GPC Streptococcus

1
GPC - Streptococcus

• All Streptococcus species are Gram Positive Cocci
• Some will only grow on an enriched agar, like 5
  Sheep Blood Agar (SBA).
• On SBA the colonies are usually gray, punctiform,
  convex, and entire.
• The various species may exhibit alpha, beta, or
  gamma hemolysis.
• Biochemical tests
• Catalase test
• Susceptibility to Bacitracin
• Susceptibility to Optochin
• Growth in High Salt Broth
• Type of Hemolysis
• Bile Esculin test
• CAMP test
• Grouping of the Streptococci is based on
  carbohydrates (antigens) imbedded in the cell
  wall.
• This characteristic was discovered by Rebecca
  Lancefield in the 1930s.
• She characterized 14 different groups using an
  alphabetic system.
• Those producing b-hemolysis on SBA are members of
  the A, B, C, and G Lancefield Groups.
• The viridans group refers to the color of the
  SBA, the greening of the agar.

2
Hemolysis

• There are three types of hemolysis on blood agar
  plates alpha, beta, and gamma (gamma hemolysis
  is actually no hemolysis).
• Alpha ( a ) hemolysis produces a greening of the
  agar (viridians) that is due to partial digestion
  of the red blood cells (RBCs) in the agar.
• Beta ( b ) hemolysis produces a clearing of the
  agar that is due to the complete digestion of the
  red blood cells (RBCs) and hemoglobin in the
  agar.
• Gamma ( g ) hemolysis produces no change in the
  agar. There is actually no hemolysis of the RBCs
  in the agar.

The first image shows hemolysis as observed when
the plate is sitting on the lab bench and the
second image shows hemolysis when the plate is
held up to the light.
3
Susceptibility to Bacitracin

• The bacteria tested is considered to be
  susceptible (S) to the antibiotic if there is any
  zone of inhibition of growth. If a red-ring can
  be seen around the disc there is inhibition of
  growth.
• No red-ring indicates that the bacteria tested
  is resistant (R) to the antibiotic.
• Record the results for the organism tested as
  either (S), for susceptible, or (R) for resistant.

4
Susceptibility to Optochin

• The bacteria tested is considered to be
  susceptible (S) to the antibiotic if there is a
  zone of inhibition of growth of 15 30 mm in
  diameter.
• Zones of inhibition of growth of less than 15 mm
  are considered to be resistant (R) to the
  antibiotic.

5
CAMP Test

• The arrowhead hemolysis pattern is considered
  positive ( ) for this test.
• No hemolysis or indistinct hemolysis patterns are
  considered negative ( - ).

6
Bile Esculin Test

• Bile Esculin agar contains bile which inhibits
  the growth of many organisms.
• Some organisms can hydrolyze esculin to esculetin
  and dextrose. Esculetin will then react with
  ferric citrate in the media to produce a
  black-brown product.
• Blackening of the agar is considered to be a
  positive ( ) test.
• No change in the color of the agar is considered
  to be negative ( - ) for this test.

7
High Salt Test

• Organisms that can tolerate a high salt
  environment ( 6.5 NaCl) will grow in broth
  causing cloudiness or turbidity.
• Turbidity is considered positive ( ) for this
  test.
• No turbidity (cloudiness) or negligible turbidity
  is considered negative ( - ) for this test.