Unknown project (microbiology)
BIOL 2420 Identification of Streptococcus species
Lab Objectives
Learn how to collect clinical specimens
Watch videos in lab exercise
Learn major characteristics of Strep species
What are characteristics of a pathogenic species?
To learn how biochemical tests can help determine species
Identification of Streptococcus
Family Streptococcaceae
Gram +, cocci, typically di- or strepto-
Facultative anaerobes
BUT they like high carbon dioxide levels
Microbiota of the skin, respiratory tract, digestive tract and oral cavity
Potentially pathogenic species
Produce a variety of virulence factors: toxins, hemolysin, and hydrolytic enzymes
S pyogenes
S pneumoniae
Some have now been placed in Enterococci
Goal is to distinguish between them through a variety of biochemical tests
Science source
Identification of Streptococcus
Gamma-hemolysis – no hemolysis
Flikr
Beta-hemolysis – complete hemolysis
Wikipedia
Throat swabs on blood agar
Hemolysis:
Streptococcus are often grouped based on hemolytic reaction
They can be alpha, beta or gamma
Enterococci which are important medically are typically gamma
alpha-hemolysis – partial hemolysis
bacterinphotos
Throat swab will give mixed results
Preferably choose one colony that is either beta- or alpha- hemolytic
Hemolysis will determine what procedure you will perform today
Streak the colony on a new CNA plate (for isolation)
Identification of Streptococcus
Identification of Streptococcus
Columbia nalidixic acid agar (CNA)
Inhibition of G- growth
Naladixic acid (antibiotic)
Hemolysis
Streptococcus most likely be alpha- or beta-hemolytic
Enterococcus could be any of the three
Identification of Streptococcus
Perform a Gram stain
What should the result be?
To help ensure that only Streptoccocus/Enterococcus were grown…
Streak plate on Columbia nalidixic acid agar
Perform a catalase test
All Streptococci are negative
Make sure yours falls into this category
Catalase test
Enzyme that breaks down hydrogen peroxide to water and bubbles (oxygen)
Streptococcus pyogenes
Enterococcus faecalis
Identification of Streptococcus
Gamma-hemolysis
Flikr
Beta-hemolysis
Wikipedia
alpha-hemolysis
bacterinphotos
Did you have alpha- or beta-hemolysis?
Test different antibiotics to help determine what species of Strep is present
Bacitracin –S.pyogenes is sensitive
Optochin – S. pneumoniae is sensitive
SXT – useful to ID Group C strep
Identification of Streptococcus
Bile esculin
Help differentiate Group D strep and enterococci
Selective – bile salt; inhibits the growth of G+ EXCEPT Group D/enterococci
Differential – esculin – when hydrolyzed will turn dark coffee brown
Salt resistance
Only enterococci will survive in 6.5% salt broth
Based on turbidity
+ turbid (growth)
- no growth