I’m a amateur and trying to look for food poisoning germs.

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Jonnyvine
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I’m a amateur and trying to look for food poisoning germs.

#1 Post by Jonnyvine » Thu Dec 13, 2018 1:46 pm

Hello.

I am an amateur microscopist and was wondering where do I go about finding and seeing food poisoning bacteria under the microscope like salmonella or E.coli?

I already have a microscope that can see up to 400x magnification and a methylene blue staining solution.

Can anyone please help?
Last edited by Jonnyvine on Thu Dec 13, 2018 2:43 pm, edited 1 time in total.

wstenberg
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Re: I’m a amateur and trying to look for food poisoning germs.

#2 Post by wstenberg » Thu Dec 13, 2018 2:29 pm

For E. coli, methylene blue isn't very useful. You will need a Gram staining kit. This consists of a series of two dyes. Gram stain kits should be easily available. The Gram stain will allow you to stain the bacterial cell wall differentially depending on the species of the bacterium. Some cells take up the Gram's crystal violet, and they show up blue colored. These are called Gram positive. The others do not pick up the crystal violet stain; they are Gram negative. They will show up as red from the counterstain.
For E. coli, you are looking for Gram negative rods; they won't show any particular orientation pattern. The problem is that E. coli is part of the normal flora, and so it is not possible to tell if these are pathogenic or normal with the Gram stain. The pathogenic and normal E. coli and the normal E. coli look the same under the microscope, so further laboratory tests are needed to differentiate them.

Coliform bacteria in drinking water can be used as a measure of water pollution, but it just means the water has bacterial pollution not that these are specifically pathogenic. When I was working aboard a ship, we would check for this by culturing the bacteria on a specific media; we did not use direct microscopy. The bacteria are too dilute to easily find them.

Perhaps some of the microbiologists on the forum can weigh in...
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Jonnyvine
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Re: I’m a amateur and trying to look for food poisoning germs.

#3 Post by Jonnyvine » Thu Dec 13, 2018 2:39 pm

Ok, thanks for the insight wstenberg.

Can anyone perhaps mention about salmonella ?

wstenberg
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Re: I’m a amateur and trying to look for food poisoning germs.

#4 Post by wstenberg » Thu Dec 13, 2018 4:59 pm

In addition, Here's a good video from this website that gives some background regarding bacterial identification with a microscope.


http://www.microbehunter.com/why-you-ca ... ope-alone/
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Re: I’m a amateur and trying to look for food poisoning germs.

#5 Post by Elapid » Sun Apr 28, 2019 12:27 pm

Another thing to consider is that you will need higher magnification to see bacteria well and determine if they are gram positive or negative. Generally I like to use a 100x oil immersion objective. There are only a few places in medicine where microscopy is useful in diagnosing bacterial disease. One is in spinal fluid which is normally crystal clear. If we suspect that a patient may have bacterial meningitis I take a sample of spinal fluid by means of a “spinal tap” and send it to the lab. They will do an immediate Gram stain and do high power microscopy and report the result to me within an hour. The results are reported in terms of bacteria “per high power field” which means 100x. If there are only a few it could represent contamination such as the needle going thru skin, but more than 50 or so is very suspicious. Certain features will give me a clue as to which species of bacteria are causing the meningitis, but the real diagnosis will not be made until a couple of days later when the culture results are reported. Joint fluid and sputum are other instances where microscopy can make a preliminary diagnosis based on Gram stain results and bacteria count. These are instances where it is essential to begin antibiotic therapy at the earliest possible moment. Just knowing if the bacteria are Gram positive or negative is very valuable in choosing an antibiotic.

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