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Revision as of 19:12, 26 September 2012

Food hygiene

The high school students brought the following items:
1) Pork ham, taken from the freezer at home, uncertain how old.
2) Amelander smoked ham, two days after the due date, taken from the local supermarket.
3) Raw, salted herring (a Dutch delicacy), one day after the due date, local supermarket.
4) Yakult®, fresh.
5) Milk, directly from the cow and from the supermarket, both fresh.
6) Beer (Hertog Jan® ), fresh.

Of 1, 2 and 3, the students defined the Total Aerobic Microbial Count. The results where surprising: while the TAMC of both of the ham products was over the legal TAMC limit of 10^6.7, the herring was still good! It was good that nobody ate the ham from the freezer.

We also let the meat samples grow on Mac Conkey Agar. This agar is selective for lactic acid bacteria and bacteria which can grow in the gut (like the well-known gut bacterium E. coli). While 2 and 3 did not or almost not contain any of those bacteria, 1 did stand out with a plate full. The yellow color of the Agar indicated that the bacteria produced a great amount of acidic compounds.

Of the other products, we checked the types of bacteria that were growing there with microscopy. It was clear that the “cow”-milk had very different bacteria than the “supermarket”-milk! The latter contained small rods and coccus, both connected in strings (probably Lactobacillus species and Streptococcus species), while the “cow”-milk contained larger rods with spores.

Trying to grow the Yakult® bacteria turned out to be very, very hard! Both on normal agar and Mac Conkey Agar, this didn’t go well. It might be that we have to grow them anaerobically.


Washing your hands, is it useful?

All students did a short experiment where they probed the microbes on their fingers. They had to push their fingerprint on a yeast-extract/glucose agar plate, which was put in the stove (37 degrees celcius) for 2 days afterwards:
1) before entering the lab
2) after washing their hands 2 minutes
3) after sterilization of their finger with 70% ethanol
4) after a whole day of working in the lab

The students were surprised by the results: the most colonies could be found at (2)! Does this mean that you shouldn’t wash your hands? No. After looking at the bacteria by microscopy, it turned out that the bacteria at (2) where mostly skin-inhabitants, while at (1) and (4), most bacteria where other sorts from the outside environment. Your skin inhabitants are there to protect you against the bacteria from the outside world. If you're interested in getting the protocols for the experiments we did with the students, feel free to contact us at team(at)igemgroningen.com!

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