Staphylococcus Gram + cocciIn clumps

Staphylococci

3 major species: S.aureus, S.epidermidis, and S.saprophyticus)

Infections are primarily associated with pathogenic strains of S.aureus

Many virulence factors

Comparison of the 3 major species (Table 64.1 p416)

S. aureus

S. epidermidisS. saprophyticus

All three species appear similar by Gram stain.

Media Used to Distinguish Staphylococcal Species

MSA

DNAse Test: Confirms S.aureus DNAse (an enzyme that degrades DNA) On medium containing DNA and methyl

green, a positive result is a clearing around the bacterial growth

S. aureus ferments manitol causing the media to turn yellow

S. epidermidis and S. saprophyticus do not Therefore, the media remains red

S. aureus

S. epidermidisS. saprophyticus

Gram+ cocci in clumpsManitol fermentation (MSA media)DNAse+

Gram+ cocci in clumpsNo Manitol fermentation (MSA media)DNAse-

Procedure: Divide a MSA plate into 3 sectors;

inoculate (single line inoculation) the plate with S.aureus, S.saprophyticus and S.epidermidis

Divide a DNAse plate into 3 sectors; inoculate the plate with the 3 organisms listed above as described above

MSA and DNAse Plates

S. aureus

S. saprophyticus

S. epidermidis

Used to distinguish S.saprophyticus from S.epidermidis and S. aureus

Identifies the novobiocin-resistant S.saprophyticus

S. epidermidisS. saprophyticus

S. saprophyticus

S. epidermidis

Novobiocin Sensitivity Test

S. saprophyticus

S. aureus and S. epidermidis

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Procedure: Divide a Mueller-Hinton Agar Plate into

two sectors Inoculate (create a small “lawn” of

bacteria in each sector) with S.epidermidis and S.saprophyticus

Place a novobiocin disk in the center of each “lawn”

Invert plate; incubate

Catalase Test

Determines the ability of microbes to degrade hydrogen peroxide (H2O2) by producing the enzyme catalase

H2O2 is produced during aerobic respiration; must be degraded

catalase 2 H2O2 2 H2O + O2

Catalase Test Results

Upon addition of H2O2 , Catalase positive organisms release oxygen gas (seen as bubbles)

Present in Staphylococcus

Coagulase Test

Coagulase: an enzyme that converts fibrinogen to fibrin in plasma to form clots.

S. aureus express coagulase.

S. epidermidis and S. saprophyticus do not.

S. aureus

S. epidermidis

S. saprophyticus

Gram+ cocci in clumpsManitol fermentation (MSA media)DNAse+Novobiocin sensitive Coagulase+Catalase+

Gram+ cocci in clumpsNo Manitol fermentation (MSA media)DNAse-Novobiocin resistantCoagulase-Catalase+

Gram+ cocci in clumpsNo Manitol fermentation (MSA)DNAse-Novobiocin sensitive (Zone of inhibition)Coagulase-Catalase+

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Catalase + + +