Lecture 4- Microbial growth Flashcards
What is bacterial growth?
an increase in population size not an increase in the size of a single bacterium
How do bacterial cells replicate?
a form of asexual reproduction called binary fission
What is generation time?
time required to complete fission cycle from parent cell to 2 daughter cells. (Doubling time). It is the amount of time needed to double the population.
What is the growth rate? What does this vary depending on?
The measure of the length of the generation time environmental condictions
What is the generation time of Mycobacterium leprae?
10-30 days (leprosy)
What is the generation time of Staphylococcus aureus?
20-30 minutes
What 4 phases does a growth curve have?
Lag, Log or exponential, stationary and decline
What is a batch culture?
a closed-system microbial culture of fixed volume with limited supplies that aren’t replemished. Cells grown in a closed system have 4 phases: Lag phase, Log or exponential phase, stationary phase and death phase
What is the lag phase?
Interval of time between when a culture is inoculated and when growth begins. (not mutiplying as it is aclimitising)
What is the expontential phase?
Number of cells doubles during each unit of time.
During exponential growth, the increase in cell number is initially slow but increases at a faster rate
What is the stationary phase?
Growth rate of population is zero.
Number new divisions=number of cells dying
Either an essential nutrient is used up or waste product of the organism accumulates in the medium
What is the death phase?
Lack of nutrients and increasing accumulation of wastes lead to… number of cell deaths > number of new divisions
What is a continuos culture?
an open-system microbial culture of fixed volume
What is chemostat and turbidostat?
most common type of continuous culture device
What effects the lag phase?
what are the condictions and where the innoculum came from e.g the freezer
What is the formula for exponential growth?
N final = (N initial) 2n
N= the number of generations
What is cryptic growth?
Growing on dying cells- cells feeding on dying cells 2 expontentail growth periods
What is viable count?
It is a direct measurement and the measurement of living and reproducing population. There are 2 main ways to perform plate counts: spread-plate method or Pour-plate method
To obtain the appropriate colony number, the sample to be counted may need to be diluted (serial dilutions)
What is filtration?
The process in which solid particles in a liquid or gaseous fluid are removed by the use of a filter medium that permits the fluid to pass through but retains the solid particles
What factors affect bacterial growth?
- availabilIty of nutrients and H2O
- temperature
- moisture and drying
- radiation
osmotic effects - mechanical and sonic stress
What is the steady state?
after 5 volume changes inside a bioreacter
the volume is constant and the flow rate is 1 litre per hour
What is the diluation rate?
Dilution rate= flow rate / volume
What is wash out?
wash out is when the dilution rate is faster than the microorganism growth rate
What is total count and viable count?
total count- what u see and visulise
viable count- out of those how many are viable (not dead)
Pros and cons of counting chambers?
advantage- easy to use, minimal set up
disadvantage- hard to tell if cells are viable or non-viable (don’t know if alive or dead)
What is serial dilution?
have to diluate samples precisely in a mathmateically way. perfect plate
What is the perfect plate with colonies
contains 30-300 colonies
Pros and Cons of spreadable agar
agar cheap, used only for counting organisms that resulted in the formation of a colony CFUs colony forming units, but
need over night incubation
What are indirect methods? and what are some examples?
indictor of microbial presense not looking at counting cells- looking at after effects
- metabolic activity
- dry weight
- turbidity
4.Spectrophotometer
What are metabolite examples?
CO2, H2O and any activity envolving metabolism and respiration
When is a growth curve obtained
If bacteria counts are made at intervals after inoculation and plotted in relation to time it is obtained
what phase are cells in the healthiest state
exponential
what do diauxic growth curves have
2 logs
what are examples of direct measurements for measuring growth
total cell count, counting chambers, viable count, filtration and most probable number
What is total cell count?
direct microscopic examination using special slides, automated counters (flow cytometry)
what is the most probable number
a statistical estimating technique
What is spectrophotometer
measures the amount of light that passes through a sample. Absorbance is related to the number of bacteria
what are looked at for measurements of growth
measurements of cell numbers, cell mass and cell constituants
what are used for measurments of cell numbers?
Pore plate, spread plate, membrane filter, plating techniques and direct counting using Petroff Hausseer counting chambers
what is used for measurements of cell mass?
dry weight, scattering of light in spectrophotometer
what measured in cell constituents?
nucelic acids, chlorophyll, ATP and total protein or nitrogen
what are pH of most bacteria
neutrophiles- pH 6.5-7.5
yeast and moulds have a pH of 4-6
some are acidophiles has a pH of less than 4
extremes sulfur oxiddisers can grow to pH 1-2
alkalophiles pH over 9- live in alkaline coils and water up to 11.5
what are extremophiles
evolved to grow opitmally under very hot or cold temperatures
what are thermophiles
loves heat and high temperatures
what are hyperthermophiles
produce enzymes widely used in industrial microbiolgy eg taq polymerase and are very high temperatures
what are psychrophiles
low temperature
what are psychrotolerants
can grow at 0 degrees but have a optima of 20-40 degrees and are more widely distributed in nature than phychrophiles
what are mesophiles
midrange temperature- found in warm-blooded animals, terrestrial and aquatic environments and temperature and tropial latitudes
what are barophiles
organisms that live under extreme pressure for their membranes and enzymes depend on this pressure to maintain their 3 dimensional and functional shape
what are aerobes
require oxygen to live
what are anerobes
do not require oxygen and may be killed by exposure
what are facultative organisms
can live with or without oxygen
what are areotolerant anareobes
can tolerate oxygen and grow in its presense even though they cannot use it
what are microareophiles
can use oxygen only when it is at levels reduced from the air
