Gram-positive bacteria - lab algorithm Flashcards
What are 2 tests to differentiate between the Gram-positive cocci?
1) appearance on Gram stain: Streptococci appear as chains(strips), and Staphylocci appear as clusters
2) catalase: Streptococci is catalase-negative, Staphyloccus is catalase-positive
What are the Gram-positive cocci?
1) Streptococcus (and Enterococcus)
2) Staphlycoccus
How to differentiate between Gram-positive cocci based on morphology?
Streptococci appear as chains(strips)
Staphylococci appear as clusters
How to differentiate between Gram-positive cocci based on catalase test?
Streptococci are catalase-negative.
Staphylococci are catalase-positive.
Streptococci are classified according to what ability?
hemolysis
alpha hemolytic - defn
partially lyse RBCs (on blood agar) leaving a greenish discoloration of the culture medium surrounding the colony (which contains unlysed RBCs and a green-colored metabolite of hemoglobin)
What type of hemolysis partially lyses RBCs and leaves a greenish discoloration of blood agar?
alpha hemolysis
beta hemolysis - defn
completely lyses RBCs, leaving a clear zone of hemolysis around the colony on blood agar
What type of hemolysis completely lyses RBCs and leaves a clear zone surrounding the colony?
beta hemolysis
gamma hemolysis - defn
non-hemolytic
What type of hemolysis is non-hemolytic (unable to lyse RBCs)?
gamma-hemolytic
What bacteria are alpha hemolytic when grown on blood agar? (2)
1) Streptococcus pneumoniae
2) Viridans streptococcus
S. pneumoniae displays what type of hemolysis when grown on blood agar?
alpha hemolytic (partial hemolysis) Streptococci pneumoniae
S. viridans displays what type of hemolysis when grown on blood agar?
alpha hemolysis (partial hemolysis) Streptococci viridans
What streptococci display beta hemolysis when grown on blood agar?
1) Group A Streptococcus (S. pyogenes)
2) Group B Streptococcus (S. agalactiae)
Group A strep displays what kind of hemolysis when grown on blood agar?
beta (complete) hemolysis
Group A = Strep pyogenes
S. pyogenes displays what kind of hemolysis when grown on blood agar?
beta (complete) hemolysis
Streptococci pyogenes = Group A strep
Group B streptococci display what type of hemolysis when grown on blood agar?
beta (complete) hemolysis
Group B strep = Streptococci agalactiae
S. agalactiae displays what kind of hemolysis when grown on blood agar?
beta (complete) hemolysis
Streptococci agalactiae = Group B strep
What streptococci are gamma-hemolytic? (2)
Group D strep: Enterococci and Nonenterococci
gamma hemolytic = non hemolytic
Group D streptococci display what type of hemolysis when grown on blood agar?
gamma-hemolytic (non-hemolytic)
What type of streptococci are non-hemolytic?
Group D strep: enterococcus, nonenterococcus
Gamma hemolytic = non-hemolytic
Which two antibiotics can differentiate among species of streptococci?
1) optochin
2) bacitracin
Optocochin is used to differentiate among which type of hemolytic streptococci?
alpha-hemolytic
The alpha-hemolytic streptococci are differentiated based on sensitivity to which antibiotic?
optocochin
Optochin is used to differentiate among which bacteria?
Streptococci alpha hemolytics: S.pneumoniae and S. viridans
S. viridans is resistant
S. pneumo is sensitive
“OVRPS” (overpass)
S. pneumoniae is (sensitive, resistant) to optochin
sensitive
“OVRPS”
Which alpha hemolytic streptococcus is optochin sensitive?
S. pneumoniae
“OVRPS”
Which alpha hemolytic streptococcus is optochin resistant?
S. viridans
“OVRPS”
S. viridans is (sensitive, resistant) to optochin.
resistant
“OVRPS”
The alpha hemolytic streptococci can be differentiated based on what 3 characteristics?
1) capsule (S. pneumo has capsule; S. viridans does not)
2) optochin (S. pneumo is sensitive; S. viridans is resistant)
3) bile (S. pneumo is lysed by (soluble in) bile; S. viridans is bile insoluble)
How can alpha hemolytic streptococci be differentiated based on presence or absence of a capsule?
S. pneumoniae has a capsule
S. viridans does not have a capsule
How can alpha hemolytic streptococci be differentiated based on bile solubility?
S. pneumoniae is bile soluble (lysed by bile).
S. viridans is bile insoluble (not lysed by bile).
Bacitracin is used to differentiate among which type of hemolytic streptococci?
beta-hemolytic (complete hemolysis)
The beta-hemolytic streptococci are differentiated based on sensitivity to which antibiotic?
bacitracin
Bacitracin is used to differentiate among what bacteria?
Streptococci beta (complete) hemolytics: S.pyogenes (Group A strep) and S.agalactiae (Group B strep)
Group B strep are resistant
Group A strep are sensitive
“B-BRAS”
Group A strep is bacitracin (sensitive, resistant)
sensitive
B-BRAS
S. pyogenes is bacitracin (sensitive, resistant)
sensitive
S. pyogenes = Group A strep
B-BRAS
Group B strep is bacitracin (sensitive, resistant)
resistant
B-BRAS
S. agalactiae is bacitracin (sensitive, resistant)
resistant
S. agalactiae = Group B strep
“B-BRAS”
Which beta-hemolytic streptococcus is bacitracin sensitive?
Group A strep (S. pyogenes)
B-BRAS
Which beta-hemolytic streptococcus is bacitracin resistant?
Group B strep (S. agalactiae)
“B-BRAS”
The gamma-hemolytic streptococci can be differentiated based on growth in what media?
bile +/- NaCl
Group D enterococci grow in bile and 6.5% NaCl
Non-enterococci grow in bile, but not in 6.5% NaCl
The Group D streptococci can be differentiated based on growth in what media?
bile +/- NaCl
Group D enterococci grow in bile and 6.5% NaCl
Non-enterococci grow in bile, but not in 6.5% NaCl
Bile +/- 6.5% NaCl is used to differentiate among what type of bacteria?
Gamma(non)-hemolytic streptococci
Group D enterococci grow in bile and 6.5% NaCl
Non-enterococci grow in bile, but not in 6.5% NaCl
Which gamma-hemolytic bacteria grow in bile and 6.5% NaCl?
Group D strep (enterococci)
E. faecalis and E. faecium
Which gamma-hemolytic bacteria grow in bile but not 6.5% NaCl?
Group D strep - nonenterococci
S. bovis and S. equinus
Which bacteria are alpha-hemolytic? (2)
1) Streptococcus pneumoniae
2) Streptococcus viridans
Which bacteria are beta-hemolytic? (4)
1) Staphylococcus aureus
2) Group A strep (Streptococcus pyogenes)
3) Group B strep (Streptococcus agalactiae)
4) Listeria monocytogenes
What bacteria is: blue on Gram stain cocci in chains negative catalase test forms green ring around colonies when grown on blood agar optochin sensitive
Streptococcus pneumoniae
What bacteria is: blue on Gram stain cocci in chains negative catalase test forms green ring around colonies when grown on blood agar optochin resistant
Streptococcus viridans
What bacteria is: blue on Gram stain cocci in chains negative catalase test forms clear area around colonies when grown on blood agar bacitracin sensitive
Streptococcus pyogenes
What bacteria is: blue on Gram stain cocci in chains negative catalase test forms clear area around colonies when grown on blood agar bacitracin resistant
Streptococcus agalactiae
What bacteria is: blue on Gram stain cocci in clusters positive catalase test forms clear area around colonies when grown on blood agar positive coagulase test
Staphylococcus aureus
