Module 18: Tests for Gram Positive Cocci

quinine derivative that has a detergent like action and causes selective lysis of pneucocci

optochin

Optochin Sensitivity test positive vs negative

positive- inhibition ring around the optochin disk

negative- absence of inhibition ring

optochin resistence on a blood agar plate confirms …

presence of S. pneumoniae

spherical bacteria that produce hemolysins capable of completely lysing(bursting open) red blood cells

Beta-hemolytic Streptococcus

area with no growth

zone of inhibition

Bacitracin Sensitivity Test positive vs negative

positive- inhibition ring around the optochin disk

negative- absence of inhibition ring around optochin disk

Blood Agar+Antibiotics test A-H

A- Substrate= RBC

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, colonies growing; ophtichon sensitivity is red around the A or no red rings around either

E- All positive organisms= Streptococcus pneumonia/alpha/optochon, Streptococcus pyogenes/beta/bacitracin, Enterococcus durans/no sensitivity

F- Differential agent= RBC

G- Selective agent= none

H- Name= Blood Agar + Antibiotics

for a Bile Esculin Test it is only positive if…

more than half the medium is dark brown or black after incubation

Bile Esculin Agar A-H

A- Substrate= esculin

B- Enzyme= many

C- Product= glucose + esculetin + FeS

D- indicator/indication= ferric ammonia citrate/black colonies

E- All positive organisms= Enterococcus durans

F- Differential agent= esculin

G- Selective agent= bile salt

H- Name= Bile Esculin Agar

Bile Esculin Test positive vs negative

positive- streak line is black

negative- streak line is clear