Cetrimide agar
Cetrimide Agar is a solid nutrient medium for growth and differentiation of Pseudomonas. This medium is recommended by the European Pharmacopoeia ( European Pharmacopoeia, Ph. Eur ) for the specific detection of Pseudomonas aeruginosa.
Operation
Cetrimide agar cetrimide ( cetyltrimethylammonium bromide ), a quaternary ammonium compound that acts as an inhibitor of various bacteria, bacteria of the genus Pseudomonas, however, does not prevent the growth. Rather, in the cultivation on Cetrimide agar production of typical P. aeruginosa pigment pyocyanin is promoted, which gives the colonies a greenish or yellowish - green color. At the same time the production of the fluorescent dye is promoted pyoverdine diffusing in the medium and this stain greenish- yellow. The fluorescence of P. aeruginosa can be visualized under ultraviolet light.
Other constituents of the finished Cetrimide agar are gelatin hydrolyzate, glycerol, potassium sulfate, magnesium chloride, and agar-agar. The agar was left uninoculated to a pH of about 7.2. The absence of available carbohydrates and by adding the ingredient cetrimide the growth of gram-negative Enterobacteriaceae is (eg E. coli ), but also Gram-positive accompanying flora (eg, Staphylococcus ) inhibited. Confirmation that there are bacteria of the genus Pseudomonas with grown colonies, provides the positive oxidase test, which should be carried out with a colony from cetrimide agar. The distinction between Pseudomonas aeruginosa and Pseudomonas fluorescens is possible when the nutrient medium is incubated at different temperatures. P. aeruginosa is mesophilic ( optimum temperature 35-37 ° C) as P. fluorescens has a temperature optimum of 25-30 ° C, which is rather psychrotolerant.
Typical Composition
The soil mostly consists of ( in grams per liter):
- Hydrolyzate of gelatin 20.0
- Potassium sulfate 10.0
- Magnesium chloride 1.4
- Cetrimide 0.3
- Agar- agar 13.6