Module Four Pre-assessment

Question 1

The catalase test is frequently used to differentiate Strep spp. from Entero spp.

Answer 1

Catalase uses hydrogen peroxide. Organisms are mixed with hydrogen peroxide. If the organism produces the enzyme catalase it will split the hydrogen peroxide into oxygen and water and this will produce a bubbling reaction. This test is commonly used to differentiate Strep spp. from Staph spp. Staph are catalase pos and Strep are catalase neg.

Question 2

A Gram-positive cocci grows on blood agar and produces beta-hemolytic, small opaque, butyrous colonies that appear slightly golden and are catalase-positive. This can be indicative of staph aureus.

Answer 2

True

Question 3

Strep spp. and Entero spp. are catalase negative, Gram positive cocci that present in pairs and chains on a Gram stain.

Answer 3

True

Question 4

The M protein is a virulence factor of Strep pyogenes that help the organism to resist phagocytosis and also aids in adherence to the host mucosal cells.

Answer 4

True

Strep pyogenes also has protein F, lipoteichoic acid, hyaluronic acid capsule, hemolysins and other toxins and enzymes

Question 5

Strep agalactiae produces alpha-hemolytic colonies on blood agar.

Answer 5

False

Strep agalactiae produces small gray-white mucoid colonies with a small zone of beta hemolysis.

Strep pneumoniae and members of viridans streptococci produce colonies on blood agar that are alpha-hemolytic.

Question 6

Novobiocin susceptibility is useful to help differentiate coagulase-negative Staph spp. from Staph aureus

Answer 6

False

Novobiocin helps to identify Staph saprophyticus from other coagulase-negative staph. It is important in urine samples to identify staph saprophyticus, it is resistant to novobiocin.