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gardenlife1 gardenlife1
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9 years ago
Earlier formulation of Columbia CNA agar using higher concentration of colistin and nalidixic but reduce to improve the recovery of gram positive organisms.  Why would higher concentrations be less effective at allowing growth of gram positive organism?
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9 years ago
Ellner et al., in 1966, reported the development of a blood agar formulation, which has been designated as Columbia Agar.1 The Columbia Agar base, which achieves rapid and luxuriant growth and sharply defined hemolytic reactions, is utilized as the base for media containing blood and for selective formulations in which various combinations of antimicrobial agents are used as additives. Ellner and his colleagues found that a medium consisting of 10 mg of colistin and 15 mg of nalidixic acid per liter in a Columbia agar base enriched with 5% sheep blood would support the growth of staphylococci, hemolytic streptococci and enterococci while inhibiting the growth of Proteus, Klebsiella and Pseudomonas species. In BBL Columbia CNA Agar with 5% Sheep Blood, the concentration of nalidixic acid has been reduced to 10 mg/L to increase the recovery of gram-positive cocci from clinical specimens.

PRINCIPLES OF THE PROCEDURE Columbia CNA Agar with 5% Sheep Blood derives its superior growth-supporting properties from the combination of peptones prepared from pancreatic digest of casein, peptic digest of animal tissue and beef extract. Yeast extract and corn starch are also included in the formulation and serve as energy sources, with yeast extract being a supplier of the B complex vitamins. Sheep blood allows detection of hemolytic reactions and supplies the X factor (heme) necessary for the growth of many bacterial species but lacks V factor (nicotinamide adenine dinucleotide, NAD), since it contains NADase which destroys the NAD. It should be noted that this medium has a relatively high carbohydrate content and, therefore, beta-hemolytic streptococci may produce a greenish hemolytic reaction that may be mistaken for alpha hemolysis. The addition of the antimicrobial agents, colistin and nalidixic acid, renders the medium selective for gram-positive microorganisms. The colistin disrupts the cell membranes of gram-negative organisms, whereas the nalidixic acid blocks DNA replication in susceptible gram-negative bacteria.2
Source  https://catalog.hardydiagnostics.com/cp_prod/Content/hugo/ColumbiaCNAAgar.htm
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Staff Member
9 years ago
low concentrations achieve fluidity
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gardenlife1 Author
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9 years ago Edited: 9 years ago, gardenlife1
Ellner et al., in 1966, reported the development of a blood agar formulation, which has been designated as Columbia Agar.1 The Columbia Agar base, which achieves rapid and luxuriant growth and sharply defined hemolytic reactions, is utilized as the base for media containing blood and for selective formulations in which various combinations of antimicrobial agents are used as additives. Ellner and his colleagues found that a medium consisting of 10 mg of colistin and 15 mg of nalidixic acid per liter in a Columbia agar base enriched with 5% sheep blood would support the growth of staphylococci, hemolytic streptococci and enterococci while inhibiting the growth of Proteus, Klebsiella and Pseudomonas species. In BBL Columbia CNA Agar with 5% Sheep Blood, the concentration of nalidixic acid has been reduced to 10 mg/L to increase the recovery of gram-positive cocci from clinical specimens.

PRINCIPLES OF THE PROCEDURE Columbia CNA Agar with 5% Sheep Blood derives its superior growth-supporting properties from the combination of peptones prepared from pancreatic digest of casein, peptic digest of animal tissue and beef extract. Yeast extract and corn starch are also included in the formulation and serve as energy sources, with yeast extract being a supplier of the B complex vitamins. Sheep blood allows detection of hemolytic reactions and supplies the X factor (heme) necessary for the growth of many bacterial species but lacks V factor (nicotinamide adenine dinucleotide, NAD), since it contains NADase which destroys the NAD. It should be noted that this medium has a relatively high carbohydrate content and, therefore, beta-hemolytic streptococci may produce a greenish hemolytic reaction that may be mistaken for alpha hemolysis. The addition of the antimicrobial agents, colistin and nalidixic acid, renders the medium selective for gram-positive microorganisms. The colistin disrupts the cell membranes of gram-negative organisms, whereas the nalidixic acid blocks DNA replication in susceptible gram-negative bacteria.2
 

Why would higher concentrations be less effective at allowing growth of gram Positive organism?
Post Merge: 9 years ago

low concentrations achieve fluidity

Could you expand on your answer?
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