lab 3 study guide
serial dilution
Dilution of a substance several times by the same amount each time
stock culture
a culture stored for use as an inoculum in later procedures
standard viable count
a method where the number of viable or live bacteria are counted by their ability to form colonies.
Spectrophotometry
a method where the turbidity of a culture is measured and gives you an estimate of the entire cellular biomass including both live and dead cells.
spread plate method
a plate count method in which inoculum is spread evenly over the surface of a solid culture medium with L shaped rod
CFU (colony forming unit)
a single cell or group of related cells that produce a colony
aspectic technique
a technique that prevents contamination of the cultures we are working with
How would you check if your loop is cool enough while streaking?
allow it to cool long enough if it sizzles that means its too hot
how should test tubes be held when preforming transfers?
always at an angle. never hold tubes upright as airborne contamination may occur
transfer of bacteria using a loop and good sterile technique is called
aseptic technique?
What would happen if the starting culture is too dilute?
concentration isn't high enough, bacteria may die
pure colony
contains only one species or strain
what are serial dilutions used for?
dilute the original bacterial culture before you transfer known volume of culture onto agar plate used to decrease a bacterial concentration for a specific test OR to a concentration that is countable.
for streak plating- In which quadrant would you expect to see isolated colonies?
fourth quadrent
streak plating
method of dilution used to obtain single, isolated colonies on solid media agar plates
isolation methods
methods used to separate a strain from a mixed population in order to observe and identify the specific bacteria
Heterogeneous culture
mixed culture
how do we store cultures?
on slants, easier to store and they don't dry out quickly (petri dishes dry out quickly)
Why is a spread plate technique used?
provides visible, isolated, countable colonies which are evenly distributed throughout a plate This method gives consistently reliable results when bacterial samples are dilute or if the medium being inoculated is highly selective.
homogeneous culture
pure culture (all the same)
benefits of streak plating
requires few materials provides isolated colonies quick and easy
Steps of spread plate method
small volume of liquid, diluted sample pipette on to surface of the medium and spread around evenly by a sterile spreading tool
most common plating method
spread plate method
two ways of determining bacteria count
standard viable count OR Spectrophotometry
types of isolation methods
streak plate, spread plate, pour plate
how would you reisolate a colony?
taking the colony and restreaking it on a sterile plate (subculturing)
what would happen if the loop wasn't cooled enough during aseptic technique?
the loop would be too hot and could potentially kill the bacteria which is targeted for observation/transfer.
purpose of burner in aseptic technique
to kill any bacteria that lives on the loop/ mouth of the tubes. prevents contamination
subculturing
transferring microorganisms from one medium to another
how would you check if the colony you isolated/picked up off your plate is pure?
you would use staining. simple staining to determine if there are different morphologies or gram staining
aspetic technique steps
1. agitate broth 2. sterilize loop with burner 3. allow loop to cool 4. remove both caps to the tubes with one hand 5. flame the mouths of the tubes, hold at slant 6. dip loop into broth A and transfer to broth B 7. flame mouths of tubes and replace caps 8. flame loop
pour plate method
A method of inoculating a solid nutrient medium by mixing bacteria in the melted medium and pouring the medium into a Petri dish to solidify