Microbiology help PLEASE!!! My major unknown may be contaminated?

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So I am in microbiology class, a prerequisite for the Registered Nurse (RN) Program at my local college.

A gram stain under the microscope shows a lot of gram negative (pink) cells, but a few gram positive (purple) cells as well. Mostly the pink cells. The purple ones are smaller cells, and there appears to be less of those.

Any tips on isolating the cells? I only want the gram negative, pink cells. Asking for a whole new specimen would cost 40 out of the 100 points. Ouchhhh :/!!!

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Inoculate a new petri dish containing agar that is selective for growing gram negative bacteria / an agar plate that inhibits the growth of gram positive.

Or, use the streak method to isolate single colonies, do gram stains for both colonies that grow on the plate, figure out which colony is the gram negative, then inoculate a new petri dish with the gram negative to ensure only one type of bacteria grows on the dish.

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Take a sample from your most isolated colony on the plate you used to gram stain from and grow it on an EMB plate.

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Following for the good advice :D we start our unknowns next week and I am a teeny bit nervous lol

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restreak it on to a macconkey plate

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Specializes in Hospitalist Medicine.
Inoculate a new petri dish containing agar that is selective for growing gram negative bacteria / an agar plate that inhibits the growth of gram positive.

Or, use the streak method to isolate single colonies, do gram stains for both colonies that grow on the plate, figure out which colony is the gram negative, then inoculate a new petri dish with the gram negative to ensure only one type of bacteria grows on the dish.

^^THIS!

Also keep in mind: did you do your initial Gram stain properly? Perhaps not rinsed properly, which is why some appear purple instead of all pink?

Good luck on your Unknowns! One of my favorites :D

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^^THIS!

Also keep in mind: did you do your initial Gram stain properly? Perhaps not rinsed properly, which is why some appear purple instead of all pink?

Good luck on your Unknowns! One of my favorites :D

She didn't say if it was bacilli or cocci, which is important here. I guess if she could answer that she'd be able to answer your question! But yes, she needs to restreak for isolation or just take her colony and put it on the macconkey agar, nothing but gram negative will grow on that.

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I'll try the streak plate isolation method you guys are talking about! The gram stain seems to appear cocci to me... both the pink and purple parts of it.... I'll provide pictures if its allowed here :D

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Specializes in Critical care.

meib92's advice is good. I hated isolating unknowns! But then, I hate bacteria, in general. :)

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diplococci? Did you put it on a Thayer martin plate?

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Specializes in ICU.

Some different bacteria can have both. When we swabbed our mouths last semester some of us had both positive and negative. But I would also check and make sure you did your gram stain properly. That was the first thing my professor asked. It could have to do with how heated it.

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I tried taking the best pictures I could!

Microbiology Gram Stain (Positive and negative?) - Imgur

I didn't put it on a special agar. Just the trypicase soy agar. And I followed this youtube video's advice on streaking the plate for isolation.

But in the pics, you can see the majority is pink with a few speckled purple through-out the stain :'(

At first I was thinking it was cocci, but i had a couple students peek and they said they think bacilli. My bacteria sample is so tiny v.v any tips on distinguishing the shape?

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