STERILIZATION, Needs, Methods and Types of Sterilization, Sterility testing, MCQs

STERILIZATION, Needs, Methods and Types of Sterilization, Sterility testing, MCQs


Sterilization is the either killing or removal of all the microorganisms from an object to make it free from any living organism. It also includes killing or removal of bacterial endospores and fungal endospores which are highly resistant in nature. [1]

All the pharmaceutical equipments, used for medical, parentral and ophthalmic preparations  are mandatory to be sterilized prior to its use. They are usually sterilized using heat method. Prefilled syringes and ophthalmic preparations are sterilized using ethylene oxide and irradiation method. For small and large parentral devices and for opthamic products sterilization, moist heat sterilization method is used.

Need for sterilization

  • The presence of microorganisms in the food increases the decay rate of the food and also responsible for food poisoning. In modern food industries, sterilization of food by various techniques like food irradiation, heat treatments, etc. are used to free the food from any sort of microbial contamination and to decrease the decay rate of food and make it safe for consumption. Pasteurization is used for the milk processing. Where sterilization is used for destruction of all the microorganisms and their spores, pasteurization only kills the pathogenic bacteria.
  • In the surgeries, all the instruments are properly sterilized before performing the surgery to prevent transmission of infection to the patient. For this, instruments that are heat sensitive are sterilized using gases such as ethylene oxide and ozone, while other instruments are sterilized using moist heat.
  • All the spacecrafts prior to the mission are strictly checked for sterilization, as there are strict rules for prevention of solar system bodies from the biological materials from Earth.

Methods of sterilization:

I. Physical methods: The physical methods for sterilization includes:

  • Dry heat
  • Moist heat
  • Pasteurization
  • Filtration
  • Cold
  • Desiccation
  • Radiation
  • Osmotic pressure

II. Chemical methods: In this, various chemicals are used for sterilization.

III. Mechanical methods: This includes filtration for sterilization.

Tests for sterility

Sterilization is very important process. There are some tests which can be used for the evaluation of the sterilization process. The basic principle behind the tests for sterility is that, whenever a microorganism is provided with a nutrient medium, suitable temperature and pressure, it grows and multiples, which can be visible as a turbidity or as a colony on the culture media.

Methods which can be used for the sterility tests:

I. Direct inoculation method

II. Membrane filtration method

III. Pyrogen test



  1. Sterilization is?

a. Process of growing microbes in laboratory

b. Process for preparation of antibiotics

c. Killing or removing of all the microorganisms from an article

d. Fragmentation of big particles into smaller one for the preparation of tablets

2. Which of the following method is used for sterilization?

a. Moist heat method

b. Staining

c. Microbial inoculation

d. Incubation

3. Parenteral preparations can be sterilized through?

a. Chemical sterilization

b. Membrane filtration

c. Desiccation

d. Dry heat method

4. Basic principle behind sterility testing is?

a. Microorganisms imparts different colors when present as contaminant in any preparation

b. Presence of microbes can be detected by naked eye in any preparation

c. Microbes will grow if they will be provided with nutrient medium, optimum temperature and pH

d. None of the above

5. Correct sequence of true/false for the following staments can be?

  • Pasteurization kills all the microorganisms present in the milk
  • Moist heat and dry heat methods are physical methods of sterilization
  • Presence of microorganism in any food decreases the decay rate of the food
  • Parenterals and ophthalmics needed to be highly sterilized





6. Which of the following statements are correct?

I. Pasteurization kills pathogens present in milk

II. Chemical cannot be used for sterilization purpose

III. Pyrogen test can be used for the test of sterility

IV. Radiations can be used for sterilization

a. I, III, IV

b. II, IV

c. III

d. I, II, III

7. Which of the following comes under physical method of sterilization?

I. Moist heat method

II. Oxidation

III. Sunlight

IV. Osmotic pressure

V. Lyophillization

VI. Ethylene oxide treatment

a. III, IV, VI

b. I, III, IV, V

c. I, V

d. II, IV, VI




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[1] Black JG, Black LJ. Microbiology: principles and explorations. John Wiley & Sons; 2018 Jan 4.


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