Bacteria are known for their rapid growth, many of the enterics

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Bacteria are known for their rapid growth, many
of the enterics will grow and then divide every
20 minutes under ideal conditions. Some bacteria
isolated from deep underground may divide once
every hundred years! Generation Time
(doubling time) the amount of time required to
double the number of cells in a
culture. Measuring doubling time theoretical
ly Nt No x 2n by direct measurement
1.) Turbidimetry Semi-log plot of optical
density (OD) vs. time 2.) Direct microscopic
count 3.) Viability count
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Semi-Log plot of Growth Data
1.0
OD (600nm)
0.1
0.01
1
5
4
3
2
Time (hrs.)
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Optical Density (OD) --- a measure of the
number of objects in a light path (beam),
generally also referred to as turbidimetry
(requires a spectrophotometer) --- Absorbance
(OD measure) is the decrease in the amount of
light getting through the sample, usually the
more sensitive measure --- Transmittance is
the total amount of light penetrating the
sample, doesnt require as much optics as
absorbance but is less sensitive --- OD
(600nm) optical density taken with 600 nm light
--- be aware that absorbance over 2.0 is not
measured accurately (scattered light is no
longer proportional to cell density), very dense
Cultures should be diluted by some known factor
before another reading is taken (1/10 dilution
is common)
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Other Means of Determining Cell Number Direct
Count Viability Count (cfu)
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Viability Count (Colony Forming Units,
CFU) Serial Dilution
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Assessing the number of bacteria in a fluid sample
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Bacterial Growth Phases
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Microenvironments within a Test Tube
What is the limiting factor to growth of a
strict aerobe in this system other than O2?
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Factors for Bacterial Growth --- availability
of nutrients (chapter 5) --- accumulation of
metabolic byproducts (wastes) ---pH (protein
structure, electron transport) --- oxygen (or
lack there of) toxicity of oxygen ---
temperature (protein structure) ---
availability of water (food storage)
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Summary Chapter 6 Bacterial Growth --- know
each phase of the growth curve and what the
cells are experiencing in each phase ---
aseptic technique -- culturing and media
types How do you measure cell density? --- OD
(growth curve) --- Direct Count --- Serial
Dilution --- Water sampling Factors
affecting bacterial growth --- be able to list
several and explain them --- be able to define
temperature classifications