Module 3: Microbial Growth Flashcards
(41 cards)
3 Types of Microbial Growth
- Binary Fission
- Budding Cell Division
- Biofilm
Binary Fission
- Organelles duplicated
- DNA replication
- Elongation; cell organelle migration to opposite poles; cleavage furrow
- Septum Formation
- Production of 2 Daughter Cells
- INTERCALARY GROWTH
Budding Cell Division
- Mother cell produces appendage which forms the daughter cell
- Mother cell retains original size; appendaged is pinched off and deteriorated
- POLAR GROWTH
Biofilm (and 3 Properties); matrix name
- an assemblage of surface-associated microbial cells that are enclosed in an extracellular polymeric substance matrix
- “microbial mat” one species on top of one another
- EPS - exopolysaccharide matrix
3 Properties:
(i) Resistant to antibiotics or harmful chemicals - prevents entry
(ii) Hides them from protist grazer e.g. planktonic organisms (suspended in lipid environments)
(iii) Prevents being washed away by water
Generation Time (g)
Time taken for a cell to double
Solve for g (generation time)
g = t/n
g = 0.301/slope
g: generation time
t: time measurement
n: number of generations
Solve for N (final cell count)
N = N(0) x 2^n
N: final cell count
N(0): initial cell count
n: number of generations
Solve for n (number of generations)
n = 3.3[log(N) - log(N(0))]
n = [(log(N) - log(n(0))] / 0.301
n: number of generations
N: final cell count
N(0): initial cell count
4 Stages of Bacterial Growth Curve
- Lag Phase
- adapting to a new, nutrient-rich environment
- metabolically active but does not increase in cell number - Exponential Phase
- Cell Division occurs at a rapid rate
- limiting factor: ATP production - Stationary Phase
- production of new cells at the same rate of cell death - Death Phase
- nutrients are depleted
- overwhelming amount of toxic waste
- cells undergo involution
- endospore cells > vegetative cells
Duration of Lag Phase depends on
- Nutrients Available
- Species
Toxic Environment of Bacteria Growth Cycle
- Damaging pH
- Depletion of O2
Define Chemostat & 2 factors affecting cell density and growth rate
- a system in which the chemical composition is kept at a controlled level, especially for the culture of microorganisms.
- Dilution Rate
- Concentration of Limiting Reactant
5 Methods of Bacterial Growth Measurement
- Direct Microscopic Count
- counting via Petroff-Hauser counting chambers (both living and dead cells) - Viable Cell Count
- colony counting (spread plate, pour plate) - Most Probable Number
- estimate number of viable cells via gas production or turbidity - Membrane Filtration count
- physical separation of cells by size - Turbidimetric Method
- measuring via optical density and absorbance
Serial Dilution
Purpose, Range, Classifications and Process
- PURPOSE: to lessen bacterial load by relegating it to single colonies
- RANGE: 30-300 colonies
- CLASSIFICATIONS: TFTC (too few to count), TNTC (too numerous to count)
- PROCESS: constantly diluting the original inoculum by 1/10 to form 1:10, 1:100, 1:1000, 1:10000 plates
Dilution Factor DEFINE; EQUATION
- DEFINE: Volume by which factor the sample was diluted
- EQUATION: volume transferred of sample/total volume
Spread Plate
Pour Plate
Streak Plate
- SPREAD: sample is pipetted onto AGAR plate; spread evenly before incubation
- POUR: sample is pipetted onto sterile plate; sterile medium is added and mixed for solidification and incubation
- STREAK: flame looped then applied like butter to agar plate
Colony Forming Units Equation
CFU/(mL or g): (# of counter colonies x dilution factor)/volume of plated sample
The Great Plate Count Anomaly
and EXPLANATION
- Direct cell counting w/ microscope of a cultivated medium reveals more than if sample was from the environment
- Plate count shows lower number of cells
WHY?
- Entire bacterial population environment cannot be isolated in the laboratory
- Some may actually be nonviable (do not grow or divide), others are viable but nonculturable (VBNC)
Solutions to Solve the Great Plate Count Anomaly
- Use of highly selective medium
- Varying incubation conditions
Most Probable Number TYPE OF SAMPLE; 2 FACTORS; PROCESS
- TYPE: Water and Air samples (It is used when samples contain too few bacteria to provide reliable viable cell numbers by classical plate count or if its unculturable in media)
- 2 FACTORS: Gas Production and Turbidity (clear-ness property of solution)
- PROCESS: undiluted mixture, 1:10, 1:100 of a bacterial sample are divided into 3 or 5 test tubes, +phenol red, results (count the # of positive test tubes) then use a table to determine the estimated number of bacteria cells
Membrane Filtration PROCESS
- physically separate
- membrane filter
- cotton plug in vacuum line ensures sterility
- each colony growth captures one species of organism (in agar medium)
Turbidimetric Method 2 FACTORS
- Optical Density
- measures amount of attenutation of light (intensity lost)
- based on light scattered
- the slower the light travels, the higher the optical density - Absorbance
- measures amount of light absorbed
- no basis on light scattered
OD measures HOW MANY cells
ABSORBANCE measures HOW LARGE cells
What are the 4 Physical Properties that affect Microbial Growth?
- pH
- Temperature
- Osmosis pressure
- Oxygen
Three classifications of pH and their pH ranges
What classification is E.coli?
- Neutrophiles
- optimum pH 5.5 - 7.9
- E.coli - Acidophiles
- <5.5 - Alkanophiles
- >=8
