Human pathogens continued

Question 1

Bacitracin Sensitivity Test used to identify which groups of bacteria? which plate is used? Positive rxn?

Answer 1

*Used to identify Group A Streptococci
*Blood agar plate is seeded with test organism, then 0.04 unit bacitracin antibiotic disk is applied
*Only Group A Streptococci are sensitive to bacitracin
- May change the plate color to yellow

Question 2

CAMP Test
Identifies Group?

What produces the CAMP substance?

CAMP substance works with________ produced by _________, causing an increased hemolytic effect.

Positive rxn?

Answer 2

*Identifies Group B Streptococci
*Group B Streptococci produce the CAMP substance
*CAMP substance works with β-hemolysins produced by S. aureus, causing an increased hemolytic effect.
*Production of arrow-head zone of hemolysis adjacent to S.aureus growth indicates a positive test

Question 3

Bile Esculin Test
Isolates?
hydrolyzes?
Positive rxn?

Answer 3

Isolates Enterococci (previously Group D streptococci)
*In the presence of bile, Group D Strep. hydrolyzes to 6,7-dihydroxy coumarin (esculetin)
*Exculetin reacts with iron salts in the medium to produce a brown-black color

Question 4

6.5% Sodium Chloride Test isolates?
Positive rxn?

Answer 4

*Isolates Enterococci (formerly Group D Streptococci) as only members of this genus can grow in medium

• pink, cloudy

Question 5

PathoDx Kit (Latex Agglutin Test) identifies?
Positive rxn and how it happens?

Answer 5

*Identifies beta-hemolytic Streptococcus groups A, B, C, F, and G
*Latex particles are coated with antibodies that recognize carbohydrates on the cell wall of the bacteria, which will cause agglutination
*First, nitrous acid is used to extract the antigen from the cell wall. The acid is neutralized, then the latex particles are added. The IgGs conjugated to the latex react with the antigen, causing agglutination

Question 6

PathoDx Procedure

Answer 6

1.Pick a sufficient amount of culture using an applicator stick and rub onto each oval

2.Add 1 drop of Strep A reagent to the first oval, 1 drop Strep B reagent to the second oval, and C, F, and G reagents to the last 3 ovals

3.Carefully mix reagent and extract using a clean stirrer end for each oval

4.Gently rock slide and examine for agglutination. Do not rock for more than 60 seconds.