Exercise 10: A Study of Gram Positive Cocci

Staphylococcus and Streptococcus are both:

gram positive cocci

Staphylococcus morphology=

cocci

Staphylococcus arrangement=

grape cluters

Streptococcus morphology=

cocci

Streptococcus arrangement=

chains

What are three examples of staphylococcus species?

-S. auerus

-S saprophyticus

-S. epidermidis

S. aureus is the causative agent of:

MRSA

S. saprophyticus is the causative agent of:

UTI's

S. epidermidis is the causative agent of:

colonizer of skin; can colonize medical implants

What are three examples of streptococcus species?

-S. pyogenes

-S. agalactiae

-S. pneumoniae

S. pyogenes is the causative agent of:

pharyngitis (strep throat), scarlet fever, rheumatic fever

S. agalactiae is the causative agent of:

neonatal infections

S. pneumoniae is the causative agent of:

pneumonia and otitis media

Who tests positive for catalase? Negative?

-positive= Staphylococcus

-negative= Streptococcus

You just tested a specimen with catalase and it tested positive. You now know you have some sort of species of Staphylococcus. What is the next media you will use to determine if the species is S. epidermis or another species?

Mannitol Agar

If the specimen you have tested positive in the mannitol agar test, what species do you have? Positive produces what color? What if it was negative? Negative produces what color?

-if positive, must do a different test; positive color produces a yellow color (means it was able to ferment mannitol)

-if negative, you have S. epidermis; negative result produces/stays a red color (means it was not able to ferment mannitol)

Your specimen tested positive on the mannitol salt agar plate. What test now must you run?

Coagulase DNase

Coagulase DNase tests for:

the ability to break down DNA

What is the indicator for DNase?

methyl green

A positive test for DNase turns what color?

green

If your specimen tested positive for coagulase DNase, what species of staphylococcus is it? What does this mean?

S. auerus; it was able to break down DNA

If your specimen tested negative for coagulase DNase, what species of staphylococcus is it? What does this mean?

S. saprophyticus; was not able to break down DNA

You just tested a specimen with catalase and it tested negative. You now know you have some sort of species of Streptococcus. What is the next media you will use to determine if the species is S. pnuemoniae or another species?

Blood Agar plate

If the specimen you have tested positive on the blood agar test, what species do you have? Positive produces what color? What if it was negative? Negative produces what color?

-if positive, must do a different test; no color is produced, but beta lysis would appear.

-If negative, it would be S. pneumoniae; no color produced, but alpha lysis would appear

Your specimen tested positive on the blood agar plate. What test now must you run?

Bacitracin (antibiotic test)

Bacitracin tests for:

resistance or sensitive to the antibiotic bacitracin

If your specimen showed resistance to bacitracin, what species of streptococcus is it? What does this mean?

S. agalactiae; means that bacitracin does not kill this bacteria

If your specimen showed sensitivity to bacitracin, what species of streptococcus is it? What does this mean?

S. pyogenes; means that bacitracin works against this bacteria