Microbial Growth Flashcards
What are cultures?
Microbes that are continuously growing and multiplying.
What are inoculum?
Microbes that are introduced into a culture
What is inoculation
The introduction of microbes into a culture
What is batch culture
Microbes in liquid media where once started, nutrients are not added further
What is the limiting components of batch culture
The limiting component is the nutrients
What is batch culture used for?
They are used to analyze how microbes grow
What is a continuous culture
These are microbes that grow in open system, where nutrients are continuously added and waste are continuously removed.
What does agar do?
Agar is a solidifying agent that is used to turn liquid broth into solid media
What is an agar
Polysaccharide derived from marine algae that can’t be degraded by bacteria
What is cultural medium
These are nutrients prepared for microbial growth and can be in liquid(broth) or solid( with agar)
Why are cultural medium important?
It allows us to grow pure bacterial culture in the lab
Why must the media be sterile prior to inoculation
So that only the cells that you want to reproduce are being grown.
What does it mean to be sterile
No living microbe is present
What can kind of medium is there
There are chemical defined and chemically undefined medium
What does chemically undefined media mean?
It means that the medium contains unknown components
What does chemically defined media mean?
It means that all of the media components are known
What is selective media used for?
It is used to suppress the growth of unwanted organism while promoting growth of desired organism
What is differential media used for?
It is used to distinguish different types of bacteria, although all types of bacteria can grow colonies of certain bacteria look different
What is an selective and differential media
MacConkey agar for example is both selective and differential media because it inhibits the growth of non-intestinal bacteria while promoting the growth of intestinal bacteria. It also differential media because bacteria that ferment lactose appear pink, while non-lactose fermenter like most intestinal pathogens appear white on the ph indicator.
What is bacterial growth
Increase in bacterial cell number and not an increase in bacterial cell size
How does bacteria reproduce
They reproduce through binary fission
How does binary fission occur
Bacteria elongates and duplicate its chromosomes then cross wall forms between the 2 chromosomes.after that 2 cells separate and form new identical daughter cell
What is generation time
The time it takes for a bacterial population to double in size
How is the bacterial growth carve graphed
It is graphed using the log of the cell number
1st phases in the bacterial growth carve
-the lag phase is a period of adaption, the cells are adapting to the new media and preparing for growth
How can bacteria be counted
They can be counted through direct and viable count
What is direct count
Cells are counted using light microscope
What is viable count
Only live cells are counted
What is the process for viable count
A liquid cultured is diluted, the dilution are plated into agar medium, and the plates are incubated until the colonies grow. Each cell from the original dilution develop into a single colony, the number of colonies are counted and used to determine the number of bacterial that were represent in the original sample. The counts are expressed as colony forming unit per mL(cfu/mL), the assumption is that 1cfu = 1 bacterial cell
2 phase in bacterial growth curve
- exponential phase is a period of maximal reproduction, this phase is used to calculate growth rate
3rd phase in the bacterial growth curve
- stationary phase, cells have reached max population density, nutrients have been depleted, growth rate equals death rate.
4th phase in the bacterial growth curve
- death phase, all nutrients are exhausted, toxic waste has accumulated and death rate exceeds growth rate.
