Cetrimide Agar Base
Cetrimide Agar Base is used for the selective e isolation of Pseudomonas aeruginosa
from clinical specimens.Composition**
**Formula adjusted, standardized to suit performance parametersDirections
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
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
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).
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
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
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
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
Cream to yellow homogeneous free flowing powderGelling
Firm, comparable with 1.5% Agar gelColour and Clarity of prepared medium
Light amber coloured, opalescent gel with a slight precipitate forms in Petri platesReaction
Reaction of 4.67% w/v aqueous solution containing 1% glycerol at 25°C (after sterilization). pH : 7.2±0.2Cultural 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 greenEscherichia 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
Inhibition after 72 hours
maltophila ATCC 13637Staphylococcus aureus
Proteus mirabilis ATCC
ATCC 14028Escherichia coli ATCC 8739
ATCC 9027Escherichia coli NCTC 9002
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
Store below 30°C and the prepared medium at 2-8°C. Use before expiry date on the label.
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The additional value of ovarian hyperstimulationin intrauterine insemination for couples withan abnormal postcoital test and a poor prognosis:a randomized clinical trialPieternel Steures, Jan Willem van der Steeg, M.D.,Peter G. A. Hompes, M.D., PhPatrick M. M. Bossuyt, J. Dik F. Habbema, Marinus J. C. Eijkemans, M.Sc., Ph.D.,Caroline A. M. Koks, Petra Boudrez, M.D.,Fulco van der Veen, M.D., Ph.D.