Plot No. C40, Road No. 21Y, MIDC, Wagle Industrial Estate,
Thane(W)-400604, MH, India.
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Fluid Selenite Cystine Medium (Twin Pack)
Enrichment medium for isolation of Salmonellae in food, dairy products and materials of sanitary importance and clinical specimens in accordance with USP/IP.
Gms/Lit : 19.01 gms of Part A, + 4 gms of Part B
21.73 Lit/500G
Gms/Lit : 19.01 gms of Part A, + 4 gms of Part B
21.73 Lit/500G
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Dehydrated Culture Media#4fa25a
Intended Use:
Used as enrichment medium for isolation of Salmonellae in food, dairy products and materials of sanitary importance in accordance with USP/IP.
Composition**
| Ingredients | g/L |
|---|---|
| Part A | |
| Tryptone | 5.000 |
| Lactose | 4.000 |
| Sodium phosphate | 10.000 |
| L-Cystine | 0.010 |
| Part B | |
| Sodium acid selenite | 4.000 |
| Final pH (at 25°C) | 7.0±0.2 |
**Formula adjusted, standardized to suit performance parameters
Directions
Suspend 4.0 grams of Part B in 1000 ml purified/distilled water. Add 19.01 grams of Part A. Mix well. Warm to dissolve the medium completely. Distribute in sterile test tubes. Sterilize in a boiling water bath or free flowing steam for 15 minutes. DO NOT AUTOCLAVE. Excessive heating is detrimental. Discard the prepared medium if large amount of selenite is reduced (indicated by red precipitate at the bottom of tube/bottle).
Principle And Interpretation
Selective inhibitory effects of selenite were first demonstrated by Klett (1). Guth (2) used it to isolate Salmonella Typhi. Leifson studied selenite and formulated a medium. Fluid Selenite Cystine Medium is a modification of Leifsons (3) formula with added cystine by North and Bartram (4). The formulation corresponds to that of recommended by the AOAC (5) for the detection of Salmonellae in foodstuff particularly egg products. It is included by APHA (6,7), USP (8) and IP (9). Recently ISO Committee also recommends this medium for the detection of Salmonellae (10). Selenite Cystine Broth is useful for detecting Salmonella in the non-acute stages of illness when organisms occur in low numbers in test samples and for epidemiological studies to enhance the detection of low numbers of organisms from asymptomatic or convalescent patients (11).
Tryptone provide nitrogenous substances. Lactose is the fermentable source of carbohydrate and also maintains the pH in medium as selenite is reduced by bacterial growth and alkali is produced. An increase in pH lessens the toxicity of the selenite and results in overgrowth of other bacteria. The acid produced by bacteria due to lactose fermentation that maintain a neutral pH counters this. Phosphate too maintains a stable pH and is a good buffering agent. L-cystine imparts ambient redox potential, which enhances and improves recovery of Salmonellae and few Shigella sp. which may be in small numbers in products to be tested. This medium to some extent prevents the growth of coliforms. Enriched broth is sub cultured on solid medium. Do not incubate the broth longer than 24 hours as inhibitory effect of selenite reduces after 6 - 12 hours of incubation (12).
Type of specimen
Food and dairy samples; Pharmaceutical sample
Specimen Collection and Handling:
For food and dairy samples, follow appropriate techniques for sample collection and processing as per guidelines (5,6,7).
For pharmaceutical products, follow appropriate techniques for sample processing in case of viscous materials as mentioned under sterility (8,9).
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 :
- Do not incubate the broth longer than 24 hours as inhibitory effect of selenite reduces after 6 - 12 hours of incubation (12).
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
Part A: Cream to light yellow homogeneous free flowing powder
Part B: Offwhite - white homogeneous free flowing powder
Colour and Clarity of prepared medium
Light yellow clear to slightly opalescent solution
pH
7.0±0.2
Growth Promotion Test
As per USP/ IP
Cultural Response
As per IP: Cultural characteristics observed after enrichment in MAP025 for 36-38°C for 48 hours, and then subcultured on Xylose Lysine Deoxycholate Agar (Agar Medium K) and Brilliant Green, Phenol red, lactose monohydrate Sucrose Agar (Agar Medium L) and incubated at 36-38°C for 18-24 hours.
As per USP: Cultural characteristics observed after enrichment in MAP025 for 30-35°C for 18-24 hours, and then subcultured on Xylose Lysine Deoxycholate Agar (Agar Medium K) and Brilliant Green, Phenol red, lactose monohydrate Sucrose Agar (Agar Medium L) and incubated at 30-35°C for 18-24 hours.
| Organism | Inoculum (CFU) | Growth | Observed Lot Recovery value (CFU) | Colour of Colony | Incubation period | |
|---|---|---|---|---|---|---|
| Growth on Brilliant Green, Phenol red, lactose monohydrate Sucrose Agar (Agar Medium L) | ||||||
| Salmonella Typhimurium ATCC 14028 (00031*) | 50-100 | luxuriant | 25-100 | >=50% | pinkish white | 24-48 hrs |
| Salmonella Abony NCTC 6017 (00029*) | 50-100 | luxuriant | 25-100 | >=50% | pinkish white | 24-48 hrs |
| Growth on Agar Xylose Lysine Deoxycholate Agar (Agar Medium K) | ||||||
| Salmonella Typhimurium ATCC 14028 (00031*) | 50-100 | luxuriant | 25-100 | >=50% | red with black centres | 18-24 hrs |
| Salmonella Abony NCTC 6017 (00029*) | 50-100 | good-luxuriant | 25-100 | >=50% | red with black centres | 18-24 hrs |
| Escherichia coli ATCC 8739 (00012*) | 50-100 | fair | 10-30 | 20-30% | yellow | 18-24 hrs |
| Escherichia coli ATCC 25922 (00013*) | 50-100 | fair | 10-30 | 20-30% | yellowish green | 18 -24 hrs |
Key: (*) Corresponding WDCM numbers
Storage and Shelf Life
Store between 10-30°C in a tightly closed container and the prepared medium at 2-8°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.
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 (13,14).
| Product Name | Fluid Selenite Cystine Medium (Twin Pack) |
|---|---|
| SKU | MAP025 |
| Customized Product Available | No |
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