culture media + pure cultures Flashcards
what is culture media
preparations that are decided to support the growth of microbes
what are the physical forms of media
solid, semisolid, and liquid/broth
how do we solidify media
by using agar
how are solid and semisolid media distinguished
the percentage of agar used will determine which form we get
who introduced the solid culture media method for growing bacteria
robert koch
what are the forms of solidified agar
agar slant, agar deep, or agar plate
what tool is used to inoculate an agar slant
inoculating loop
what tool is used to inoculate an agar deep
inoculating needle
what are the types of media based on chemical composition
defined/synthetic media and complex media
what is defined/synthetic media
a medium in which all components and their concentrations are known
what is a complex media
contains some ingredients of unknown composition and/or concentration
what is complex media used for
used for most heterotrophic bacteria that one works with in an introductory lab
give some examples of complex media that one would use in an intro lab
nutrient broth, tryptic soy broth
what are some complex media components
tryptones, peptones, and extracts
what is tryptone
derived from a digest of casein by the enzyme trypsin
- it’s an assortment of peptides
what are peptones
protein hydrolysates prepared by the partial digestion of various proteins
describe the extracts used in complex medium
aqueous, usually from beef or yeast, and they contain a mixture of peptides, amino acids, minerals, vitamins
why is complex media useful
useful when you don’t know the nutritional needs of a particular bacterium you want to grow, or when you want a general purpose media that can fit the needs of many microbes
give examples of common complex media
tryptic soy broth, tryptic soy agar, luria broth, nutrient broth/agar
how do we solidify a liquid media
use agar
what is agar
a polysaccharide that is exracted from a marine alga
where does agar come from
marine alga
how much agar do we add to solidify a liquid media
1.5% agar is added (15g/L)
list two advantages of agar
it isn’t degraded by most microbes
it liquifies at 100 C and can be cooled to 42-45 C before it hardens (easy to work with)
list the functional types of media
general purpose, enriched, selective, differential, mannitol salt agar
what is general purpose media
a media that supports the growth of many microbes (it’s like our baseline media)
give examples of general purpose media
tryptic soy agar/broth
what is enriched media
general purpose media supplemented by blood or other special nutrients
give an example of enriched media
blood agar, chocolate agar
what is selective media
favors the growth of some microbes and inhibits the growth of others
give examples of selective media
eosin methylene blue agar (EMB), MacConkey agar, mannitol salt agar (MSA)
describe what eosin methylene blue agar does (why is it a selective media)
used for E coli detection (suppresses growth of gram positive bacteria)
describe what MacConkey agar does (why is it selective media)
it contains bile salts and crystal violet that inhibits the growth of gram positive organisms
describe differential media
allows one to distinguish between dif groups of microbes based on their biological characteristics
give an example of differential media
blood agar, EMB
explain why blood agar is a differential medium
it can differentiate between hemolytic (can lyse RBCs) and nonhemolytic bacteria
- hemolytic bacteria will have clear-ish rings around their colonies
explain why EMB is a differential medium
allows one to distinguish between bacteria that can ferment/break down lactose from those that cannot
- ie E coli, a lactose fermenter, turns metallic on EMB
what type of medium is mannitol salt agar
differential and selective
describe mannitol salt agar as a differential + selective medium
differentiates between those that ferment mannitol to produce acids from those that cannon
- those that can ferment will form yellow zones around their colonies
- is selective because salt concentration inhibits some bacterial growth
define a pure culture
a population of cells arising from a single cell
how can you derive a pure culture from a sample?
spread plate technique, streak plate technique, or the pour plate technique
define colony
visible growth or cluster of microorganisms on an agar surface
describe the spread plate technique
you spread a mixture of cells on an agar surface so that individual cells are well separated from each other. Makes use of a spreader
describe the streak plate technique
involves spreading a mixture of cells on an agar surface so that individual cells are well separated. Makes use of an inoculating loop + the T streak method
what is the T streak method
on a plate, go back and forth with your loop to distribute the concentrated cells. then streak from that area to a sterile part on the plate, and continue until it’s dilute enough that the colonies will be separated from each other
describe the pour plate technique
sample is diluted several times, then put into empty petri dishes. Agar is poured in, and the plates are swirled to mix them, and then it hardens
how do you make a pure culture broth
isolate one colony + put it into broth
what do we look at during colony identification
morphology
what morphological factors do we look for during colony identification
form, elevation, margin, texture, appearance, optical property, pigmentation
list the different forms of colonies
punctiform (little dots), circular, filamentous, irregular, rhizoid (protruding/branched lines), and spindle
list the different elevations colonies can have
flat, raised, convex (contact lens shaped), pulvinate (like a bubble), umbonate (irregular/lumpy)
what are the different margins a colony can have?
entire, undulate, lobate, erose, filamentous, curled
colonies more that 5mm in diameter or are irregular shape are likely made up of ___ cells
motile
where on the plate is colony growth most rapid
at the edge of the plate
why is colony growth most rapid at the edge of the plate
these cells have more access to oxygen and nutrients
where is colony growth the slowest on a plate
in the center
