Question
Asked 24th Nov, 2015

In Gram staining, what are the tiny dark purple dots inside or outside the bacterial cells?

Can anyone please view the attached pictures and tell me what are tiny dots inside or outside the bacterial cells that have been stained dark purple as opposed to lighter purple cells? Cells are one day old on LB plate.
Thank you in advance.

Most recent answer

Maria de Lurdes Enes Dapkevicius
University of the Azores
I get the same thing: pinkish cells that have distinct, purple granulations inside when Gram-stained. I don't think these would be fungi, as suggested above: dimensions of yeast cells are different and what I see definitely isn't fungal hyphae. The inclusion hypothesis seems interesting. Robert John Wolff Could you please share older references on this?
I'm adding a photo of one of our strains, for reference. Sorry for the poor quality - it was taken with the amateur microscope and camera I have at home.

Popular answers (1)

Wouter van der Westhuizen
Clinomics Bloemfontein
There is a possibility that you might be heating the cells too much during the fixing to the slides, which could cause damage to the cell walls. Try gentler heat fixation and see if you get a similar result with the Gram stain?
3 Recommendations

All Answers (18)

Debdeep Dasgupta
University of Calcutta
Looks like they are mostly endospores. Your cells were old?
Vijitra Luang-In
Mahasarakham University
 One day old on plate. Can bacteria have several spores in one cell at the same time?
Debdeep Dasgupta
University of Calcutta
Basically one endospore  is formed from one vegetative cell. 
Wouter van der Westhuizen
Clinomics Bloemfontein
Those don't look like spores,; looks like structures on the outside of the cells. Are you growing the bacteria in any detergents or any other environmental stress factors?
Vijitra Luang-In
Mahasarakham University
I do not think they are spores either. Yes you are right the dots look like they are on the cell surface. These are grown on normal LB agar in anaerobic conditions. It is so perplexing to me.
Wouter van der Westhuizen
Clinomics Bloemfontein
There is a possibility that you might be heating the cells too much during the fixing to the slides, which could cause damage to the cell walls. Try gentler heat fixation and see if you get a similar result with the Gram stain?
3 Recommendations
Elsayed Khalaf Bakhiet
Faculty of Science, Al-Azhar University, Assiut
spore
Larry P Elliott
Western Kentucky University
Endospores are colorless when the Gram stain is done.
2 Recommendations
Heba Kamal Issa
Port Said University
can you send me these figures as it can't be open
Phawinee Subsomwong
Hirosaki University
I could not open your figures. Could you upload again or sent me the figures.
Tamara Bell
Mississippi College
Vijitra Luang-In Did you ever find the answer to this question? I have the same question.
Vijitra Luang-In
Mahasarakham University
@Tamara bell, still now I am not sure what it is.
Kaisa Roots
Tallinn University of Technology
I am experiencing something similar. I have grown Lactobacillus salivarius culture on MRS agar, Gram-stained them and I see that cells have stained pink with purple regions inside. I suppose that if they were endospores, the staining would be other way around. Could this be an indication of cell stress?
Robert John Wolff
South University
Just happened to run into this question. First, they are definitely not endospores as these would be clear areas in gram stains (and Lactobacillus does not have endospores). What species is in the original pictures?
Inclusions are my first guess, and there is some basis for this in the older literature. It almost appears to be a bacterial infection of the cultured species by a gram positive organism, but that seems to be a reach.
1 Recommendation
Elesa McDonald
Indiana State University
I have a fomite bacteria I isolated from the environment that has these purple dots in it, my mentor and I don't know what is causing it. She thinks it might be a fungus I picked up from the environment. I think it might be a bacterial inclusion that has extra protein within the cell that a stock culture would not have.
Maria de Lurdes Enes Dapkevicius
University of the Azores
I get the same thing: pinkish cells that have distinct, purple granulations inside when Gram-stained. I don't think these would be fungi, as suggested above: dimensions of yeast cells are different and what I see definitely isn't fungal hyphae. The inclusion hypothesis seems interesting. Robert John Wolff Could you please share older references on this?
I'm adding a photo of one of our strains, for reference. Sorry for the poor quality - it was taken with the amateur microscope and camera I have at home.

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