Alkaline Peptone Water
- It is a broth medium which is used for the enrichment of Vibrio species from food, water and clinical samples.
- Shread, et al. formulated peptone water touse as a nonselective enrichment broth for the cultivation of Enterobacteriaceae from foodstuffs and other specimens.
- It is a modified form of peptone water with the pH adjusted to 8.4.
- This alkaline pH helps in the optimal growth of Vibrio organisms, on the other hand, it inhibits the growth of commensal intestinal bacteria.
Composition of Alkaline Peptone Water
Final pH (at 25°C): 8.6 ± 0.2
Principle And Interpretation of Alkaline Peptone Water
Clinical materials containing small numbers of Vibrio should be inoculated into an enrichment medium prior to plating onto a selective medium, such as TCBS Agar (M189). Alkaline Peptone Water is a suitable enrichment broth for this purpose.
The relatively high pH of the medium (approximately 8.4) provides a favorable environment for the growth of Vibrio’s. This medium is recommended by APHA for enrichment of Vibrio species from seafood, infectious materials and other clinical specimens such as faeces. Peptone provides nitrogen and carbon source, long chain amino acids, vitamins and other essential nutrients. Sodium chloride maintains osmotic equilibrium.
Add 10 grams of seafood to 90 ml of Alkaline Peptone Water and incubate for upto 18-20 hours at 37°C. Prolonged incubation will result in growth of the suppressed contaminating organisms to develop.
Growth in tubes is indicated by turbidity compared to an un-inoculated tube (control). Growth from the enrichment broth is used for plating on selective media. For biochemical identification a pure culture is recommended
Preparation of Alkaline Peptone Water
- Suspend 20.0 grams in 1000 ml purified/distilled water.
- Apply Heat if necessary to dissolve the medium completely.
- Dispense the medium in tubes or flasks as desired.
- Sterilize the media by autoclaving at 15 lbs pressure (121°C) for 15 minutes.
- Date the medium and give it a batch number. Label the bottles and record on each the expiry date of the medium (2 years from preparation).
- Store in a cool dark place with the bottle caps screwed tightly to prevent a change in pH.
Result Interpretation on Alkaline Peptone Water
Growth in tubes is indicated by turbidity compared to an un-inoculated tube (control).
|Vibrio parahaemolyticus||Turbid growth|
|Vibrio vulnificus||Turbid growth|
|Vibrio furnissii||Turbid growth|
|Vibrio cholerae serotype Inaba||Turbid growth|
|Vibrio cholerae serotype Ogawa||Turbid growth|
Storage and Shelf Life
- Store between 10-30°C in a tightly closed container and the prepared medium at 15-25°C.
- Use before expiry date on the label.
- On opening, product should be properly stored dry, after tightly capping the bottle inorder to prevent lump formation due to the hygroscopic nature of the product.
- Improper storage of the product may lead to lump formation.
- Store in dry ventilated area protected from extremes of temperature and sources of ignition Seal the container tightly after use.
- Product performance is best if used within stated expiry period.
Application of Alkaline Peptone Water
- It is used for the enrichment of Vibrio cholera and Vibrio species from food, water and clinical samples.
- Used in hanging drop method for direct microscopic examination of samples.
- It is also used as a transport media.
- Used as a non-selective enrichment broth for the cultivation of Aeromonas.
Limitations of Alkaline Peptone Water
- Certain strains of Vibrio species requiring higher sodium chloride concentration may show poor growth.
- Further recovery from this enriched broth onto selective media is required.
- Biochemical characterization is carried out from pure isolates for complete identification.
- Growth from the enrichment broth is used for plating on selective media. For biochemical identification a pure culture is recommended.
- Performance of the medium is expected when used as per the direction on the label within the expiry period when stored at recommended temperature.
- User must ensure safe disposal by autoclaving and/or incineration of used or unusable preparations of this product. Follow established laboratory procedures in disposing of infectious materials and material that comes into contact with clinical sample must be decontaminated and disposed of in accordance with current laboratory techniques.