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Edward’s Medium Base, Modified
A selective medium for the rapid isolation of Streptococcus agalactiae and other streptococci associated with mastitis and also from other clinical samples.
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Streptococcus agalactiae#CC293D
Intended Use
Recommended for selective and rapid isolation of Streptococcus agalactiae and other Streptococci associated with bovine mastitis
Composition**
| Ingredients | g/L |
|---|---|
| Peptone | 10.000 |
| HM peptone B # | 10.000 |
| Esculin | 1.000 |
| Sodium chloride | 5.000 |
| Crystal violet | 0.0013 |
| Thallous sulphate | 0.330 |
| Agar | 15.000 |
| Final pH (at 25°C) | 7.4±0.2 |
**Formula adjusted, standardized to suit performance parameters
# Equivalent to Beef extract
Directions
Suspend 41.33 grams in 1000 ml purified / distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at A115°C for 20 minutes. Cool to 45-50°C and aseptically add 5 to 7% v/v sterile sheep blood. Mix well and pour into sterile Petri plates.
(A corresponds to 10lbs pressure)
Principle And Interpretation
Streptococci are gram-positive facultatively anaerobic bacteria, which constitute normal commensal flora of mouth, skin, intestine and upper respiratory tract of humans. Group B Streptococci are an important cause of systemic infections in infants and occasionally of bacterial endocarditis (1). Mastitis is a disease of cattle caused by the organisms Streptococcus agalactiae. It belongs to the Lancefield group B Streptococci .
The most common selective agents used for selective isolation of Streptococci are crystal violet and thallium salts. A selective medium containing crystal violet was used by Haxthausen to isolate skin Streptococci (2). Subsequently it was observed that Streptococci from milk were able to grow on Gentian Violet Blood Agar whereas the other saprophytic milk bacteria were inhibited on this medium (3). An Esculin Blood Agar containing crystal violet was used by Edwards to isolate the causative agent of mastitis (4). A similar medium containing thallous acetate was also used to isolate the causative agent of mastitis (5).
Peptone and HM peptone B serve as sources of carbon, nitrogen and other essential nutrients. Esculin helps to differentiate esculin-positive (group D Streptococci) organisms from esculin- negative (S. agalactiae) organisms. Sodium chloride helps to maintain the osmotic equilibrium of the medium. Crystal violet and thallous sulphate serve as the selective agents for Streptococci. Supplementation with blood provides additional nutrients in addition to serving as an indicator of haemolysis. Mastitis Streptococci show alpha, beta or gamma type of haemolysis. Esculin differentiates esculin- positive group D Streptococci (black colonies) from esculin-negative Streptococcus agalactiae (blue to colourless colonies). Centrifuged test milk sample is directly inoculated on the surface of the medium plate. Esculin-negative (blue to colourless) S. agalactiae organisms are further subcultured for identification tests.
Type of specimen
Clinical samples - faeces, vaginal swabs,; Dairy samples
Specimen Collection and Handling
For clinical samples follow appropriate techniques for handling specimens as per established guidelines (6,7).
For dairy samples, follow appropriate techniques for sample collection and processing as per guidelines (8,9).
After use, contaminated materials must be sterilized by autoclaving before discarding.
Warning and Precautions :
In Vitro diagnostic Use only. For professional use only. 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 clinical specimens. Safety guidelines may be referred in individual safety data sheets.
Limitations :
- Individual organisms differ in their growth requirement and may show variable growth patterns on the medium.
- Each lot of the medium has been tested for the organisms specified on the COA. It is recommended to users to validate the medium for any specific microorganism other than mentioned in the COA based on the user's unique requirement.
- Further biochemical and serological tests must be carried out for complete identification.
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
Gelling
Firm, comparable with 1.5% Agar gel
Colour and Clarity of prepared medium
Basal medium : Amber coloured, clear to slightly opalescent gel. After addition of 5-7% v/v sterile defibrinated sheep blood : Cherry red coloured opaque gel forms in Petri plates
Reaction
Reaction of 4.13% w/v aqueous solution at 25°C. pH: 7.4±0.2
pH
7.20-7.60
Cultural Response
Cultural characteristics observed with added 5-7%v/v sterile defibrinated sheep blood after an incubation at 35-37°C for 24-48 hours.
| Organism | Inoculum (CFU) | Growth | Recovery | Colour of Colony |
|---|---|---|---|---|
| Enterococcus faecalis ATCC 29212 (00087*) | 50-100 | good-luxuriant | >=50% | greyish blue |
| Escherichia coli ATCC 25922 (00013*) | >=104 | inhibited | 0% | |
| Staphylococcus aureus subsp. aureus ATCC 25923 (00034*) | >=104 | inhibited | 0% | |
| Streptococcus agalactiae ATCC 13813 | 50-100 | good-luxuriant | >=50% | greyish blue to colourless w/ haemolysis |
Key: (*) Corresponding WDCM numbers.
Storage and Shelf Life
Store between 10-30°C in a tightly closed container and the prepared medium at 20-30°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 clinical sample must be decontaminated and disposed of in accordance with current laboratory techniques (6,7).
| Product Name | Edward’s Medium Base, Modified |
|---|---|
| SKU | M748 |
| Product Type | Regular |
| Physical Form | Powder |
| Origin | Animal |
| Packaging type | HDPE |
| References | 1. Cruickshank R., Duguid J. P., Marmion B. P. , Swain R. H. A., (Eds.), 1975, Medical Microbiology, The Practice of MedicalMicrobiology , 12th Edition, Vol. II , Churchill Livingstone. 2.Haxsthausen H., 1927, Ann. Derm. Suph., 8.201. 3.Bryan C. S., 1932, Am. J. Public Health, 2 2.749. 4.Edwards S. J., 1933, J. Comp. Path. Therap., 46:211-217. 5.McKenzie D. A., 1941, Vet. Rec., 53:473-480. |
| Customized Product Available | No |
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