Sterilized / Purpose	Observation	Result
Hot Air Oven	Dry heat at 160–170°C for 2–3 hrs	Glassware, metal instruments, powders, oils	Glassware came out dry and sterile	Effective for sterilizing dry materials
Autoclave	Moist heat at 121°C, 15 psi, 15–20 min	Culture media, dressings, solutions, instruments	Media showed no contamination	Reliable for sterilizing moist materials and killing spores
Bunsen Burner	Direct flame (incineration)	Inoculating loop/needle, aseptic zone creation	Loop became red-hot before inoculation	Provided aseptic handling during transfers
Laminar Air Flow	HEPA-filtered sterile air flow	Used for aseptic transfers, inoculation, plating	Cultures remained free from airborne contamination	Maintained contamination-free environment

Discussion

Dry heat (oven) is best for materials that cannot tolerate moisture whereas autoclave is most reliable for destroying all microorganisms, including spores. The bunsen burner ensures spot sterilization and creates an aseptic working zone.The Laminar Air Flow prevents airborne contamination during inoculation.The choice of sterilization depends on the type of material (e.g., glassware vs. media).

Precautions

• Do not overload oven or autoclave.
• Allow autoclave pressure to normalize before opening.
• Keep flammable materials away from the Bunsen burner.
• In LAF, never block airflow or perform unnecessary movements.
• Use gloves and lab coat while handling sterilized materials.

Conclusion

Sterilization equipment plays a vital role in microbiology laboratories. Each has its own principle and use: hot air oven for dry heat, autoclave for moist heat, Bunsen burner for incineration, and LAF for aseptic handling.

References

• Pelczar, M.J., Chan, E.C.S., & Krieg, N.R. (2010). Microbiology. Tata McGraw-Hill.
• Aneja, K.R. (2014). Experiments in Microbiology, Plant Pathology and Biotechnology. New Age Publishers.