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:
Collect a throat swab
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 beta-hemolytic colony.
Explain beta-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.
Modified from Step1
Differentiate using antibiotics:
You chose a beta-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 beta-hemolytic sample against bacitracin (A) and sulfamethoxazole (SXT).
What is the purpose of bacitracin?
Why bacitracin and not optochin?
What is the purpose of SXT?
After incubation:
Is this sample sensitive or resistant to Bacitracin (A)?
Zone is 20mm
What does that tell you about this sample?
Is this sample sensitive or resistant to SXT?