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How many arrows do you see in the following shape?. Microbial Growth. Microbiology 2314. Bacterial Growth. Bacterial Growth is Bacterial Reproduction The Numbers of Bacteria are Increasing We see: 1. Observable Increases in Colonies Growing on Solid Media
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How many arrows do you see in the following shape?
Microbial Growth Microbiology 2314
Bacterial Growth • Bacterial Growth is Bacterial Reproduction • The Numbers of Bacteria are Increasing • We see: 1. Observable Increases in Colonies Growing on Solid Media 2. Turbidity, Sediment, Scum or a Change in Color in Broth Cultures
Generation Time The Time Required for a Cell to Divide
Generation Time N = (log10Nf – log10No ) / .301 N Number of generations Nf Final Concentration of Cells No Original concentration of cells .301 Conversion Factor to Convert Log2 to Log10
What is a Logarithm? • Logarithm is a functionthat gives the exponent in the equation bn = x. It is usually written as logbx = n. • For example: 34 = 81 Therefore log3 81 = 4
Example 1N = (log10Nf – log10No ) / .301 Measure Culture at 9:00 a.m. 10,000 cells / ml Measure Culture at 3:00 p.m. 100,000 cells / ml Calculate N N = (log10Nf – log10No ) / .301 N = (5-4)/0.301 N = 1/0.301 N = 3.33 Generations in 6 Hours We Know: 6 Hours = 360 Minutes Therefore: Generation Time = 360 Minutes / 3.33 Generations N = 108 Minutes to Generate
Example 2N = (log10Nf – log10No ) / .301 Measure Culture at 9:00 a.m. 10,000 cells / ml Measure Culture at Noon 1,000,000 cells / ml Calculate N
Example 2N = (log10Nf – log10No ) / .301 Measure Culture at 9:00 a.m. 10,000 cells / ml Measure Culture at Noon 1,000,000 cells / ml Calculate N N = (log10Nf – log10No ) / .301 N = (6-4)/0.301 N = 2/0.301 N = 6.64 Generations in 3 Hours We Know: 3 Hours = 180 Minutes Therefore: Generation Time = 180 Minutes / 6.64 Generations N = 27 Minutes to Generate
Example 3N = (log10Nf – log10No ) / .301 Measure Culture at 9:00 a.m. 2000 cells / ml Measure Culture at 1:00 p.m. 18,000 cells / ml Calculate N
Example 3N = (log10Nf – log10No ) / .301 Measure Culture at 9:00 a.m. 2000 cells / ml Measure Culture at 1:00 p.m. 18,000 cells / ml Calculate N N = (log10Nf – log10No ) / .301 N = (4.25-3.30)/0.301 N = .95/0.301 N = 3.16 Generations in 4 Hours We Know: 4 Hours = 240 Minutes Therefore: Generation Time = 240 Minutes / 3.16 Generations N = 75.9 Minutes to Generate N = 1.27 Hours to Generate
Typical bacterial exponential Growth Curve. In a rich culture medium bacteria, grown under aerobic conditions, achieve a final concentration of 2-5 x 109 cells per ml in about 12-18 hours. Although plotted on a different time scale the human growth curve looks the same; the human population at similar points on the growth curve are shown in red.
Remember the Four Main Stages • Lag Phase Initial Phase / Metabolic Activities • Exponential Phase 2nd Phase / Optimum Growth / Doubling • Stationary Phase 3rd Phase / Exhaustion of Nutrients / Accumulation of Wastes • Death Phase Final Phase / Continued Accumulation 90% of Cells Die, then 90% of Remaining Cells Die, etc.
Quantification of Bacteria • Cell Numbers • Total Mass of the Population • Population Per Media cells / ml or cells / gram • Direct County Methods and Indirect Counting Methods
Direct Counting Methods • Normally Viable Counts • Remember that a Colony Starts Out as 1 Bacteria that Reproduces • Colonies May Not All Be The Same Size
Types of Direct Measurements • Plate Count a. Spread (Streak) Plate b. Pour Plate 2. Direct Observation on Slides a. Petroff-Hausser Chamber Slide 3. Filtration 4. Most Probable Number
Direct Count Spread or Streak Plate
Direct Count Pour Plate
Direct Method Filtration
Most Probable Number • Statistical Procedure used to estimate the number of bacteria that will grow in liquid media. • Gives a 95% probability that the bacterial numbers will fall within a certain range.
Indirect Measurements Turbidity a. No turbidity = < 107 cells/ml b. Slight = 107 – 108 cells/ml c. High = 108 – 109 cells/ml d. Very High = > 109 cells/ml Metabolic Activity Dry Weight
There Are More Accurate Methods to Determine Turbidity Levels
Cardinal Temperatures • Minimum Temperature • Optimum Temperature • Maximum Temperature
Buffers Are Added to Media to Maintain Proper pH • Phosphates • Peptones • Amino Acids