DRIGALSKI LACTOSE AGAR
A selective medium for the isolation of the Gram-negative bacteria.
Code: CB1/8302
Typical formula g/l
| Peptone | 15.0 |
| Beef extract | 3.0 |
| Yeast extract | 3.0 |
| Sodium desoxycholate | 1.0 |
| Sodium thiosulphate | 1.0 |
| Lactose | 15.0 |
| Agar | 13.0 |
| Crystal violet | 5 mg |
| Brom Thymol blue | 80 mg |
pH 7.4 +/- 0.2
Directions
Suspend 51g in 1000ml of cold distilled water; heat to boiling, and sterilise by autoclaving at 115°C for 20 minutes.
Description and Method
Drigalski Lactose Agar is a selective medium used for the isolation of the Gram-negative bacteria from urine, faeces and other clinical specimens. The Gram-positive bacteria are inhibited by crystal violet and sodium desoxycholate. The Gram-negative bacteria grow with different characteristics depending on their ability to ferment lactose. Coliform organisms (E.coli, Klebsiella, Citrobacter, Enterobacter) ferment lactose with production of acids, and a colour change of bromothymol blue indicator grow with yellow colonies. Gram-negative lactose non fermenting bacteria (Salmonella, Shigel!a, Proteus, Alcaligenes, Pseudomonas, etc.) grow with green-blue colonies.
Quality assurance (37°C-24 hrs)
Productivity control
E.coli ATCC 25922: growth, yellow colonies
P.mirabilis ATCC 12453: growth, blue-green colonies
S.typhimurium ATCC 14028: growth, blue-green colonies
Selectivity control
E.faecalis ATCC 29212: inhibited
Storage
Dehydrated medium: 15-30°C
User prepared plates: 7 days at 2-8°C