改良爱德华培养基（Edwards Medium Modified）

分离无乳链球菌（B群）

A selective medium for the rapid isolation of Streptococcus agalactiae and other streptococci involved in bovine mastitis.

Typical Formula*	gm/litre
`Lab-Lemco’ powder	10.0
Peptone	10.0
Aesculin	1.0
Sodium chloride	5.0
Crystal violet	0.0013
Thallous sulphate	0.33
Agar	15.0
pH 7.4 ± 0.2

* Adjusted as required to meet performance standards 

POISON - Contains Thallium Salt

Directions
Suspend 41g in 1 litre of distilled water. Bring to the boil to dissolve completely. Sterilise by autoclaving at 115°C for 20 minutes. Cool to 50°C, add 5-7% of sterile bovine or sheep blood, mix well and pour plates.

Description
A selective medium for the rapid isolation of Streptococcus agalactiae and other streptococci involved in bovine mastitis.

Crystal violet or gentian violet and thallium salts have long been used in selective media for streptococci. Haxthausen¹ employed a selective crystal violet medium for the isolation of skin streptococci. Bryan² using gentian violet blood agar, found that the growth of saprophytic milk bacteria was prevented whilst that of streptococci was unaffected. Edwards³ employed a crystal violet aesculin blood agar for the cultural diagnosis of bovine mastitis, whilst McKenzie⁴ used a medium containing thallium acetate for the same purpose.

Hauge et al.⁵ described a composite medium containing all the components of modified Edwards Medium.

Aesculin differentiates the negative Streptococcus agalactiae (blue colonies) from aesculin-positive Group D streptococci (black colonies).

Technique
Inoculate the surface of the medium with centrifuged deposits from milk samples and incubate at 35°C.
Look for pale blue colonies which should then be subcultured for further identification tests.

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C. and use before the expiry date on the label.
Store the prepared plates at 2-8°C.

Appearance
Dehydrated medium: Straw coloured, free-flowing powder
Prepared medium: Straw coloured gel with blue hue