Which bacteria are grouped according to their hemolytic patterns?
Which groups of Streptococci are beta hemolytic?
Group A (GAS), F, and G
Which Streptococci (species) are alpha hemolytic?
S. pneumoniae and S. viridans
True/False: Alpha hemolytic Streps are the predominant natural flora?
When doing a gram stain of respiratory samples what is acceptable and not acceptable?
Acceptable: WBC's > epithelial cells
Unacceptable: WBC's < epithelial cells
What does BHI stand for?
Blood heart infusion
Characteristics of Streptococci
Fastidious, gram + cocci in pairs and chains, catalase -, falcultative anaerobes,
How are Streps classified?
Based on antigens found in their cell walls (Lancefield)
What is the purpose of the hippurate hydrolysis test?
To test for the ability of Streptococcus agalactieae to hydrolyze hippurate
What is the indicator in the hippurate hydrolysis test?
What does the hippurate hydrolysis test detect?
Glycine (hippurate by-product) causes blue/purple color change
What denotes a positive result in the hippurate hydrolysis test?
Purple color change
What is the purpose of the PYR test?
It differentiates gram + cocci that hydrolyze the PYR substrate
What is the reagent in the PYR test?
What does hydrolysis of the substrate yield that combines with the reagent in the PYR test to form a positive result?
What denotes a positive result in the PYR test?
A bright pink to cherry red color
What organisms are PYR positive (2)?
1. S. pyogenes
What is bacitracin used to identify (group and species)? What growth medium is used?
Group A beta-hemolytic Streptococci. S. pyogenes. Blood agar plate.
What organisms are sensitive to trimthoprim/sulfametoxazol?
Group A and B Streptococci
What shows that an organisms is susceptible to bacitracin?
Any zone of inhibition
What is optochin used to identify (type and species)? What medium is used?
Used for differentiation of alpha-hemolytic Streptococci. S. pneumoniae. Sheep blood agar.
What is the purpose of the bile esculin test? What medium is used?
To differentiate group D Streptococci and Enterococci. Slant.
What does the bile esculin test detect?
What denotes a positive result in the bile esculin test?
Dark brown to black color in medium.
What is the purpose of the NaCl broth?
To differentiate gram + cocci that will grow in 6.5% NaCl concentration from those that are inhibited by this salt concentration.
What denotes a positive result in the NaCl broth test?
Turbidity or color change in the medium
What is the QuickVue Test?
A rapid test used to identify GAS or S. pyogenes; a lateral-flow immunoassay containing a highly specific antibody to Group A strep antigen.
Which group of Streptococci is the most significant cause of pharyngitis?
How quickly does the QuickVue test work?
In 5 minutes
What reagents are used in the QuickVue test and what are their purposes?
Reagents A and B extract the antigen and solubilize the cell wall of the bacteria.
What denotes a positive result in the QuickVue test? The control?
A pink line is positive for GAS. Blue lien is the control.
How does serology for streptococci work?
It identifies Lancefield's groups (A,B,C,D,F, and G). Antigens in cell wall are liberated using nitrous acid extraction + rabbit antibodies.
What is the purpose of the Snyder test?
It helps predict susceptibility to dental caries based on acid production by using Snyder medium.
Which organisms grow and produce acid as a result of their metabolism that can be detected in the snyder test?
Streptococcus mutans, S. sobrinus, and Lactobacillus spp.
What is the indicator in the Snyder test?
What denotes a positive result in the Snyder test?
The media turns from green to yellow indicating a lowering of pH due to the growth and plaque formation of specific organisms in the mouth.
Example of a gamma hemolytic organism
Example of a Bacitracin sensitive organism
Example of a SXT sensitive organism
Group C Strep
Example of an Optochin sensitive organism
Example of an Optochin resistant organism
Example of bile-esculin positive organism
Example of hippurate positive organism
Example of an organism that can grow in 6.5% NaCl
Which streps hemolytic group require CO2 for growth?
Purpose of BHI medium?
Grow Strep on it to test hemolysis because sometimes organisms can give false positive results in the catalase test if grown on SBA.
In the snyder test, how many hours will it take to produce a result that shows that there is high degree of susceptibility to caries? Moderate, low, and minimal?
High= 24 hrs
Moderate= 48 hrs
Low= 72 hrs
Minimal= no change after 72 hrs