Ashby′s Mannitol Agar
STANDARD COMPOSITION
Mannitol 20.0 g, potasium phosphate dibasic 0.2 g, magnesium sulfate 0.2 g, sodium
chloride 0.2 g, potassium sulfate, 0.1 g, calcium carbonate, 5.0 g, agar 15.0 g.
Distilled water ad 1000 ml, adjust pH to 7.4 ± 0.2.

MODIFIED MEDIUM (unpublished data - admin note)
D-glucose 5.0 g, mannitol, 5.0 g, K
2HPO4 0.9 g, KH2PO4 0.1 g, MgSO4 * 7H2O 0.1 g,
NaCl 0.2 g, FeSO
4 *7H2O 0.01 g, Na2MoO4 * 2H2O 0.005 g, CaCO3 5.0 g, CaCl2 *2H2O
0.1 g, agar 15.0 g.
Distilled water ad 1000 ml, adjust pH to 7.3.


PROCEDURE
Sterilize by autoclaving at 121 ºC for 15 minutes. Cool to 45-50 ºC. Mix well and pour
into sterile Petri plates.


NOTE
Due to presence of calcium carbonate, the prepared medium forms opalescent
solution with white precipitate.
As the strain grows and acid is produced this will react
with the calcium carbonate, causing it to dissolve and form clear zones around the
colonies.
Ashby′s Mannitol Agar
(c) Costin Stoica
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PROKARYOTAE
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Calcium carbonate solubilization by A. chroococcum
on Ashby's Mannitol Agar: clear halos around
colonies. (7 days old culture)
DESCRIPTION
Medium for the isolation and cultivation of
Azotobacter spp. that use mannitol as a source of carbon. Azotobacter is nitrogen fixing
bacteria which can use mannitol as a carbon source and atmospheric nitrogen as nitrogen source.
REFERENCES
  1. Himedia Laboratories. Ashby’s Mannitol Agar (M706) -  technical data.
    Available at https://himedialabs.com/TD/M706.pdf.
  2. Merck Millipore. Ashby’s Mannitol Agar (A1840) -  technical data. Available at
    https://www.sigmaaldrich.com/
  3. Costin Stoica Azotobacter chroococcum in  ABIS Encyclopedia, Regnum
    Prokaryotae. Available at https://www.tgw1916.
    net/Pseudomonas/azotobacter_chroococcum.html
  4. Leibniz Institute DSMZ-German Collection of Microorganisms and Cell
    Cultures GmbH. AZOTOBACTER MEDIUM. https://www.dsmz.
    de/microorganisms/medium/pdf/DSMZ_Medium3.pdf accessed Nov. 2022.