Sterilization Methods – Practical & Viva Guide for BHMS Students
Introduction
Sterilization is a core topic in Microbiology and Pharmacy practicals and a frequent viva question in BHMS examinations. Many students lose marks not because they don’t know the methods, but because they cannot explain them clearly, systematically, and in examiner-friendly language.
This article explains sterilization methods from a practical and viva perspective, focusing on definitions, classification, principles, examples, and common viva traps. The content is strictly academic and aligned with BHMS syllabus expectations.
What Is Sterilization? (Viva Definition)
Sterilization is the process by which all forms of life, including bacteria, viruses, fungi, spores, and resistant microorganisms, are completely destroyed or removed from an object or substance.
👉 Key viva point:
Sterilization is different from disinfection. Disinfection does not destroy all spores.
Why Sterilization Is Important (Viva Answer)
Sterilization is essential to:
Prevent contamination
Maintain asepsis in laboratory work
Ensure accuracy of experiments
Protect laboratory personnel
Avoid false results in practical examinations
Classification of Sterilization Methods
In practicals and viva, sterilization methods are broadly classified into:
Physical methods
Chemical methods
This classification must be stated clearly before explanation.
I. Physical Methods of Sterilization
Physical methods use heat, radiation, or filtration to destroy microorganisms.
A. Heat Sterilization
Heat is the most commonly asked method in viva.
Heat sterilization is divided into:
Dry heat
Moist heat
1. Dry Heat Sterilization
Dry heat kills microorganisms by oxidation and protein denaturation.
(a) Hot Air Oven
Principle:
Dry heat causes dehydration and destruction of microbial proteins.
Temperature & Time:
160°C for 2 hours
OR 170°C for 1 hour
Articles Sterilized:
Glassware
Petri dishes
Pipettes
Test tubes
Metal instruments
Viva Tips:
Used for glass items
Not suitable for culture media
Common viva favorite
(b) Flaming
Principle:
Direct exposure to flame destroys microorganisms instantly.
Used For:
Inoculating loop
Forceps tips
Viva Point:
Flaming is an immediate but localized method.
(c) Incineration
Principle:
Complete burning reduces materials to ash.
Used For:
Biomedical waste
Contaminated materials
2. Moist Heat Sterilization
Moist heat kills organisms by coagulation of proteins and is more effective than dry heat.
(a) Autoclave (Most Important for Viva)
Principle:
Steam under pressure penetrates materials and coagulates proteins.
Standard Conditions:
121°C
15 lbs pressure
15–20 minutes
Articles Sterilized:
Culture media
Surgical dressings
Linen
Rubber goods
Viva Gold Points:
Autoclave uses steam, not dry heat
Pressure allows steam to reach higher temperature
Most reliable sterilization method
(b) Boiling
Temperature:
100°C for 10–30 minutes
Limitations:
Does not destroy spores
Viva Trap:
Boiling is not true sterilization.
(c) Pasteurization
Used For:
Milk and liquids
Methods:
Holder method: 63°C for 30 minutes
Flash method: 72°C for 15 seconds
Viva Point:
Pasteurization reduces pathogens but does not achieve sterilization.
B. Filtration
Principle:
Microorganisms are removed by physical separation, not killed.
Used For:
Heat-sensitive liquids
Vaccines
Serum
Antibiotic solutions
Filters Used:
Membrane filters
Seitz filters
Viva Key Line:
Filtration is a mechanical method, not a killing method.
C. Radiation
(a) Ultraviolet (UV) Radiation
Used For:
Operation theatres
Laboratories
Air sterilization
Limitation:
Poor penetration
(b) Ionizing Radiation
Used For:
Disposable medical items
Syringes
Catheters
Viva Note:
Used on an industrial scale.
II. Chemical Methods of Sterilization
Chemical agents are used when heat methods are unsuitable.
A. Gaseous Sterilization
Ethylene Oxide
Used For:
Plastic items
Electrical instruments
Advantages:
Effective at low temperature
Disadvantages:
Toxic
Requires aeration
B. Liquid Chemical Sterilants
Examples:
Formaldehyde
Glutaraldehyde
Hydrogen peroxide
Used For:
Instruments sensitive to heat
Viva Point:
These require proper exposure time.
Difference Between Sterilization and Disinfection (Viva Table)
| Sterilization | Disinfection |
|---|---|
| Destroys all forms of life | Destroys most organisms |
| Includes spores | Usually excludes spores |
| Complete process | Partial process |
| Used in labs & surgery | Used on surfaces |
Common Viva Questions Examiners Ask
Define sterilization
Principle of autoclave
Difference between dry and moist heat
Why pressure is used in autoclave
Items sterilized by hot air oven
Is boiling a sterilization method? Why?
Which method is best and why?
Common Mistakes Students Make
Confusing sterilization with disinfection
Forgetting temperature and pressure values
Not stating the principle
Giving clinical answers instead of academic ones
Skipping classification
These mistakes directly reduce viva marks.
How to Answer Sterilization in Viva (Exam Strategy)
Always follow this order:
Definition
Classification
Principle
Examples
One advantage or limitation
This structure signals confidence and clarity.
Conclusion
Sterilization methods are high-yield practical and viva topics in BHMS. Scoring well does not require memorizing everything—it requires clear concepts, correct classification, and precise explanation.
Students who present sterilization answers in a structured, academic, and exam-oriented manner consistently score higher in practicals and viva.
Disclaimer
This article is written strictly for educational and examination purposes for BHMS students. It does not provide clinical, diagnostic, or treatment guidance.
