4.3: Obtaining a Pure Culture Flashcards
What is a clinical specimen?
Is a sample that is collected from a patient in order to identify the pathogen that may be causing their infection or disease.
What is a pure culture?
A Pure Culture is a culture only growing one species of cells.
A culture only growing one species of cells.
Pure Culture
The process of spreading a bacterial culture onto a petri dish filled with agar is called ______.
Plating
What is Plating?
The process of spreading a bacterial culture onto a petri dish filled with agar is called plating
Plating can be done using a ___1___, ___2___, and ___3___.
- sterile loop
- sterile swab
- sterilized wire loop.
The primary advantage of plating a bacterial sample onto agar is……
……that cells are held in place.
Bacteria plated onto agar are fixed in such a way as to support the ______ of colonies.
formation and visualization
True or False: Colonies are visible to the naked eye but only after the bacterial cell has multiplied, often a million times over.
True
Each colony is derived from a single ______.
Cell
To isolate a microbe on an agar plate, microbiologists often utilize a ______ approach.
quadrant streak (or phase-dilution)
A pure culture is free of ___1___ and can be traced back to a single origin.
outside contaminants
Once isolated and expanded, a pure culture can be further examined for its……
…… size and shape, motility, Gram status, biochemical properties, etc.
The sample is spread across the plate in such a way as to establish a ______.
dilution gradient
For a ______, the sample is spread into four regions where each new region is perpendicular to the previous region, such that each region will become more diluted than the previous.
four-phase dilution gradient
True or False: As the four-phase dilution gradient process is carried out, the same loop must be used each time a new phase is started.
False. As the four-phase dilution gradient process is carried out, a new (or sterilized) loop must be used each time a new phase is started.
Once the samples are appropriately streaked onto the media (and the lids placed back onto the plate), they are ___1___ to prevent any potential contaminants from settling onto the surface of the agar and placed in an incubator set at 37°C for ___2___.
- inverted
- ~12-24 hours
What temperature is most commonly used for incubation and why?
Maintaining a temperature of 37°C is optimal for promoting growth and is the temperature most commonly used by researchers.
Individual colonies are then isolated, picked, and ___1___ in nutrient ___2___ for the expansion of the now pure culture to be used for laboratory testing.
- re-inoculated
- broth (or onto nutrient agar)
True or False: Different strains of bacteria vary in their generation time (time it takes them to divide or double).
True
Unlike bacteria, other organisms such as yeast preferentially grow at ______.
30°C
True or False: Pathogenic strains of bacteria tend to grow faster than non-pathogenic strains at 37°C, researchers may set incubators at 25°C to restrict pathogenic growth.
True
Describe what is being shown in the picture.
Agar Streak. A 4-phase dilution streak is shown beginning with the first phase (P1) and ending with the fourth phase (P4). A sterile loop must be used when switching between phases in order to accurately generate a dilution series. Single colonies should be evident within P3 or P4.
