Agar medium intended for the isolation and detection of Escherichia coli 0157 H7. Escherichia coli serotype 0157:H7 was implicated in causing hemorrhagic colitis. Farmer and Davis noted that 95% of E. coli strains ferment sorbitol while almost all strains of E coli 0157:H7 did not ferment sorbitol They used this medium in their studies to estimate the number of sorbitol-negative E. coli present in stool specimens. Sorbitol fermenting bacteria appear as reddish-pink colonies and non-sorbitol fermenting bacteria appear as colorless or transparent colonies.
Appearance
Light pinkish-beige, homogeneous, free-flowing powder.
Microbiological Tests
The medium was prepared according to formulation and inoculated with the organisms listed below.
Escherichia coli ATCC 25922
Growth, pink colonies (Sorbitol positive)
Escherichia coli 0157:H7 ATCC 35510
Growth, colorless colonies (Sorbitol negative)
Enterococcus faecalis ATCC 29212
Inhibited (No sorbitol reaction (N/A))
Klebsiella pneumoniae ATCC 13883
Growth, pink mucoid colonies (Sorbitol positive)
Proteus mirabilis ATCC 12453
Colorless colonies, swarming inhibited (Sorbitol negative)
Pseudomonas aeruginosa ATCC 27853
Growth, colorless colonies (Sorbitol negative)
Staphylcoccus aureus ATCC 25923
Inhibited (No sorbitol reaction (N/A))
Storage and Stability
Store the sealed bottle containing the dehydrated medium at 2-30°C. Once opened and recapped, place the container in a low humidity environment at the same storage temperature. Protect it from moisture and light. The dehydrated medium should be discarded if it is not free flowing or if the color has changed from the original light pinkish-beige color.
Final pH: 7.1 ± 0.2 at 25.0°C
Appearance
Light pinkish-beige, homogeneous, free-flowing powder.
Mix 50 grams of the medium in one Liter of purified water until evenly dispersed. Heat with repeated stirring and boil for one minute to dissolve completely. Distribute and autoclave at 121.0°C for 15 minutes.
Storage and Stability
Store the sealed bottle containing the dehydrated medium at 2-30°C. Once opened and recapped, place the container in a low humidity environment at the same storage temperature. Protect it from moisture and light. The dehydrated medium should be discarded if it is not free flowing or if the color has changed from the original light pinkish-beige color.
Components shown as grams/liter
| Pancreatic Digest of Gelatin | 17.0 |
| Sorbitol | 10.0 |
| Casein Digest Peptone | 1.5 |
| Bile Salts Mixture | 1.5 |
| Peptic Digest of Animal Tissue | 1.5 |
| Sodium Chloride | 5.0 |
| Neutral Red | 0.03 |
| Crystal Violet | 0.001 |
| Agar | 15.0 |
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