Streptococci (F) Flashcards
What are the 3 types of hemolysis?
1) Gamma-hemolysis
2) Alpha-hemolysis
3) Beta-hemolysis
What is gamma-hemolysis?
No hemolysis
What is alpha-hemolysis?
Appears as a greening of the agar around the bacterial colony
What is beta-hemolysis?
The RCs surrounding the colony are completely lysed, w/c results in a clear zone around the colony
What is the purpose of bacitracin susceptibility?
To differentiate Strep pyogenes from other beta(sign)-hemolytic streptococci
What is the sx used for bacitracin susceptibility?
Isolated colonies of test organism on SBA
What is the medium used in bacitracin susceptibility?
5% SBA plate
What is the rgnt used in bacitracin susceptibility?
Bacitracin disk, 0.04 unit
What is the principle in bacitracin susceptibility?
Grp A streptococci are susceptible to low lvls (0.04 units) of bacitracin, whereas other grps of beta(sign)-hemolytic streptococci are resistant. Rare strains of grp A streptococci are resistant (approx 1%), whereas some strains of grps B, C, and G streptococci are sensitive (5% - 10%).
Sensitivity to bacitracin presumptively identifies an isolate as Strep pyogenes. This procedure was designed for use only w/ pure cultures; however, some clinical microbiologists will add a bacitracin disk to a primary throat culture to screen for Strep pyogenes
What is the procedure (or steps) of bacitracin susceptibility?
1) Streak surface of agar plate to obtain isolated colonies
2) Aseptically place bacitracin disk onto inoculated surface. Press down gently on the disk to ensure complete contact w/ the agar surface
3) Incubate the plate at 35 DC for 18 - 24 hrs in a CO2 incubator
What is the temp needed for incubation in bacitracin susceptibility?
35 DC
What is the time duration for incubation in bacitracin susceptibility?
18 - 24 hrs
What type of incubator is used in bacitracin susceptibility?
CO2 incubator
What are the interpretations for bacitracin susceptibility?
1) Susceptible: any ZOI around the bacitracin disk
2) Resistant: uniform lawn of growth up to the edge of the disk
What is the principle (including the purpose) of bile solubility test?
The bile solubility test differentiates Strep pneumoniae (+) from alpha-hemolytic streptococci (-). Bile or a solution of a bile salt, such as sodium desoxycholate rapidly lyses pneumococcal colonies.
Lysis depends on the presence of an intracellular autolytic enzyme. Bile salts lower the surface tension bet the bacterial cell membrane and the medium, thus accelerating the organism’s natural autolytic process
Grp D streptococci and enterococci grow in the presence of bile and also hydrolyze esculin to esculetin and glucose
Esculetin diffuses into the agar and combines w/ ferric citrate in the medium to produce a black complex
What is the purpose of sodium desoxycholate?
To rapidly lyse pneumococcal colonies
What is the purpose of bile salts?
It lowers the surface tension bet the bacterial cell membrane and the medium, thus accelerating the organism’s natural autolytic process
What bacteria grow in the presence of bile and also hydrolyze esculin to esculetin and glucose?
1) Grp D streptococci
2) Enterococci
What is the action of esculetin?
It diffuses into the agar and combine w/ ferric citrate in the medium
What is the product when esculetin diffused into the agar and combined w/ ferric citrate?
Black complex
What is the procedure (or steps) of bile solubility test?
1) Place 1 - 2 drops of 10% sodium desoxycholate to the side of a young (13 - 24 hr), well-isolated colony growing on 5% SBA
* note: a tube test is performed w/ 2% sodium desoxycholate
2) Gently wash liquid over colony, w/out dislodging the colony from the agar
3) Incubate the plate at 35 DC in ambient air for 30 mins
4) Examine for lysis of colony
What is the temp needed for incubation in bile solubility test?
35 DC
What is the time duration of incubation needed in bile solubility test?
30 mins
What are the results (expected results) of bile solubility test?
1) (+): colony disintegrates; an imprint of the lysed colony may remain within the zone
2) (-): intact colonies