Observing a bacteria culture

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ratapenado
Posts: 5
Joined: Thu Jan 13, 2022 7:21 am

Observing a bacteria culture

#1 Post by ratapenado » Fri Jan 14, 2022 11:35 am

Hello,

I pressed my fingers on a agar plate and I see the bacteria growing. It's fascinating but I have some questions:

- I should have asked before but is it something stupid to do and I should kill the bacteria before it's too late ?

- if not, how to properly observe the bacteria under a microscope (old Leitz HM LUX)

- and is there an online guide to recognise/classify these bacterias ?

Thanks !

Alexander
Posts: 106
Joined: Fri Jun 11, 2021 7:10 pm

Re: Observing a bacteria culture

#2 Post by Alexander » Fri Jan 14, 2022 12:05 pm

Take a bit of the culture and place it in a drop of water on the slide. Make sure not to bring any agar onto the slide. Mix bacteria and water. Distribute the water over the slide. Let it dry. Fix it with heat by putting it through a flame a few times. Stain it. Put it onto the microscope. A simple staining is methylene blue. All bacteria are blue now. A more sophisticated staining is gram's staining. Gram-negatives are red or orange and gram-positives are blue or violet. There are other stainings for specific purposes.

It is almost impossible to classify bacteria by microscope observation only.

ratapenado
Posts: 5
Joined: Thu Jan 13, 2022 7:21 am

Re: Observing a bacteria culture

#3 Post by ratapenado » Fri Jan 14, 2022 2:45 pm

Thank you ! For classification I was more thinking about the structure that the bacteria makes on the agar, but maybe it's not characteristic

Alexander
Posts: 106
Joined: Fri Jun 11, 2021 7:10 pm

Re: Observing a bacteria culture

#4 Post by Alexander » Fri Jan 14, 2022 11:12 pm

The culture on the agar will give some information. A CLED agar plate for example bacteria changes color depending wether the bacterias metabolism consumes lactose or not. With lactose-positive bacteria the agar changes color to yellow. With lactose-negative bacteria it remains blue. There are many different types of agar which help to narrow the classification.

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