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