g positive cocci nursing-dr manar

Identification of Gram positive cocci

Dr. Manar AkasMicrobiology & Immunology

26/2/2015

Gram Positive cocci• 1- staphylococci• 2- streptococci• 3- pneumococci

Staphylococcus streptococci

Staphylococci-Staphylococcus aureus • (culture)Growth on Blood agar:• –yellow colonies (golden staph)• –Narrow zone of beta hemolysis• –Consistency of colonies is like butter, can be picked up easily by bacterial loop.

Streptococci-Streptococcus pyogenes• (culture) Growth on Blood agar:• –Pin point size colonies• –Wide zone of beta hemolysis• –Consistency of colonies is tough, can not be picked up easily by bacterial loop.

Catalase Test

Catalase production. •is responsible for the splitting of hydrogen peroxide (H2O2) into oxygen and water. •The oxygen is detected as a steady evolution of gas bubbles from the culture.

Staphylococci

• Coagulase test:

+ve : Staphylococcus aureus-ve : •Staphylococcus epidermidis•Staphylococcus saprophyticus •The enzyme coagulase

acts with a plasma factor to convert fibrinogen to a fibrin clot.

(clouding and solidification of plasma)

Staphylococcus aureus is known to produce coagulase, which can clot plasma into gel in tube. This test is useful in differentiating S.aureus from other coagulase-negative staphylococci.

Streptococci

*Lancefield grouping is a method of grouping beta hemolytic bacteria based on the carbohydrate composition of bacterial antigens found on their cell walls.

s. pyogenes: I live in the nose and mouth.pharyngitis - 'strep throat‘, abscesses, otitis media and sinusitis, cellulitis, rashes, gangrene, rheumatic fever and toxic shock.

S. agalactiae: I'm a Gram Positive coccus and a Beta hemolytic strept.In pregnant women, I cause premature labor & urinary tract infections - in the baby.I cause pneumonia, meningitis, shock and bacteraemia.

-ve CAMP testGroup A streptococcus

Staph aureus ferments mannitol turns pink to yellow( due to acid production)Staph epidermidis non mannitol fermenter> no color change( pink).

Thank you

Questions?