Streptococci assignment
rissak54
Strepexerciseset3-PPt.pptxBIOL 2420
Identification of Streptococcus Species
Objectives:
To learn the characteristics of Streptococcus
To learn how clinical specimens are collected
To learn the uses of selective and differential agar to determine characteristics of bacteria
To be able to identify different types of hemolysis
To understand how to use different tests to narrow down and presumptively identify streptococci
How to collect a throat swab for isolation of a potential Streptococcus:
Watch the following video:
Grow your sample on blood agar:
Blood agar
What is the purpose of blood agar?
Does the blood provide anything special for growth?
What was the purpose of doing a streak plate with your throat sample?
Why will all the samples be grown in a candle jar?
What are some concerns with handling patient samples?
Plate from ward science catalog
After incubation:
Choose one colony to further grow and isolate.
Is this a mixed sample or axenic plate? How do you know?
You are going to preferentially collect a gamma-hemolytic colony.
Explain gamma-hemolysis.
Uninoculated
Pearson
Streak your isolate on CNA
Columbia nalidixic acid agar (CNA) plates
What makes the plate selective?
Why is this important to help presumptively identify this bacteria as Streptococci?
What makes the plate differential?
Explain these three types of hemolysis.
What is the purpose of streaking your sample on CNA before continuing with the experiment?
Uninoculated
24-48 hour incubation
Now that you have an isolated presumptive Streptococcus species:
Gram stain to confirm cell morphology
By what cell structure does does the Gram stain differentiate bacteria?
Can you list the reagents used in the Gram stain? Explain the purpose of each.
Give the Gram reaction.
Gram + or Gram -?
Describe the cell morphology.
Pearson
Differentiate using antibiotics:
You chose an gamma-hemolytic sample
First, you will create a lawn on the plate.
What is a lawn?
How does it allow you to test antibiotics?
Test your gamma-hemolytic sample against optochin (P) and sulfamethoxazole (SXT).
What do you think the reaction to optochin will be?
What is the purpose of SXT?
After incubation:
Is this sample sensitive or resistant to SXT?
Zone is 0mm
What does that tell you about this sample?
What about Optochin (P)?
What does this tell you about this sample?
Before incubation
After incubation
Adapted from microbiologylearning
Now that you have an isolated presumptive Streptococcus species:
You will perform a catalase test
Describe the procedure you would do in the lab.
What enzyme does this test test for?
Do you use an indicator or reagent? Name it.
Is the result catalase + or catalase -?
More tests to differentiate potential streptococci
Bile esculin slant
Use to help differentiate streptococci and enterococci/Group D streptococci
What makes this slant selective?
What does it select for?
What makes this slant differential?
How does it differentiate?
What are your results?
Bile + or bile -?
Esculin + or esculin -?
What does this mean for your potential streptococci?
24-48 hour incubation
uninoculated
More tests to differentiate potential streptococci
6.5% sodium chloride broth
Use to help differentiate streptococci and enterococci
How is this selective?
The results are determined by turbidity. What does this mean?
What are your results?
+ or -?
What does this mean for your potential streptococci?
24-48 hour incubation
Adapted from microbenotes
Use your test results and the provided charts to determine the species of your Streptococcus
What is the most likely species of your streptococci?
Good lawn Bad lawn
Good lawn
Bad lawn
A SX TP
A
S
X
T
P
A SX TP
A
S
X
T
P
P SX T
P
S
X
T
Examples of salt broth - +
Examples of salt broth
-+
