Unit 2 Lab Exam Flashcards
What does sterile mean
lacking ALL life forms
Define a pure culture
a growth of microorganisms that contain only one specific kind (strain) of microbe
What is the most common way to obtain pure cultures
streaking a culture of microbes for single colonies on a solid medium (agar plate)
How much should we turn the bunsen burner for gas flow
1-half of a turn
When should we take the wire out of the flame for sterlization
when it turns orange
How long should we let the flamed wire cool before use
10-15 seconds–do not wave it around
When re sterilizing the wire which direction should we move
towards the tip so that the inoculum doesn’t spatter and create aerosol of viable cells
Do we hold the tube containing the inoculum source and the tube with the recipient medium in the same or different hands for a tube to tube transfer
same
How should the plugs or caps be removed for tube to tube transfer
with the last two fingers of the hand holding the needle or loop, leaving the thumb and index finger free to hold and manipulate the loop with the middle finger as a guide
With a plate to tube transfer should both be handled at the same time
no
For a plate to tube transfer where do we want to place the inoculum in the tube? How do we mix it?
rub the wire on the moistened side of the tube just above fluid level and slant it to wash the inoculum down; do not rattle the wire against the sides of the tubes to shake it into broth
What is the streaking plate method used for
mechanically diluting a concentrated sample of microorganisms to a small, scattered population of cells over the surface of the solid medium
What is the primary purpose of plating
obtain well-isolated colonies on a large part of the plate surface
What must be done to the wire when streaking a plate
re sterilize the loop with the flame between each streak
How big should our first phase of the streak be
1/4th of the plate
How big should our second phase of the streak be
1/2 of the plate
________ _________ are essential in pure culture techniques
isolated colonies
What does colony formation result from
growth and replication of a cell that can use the medium as a source of nutrients and that can tolerate the physical conditions present
After streaking a plate, the cell should multiply and result in
resulting, during incubation, a colony of identical cells
Define colony
visible (to the naked eye) mass of millions of cells that arose from a common source
What do we use when we consider the common origin for the cells of a colony
CFU–colony forming unit
Define a spore
dormant type of cell whose main advantage is being able to withstand harsh environmental conditions
When will a spore become a vegetative cell again
when growth conditions return
Spores qualify as colony forming units T/F
True
What type of growth is the first streaking of a streak plate
confluent growth
What are the three reasons that we should treat all cultures as pathogenic
- cultures may have been contaminated
- they may contain unknown environmental microbes
- microbes may have acquired virulence by mutation or natural transformation
What is Nutrient broth medium for
organisms that are not nutritionally fastidious
Glucose is added to NB for what
to allow fermentation under the low oxygen conditions by incubating the tubes in non shaking incubator
What is the purpose of sterlizing between streaks
to ensure that we will eventually dilute the culture to have isolated colonies in the last streaking quadrant
Streaking a plate will check ______ among colonies
uniformity
Cloudiness =
turbidity
Can you tell if you aseptic technique in the tube transfers are only the desired microbes
no, we can’t be certain because it could have been contaminated during the incovulation procedure
