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HiMedia Laboratories
Cetrimide Agar Base
Cetrimide Agar Base is used for the selective e isolation of Pseudomonas aeruginosa from clinical specimens.
Composition**
Ingredients
**Formula adjusted, standardized to suit performance parameters
Directions
Suspend 46.7 grams in 1000 ml distilled water containing 10 ml glycerol. Heat, to boiling, to dissolve the medium
completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. If desired, rehydrated contents of 1 vial of Nalidixic Selective Supplement (FD130) may be added aseptically to 1000 ml medium. Mix well and pour into sterile Petri plates.
Principle And Interpretation
Pseudomonas aeruginosa grows well on all normal laboratory media but specific isolation of the organism, from
environmental sites or from human, animal or plant sources, is best carried out on a medium, which contains a selective agent and also constituents to enhance pigment production. Most selective media depend upon the intrinsic resistance of the species to various antibacterial agents. Cetrimide inhibits the growth of many microorganisms whilst allowing Pseudomonas aeruginosa to develop typical colonies.
Cetrimide is a quaternary ammonium salt, which acts as a cationic detergent that reduces surface tension in the point of contact and has precipitant, complexing and denaturing effects on bacterial membrane proteins. It exhibits inhibitory actions on a wide variety of microorganisms including Pseudomonas species other than Pseudomonas aeruginosa . King et al developed Medium A for the enhancement of pyocyanin production by Pseudomonas (1). Cetrimide Agar developed by Lowburry (2) is a modification of Tech Agar (Medium A) with addition of 0.1% cetrimide for selective isolation of P.aeruginosa . Later, due to the availability of the highly purified cetrimide, its concentration in the medium was decreased (3). The incubation was carried out at 37°C for a period of 18-24 hours (4).
P.aeruginosa can be identified due to their characteristic production of pyocyanin, a blue, water-soluble, non- fluorescent phenazine pigment coupled with their colonial morphology and the characteristic grape-like odor of aminoacetophenone (5). P.aeruginosa is the only species of Pseudomonas or gram-negative rod known to excrete pyocyanin. These media are therefore, important in the identification of P.aeruginosa . These media are used for the examination of cosmetics (6) and clinical specimens (5, 7) for the presence of P.aeruginosa , as well as for evaluating the efficacy of disinfectants against this organism (8).
Pancreatic digest of gelatin provide necessary nutrients for P.aeruginosa . Sodium chloride maintains osmotic equilibrium in the medium. Magnesium chloride and potassium sulfate stimulates pyocyanin production. (9).
For the isolation of P.aeruginosa , plates of Cetrimide Agar should be inoculated from non-selective medium such as Brain Heart Infusion Broth (M210) or Soyabean Casein Digest Medium (M011). If the count is high, the test sample can be directly inoculated onto Cetrimide Agar. P.aeruginosa colonies may appear pigmented blue, blue-green or non- pigmented. Colonies exhibiting fluorescence at 250nm and a blue green pigmentation are considered as presumptive P.aeruginosa may lose its fluorescence under UV if the cultures are left at room temperature for a short time.
Fluorescence reappears after the plates are re-incubated (4). Type of peptone used in the base may also affect pigment production (4, 10). Certain strains of P.aeruginosa may not produce pyocyanin. Other species of Pseudomonas do not produce pyocyanin but fluoresce under UV light. Most non-! Pseudomonas species are inhibited on Cetrimide Agar, and some species of Pseudomonas may also be inhibited. Some non-fermenters and some aerobic spore formers HiMedia Laboratories
may exhibit a water-soluble tan to brown pigmentation on this medium. Serratia may exhibit pink pigmentation (3).
Biochemical tests and serological procedures should be performed to confirm the findings.
Quality Control
Appearance
Cream to yellow homogeneous free flowing powder
Gelling
Firm, comparable with 1.5% Agar gel
Colour and Clarity of prepared medium
Light amber coloured, opalescent gel with a slight precipitate forms in Petri plates
Reaction
Reaction of 4.67% w/v aqueous solution containing 1% glycerol at 25°C (after sterilization). pH : 7.2±0.2
Cultural Response
Growth Promotion is carried out in accordance with the harmonized method of USP/EP/BP/JP. Cultural response was
observed after an incubation at 35-37°C for 18-48 hours. Recovery rate is considered as 100% for bacteria growth on
Soyabean Casein Digest Agar.
Pseudomonas aeruginosa ATCC 27853
luxuriant yellow green
Escherichia coli ATCC 25922
>=10³ inhibited 0%
Cultural Response
M024: Cultural characteristics observed after incubation at 30-35 °C for 18-72 hours. Recovery rate is considered as
100% for bacteria growth on Soyabean Casein Digest Agar.
Organism
Inoculum
Recovery
Lot value
Inhibition after 72 hours
Stenotrophomonas
maltophila ATCC 13637Staphylococcus aureus ATCC 25923
Additional Microbiological
testing
Proteus mirabilis ATCC
ATCC 14028Escherichia coli ATCC 8739 >= 10³ ATCC 9027Escherichia coli NCTC 9002 >= 10³ ATCC 6538
Reference
1.King, Ward and Raney, 1954, J. Lab. Clin. Med., 44:301.
2.Lowbury, 1951, J. Clin. Pathol., 4:66.
3.Lowbury and Collins, 1955, J. Clin. Pathol., 8:47
4.Brown and Lowbury, 1965, J. Clin. Pathol., 18:752.
5.Murray P. R., Baron J. H., Pfaller M. A., Jorgensen J. H. and YolkenR. H., (Ed.), 2003, Manual of Clinical
Microbiology, 8th Ed., American Society for Microbiology, Washington, D.C.
6.USFDA Bacteriological Analytical Manual, 2005, 18th Ed., AOAC, Washington, DC.
7.Forbes B. A., Sahm A. S. and Weissfeld D. F., Bailey & Scotts Diagnostic Microbiology, 10th Ed., 1998, Mosby,
Inc., St. Louis, Mo.
8.Williams, (Ed.), 2005, Official Methods of Analysis of the Association of Official Analytical Chemists, 19th Ed.,
AOAC, Washington, D.C.
9.MacFaddin J. F., 1985, Media for Isolation-Cultivation-Identification -Maintenance of Medical Bacteria, Vol. I,
Williams and Wilkins, Baltimore.
10. Goto and Enomoto, 1970, Jpn. J. Microbiol., 14:65.
Storage and Shelf Life
HiMedia Laboratories
Store below 30°C and the prepared medium at 2-8°C. Use before expiry date on the label.

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