Microbio section 5 and experiment 17 fram-positive pathogenic cocci and ID of pathogens from a clincial specimen

Strep pnemoniae cellular arrangement

diplococci

Streptococcus faecalis (Enterococcus faecalis)

Chains or pairs

Streptococcus pyogenes

Long chains

Staphylococcus aureus

clusters

Staphylococcus saprophyticus

Clusters

Staphylococcus epidermidis

clusters

beta hemolysis

Complete hemolysis, giving a clear zone with a clean edge around the colony

alpha hemolysis

partial hemolysis (green)

gamma hemolysis

no hemolysis

bile esculin positive/negative

positive= blackening → hydrolysis of esculin in presence of bile

negative= no darkening

catalase positive/neg

positive=bubbles

negative=no bubbles

coagulase positive/negative

positive= clotting (s.aureus)

negative= no clotting

Mannitol salt agar

selective for salt growing organism differential for mannitol fermenting organisms (s. aureus)

If positive for mannitol fermentation what color will the plate be?

yellow

MAC plates are

selective for gram negative and differential for lactose fermentors (hot pink if ferments lactose)

A discs

bacitracin

-8-10 mm = positive

-sensitive for group A strep species

P discs

-Optochin

-Distinguishes Strep pneumoniae

-10-12 mm

how to perform a catalase test?

hydrogen peroxide drop, loop with bacteria,

bubbles=positive

Direct smear

smear made directly from a clinical sample, not from a culture plate or broth. Example, a smear of asputum sample

State the correlation between the catalase test and cellular arrangement

taphylococci grow in clusters and are catalase positive (bubble with H₂O₂).

Streptococci/Enterococci grow in chains or pairs and are catalase negative (no bubbles).

how to tell if immunoassay is positive for strep Pyogenes ?

pink and blue line (just blue is negative for control)