Description
Use and description:
A dehydrated culture medium recommended for the isolation and enumeration of urinary microorganisms. Due to the presence of bromothymol blue, lactose-fermenting bacteria are detected by producing yellow halo around colonies. An additional dye, acid fuchsin cause lactose fermenting bacteria to produce pink colonies, non-fermenting species are colourless. It is electrolyte deficient to prevent the swarming of Proteus sp. Cystine helps the growth of coliforms.
Composition per litre:
Peptones…………….…………………………….10.000 g
L-cystine……………………………………………..0.128 g
Acid fuchsin…………………………………….… 0.100 g
Beef extract………………………………………..3.000 g
Lactose……………………………………………..10.000 g
Bromothymol blue………………………..……0.020 g
Agar………………………………………………….14.000 g
Final pH of the ready to use medium: 7.5 +/- 0.2
Medium preparation:
Add 37.2 grams of dehydrated culture medium to 1 litre of distilled water. Heat with repeated stirring and boil for one minute to dissolve completely. Autoclave at 121°C for 15 minutes cool down and distribute.
Quality specifications:
Dehydrated medium: homogeneous, light beige fine powder.
Ready to use medium: clear, light blue-green.
Microbiological response after 18-24 hours incubation at 37 °C:
The plates should not be incubated more than 24 hours as the lactose fermenting organisms will mask the non-lactose fermenter.
| Organism | Result / colour |
| Escherichia coli ATCC 25922 | Growth/ deep orange-red |
| Salmonella typhimurium ATCC 14028 | Growth/ blue |
| Staphylococcus aureus ATCC 25923 | Growth/ gold yellow |
| Proteus mirabilis ATCC 12453 | Growth/ blue |
Storage:
Dehydrated medium should be stored between 10 to 25°C. Once opened, place the container in a dark, dry place. The dehydrated medium should not be used if there is any lump or the colour has changed from the original.