Module 17: Tests for Gram Positive Cocci

allows organisms to break down harmful metabolites of aerobic respiration

catalase

test that determines if the organism produces the enzyme “Catalase” which breaks down hydrogen peroxide (H2O2)to water and oxygen

catalase test

Positive vs Negative Catalase results

positive- bubbles

negative- no bubbles

Catalase A-H Reaction Info

A- Substrate= hydrogen peroxide (H2O2)

B- Enzyme= catalase

C- Product= H2O + O2

D- Indicator/Indication= no indicator/bubbles

E- All positive organisms= Staphylococcus epidermis, Mircrococcus luteus, Staphylococcus aureus, Bacillus subtilis

F- Differential agent= H2O2

G- Selective agent= none

H- Name= Catalase test

contains a high salt concentration

mannitol salt agar

mannitol salt agar contains what pH indicator

Phenol Red (at neutral pH)

Mannitol Salt Agar test A-H Reaction

A- Substrate= mannitol sugar

B- Enzyme=mannitol dehydrogenase

C- Product= pyruvic acid

D- Indicator/indication= phenol red pH indicator/yellow, red with colonies, or no color colonies

E- All positive organisms= Staphylococcus aureus

F- Differential agent= mannitol

G- Selective= NaCl 8%

H- Name= Mannitol Salt Agar or MSA

positive vs negative mannitol salt agar

positive- growth and yellow negative= growth and any other color

Gram negative negative bacillids all have

gamma hemolysin

Blood Agar A-H Results

A- Substrate= RBC+other blood proteins

B- Enzyme= alpha, beta, gamma hemolysin

C- Product= amino acids

D- Indicator/indication= none/changes in the agar alpha=olive, beta= clear, gamma no color change , colonies growing

E- All positive organisms= Staphylococcus epidermis, Micrococcus luteus, Staphylococcus auerus, Bacillus subtilis

F- Differential= RBC

G- Selective agent= none

H- Name= Blood Agar

hemolysis evident by color change from bright red to olive, surrounding the area around the colonies

Alpha

hemolysis is evident by color change from bright red to clear area around the colonies

Beta

Hemolysis is evident by colony growth on the medium with no noticable change in color in the agar around the medium

Gamma

coagulase test positive vs negative

positive- solid substrate in the bottom of the tube

negative- liquid throughout the tube

Coagulase test A-H reaction info

A- Substrate= prothrombin

B- Enzyme= coagulase

C- Product= fibrin(solid mass)

D- Indicator/indication= none/hard nodule or mass

E- All positive organisms= Staphylococcus aureus

F- Differential agent= prothrombin

G- Selective agent= none

H- Name= Coagulase test

A differential medium that tests the ability of an organism to produce an exoenzyme (deoxyribonuclease/DNase)

DNase

DNase Agar positive vs negative results

positive- clear around streak

negative- no clear area around the streak or remains blue

DNase A-H Reaction

A- Substrate= DNA

B- Enzyme= DNase

C- Product= Oligonucleotides

D- indicator/indication= methyl green DNA stain/clear zone around colonies

E- All positive organisms= Staphylococcus aureus

F- Differential DNA= DNA

G- Selective agent= none

H- Name= DNase Agar