Buffered Peptone Water w/ Casein

Intended Use

Recommended as pre-enrichment medium for increasing the recovery of injured Salmonella species from food particularly cocoa, chocolate, confectionary etc. prior to selective enrichment and isolation.

Composition**

Final pH ( at 25°C) 7.0±0.2

**Formula adjusted, standardized to suit performance parameters

# - Equivalent to Casein

Directions

Suspend 70.07 grams (equivalent weight of dehydrated medium per litre) in 1000 ml purified / distilled water. Heat if necessary to dissolve the medium completely. Mix well and dispense into tubes or flasks as desired. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes.

Principle And Interpretation

Microorganisms that are subjected to environmental stress may become structurally or metabolically damaged or injured. These microorganisms are unable to replicate in selective environments. Therefore these injured organisms must be resuscitated or permitted to repair the damage by incubation in an appropriate, non-selective environment (9). Edel and Kampelmacher (3) noted that sub-lethal injury to Salmonella may occur in many food preservation processes. Enriching injured cells in Lactose Broth (pH 6.9) may be further detrimental to their recovery (2). Pre-enrichment in Buffered Peptone Water (M1494I) at 35°C for 18-24 hours results in repair of injured cells (7). The buffering system prevents bacterial damage due to change in the pH of the medium. Recently ISO committee has also recommended this pre enrichment medium for the detection of Enterobacteriaceae from food stuffs and other materials (4). Addition of 50g/l M-Protein Powder or skimmed milk is recommended for testing cocoa and cocoa containing products (more than 20%) as recommended by ISO (4). The addition of M-Protein Powder is necessary to inhibit bactericidal substances present in cocoa or cocoa containing products. The sample is enriched in Buffered peptone water w/casein (M1919), further enriched in selective enrichment media and then subcultured on XLD Agar (M031I).

Type of specimen

Food and dairy samples - cocoa, chocolate, confectionary, milk and milk products, etc. (4)

Specimen Collection and Handling

For food and dairy samples, follow appropriate techniques for sample collection and processing as per guidelines (1,8,10). After use, contaminated materials must be sterilized by autoclaving before discarding.

Warning and Precautions

Read the label before opening the container. Wear protective gloves/protective clothing/eye protection/ face protection. Follow good microbiological lab practices while handling specimens and culture. Standard precautions as per established guidelines should be followed while handling specimens. Safety guidelines may be referred in individual safety data sheets.

Limitations

1. Further enrichment in selective medium is required and then subcultured on XLD Agar (M031I).

Performance and Evaluation

Performance of the medium is expected when used as per the direction on the label within the expiry period when stored at recommended temperature.

Quality Control

Appearance: Cream to yellow homogeneous free flowing powder

Colour and Clarity of prepared medium: Cream coloured opaque solution

Reaction: Reaction of 7.0% w/v aqueous solution at 25°C. pH : 7.0±0.2

pH: 6.80-7.20

Cultural Response: Cultural characteristics observed after an incubation at 35-37°C for 18-24 hours.(Recovery is observed on XLD Agar, M031I)

Key : (*) Corresponding WDCM numbers.

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 in order 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.

Disposal

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 sample must be decontaminated and disposed of in accordance with current laboratory techniques (5,6).

Reference

1. American Public Health Association, Standard Methods for the Examination of Dairy Products, 1978, 14th Ed., Washington D.C.
2. Angelotti R., 1963, “Microbiological Quality of Foods”, Academic Press, New York.
3. Edel W. and Kampelmacher E. H., 1973, Bull. Wld. Hlth. Org., 48: 167.
4. International Organization for Standardization (ISO), 2002, Draft ISO/DIS, 6579.
5. Isenberg, H.D. Clinical Microbiology Procedures Handbook. 2nd Edition.
6. Jorgensen, J.H., Pfaller , M.A., Carroll, K.C., Funke, G., Landry, M.L., Richter, S.S and Warnock., D.W. (2015) Manual of Clinical Microbiology, 11th Edition. Vol. 1.
7. Sadovski A. Y., 1977, J. Food Technol., 12.85.
8. Salfinger Y., and Tortorello M.L. Fifth (Ed.), 2015, Compendium of Methods for the Microbiological Examination of Foods, 5th Ed., American Public Health Association, Washington, D.C.
9. Vanderzant C. and Splittstoesser D. F., (Eds.), 1992, Compendium of Methods for the Microbiological Examination of Foods, 3rd Ed., APHA, Washington, D.C.
10. Wehr H. M. and Frank J. H., 2004, Standard Methods for the Microbiological Examination of Dairy Products, 17th Ed.,APHA Inc., Washington, D.C.