Cetrimide agar

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Colonies of Pseudomonas aeruginosa on cetrimide agar.

The cetrimide agar is a solid nutrient medium for the cultivation and differentiation of pseudomonads . This medium is recommended by the European Pharmacopoeia (Pharmacopoea Europaea, Ph. Eur.) For the specific detection of Pseudomonas aeruginosa .

Mode of action

Cetrimid agar contains cetrimide ( cetyltrimethylammonium bromide ), a quaternary ammonium compound that acts as an inhibitor against numerous bacteria, but does not prevent bacteria of the genus Pseudomonas from growing. Rather, cultivation on cetrimide agar promotes the production of the pyocyanin pigment typical of P. aeruginosa , which gives the colonies a greenish or yellowish-green color. At the same time, the production of the fluorescent dye pyoverdin is promoted, which diffuses into the medium and stains it greenish-yellow. The fluorescence of P. aeruginosa can be visualized under UV light.

Further components of the finished cetrimide agar are gelatine hydrolyzate, glycerin , potassium sulfate , magnesium chloride and agar agar . The uninoculated agar has a pH of about 7.2. Due to the absence of usable carbohydrates and the addition of the ingredient cetrimide, the growth of gram-negative Enterobacteriaceae (e.g. E. coli ), but also gram-positive accompanying flora (e.g. Staphylococcus ) is inhibited. Confirmation that the colonies that have grown are bacteria of the genus Pseudomonas is provided by the positive oxidase test , which should be carried out with a colony of cetrimide agar. The distinction between Pseudomonas aeruginosa and Pseudomonas fluorescens is possible if the nutrient medium is incubated at different temperatures. P. aeruginosa is mesophilic (temperature optimum at 35–37 ° C), while P. fluorescens has a temperature optimum of 25 to 30 ° C, so it is more psychrotolerant .

Typical composition

safety instructions
Surname

Cetrimide agar

GHS labeling of hazardous substances
09 - Dangerous for the environment

Caution

H and P phrases H: 400
P: 273-391

The nutrient medium usually consists of (data in grams per liter ):

See also

Individual evidence

  1. ↑ European Pharmacopoeia 7.0 - 7.4 . Official German edition. 2012, ISBN 978-3-7692-5992-6 .
  2. ↑ a b Michael T. Madigan, John M. Martinko, Jack Parker: Brock Mikrobiologie. German translation edited by Werner Goebel. 1st edition. Spektrum Akademischer Verlag, Heidelberg 2000, ISBN 978-3-8274-0566-1 , pp. 524-527.
  3. ↑ a b c d Product data sheet Cetrimid Agar Basis (PDF; 104 kB) from Carl Roth GmbH, accessed on February 8, 2017.
  4. ↑ F. Naglitsch: Pseudomonas aeruginosa. In: Eberhard Schulze (Hrsg.): Hygienic-microbiological water tests. 1st edition. Spektrum Akademischer Verlag, Jena 1996, ISBN 978-3-8274-0874-7 , pp. 65-71.
  5. ↑ a b Data sheet cetrimide agar (base) (PDF) from Carl Roth , accessed on February 8, 2017.