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Thread: Microscope to see bacteria

  1. #1 Microscope to see bacteria 
    Forum Cosmic Wizard icewendigo's Avatar
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    What level of microscope magnification is enough to see bacteria in a drop of water?


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  3. #2 Re: Microscope to see bacteria 
    Moderator Moderator TheBiologista's Avatar
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    Quote Originally Posted by icewendigo
    What level of microscope magnification is enough to see bacteria in a drop of water?
    Normally I look at mammalian cells which are huge by comparison to bacteria, so I may be a bit off on this. I reckon you'd need a high power objective lens (>20x) plus a 10x eyepiece. 200x total magnification, would probably be the minimum for bacteria. Not even sure you'll see them at that. 400x would probably be needed to see them clearly, and they'll still look quite small. Bigger problem is that they're often quite hard to see untreated. You may need to add a stain of some kind, depending on the bacterial species.


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  4. #3  
    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
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    You can see bacteria at 40x-50x but they're practically just dots, so 100x is best. However, those are standard objective lens* magnifications for a basic light microscope. It is very hard to see bacteria in water though, usually the population is so dispersed that you probably wouldn't notice them (unless it's some scummy swamp water with a heavy film of photosynthetic bacteria).

    A typical rule of thumb if you want to see something under the microscope is to take what the human eye is able to see, approximately 100um, and figure out how much magnification you need to make that visible.

    So, E. coli is like 0.5 um, 100x lens * the eyepiece magnification (usually 10x) gives you 1000x magnification, making the bacterium 0.5mm. That is a pretty comfortable size to be able to make out the shape of the bacteria. Although, you have to realize that many bacteria are practically translucent without stain and will still be difficult to see.

    Edit: * for clarifications purposes.

    Edit2: At work I use 100x objective with a basic crystal violet stain to identify bacteria in urine, I think there are hobby shops that sell stains. I had a microscope as a child that came with bottles of crystal violet and safranin so they're probably commercially available somewhere out there.
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  5. #4  
    Forum Radioactive Isotope skeptic's Avatar
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    I like to use 1000 times oil immersion. However, there are some bacteria that are filamentous, and can be seen at much lower magnification. To see bacteria clearly requires staining, which needs some preparation. Simply peering at a drop of water through a microscope is unlikely to be very rewarding.
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