Microbial Growth Flashcards
What is a Defined medium?
Is a synthetic medium in which all ingredients are known (simple)
What is a complex medium?
contains ingredients of unknown chemical composition such as beef or yeast extract and peptone
What is a selective medium?
Favours or disfavours the growth of specific bacteria.
What is a differential medium?
distinguishes different types of bacteria based on chemical properties
A MacConkey plate is an example of what medium?
A selective medium. It can also be considered a differential medium.
What do Bile salts do?
Favour the growth of gram negative bacteria
Disfavour the growth of gram positive
What will cause a MacConkey plate to go red?
macconkey plates contain lactose and a neutral red dye. If a bacteria can ferment the lactose and create an acidic bi-product, the plate goes red. The acid reacts with dye.
What are the three stages of getting a bacteria in pure culture? starting from environmental sample?
1) get an environmental sample in a mixed liquid culture
2) place this on a solid media that contains many colonies of different bacteria. The isolated colony is favourd
3) isolated colony is transferred to a liquid culture.
what is the definition of inoculation?
introduce into a culture medium
What colour is a MacConkey plate with E. Coli in it?q
Red because E. Coli produce acid bi products in lactose presence.
Nutrients: Explain the 2 sections of macromolecules
1) components of Lipids, nucleic acids, carbohydrates, and proteins: C,O,H,N,S,P elements
2) co-factors and cytochromes: Fe,K,Ca,Mg
Explain trace elements
are also co-factors. they exist as micrograms per litre unlike COHNSP which is grams per litre.
Co,Ni,Cu,Mn,Mo
How do bacteria normally get C, O, H? what are autotrophs?
COH requirements are usually met in sugar consumption. CO2 is an exception in which autotrophs use it. (No hydrogen). Autotrophs can take inorganic substances such as CO2 and turn them into nutritional organic substances.
Carbon consuming organisms can be classified as.. explain both
Autotrophs - Produce their own food from CO2. Photosynthesis in plants is autotrophic
Heterotrophs - cannot synthesize their own food. They prefer reduced organic molecules such as sugar.
In terms of how organisms obtain energy what are organisms classified as? explain both?
Chemotrophs - oxidize inorganic or organic compounds
phototrophs - Use light
In terms of how organisms obtain hydrogen or electrons how are they classified? explain both
Lithotrophs - Reduce inorganic molecules
Organotrophs - Reduce Organic molecules
Name the 5 main kinds of bacteria in terms of carbon source, energy source, and hydrogen/electron source.
EnergyHydrogen Carbon
1) Photolithotrophic autotrophs
Capture protons for energy, reduce inorganic molecules, and get CO2 from environment
2) Photoorganotrophic Heterotroph
3) Chemlithotrophic Autotroph
4) Chemoorganotrophic Heterotroph
Oxidize to get energy, reduce organic molecules, and get C from sugar
5) Chemoolithotrophic heterotroph
Most bacteria are what in terms of energy, food, etc
What about pathogens?
Most bacteria are either
Photolithotrophic autotrophs or
chemoorganotrophic heterotrophs
almost all pathogens are the second
what are the 4 stages of cell growth ( really considered population growth)
lag log stationary death describes population growth
Explain Lag phase
- Newly inoculated bacteria is acclimatizing
- cells are producing new compartments
- cells may be starved of nutrients
- no growth in cell # or mass
- not seen if new media is same composition as previous media
Log phase?
- exponential growth
- this phase cells are most uniform in chemical composition and physiological properties.
stationary phase?
Growth ceases due to
a) low nutrients in media
b) to much toxic waste in media
Death phase?
Nutrients deprivation and toxic waste lead to cells dying off. some cells will lyse but not always. death is usually logarithmic
What is Batch Culture?
inoculation of bacteria by which we leave the waste and do not add additional nutrients.
Explain doubling time
- Aka a colonies generation time
- can be 10 min, weeks, even years
- it is measured on the growth curve plotted on a semi-log plot
- may be influenced by nutrient availability
- E. Coli have a very short generation time
What is a plate count?
- Also known as a viable count
- A way to evaluate bacteria growth in a media
- Plate counts are sensitive because we only use small number of colonies (30-300)
Explain the plate count process
- bacteria is diluted and added to a solid surface
- incubated over one night
- From the number of colonies and dilution we can calculate the original titer (concentration)
- Only living cells form colonies hence viable count
- Usually expressed As CFU’s (colony forming units) assuming all living cells produce a colony
Petroff - Hausser counting chambar?
Easy and inexpensive way to observe growth
Has a a known depth and etched grid on bottom
requires many cells to start with (10^7)
DOES NOT DISTINGUISH BETWEEN LIVING AND DEAD CELLS
If w plot the growth curve of a PH counting chamber, what will we see if the cells lyse at death vs. not lyse?
Because this method for observing growth only counts bodies, if they dont lyse our growth curve will not distinguish between the stationary phase and the death phase.
If they do lyse then the plot will be normal .
We can also observe cell growth by looking at cell mass. How?
When cells grow in population their mass grows too
- we can use optical density measurements with a spectrophotometer
- must have a high density of cells to get proper Optical density reading (10^7)
- DOES NOT DISTINGUISH LIVING AND DEAD CELLS
What does a high OD indicate?
- this means less light is detected
- this means their is more “scattered light” which indicates more cells.
the more cells there are in a sample the more the light is scattered which means less light is detected. This is referring to high or low optical density?
High OD’s scatter light the most.
What is Turbidimetric measurement?
- measuring the loss of light intensity
- OD measurements for cell mass are Turbidimetric measurements
What is a consortia?
two or more microbial groups living symbiotically
What is a biofilm?
Thin slimy layer of bacteria that adheres to a a surface
Explain nature conditions for bacteria
- usually starvation conditions
- often as a consortia in a biofilm (rarely purified)
- ## Interactions with other bacteria can be symbiotic, beneficial, predatory, etc
True or false, the vast majority of bacteria have been grown in the lab?
False. Less than 1% is.
What is a Microaerophile?
Cant have to much oxygen or it will die. Needs O2 in small portions. Ex. magnetotactic bacteria
What is a Psychrophile?
Microbes that can exist at cold temperatures of -20 to 10 degrees
What is a Psychrotroph?
Microbes capable of surviving or thriving in very cold temperatures
What is a Facultative Anaerobe?
- makes ATP by aerobic respiration if O2 is around
- if no O2 it performs fermentation
What is a Piezophile?
Thrives at high pressures such as deep sea bacteria
Hyperthermophile
thrives at temperatures above 80 degrees such as sea bacteria by hydrothermal vents
