Dear Researcher, As far I know that Azotobacter species gram negative.Is it possible to have gram positive Azotobacter species by gram staining procedure ?
Dear colleague,
Generally speaking, old cultures of Gram positive bacteria tend to give Gram negative reaction with Gram’ s method. For this reason, one should examine young cultures before the end of the logarithmic phase of bacterial growth. In your case, old cultures of Azotobacter, a Gram negative bacteria, become spherical producing a cyst with thick layer of mucous. This thick layer might resist decolorization by alcohol or acetone leading to a false Gram positive reaction. I recommend to check your Gram’s staining protocol and to stick to a standard method.
This might help;
The Production of Gram-positive Variants by Azotobacter chroococcum
BY K. A. BISSET, A. C. BAIRD-PARKER, C. M. F. HALE,
M, H. JEYNES AND J. C. LAWRENCE
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