Leah is loving Coliforms? Today....yes indeed!

More work stuffs

Exciting stuff today (if you are a nerd!). We get standard tests once a month from a company to investigate whether or not we use correct procedure. It's basically to prove that we get positives where they should be and that we are able to identify the bugs that grow. Yesterday I took a sample and put 10g of it into a tube. Below are the results:

See how the agar is spread out? That's the bacteria literally blowing it apart. Very stupid of me to pick it up without gloves but they haven't yet got latex free gloves and I always wash my hands. Kids, don't try this at home (especially when you have an inkling it's Salmonella sp. in the tube! That was diluted 1/10 and that means that I put 1ml of dissolved sample into 10ml of agar. Below are 1/100 (take 1ml from the 1/10 sample and put it in 10ml of agar) and 1/1000.




Many teeny colonies here, look at them all floating!



Just a few colonies here. The reason we dilute is so that we can count correctly then multiply the number of colonies by the dilution to work out how many colony forming units (CFU) are in one sample. I should also add that the agar solidifies so the contents of that tube is solid. It's "squishy" enough for the colonies to grow though. They "eat" the agar for nutrition.

You remember a few posts back? My pretty agar plates? Look at the nasties growing!

The reason for the squiggle is to drag out one drip. You want it concentrated at one end and "running out". See how you've got a big blob on one end and just a few dots as the trail ends? The dots are individual colonies. these are 3 different types of agar: MSA, VJ and Cetrimide. If things grow on a few but not all it helps us identify them! You also see how the orange agar (MSA) has faded where the more bacteria are? That identifies where the bacteria have used the nutrients in the agar! This is more obvious below:



27 is the sample number and 8/6 is the date. We incubate the plates for 24hours (well for these plates) and we keep different ones for 48hrs and 5days so the date is as important as the sample number.

These plates show yellow bacterial growth. This is not good at all. If the colonies were pink or black then they are safe for human consumption (YEUCH!). I won't elaborate, especially if you are eating your dinner!

I'll come back to those tubes in a few days!
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