BIOL-M 250 Lecture Notes - Lecture 5: Stringent Response, Lysis, Closed System
Document Summary
Advantages: do not need to grow cells, works for any sample. Disadvantages: cells must be evenly distributed, cant distinguish which cells are dead or alive. Viable counting: spreading culture on petri plates & counting colony forming units(cfu) Assumption: each living cell is a colony forming unit(cfu) & will grow to become a colony over time. Counting rule: 30-300~less than 30 is statistically insignificant, greater than 300 is too crowded. Advantages: allows you to measure the number of viable cells by cfu. Disadvantages: only works with cultural bacteria assumes each colony originates from single cell clumping issues. Spectrophotometry: measuring turbidity of culture by shining light through a culture. The more dense the culture, the more light is absorbed. Od600(turbidity)= optical density at 600nm wavelength: . 1= not dense, 1. 0=very dense & meaningful* To indirectly count, take od600 & also use viable or direct counting set conversion for bacterium: ex) if 1. 0 od600=5x 10^8 bacteria/ml then . 20 od600=1x10^8 bacteria/ml.
