1. The Staphylococci: Isolation and Identification

2. Staphylococci
Collectively, the staphylococci and streptococci are referred to as pyogenic (pus-forming) gram-positive cocci
Implicated in many different type of infections
Skin infections like acne or boils, urinary tract infections , pneumonia, endocarditis, septicemia
Staphylococci occur in “grape-like” clusters
Staphylococci are part of the normal flora of nasal membranes, hair follicles, skin, and perineum in healthy individuals.
At least 40 different species of Staphylococcus
Staphylococcus are catalase positive
One way to differentiate Staph from Strep

3. Staphylococcus aureus
Produces certain enzymes that help distinguish from non-pathogenic staph
Pathogenic enzymes
Coagulase: promotes the formation of clots
Help seals the organism off from the immune system
Enterotoxin: toxin protein that causes food poisoning
Leukocidin: protein that destroys white blood cells
Hemolysins: enzymes that destroy red blood cells

4. Coagulase Negative Staphylococci
Coagulase Negative Staphyloccocus
Make up approximately 40 different species
Staphylococcus epidermidis
Normal skin flora
Can cause severe infections in immunocompromised patients and those with catheters or ports
Staphyloccous saprophyticus
Normal vaginal flora
Implicated in urogenital tract infections

5. Coagulase TEst
Coagulase is an enzyme that causes the fibrin of blood plasma to clot.
If test is positive: Staph aureus
If test is negative: Coagulase negative Staph

6. Slide agglutination Latex beads are coated antibodies for Protein A.
Protein A is a surface protein found on
Staphylococcus aureus
If test is positive: Staph aureus
If test is negative: Not Staph aureus
Note: You cannot say coagulase negative Staph because you have not performed a coagulase test

7. Streptococci: Isolation and Identification

8. Streptococci We will look at 2 systems to classify the Streptococci
Differ from Staphylococci:
Occur in chains
Lack the enzyme catalase
Can cause mixed infections with Staphylococci
Independently can cause:
Pneumonia, meningitis, endocarditis, pharyngitis, erysipelas, and glomerulonephritis
Fastidious microaerophilic organisms
Need extra nutrients for growth
More CO2 and less O2 than atmospheric levels
We will look at 2 systems to classify the Streptococci
Hemolytic patterns
antigens associated with the cells –Lancefield classification System

9. Hemolytic Patterns
Hemolysis: Ability of the bacteria to cause lysis of the red blood cells when grown on blood agar
Beta(β)- hemolytic
Complete destruction of the red blood cells and degradation of hemoglobin
Results in a clear area around the bacterial colony
These bacteria produce streptolysin O or S that are responsible for the lysis.
Alpha(α)-hemolytic
Viridians group of streptococci
Produce greenish/brownish zone around the colonies
Partial hemolysis (lysis of RBCs, but not breakdown of
hemoglobin
Gamma(γ)-hemolytic
Absence of hemolysis-no reaction surrounding the colony
NOTE: Pay attention to the color of the agar where the plate has been innoculated.

10. Lancefield Classification
Classification on the basis of immunological groups related to carbohydrate antigens associated with the cell
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Separates the streptococci into groups A, B, C, D and etc.

11. Lancefield Classification
Group A Streptococci
Beta hemolytic
Streptococcus pyogenes- strep throat
also can cause a variety of secondary infections if strept throat is not treated
Includes rheumatic fever, glomerulonephritis
A certain strain of group A can be known as flesh-eating bacteria
Sensitive to Bacitracin
Group B Streptococci
Streptococci agalactiae
Can be found in the normal flora of the vaginal mucosa but can be severely harmful to babies when they are born
Causes neonatal meningitis and septicemia

12. Lancefield Classification
Group D Streptococci
Alpha-hemolytic
Includes many non-pathogens
Enterococci
Occurs in the intestinal tract
Nonenterococci
Streptococci bovis
Found in the intestinal tract of humans and cows, sheep and other ruminants

13. Streptocard Acid Latex Test
Rapid test for Lancefield grouping
Does NOT work for Strep pneumoniae
Antibody-Antigen reaction- agglutination
A reagent with latex beads coated with a specific Lancefield antibody
Presumably only one antibody would recognize the antigen of the Streptococcus
Agglutination occurs when the antibody coated latex beads specifically bind to the specific antigen and crosslinks of multiple latex beads result
Visual Clumping of the latex beads

15. Staphylococcus vs Streptococcus
Staphylococci
Occurs in clusters
Catalase positive
Coagulase positive
Protein A - surface protein
Streptococci
Occurs in chains
Catalase negative
Lancefield Classification System