Quick Review Cards for Medical Laboratory Science

Streptococci/Enterococci Clinical Microbiology Review 161

ORGANISM PATHOGENICITY GRAM STAIN COLONIES ON SBA KEY CHARACTERISTICS OTHER

Streptococcusspp

Group A streptococci
(GAS)

Facultative anaerobes.

Require enriched

media. Chaining best

in broth cultures.

Most common is

S. pyogenes. Hemolysis

due to O 2 -stable

streptolysin S & O 2 -

labile streptolysin O.

To detect species that

produce streptolysin

O only, stab into agar,

place coverslip over

inoculum, or incubate

anaerobically.

Oval GPC in chains

& pairs

Oval GPC in chains

<1 mm, white to

gray, translucent,

or semiopaque.

Variable hemolysis.

Pinpoint. Grayish

white. Translucent.

Usually beta

hemolytic (wide

zone).

See specific organ-

isms below

Causes 90% of

strep infections.

Strep sore throat,

rheumatic fever,

glomerulonephritis,

scarlet fever (scar-

latina), erysipelas,

puerperal sepsis,

impetigo

Catalase neg

Sensitive to bacitracin.

Resistant to SXT. PYR pos

continued...