Lab Notes Jan 14

Bacteria are very small – 1 to 5 micrometers (um) (1*10^6 meter)
Bacteria are everywhere
Must learn techniques to prevent bacterial contamination of experiments – aseptic technique (keep empty test tubes and sterile broth near Bunsen burner – tower of air keeps bacteria up high – hot air doesn’t allow bacteria to contaminate test tubes)
Can’t see bacteria with naked eye – why they easily contaminate

Volumes
Based on 1 liter
mL – 1 thousanth of a liter
microL= 1*10^6 L (microliters)
1000 microliters in one mL

Serial dilution and spread plating
Answers question: how many bacteria in a sample?
Have sample (vol = 10 mL) full of bacteria
Need 8 sterile test tubes – put 0.9 of a mL of sterile broth into each test tube
Put .1 mL of bacteria into 1st test tube (1/10th concentrated or 10^1)
2nd test tube 1/100th concentrated or 10^2
3 rd test tube 1/1000th concentrated
End of series – 1/10^8 concentrated as original
Take .1 mL of concentrated solution and spread it out on petri dishes with a glass hockey stick that has been sterilized by being dipped into rubbing alcohol and then set aflame

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