MicroLecE2Ch6 Flashcards
What are the physical requirements for Microbial growth?
1) Temperature: minimum growth temp, maximum growth temp, optimal growth temp
2) pH: most bacteria grow btwn 6.5 & 7.5
3) Osmotic Pressure: salt concentration
Psychrophile
0-10 C
Found in ocean floor, polar regions
Can grow below freezing
Psychotroph
20 C
Causes food spoilage
Mesophile
37 C
Most of pathogens
Found on other living organisms
Thermophile
60 C
Found in sunlit soil
Hyperthermophile
90 C
Survives in very hot environments
Deep sea thermal vents
Neutrophile
Bacteria that prefer neutral pH
Most pathogens
Acidophile
Grow in acidic environments
Exs: molds & yeasts grow btwn pH 5-6
Halophile
Bactera that like to live in high salt environment
Exs: S. Epidermidis, S. Aureus
What are the chemical requirements for Microbial growth?
1) Carbon: structural organic molecules, energy source, used in all 4 chemical groups; from organic carbon sources or CO2
2) Nitrogen: amino acids and proteins; from ammonia, nitrogen fixation, and atmospheric nitrogen
3) Sulfur: amino acids, thiamine, biotin; get from sulfate, hydrogen sulfide
4) Phosphorus: DNA, RNA, ATP, membranes, nucleic acids; get from recycling broken down nucleic acids
5) Trace Elements: inorganic elements required in small amounts, usually as enzyme cofactors; get from the environment
6) Oxygen
7) Organic Growth Factor: organic compounds obtained from environment; vitamins, amino acids, purines, pyrimidines
Sterile
No living microbes
Inoculum
Introduction of microbes into medium
Culture
Microbes growing in and on culture medium
Agar
Complex polysaccharide from seaweed used as solidifying agent for culture media
Better than gelatin b/c stays solid at 37 C and is not broken down by microbes
Chemically Defined Media
Exact chemical composition is known
Complex Media
Pre-prepared media, most of the media used in Micro lab
Exs: nutrient broth, nutrient agar
Reducing Media
Specialized media containing thioglycollate or oxyrase that removes oxygen, typically has an oxygen gradient
Anaerobic chamber
Obligate anaerobes must be grown within here where all the oxygen has been removed
Obligate Aerobe
Must have presence of oxygen to grow
Growth on the surface of the thioglycollate broth
Facultative Anaerobe
Can use oxygen but does not require it
Growth throughout tube with concentration on the surface of broth
Obligate Anaerobe
Cannot grow in presence of oxygen
Growth at bottom of tube where there is least oxygen in the broth
Microaerophile
Prefer less oxygen than aerobes; halfway btwn aerobe and anaerobe
Grows in a band in the middle of thioglycollate broth
Capnophile
Requires higher level of CO2
Grows in a Candle Jar so when the candle flame goes out it raises the level of CO2 in the jar
BSL 1
No special precautions
BSL 2
Lab coat, gloves, eye protection
BSL 3
Known pathogenic bacteria that is contagious
BSL 2 + biosafety cabinets to prevent airborned transmission
BSL 4
Extremely contagious, very pathogenic microorganisms
BSL 3 + sealed negative pressure, exhaust air filtered twice, maybe govt security clearance
Selective Media
Has a chemical that will inhibit growth of some bacteria but select for growth of some bacteria
Ex: salt
For ID-ing a bacteria
Differential Media
Test built into the media that has a color change; makes it easy to distinguish colonies of different microbes
Ex: mannitol (sugar)
For ID-ing a bacteria
Most of the time media will be both selective and differential
Enriched Media
Has a molecule in it that encourages the growth of the deried microbe, enriching for the target bacteria
For isolating a bacteria
Colony
Population of cells arising from a single cell or spore or from a group of attached cells
Often called a colony-forming unit (CFU)
Streak Plate Method
Used to isolate pure cultures
Every time original streak is streaked to another quadrant of the dish it is diluted until eventually the bacteria will be isolated
Preserving Bacteria
1) Deep Freezing
2) Lyophilization (freeze drying)
Binary Fission
1) cell elongates and DNA is replicated
2) cell wall and plasma membrane begin to constrict
3) cross-wall forms, completely separating the two DNA copies
4) cells separate
Phases of Growth
1) Lag phase: bacteria sensing its environment once introduced in it, prepare for binary fission
2) Log phase: highest rate of growth, population dramatically increases, binary fission happens
3) Stationary phase: no active growth; bacteria has run out of nutrients and space
4) Death phase: bacteria die off at exponential rate; waste products have built up becoming toxic to the bacteria cells
Direct vs. Indirect Count
Direct count - directly/actually counting
Indirect count - estimating
Direct Count Methods
1) Serial Dilutions: several dilutions done and each one is plated; # of colonies x dilution factor
2) Plate Counts: pour plate method and spread plate method (count colonies on plates that have 25-250 colonies or 30-300 colonies)
3) Membrane Filtration (non-viable direct count)
4) Direct Microscopic count
Indirect Count Methods
1) Turbidity: estimate by cloudiness using Spectrophotometer that shines light through it and measures the amount of light coming out the other side
2) Metabolic activity: measure amount of ATP and use that to estimate # of bacteria
3) Dry Weight: dehydrate a culture, weight resulting powder, estimate how much bacteria in it
Turbidity
Scientific term for cloudiness
Higher the concentration of bacteria, the more turbid it is
Generation Time
Time it takes for one bacteria to divide into two, or for the population to double. Bacterial growth is logarithmic
