Mirco Lab 8- Staphylococcus vs Streptococcus

What are the Gram staining properties and morphology of Staphylococci?

They are Gram-positive cocci commonly seen as irregular clusters or spherical cells

What are the Gram staining properties and morphology of Streptococci?

They are Gram-positive, spherical cells usually seen as single cells, pairs, and chains.

Which test is used to differentiate Staphylococci from Streptococci based on the enzymatic degradation of hydrogen peroxide?

The catalase test

The accumulation of _____ during aerobic respiration can result in the death of a microorganism unless it produces catalase.

hydrogen peroxide

A positive catalase test is indicated by the formation of _____ when hydrogen peroxide is added to a bacterial colony.

bubbles

Which Gram-positive cocci is typically catalase-positive?

Staphylococcus

Which genus of Gram-positive cocci is typically catalase-negative?

Streptococcus

What is the purpose of the coagulase test?

To differentiate potentially pathogenic Staphylococci, like Staphylococcus aureus, from other Gram-positive, catalase-positive cocci.

The coagulase test identifies whether an organism produces the exoenzyme coagulase, which causes the _____ of blood plasma to clot

fibrin

Which species of Staphylococcus is coagulase-positive?

Staphylococcus aureus

What is the visual indicator of a positive coagulase test on a slide?

Clumping of the bacterial cells after adding rabbit plasma

What is the biochemical presentation of Staphylococcus aureus?

Catalase positive → coagulase positive, ferments mannitol (so it appears yellow on MSA)

What is the biochemical presentation of Staphylococcus epidermidis?

catalase positive → coagulase negative, doesn’t ferment mannitol so it stays red

What is the biochemical presentation of Streptococcus pyogenes?

catalase negative → beta hemolytic (clear done on BAP)

What is the biochemical presentation of Streptococcus pneumoniae?

Catalase negative → alpha hemolytic (green on BAP)

What is the biochemical presentation of Entereococcus?

 catalase negative → gamma hemolytic (no change on BAP)

Mannitol Salt Agar (MSA) is what type of medium?

Selective and differential 

What component of Mannitol Salt Agar (MSA) makes it selective for Staphylococci?

The very high NaCl concentration

What two components of Mannitol Salt Agar (MSA) make it differential?

The presence of mannitol and the pH indicator phenol red.

On MSA, what color change occurs if a bacterium ferments mannitol?

The phenol red indicator changes from red to yellow due to acid production

Which species of Staphylococcus is known to ferment mannitol, causing a yellow color change on MSA?

Staphylococcus aureus

Which species of Staphylococcus does not ferment mannitol, leaving the MSA medium red?

Staphylococcus epidermidis

What type of medium is Blood Agar (BAP) primarily used as in this context?

A differential medium, based on the type of hemolysis produced

Define Beta (β) hemolysis on a blood agar plate.

The complete breakdown of red blood cells around a colony, resulting in a 'Zone of Clearing'

Define Alpha (α) hemolysis on a blood agar plate

An incomplete hemolysis that manifests as a 'greening' reaction around the colony.

Define Gamma (γ) hemolysis on a blood agar plate.

The absence of any hemolysis around the colony.

Strains of S. epidermidis and S. saprophyticus are generally considered _____.

avirulent

Under special circumstances, S. epidermidis can be the etiological agent for what two conditions?

Skin lesions and endocarditis

Staphylococcus saprophyticus has been implicated in what type of infections?

Urinary tract infections (UTIs)

What is the causative agent of pharyngitis, commonly known as strep throat?

Group A Streptococci (S. pyogenes)

Name complications that can arise from a Group A Strep infection.

1. Rheumatic fever

2. glomerulonephritis

3. Scarlet fever

4. toxic shock syndrome

5. pneumonia

6. septicemia

7. skin infections

What is the descriptive name for the severe skin infection, necrotizing fasciitis, caused by S. pyogenes?

Flesh-eating strep

Although they are part of the normal body flora, _____ Streptococci can cause endocarditis and are implicated in dental caries.

Viridans

Name diseases that can be caused by Streptococcus pneumoniae

1. Pneumonia

2. Sinusitis

3. Ear infections

4. Bacteremia

5. Meningitis

Some Group D Streptococci, such as those that can cause UTIs, are now classified in the separate genus _____.

Enterococcus (can be antibiotic resistant)

In smaller labs, all beta-hemolytic strep isolates are presumptively identified as what?

Group A strep (*S. pyogenes*)

In smaller labs, all alpha-hemolytic strep isolates are presumptively identified as what?

S.pneumoniae

What serves as a portal of entry for Staphylococci into underlying tissues?

Breaks in the skin and mucous linings

What does Staphylococcus aureus cause?

It’s pathogenic, so it can cause boils, toxic shock syndrome, food poisoning, and infections dealing with a wound