Biology Forum Microbiology Colony growth

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    • #16203

      I need help with confirming what the colonies on my streak plates might be. For some reason the plates did not streak as well as normal. There was no growth on the mannitol plate but there was some on the nutrient agar and mac plates. I am pretty sure the yellow colonies on the nutrient agar are M. luteus.

      I do not know if the white opaque colonies on the nutrient agar plate are immature M. luteus or my other unknown. I was pretty certain that the mac plate showed S. marscens due to the pink to beige, red colonies ( I thought). The more I’ve researched, I’ve seen some E.coli that look similar and R. rubrum stood out (haven’t researched this one much yet though). My colonies are not regurlar in shape though. The shape is what I would call irregular with undulated margins. In the center of the colonies on my mac plate they do "sink" in.
      My gram stains did very little to help. I know I had tiny gram+ cocci that appeared to be in tetrads of strepto clusters and this pretty much helps seal the deal for me that I do have M. luteus on my nutrient agar. I saw some pink for gram+ but the shape was off( very irregular) and don’t know if it was just some trash on the slide. I also saw something that could be bacili in shape or maybe it was something I messed up while preparing the smear and stainging. Appreciate any help in sending my thoughts in research in a good direction!!!


    • #110077

      Think you need to read more carefully the description of media – esp. MacConkey agar. In any case – isolate pure cultures, Gram stain, and apply appropriate keys.

    • #110078

      I will read up on the Mac-thanks. No isolating anything now. We have done away with our mixed culture stock broths and and various agar plates. We have only covered staining and various plating methods thus far or I would have used more test to be sure…. Out of our list of unknowns I have 4 that cold grow on the Mac, so I will just take another look at the data I have and see.

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