I was about to have some yogurt as a snack when I noticed the "Live & Active Cultures" advertising on the side. Hmmmm, I wondered, and got out the microscope. I smeared some delicious Strawberry Breyers on a slide and then ate my snack--I wasn't sure I would still want to eat it after I looked at the slide.Once I looked in the microscope, it was anti-climatic. It wasn't until 1000x that I saw some bacteria, and even then they are quite small, as you can see below. I'm pretty sure they are Streptococci thermophilis, because of all the bacteria they put in yogurt, these are the only ones which are spherical, whereas the others are rod-shaped.
None of the bacteria in yogurt are supposed to swim, but these little diplococci (double-berries) seemed to. However, they all "swam" in the same direction and are probably just flowing on some kind of micro-stream. The microscope lens pushed on the sample and it could have created a micro-flow. Here's a short movie showing them moving:Why are bacteria in my yogurt? When these bacteria are added to milk, they feed on the lactose and make lactic acid as a by-product (see below). The acidity then curdles the milk proteins and also gives the final product--yogurt--its characteristic tangy flavor. Anyone else hungry for some delicious Live & Active Cultures?
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