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2 Photos - 2 Questions: Gram Stain - (Mar/23/2014 )



I did gram staining of a 24h old B. megaterium culture from plate. Some bacteria stain positive, some negative. I read that endospore forming organisms are prone to staining gram negative if they are not fresh. But my culture was fresh. What happened?


Then, I did another Gram Stain of bacteria I isolated from animals.On Columbia sheep blood agar and LB agar they are growing in small yellow colonies (after 24h incubation). For me it looks like M. luteus. What do you think? Are there other species these bacteria could be?



Thanks for your Help.


It could be that you didn't do your Gram stain properly...


It could be Micrococcus luteus, but there are other Gram +ve cocci that grow as yellow colonies... where did you get the sample?  scale is important in images!


Micrococcus spp. are oxidase positive - give it a try.

-Phil Geis-

Hi I did oxidase test which was negative. now I'll sequence 16s and see what it is thanks for the help!


It is M luteus although it proved negative for oxidase!