Introduction
Peptone water is one of the simplest basal liquid media used in microbiology. It provides the essential nutrients for the growth of many non-fastidious bacteria. Although not very nutritious by itself, it serves as an excellent base medium for preparing sugar media and for performing certain biochemical tests.
Media Type
Category: Simple basal liquid medium
Purpose:
Used as a base for sugar fermentation tests.
Serves as an enrichment medium for preliminary bacterial growth.
Composition & pH of Peptone Water
A standard peptone water contains (per liter of distilled water):
| Component | Function |
|---|---|
| Peptone (10 g) | Source of nitrogen, amino acids |
| Sodium chloride (5 g) | Maintains osmotic balance |
| Distilled water | Solvent |
Sterilization
Method: Autoclaving
Conditions: 121°C at 15 psi (1.05 kg/cm²) for 15 minutes
Preparation of Peptone Water
Dissolve 10 g peptone and 5 g sodium chloride in 1 liter of distilled water.
Adjust pH to 7.4.
Dispense into test tubes or flasks.
Sterilize by autoclaving at 121°C for 15 minutes.
Store at 2–8°C until use
Uses of Peptone Water
Base for sugar fermentation tests (glucose, lactose, mannitol, etc.).
Indole test medium (addition of tryptophan → detection of indole production by E. coli).
Motility test medium (when used as a semi-solid base).
Serves as a general-purpose medium for preliminary bacterial growth.
Useful as a pre-enrichment broth before subculturing onto selective/differential media.
Conclusion
Peptone water is a fundamental basal medium in microbiology. Its simple composition and multiple laboratory applications make it invaluable in both diagnostic and research microbiology. For MBBS students, understanding its preparation, sterilization, and uses is crucial for practical microbiology and exams.
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