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Growth Conditions and Detection (Temp (minimum growth temp: lowest temp at…
Growth Conditions and Detection
Temp
minimum growth temp: lowest temp at which a species will grow
maximum growth temp:highest temp at which a species will grow
optimum growth temp: temp at which a species grows best
Pychrophiles (-8 to 18), Psychrotrophs (-2-30), Mesophiles (10-48, human pathogens), Thermophiles (40-72), Hyperthermophiles (66-110)
T<0: no significant growth; 0-5: refrigerator temp. slow growth; 5-15: slightly faster growth; 15-53: rapid growth, some produce toxins; 53-63: very slow growth; T>63: destroy most microbes
pH
acidophiles: 1-4.5
neutrophiles: 5.5-8.5 (6.5-7.5 majority of microorganisms)
alkaliphiles: 8.5-11
household bleach has a pH of 13, one reason why it is such an effective antimicrobial compound (most organisms can't survive)
Pressure
halophiles: tolerate high salt concentration (high osmotic pressure)
osmophiles: tolerate high sugar concentration (high osmotic pressure)
xerophiles: tolerate dry conditions (low osmotic pressure)
piezophiles (barophiles): tolerate intense pressure (high atmospheric pressure); bacteria that grows at the bottom of the ocean
Available chemicals
oxygen
obligate aerobes: require O2 to live (all at top)
top of tube has O2 and bottom has no O2
facultative anaerobes: can tolerate absense of O2 but prefer to use it (can switch to fermentation) (most on top but all over)
obligate anaerobes: require absense of O2 (all bottom)
aerotolerant anaerobes: cannot use O2 but can tolerate it (everywhere)
microaerophiles: low dose of O2 (middle)
experimental atmospheres
candle jar: make anaerobic environment; candle uses the O2
gas pak: regulate amount of O2 and other gases
glove box: regulate atmosphere, sterile environment
cultural media and Agar
culture medium: nutrient material prepared for microbial growth
chemically defined media: composition and why the cells need it to grow is known
complex media: composition and why necessary is unclear, just know bacteria won't grow if you take it out
selective media: suppress growth of unwanted bacteria
differentiated media: helps to differentiate colonies of different organisms
Mannitol Salt Agar (1, 3 and 4): only grows staph, staph aureus turns yellow because it ferments to make sugar
Other organisms
act differently because signals bind to receptors
quorum sensing: know how many organisms are around them
turns on genes for pathogenicity to compete with the cells around it to survive
Measuring Growth
Indirect
dry weight: dry everything out to measure amount; don't know if living or dead; not very accurate; may not have removed all nutrients
metabolic activity: measure amount made and used by cells to determine amount of cells
turbidity: cloudy culture=more cells; measure amount of light that passes through; not good for small amounts; can't tell if living or dead
Direct
direct cell count
coulter counter: vacuum pulls cells through electrical current; count disruptions; tells size of cell
flow cytometry: run cells through laser beam; differentiated cells and dead/alive based on color of florescense
put a drop of media in chamber (kind of like a square in a graph); multiply by amount to find total; don't know if it is living or dead
standard plate count: dilute culture; see how many colonies of live cells there are; calculate colonies per ml
filtration: pour sample through membrane and count colonies
most probable number: take dilutions and look for presence; compare positive tests to table; used by waste management
spectrophotometry