Lecture #5 Flashcards
What are the 3 physical requirements needed for microbial growth?
- Temperature
- pH
- Osmotic pressure
What is a psychorophile? What temperature do they grow at?
A bacteria that loves the cold.
-5 to 15 degree celsius
Where are psychorophiles found?
Deep ocean and polar environments
What are pschrotrophs? What temperature do they grow at?
Bacteria with a very broad temperature range. Grow 0-35 (optimal 15-30)
Which of the 5 microbial temperature groups will cause food spoilage?
Psychrotrophs
What are mesophiles? What temperature do they grow at?
Moderate temperature loving bacteria. 10-45 degrees celsius
Which of the 5 microbial temperature groups is most common?
Mesophiles
What are thermophils optimal temperature growth? What is their growth range?
60, 45-70 degrees celsius
Can thermophils cause disease in the human body?
No
What are hyperthermophiles temperature range?
65-110
Why are hyperthermophiles so limited to places they live on earth?
Because they live in the few places where water reaches that high of temperatures
What two things are needed to control bacterial populations in food growth?
Both hot and cold temperatures
What is used to kill mesophiles and psychrotrophs living in food products?
Heat
What is cold temperatures used to do regarding food safety?
Slow the growth of microorganisms
Which of the 5 temperature groups of microbial growth is able to grow in the fridge?
psychrotrophs
What is pH?
The measurement of the acidity or alkalinity of a substance
If a substance is below 7 pH, what is it called?
Acidic
If is a substance pH is 7, what is it called?
Neutral
At a pH of 7, what happens to proteins? Why?
Allows proteins to fold because charges attract
If a substance is above 7pH what is it called?
Alkaline
What pH do most bacteria grow at?
7
Bacteria the grow at a low pH, it is called?
Acidophile
What is a alkalophile?
Bacteria that grow at a very high pH
What is a neutrophil?
Bacteria that grow at a pH between 5 and 8
What is osmosis?
the movement of solvent molecules across a membrane or a barrier of some sort
Water always moves from a area of ______ concentration to an area of _______ high concentration
Low to high (up the concentration gradient)
What is a hypertonic solution?
Solution very concentrated with solute
What happens to a cell when placed in a hypertonic solution
Water wil rush out of cell (cell shrivels)
What is a hypotonic solution?
Low concentration of solute
What happens to cell when placed in a hypotonic solution
Water rushes into the cell (cell can burst)
What is an isotonic solution?
When two solutions are of = concentration
What is a halophile?
A bacteria that can survive in very high salt concentrations
Why can’t microorganisms grow in blood?
Salt concentration is too low
What are the 4 chemical requirements for micro bacterial growth
- Carbon
- Nitrogen, sulfur, phosphorus and iron
- Trace elements
- oxygen
What is the backbone for all living matter
Carbon
How do heterotrophs obtain their carbon?
From organic material (sugars, proteins and lipids)
How do autotrophs obtain their carbon?
From inorganic matter (CO2)
Are nitrogen, sulfur, phosphorus and iron required more or less than carbon?
Less
What are nitrogen, sulfur, phosphorus and iron used for in micro bacterial growth?
Synthesis of cellular material, enzyme function, etc
What are trace elements used for in a micro bacteria?
Essential for the function of certain enzymes
Is oxygen required for all micro bacteria?
No
What are the 5 classes of microorganisms based on oxygen tolerance?
- Obligate Aerobes
- Facultative anaerobes
- Obligate anaerobes
- Microaerophiles
- Aerotoleran Anaerobes
What is culture
microbes that are continuously growing and multiplying
What are microbes called that are induced into a culture?
Inoculum
Obligated aerobes use does or does not require oxygen?
Does require oxygen
Facultative anaerobes do or do not need oxygen to grow?
Grows best with oxygen but can also grow without
Obligated Anaerobes can or cannot grow with O2?
Cannot
Microaerophiles do or do not grow with oxygen?
Grow only if small amounts are available
Aertolerant anaerobes do or do not use oxygen to grow?
They grow equally fine with or without oxygen
What is batch culture?
Liquid media
Do batch cultures need nutrients added along the way?
No, once started they do not require additions
What happens in batch culture when nutrients get used up?
Bacteria begin to die
What is the limiting component of batch culture?
The amount of nutrients
What is continuous culture?
When nutrients are continually added to the culture and wastes are continually removed
How long can batch culture grow? Continuous culture?
Batch- until nutrients are used up
Continuous- indefinitely
What is solid media?
Densely packed groups of cells
What does solid media allow for?
Growth of colonies and isolation of pure cultures
Does solid media need nutrients added?
No, it contains all the nutrients required by the cell
What is solid media that is the solidifying agent?
Agar
What is culture medium?
Nutrients prepared for microbial growth
What does culture medium allow for?
Allows us to grow pure bacterial culture in a lab
Medium can be chemically ______ or chemically _______
defined or undefined
What is the difference between chemically defined and chemically undefined media?
Undefined- contains unknown components
Defined- All the media components are known
What is selective media used for?
To suppress the growth of unwanted organisms
How does selective media suppress growth of unwanted organisms?
Promotes the growth of desired bacteria
What is an example of selective media and how does it work?
Bismuth Sulfite Agar- inhibits the growth of gram positive and most other gram negative bacteria
What is differential media used for?
To distinguish in between different types of media
How does differential media work?
All types of bacteria are able to grow but colonies of certain bacteria look different on plate
What type of agar is both selective and differential media?
McConkey Agar
Most bacteria reproduce by? How does it work?
Binary fission- cell elongates and duplicates chromosome, the cell with two chromosome continue to grow and forms a wall between the two chromosome then separate
What is generation time?
The time it takes for a bacterial population to double in size
Generation time varies between..?
Different bacteria
E.coli is fast or slow in generation time? Why?
It is very fast because it is rich in media
How long is the generation time of M.tuberculosis?
Very slow, 24 hours
Why do we use log when showing growth time of bacteria?
Because it is easier to show on graph since numbers are smaller
What are the 4 stages in the bacterial growth curve?
- Lag phase
- Exponential Phase
- Stationary phase
- Death phase
What occurs in the lag phase
Cells adjust to new media and prepare for growth
What occurs in the exponential phase (log phase)
Cells are increasing exponentially
Which phase is used to calculate the growth rate? Which period has maximal reproduction?
Exponential phase
What occurs in the stationary phase?
Nutrients have been depleted and cells have reached max population density
Which phase is at the peak of cell growth?
Stationary growth stage
What occurs in the death stage?
All nutrients have been exhausted, toxic waste has accumulated and death rates exceed growth rate
What are the two primary ways bacteria can be counted?
Direct count and Viable count
How are cells counted with the direct count method?
Using a light microscope
Why is the direct counting method very inaccurate?
It counts both dead and alive cells
How does viable counting method work?
A liquid culture is diluted, dilutions are plated onto agar plates and plies are incubated until the colonies grow
Each cell from its original dilutions develop a single colony
In viable counting method, what form are the counts expressed in?
Colony forming units/ mL (cfg/mL)
Why is viable count more accurate?
It only counts live cells
