Download The Staphylococci - IRSC Biology Department

THE
STAPHYLOCOCCI:
ISOLATION AND IDENTIFICATION
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
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
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
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
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
STREPTOCOCCI:
ISOLATION AND
IDENTIFICATION
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
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.
LANCEFIELD CLASSIFICATION
• Classification on the basis of immunological groups related to
carbohydrate antigens associated with the cell
• Page 115
• Separates the streptococci into groups A, B, C, D and etc.
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
– Beta hemolytic
– 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
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
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
STAPHYLOCOCCUS VS STREPTOCOCCUS
Staphylococci
•
•
•
•
Occurs in clusters
Catalase positive
Coagulase positive
Protein A - surface protein
Streptococci
• Occurs in chains
• Catalase negative
• Lancefield Classification
System