Chapter 4 Flashcards
The greatest contributor to methods of cultivating bacteria
Robert Koch
How do bacteria and archaea generally multiply
By binary fission
Binary fission
A process in which a cell increases its size and then divides
Microbial growth
An increase in the number of cells in a population.
Generation time
Time it takes for a population to double.
What two factors must be know in order to calculate how many bacterial cells will be present in a product after a certain amount of time
- Number of cells in the original population
- The number of times the cells will divide during the stated period.
Formula for calculating number of cells
Not = N0 x 2^n
Nt = number of cells in a given time.
Biofilm
Polymer encased community of microorganisms
Steps of biofilm formation
- Begins when planktonic cells move to surface and adhere.
- They then multiply and release polysaccharides, DNA and other hydrophilic polymers to which unrelated cells may attach and grow.
- EPS gives biofilm its skimpy appearance.
- Cells communicate with one another by synthesizing and responding to chemical signals an exchange important in establishing structure.
Pure culture
Population descended from a single cell and therefore contains only one species
Aseptic technique
A set of procedures that minimize the chance that other organisms will accidentally be introduced.
Medium the cells are grown on for pure culture
Culture medium
Basic requirements for obtaining pure culture
- solid culture medium
- a container to hold and maintain the medium in an aseptic condition
- method to separate individual microbial cells
Colony
A distinct mass of cells arising from a single cell.
Melted agar stays liquid until cooked to what temp
Below 45 degrees
Agar medium will remain solid until heated above what temp
95 degrees
Petri dish
A two part covered container made of glass or plastic.
Although not airtight, the dish excludes airborne contaminants.
Streak plate method
Simplest and most commonly used technique for isolated microorganisms
Streakplate method steps
- Sterile inoculating loop is dipped into a microbe containing sample and then lightly drawn several times across the surface of an agar plate, creating a set of parallel streaks covering approximately one third the agar.
- The loop is then sterilized and a new series of parallel streaks is made across and at an angle to the previous ones, covering another surface section. This drags some of those cells streaked onto the first portion over to a fresh section, effectively inoculating it with a diluted sample.
…
By third set of streaks, cells should be separated enough so that distinct well,
Isolated colonies will form.
Stock culture
Culture stored for use as an innocuous in later procedures.
Closed system
A system such as a tube, flask, or agar plate in which nutrients are not replenished and waste are not removed as microorganisms grow.
What happens to cells that grow in closed system
As cells grow in closed system, the population increases in a distinct patter of stages and then declines.
Growth curve
Growth pattern observed when cells are grown in a closed system; consists of five stages.
Five distinct stages of growth curve
- Lag
- Exponential or log
- Stationary phase
- Death phase
- Prolonged decline
Lag phase
Stage characterized by extensive macromolecule and ATP synthesis but no increase in cell number.
Exponential phase or log phase
Stage in the bacterial growth curve during which cells divide at a constant rate
Generation time is measured during this period of active multiplication.
Why is exponential phase medically important
Because bacteria are most sensitive to antimicrobial medications when cells are actively multiplying.
Primary metabolites
Compounds synthesized by a cell during the log phase.
What occurs during later stages of exponential growth
Nutrients gradually depleted
Cell activities shift to prepare for starvation conditions.
Secondary metabolites
Microbial compounds that begin accumulating at this stage are made for purposes other than growth
Metabolic products synthesized during late log and stationary phases.
Stationary phase
Cells enter the stationary phase when the nutrient levels are too low to sustain growth.
Stage in which the number of viable cells remain constant
How can cells multiply in the stationary phase when they have exhausted their supply of nutrient?
Dead cells often burst, releasing nutrients that then fuel the growth of other cells.
Death phase
Is the period when the total number of viable cells in the population decreases as cells die off at a constant rate.
Prolonged decline
Final stage of growth curve
Most cells die during this phase, but few are able to grow.
Cells at edge of colony
Cells multiplying on the edge of the colony face relatively little competition for O2 and nutrients.
Cells at the edge may grow exponentially.
Cells at the center of the colony
In the center of the colony where cell density is high, available O2 and nutrients become depleted and harmful waste such as acids accumulate.
Open system
Method used to maintain cells in a state of constant growth by continuously adding nutrients and removing waste products; also called a continuous culture.
Extremophiles
Organisms that live under extremes of temp, pH, or other environmental conditions.
Major environmental factors that affect growth
- Temperature
- Atmosphere
- pH
- Water availability
Optimum growth temperature
The temperature at which organism multiplies most rapidly.
Five groups of organisms affected by temperature
- Psychrophiles
- Psychrotrophs
- Mesophiles
- Thermophiles
- Hyperthermophiles
Psychrophiles
Have a optimum temp between -5 and 15 C.
Psychrophiles means cold
Psychrotrophs
Have a optimum between 15 and 30.
Important cause of food spoilage in refrigerated foods.
Mesophile
Have an optimum between 25 and 45.
Ecoli and other common bacteria are in this group.
Thermophiles
Have an optimum temp between 45 and 70.
Commonly live in hot springs and compost heaps.
Hyperthermophiles
Have an optimum of 70 or higher
Usually archaea
Why can some microbes withstand very high temperatures while most cannot?
Proteins from thermophiles are not denatured at high temperatures.
Thermostability is due to the amino acid sequence of the protein.
Refrigeration temperatures
Approximately 4 C.
Slow spoilage because they limit the multiplication of otherwise fast growing mesophiles.
Aerobic environments
O2 is present
Anaerobic environments
Little to no O2 is present.
Obligate aerobes
Have absolute requirement for O2.
Facultative anaerobes
Grow better if O2 is present, but they can also grow without it.
Growth is faster if O2 is available.
Obligate anaerobe
Cannot multiply if O2 is present
Microaerophiles
Require small amounts of O2.
Aerotolerant anaerobes
Are indifferent to O. They can grow in its presence but they do not use it to harvest energy.
Also called obligate fermenters.
Reactive oxygen species
Harmful by products of using O2 in aerobic respiration.
Examples of ROS
Superoxide
Hydrogen peroxide
What does ROS do?
Can damage cell components
Virtually all organisms that grow in the presence of O2 produce the enzyme …
Superoxide dimutase
Catalase
Superoxide dismutase
Which inactivated superoxide by converting it to O2 and hydrogen peroxide
Catalase
Converts hydrogen peroxide into O2 and water.
Neutrophiles
How most microbes are
Live and multiply in the range of 5 to 8.
pH optimum near neutral 7.
Acidophiles
Grow optimally at pH below 5.5 .
Alkaliphiles
Grow optimally at pH above 8.5
Plasmolysis
Dehydration and shrinkage of cytoplasm from the cell wall as a result of the diffusion of water out of a cell.
Halotolerant
Microbes that tolerate high salt concentrations, up to approximately 10% NaCl.
Halophiles
Require high levels of sodium chloride
Major elements
Chemical elements that make up cells
Examples of chemical elements
Carbon
Oxygen
Hydrogen
Nitrogen
Sulfur
Phosphorus
Calcium
Heterotroph
Use organic carbon
Autotroph
Use inorganic carbon in the form of CO2.
Carbon fixation
Process converts inorganic carbon to organic form.
Nitrogen
Needed to make amino acids and nucleic acids
Nitrogen fixation
Conversion of nitrogen gas to ammonia.
