Sellers Agar is a very useful medium to identify and differentiate gram-negative, non-fermenting bacilli, such as Pseudomonas aeruginosa and Alcaligenes faecalis. The differentiation is based on the detection of fluorescence, glucose oxidation, production of nitrogen gas and pH changes, from clinical samples and other materials. Gelatin peptone provides nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly of the B-group. Magnesium sulfate is a cofactor for various metabolic reactions. Sodium nitrite provides nitrogen to some organisms. L-Arginine provides amino acids for growth. Sodium chloride maintains the osmotic balance. Dipotassium phosphate acts as a buffer system. D-Mannitol fermentation is detected by Bromothymol blue as a yellow halo around the colonies. Phenol red is a pH indicator. Bacteriological agar is the solidifying agent. Acinetobacter calcoaceticus morphologically resemble Neisseria and are frequently erroneously reported as causes of gonococcal urethritis and meninogococcal meningitis (resistant to penicillin). To aid in the identification of the non-fermenters, other media such as OF Basal Medium (Cat. 1500), Indole Nitrate Medium (Cat. 1504), etc., should be used. Under UV light only the Pseudomonas exhibit fluorescence, which is stimulated by magnesium and mannitol in the medium. At times, it is necessary to hold the tubes for 2 days for Pseudomonas to produce a typical alkaline (blue color) reaction in the medium. After incubation, check for glucose oxidation by the appearance of a yellow band, which can disappear after 24 hours.
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