(exam 1) chapter 6 microbial growth Flashcards
what are two broad requirements for growth?
physical and chemical requirements
what are three physical requirements?
1) temperature
2) pH
3) osmotic pressure
what are five chemical requirements?
1) Carbon
2) Nitrogen, sulfur, and phosphorous
3) Trace elements
4) Oxygen
5) Organic growth factors
what type of growth requirement is oxygen?
chemical requirement!
what are extremophiles?
microbes that thrive in physical or chemical conditions that typically kill most microbes
when do microbes grow well regarding temperature?
in a limited temperature range- optimum (best temperature for fastest growth)
what are three primary groups based on preferred temperature ranges?
1) meophiles
2) psychrophiles
3) thermophiles
what are mesophiles?
moderate-temperature-loving (25-40oC)
Most common type of microbe (not extremophiles)
what are psychrophiles?
cold-loving (15oC)
Found in polar regions or deep within the ocean
what are thermophiles?
heat-loving (50-60oC)
Found in hot springs and sunlit soil
what are psychrotrophs?
psychrophiles that can cause food spoilage (20-30oC)
what are Hyperthermophiles?
thermophiles that grow at much higher temperatures than thermophiles (≥80oC)
what pH do most bacteria grow near?
most bacteria grow near neutral pH (6-8)
acids produced during bacterial fermentation do what?
inhibit growth (food preservation)
what pH do molds and yeasts grow between?
pH 5 and 6
what are Acidophiles?
bacteria that grow in acidic environments- such as the Stomach
what are Alkaliphiles?
bacteria that grow in basic environments
alkali lakes and desert soil
what is the concentration of hypertonic solutions?
Hypertonic solutions contain a higher concentration of solutes (i.e. NaCl) than inside the cell and water moves out of the cell.
what do hypertonic solutions cause?
plasmolysis
what is plasmolysis?
(shrinkage of the cell cytoplasm) due to high osmotic pressure
what are halophiles?
bacteria that requires high osmotic pressure
Found in Great Salt Lake
what is the concentration of hypotonic solutions?
solute concentration is lower outside than inside the cell; water moves into cell
what type of solutions do most bacteria live in?
hypotonic solutions
what is the importance of the cell wall?
Cell wall prevents osmotic lysis (Plasma membrane rupture due to excess water moving into cell)
most bacteria (like most organisms) are what mode of nutrition?
heterotrophs (use organic molecules as a carbon source)
what are nitrogen, sulfur, and phosphorous?
Synthesis of proteins, nucleic acids, phospholipids, ATP, and vitamins
what are trace elements?
Inorganic elements (i.e. iron, copper, zinc) Required in small amounts, typically enzyme cofactors
what are organic compounds?
Cannot be synthesized; obtained from the environment; Often are vitamins that act as enzyme cofactors
what do we know about microbes that use molecular oxygen?
they obtain more energy from nutrients than those that do not
when is O2 very toxic?
O2 radicals “steal” electrons from other molecules, converting them to dangerous forms and disrupting essential cellular processes
what type of immune cells in humans use these radical forms of O2 to destroy pathogens?
Phogocytic immune cells
bacteria that grow in the presence of O2 produce what?
superoxide dismutase (SOD)
what is superoxide dismutase (SOD)?
Enzyme that converts superoxide radicals (O2−) into molecular oxygen (O2) and hydrogen peroxide (H2O2)
is the peroxide anion (O22-) of hydrogen peroxide toxic?
yes
what is The peroxide anion (O22-) of hydrogen peroxide converted by?
catalase or peroxidase
(oxygen requirement for) Obligate aerobes?
require oxygen
(oxygen requirement for) Facultative anaerobes?
grow via fermentation or anaerobic respiration when oxygen is not available
(oxygen requirement for) Anaerobes?
unable to use oxygen and most are harmed by it
(oxygen requirement for) Aerotolerant anaerobes?
tolerate but cannot use oxygen
(oxygen requirement for) Microaerophiles
require oxygen concentration lower than air
what is a culture?
microbes growing in or on a culture medium
what is Inoculum?
when microbes are introduced into a medium
what is Culture/Growth media?
Nutrients prepared for microbial growth
what are two criteria’s for growth?
1) Physical and chemical requirements of microbe must be met
2) Starting media must be sterile
what does sterile mean?
contain no living microbes`
what are two main forms of culture media?
1) Liquid (broth) media
2) Solid media (contain agar)
what is ager?
solidifying agent for culture media; Complex polysaccharide isolated from marine algae
what three things can ager be used to create?
1) petri plates
2) slants
3) deeps
what are petri plates?
shallow dishes with a lid to prevent contamination (Useful for examining colony morphology, counting colonies, and preparing pure cultures)
what are slants?
agar solidifies while the tube is at an angle (Increases the surface area for growth)
what are deeps?
agar solidifies in a vertical tube
Used to examine gas requirements of microbes
what are two main categories of media?
1) Chemically defined media
2) Complex media
what is Chemically defined media ?
exact chemical composition is known - pricy
Fastidious (picky eaters) organisms require many growth factors provided in chemically defined media
what is Complex media?
extracts and digests of yeasts, meat, or plants; chemical composition varies batch to batch; typically feeds many different types of bacteria
nutrient broth - liquid complex media
nutrient agar - solid complex media
what do anaerobic cultures require?
reducing media; Contain ingredients that deplete O2
Sodium thioglycollate
- Medium is anaerobic after preparation, but O2 diffuses in over time, creating an oxygen gradient
what are Capnophiles?
Microbes that require high CO2 conditions
what is Selective media ?
suppress unwanted microbes and encourage desired microbes
-Contain inhibitors to suppress growth
what are Differential media?
distinguishes between different microbe colonies growing on the same plate
-Media can have selective and differential characteristics
what is enrichment media?
– favors growth of a particular microbe that is in very small numbers; Like selective media but growth of other microbes is not inhibited
What is the streak plate method used for?
to isolate individual bacterial colonies
what is a colony?
is a population of cells arising from a single cell or spore or from a group of attached cells
A colony is often called a colony-forming unit (CFU)
what is a pure culture?
a culture containing only the microbe of interest; Aseptic technique is critical for the creation and maintenance of pure cultures
What is inoculum?
the substance used for inoculation
what is bacteria growth?
when bacteria increase in cell number (not cell size)
how to bacteria reproduce?
typically through binary fission where one parent cell splits into two new cells
what is generation time?
time required for a cell to divide (20min-24hrs)
how are bacteria growth curves represented and why?
typically represented logarithmically because arrhythmic graphs are not meaningful
what are the four main phases of bacteria growth curves?
1) Lag phase (intense activity preparing for growth but no increase in population)
2) Log phase (logarithmic / exponential increase in the population)
3) stationary phase (period of equilibrium; microbial deaths balance production of new cells)
4) death phase (population is decreasing at a logarithmic rate)
what can stationary and death phase be due to?
factors such as accumulation of waste, depletion of available nutrients, pH changes, etc.
what are four ways of counting microbial cells?
1) plate count
2) filtration
3) most probable number MPN method
4) direct microscopic count
what range of microbial colonies is best for plate counts?
30-300 colonies (CFUs)
what is the purpose of a serial dilution?
when you perform a serial dilution of the original sample it provides plates with 30-300 colonies for accurate measurement (plate count)
what two methods work with plate counts?
counts performed on plates that used pour plate method (bacteria mixed into a dish with agar) or spread plate method (bacteria spread on the surface)
what is the filtration counting method?
Solution passed through a filter that collects bacteria; Filter is transferred to a Petri dish and grows as colonies on the surface
what is the most probable number MPN method counting method?
Often used for water analysis; Statistical estimating technique-Count positive tubes and compare with a statistical table
what is direct microscopic count method?
Volume of a bacterial suspension placed on a slide; Average number of bacteria per viewing field is calculated
what is turbidity (indirect measurement of bacteria growth)?
measurement of cloudiness with a spectrophotometer
what are three ways to indirectly measure bacteria growth?
1) turbidity
2) metabolic activity
3) dry weight
what is metabolic activity (indirect measurement of bacteria growth)?
amount of metabolic product is proportional to the number of bacteria
what is dry weight (indirect measurement of bacteria growth)?
bacteria are filtered, dried, and weighed; used for filamentous organisms
