test two lec 8 Flashcards
for detailed studies of microbes they need to be grown separately in a….
pure culture
how many organisms have we cultured
.1%
what are the two main types of culture media
liquid or broth medium
solid medium
anaerobes use slant tubes
what are the two ways to isolate pure cultures
dilution streaking
spread plate technique
what is dilution streaking
dragging loop across the surface of an agar plate
what is spread plate technique
serial dilutions are performed on a liquid culture
a small amount of each dilution is then plated
early dilution of spread plate technique show
confluent growth
what is important about spread plate technique
viable bacteria produced and used to replicate
what does viable bacteria mean
one that successfully replicates to form a colony
what do we call organisms that metabolize but don’t replicate
viable but non culturable
maybe didnt find proper plate conditions
what is a complex media
bacterial growth solution that is nutrient rich but poorly defined
difficult to characterize metabolism of an organism
what is enriched medium
complex medium plus additional components
such as blood
helps mimic host environment
what kind of nutrients are found in complex media
yeast extract beef extract amino acids peptides nucleosides vitamins some sugars
what is synthetic media
bacterial growth solution that contains defined known components
why use synthetic media
used to study metabolic needs of different types of organisms
what are some components in synthetic media
H2O
various salts
C, N
energy sources
what is selective media
favor the growth of one organism over another
example of selective media
medium containing bile salts and crystal violet favors growth of gram neg over pos
what is differential media
exploit differences between two species that grow equally well, but differ in some biochemical aspect
example of differential media
e coli and salmonella
both gram neg
e coli ferment lactose which lower ph and changes dye of med to red
what is a macconkey medium
both selective and differential
selects gram neg due to bile salts and crystal violet
includes lactose, ferment and turn red
non fermenting is white
what is a petroff hausser counting chamber
microorganisms can be counted directly by placing dilutions on a special microscope slide
hemocytometer
what does propidium iodide do in fluorescence microscopy
cant penetrate membrane of living cells
only dead cells are stained red
what does syto-9 do in fluorescence microscopy
penetrates both living and dead cells
green color
what does acriding orange do in fluorescence microscopy
intercalates between DNA and RNA bases
DNA is green
RNA is orange
can see live and dead
what does DAPI do in fluorescence microscopy
binds strongly to A-T rich regions in DNA; penetrates both living and dead cells
what is fluorescence activate cell sorters
fluorescent cells are passed through a small orifice and then past a laser
detectors measure light scatter in the forward direction and to the side
what is coulter counter
culture is forced through a small orifice, through which flows and electric counter
electrodes placed on both sides measure resistance
every time a cell passes through the orifice, the electrical resistance increases and the cell is counted
works best for EUK cells
how can viable counts be counted
pour plate method
what is the pour plate method
dilutions of liquid culture are placed directly onto a petri dish and then cooled liquid agar is added or the dilutions are needed to liquid agar is added or the dilutions are added to liquid agar and cooled then subsequently poured into an empty petri plate where the agar continues to cool and solidify
what is pour plate method used to find
pathogens bc survive temps
whats another way to find viable counts
counted indirectly by biochemical assays of cell mass, protein content, or metabolic rate
why is biochemical assays not used in viable counts
can still have dead cells contributing to count
what is optical density measuring
used to measure viable counts
a measure of how many particles are suspended in solution, based on light scattering by the suspended particles, still show dead cells
most bacteria divide by
binary fission
how does binary fission work
expansion of nucleoid as DNA replicates
creates equatorial septum
one parent cell splits into 2 equal daughter cells
can cell division be asymmetric
yes, Hyphomicrobium
divide by budding
stalked parent and flagellum daughter
what is exponential growth
growth rate, or the rate increase in population number or biomass, is proportional to the population size at a given time
what kind of slope does an exponential curve have
continually increase
what is generation time
time it takes for a population to double
when does exponential growth occur
short periods of time when all nutrients are in full supply and toxic waste products have not become a limiting factor
does exponential growth last indefinitely
no
what is a batch culture
a liquid medium within a closed system
no fresh medium added
model effects changing environment
what is lag phase
period of cell culture occuring right after inoclulation into new media, slow growth or no growth
cells need time to detect environment, express specific genes, synthesize components
what is early log phase (exponential phase)
bacteria grow exponentially at their maximal possible rate
explain bacterial cells in exponential phase
cell are largest
linear part of curve
cell components synthesized at constant rates relative to each other
what is nutritional down shift and upshift
down: move cells to poor C source
up: move cells to better C source
what is late log phase
as cell density increases, the rate of doubling eventually slows and a new set of growth phase-dependent genes is expressed
top of curve
what is stationary phase
period of cell culture, following exponential phase, during which there is no net increase in replication
rate of cell division equals rate of cell death
how do some cells respond to to stationary phase
turn into spores
decrease in size
minimize nutrient need
produce stress resistance enzymes
what is death phase
period of cell culture following stationary phase in which bacteria die faster that they replicate
negative exponential function
can be prolonged
what is continuous culture
fresh medium continuously added to a culture, and equally amount of culture is taken away
what is a chemostat
continous culture system in which the diluting medium contains a limiting amount of an essential nutrient
what is the point of chemostat
ensures logarithmic growth
growth rate directly related to dilution rate
what is a washout
at faster and faster flow rates, cells are eventually removed more quickly that they can be replenished via replication so cell density decreases
