Staph and strepto

1. Lecture 5 & 6
Staphylococci & Streptococci
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2. Lecture-5
Staphylococci
Common inhabitant of the nasopharynx, skin and mucous
membranes
1. Morphology
Gram +ve cocci arranged in grape-like clusters
Non-motile and non-sporing
Species :
Staphylococcus aureus : main pathogen
S. epidermidis : opportunistic
S. saprophyticus : UTI
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3. Laboratory Characteristics
2. Culture:
 They grow on ordinary media
 Optimal temperature 370c & pH= 7.4-7.6
 Aerobic & facultative anaerobic
Colonies on different Culture media :
 Nutreint & Blood agar: smooth, circular, golden yellow
pigmented appearance
 MacConkey agar: pink due to lactose fermentation
 Mannitol salt agar: colonies yellow color due to
fermentation of Mannitol
 can tolerate 8-10 % NaCL.
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4. NA
BA
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5. Staph aureus Staph
epidermidis
 Coagulase +ve -ve
 Dnase +ve -ve
 Phosphatase +ve -ve
 Growth on Yellow Red
Mannitol salt agar
 α-lysin +ve -ve
3. Biochemical Reactions; Differentiating Tests
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6. Virulence Factors:
A. Toxins and enzymes produced by S. aureus
Toxins Activity
Haemolysins α, β, γ, and δ Cytolytic, lyse erythrocytes of
various animal species
Fibronolysin Digests fibrin
Leucoccidin Kills leucocytes & macrophage
Entrotoxin food poisoining
Enzymes Activity
Hyaluronidase Breaks down hyaluronic acid
DNAase Hydrolysis DNA
Coagulase Clots Plasma
Other virulence factors include:
Peptidoglycan of the cell wall
Teichoic acid 6

7. Treatment: Drain Pus if any + Antibiotics
Antibiotic Sensitivity (Staphylococcus aureus)
1. Penicillin 95% ®: if sensitive, it is the best drug
2. Flu/Cloxacillin (Methicillin) Drug of choice
3. Fucidic Acid penetrate well in bones
4. Vancomycin if the organism is resist to
methicillin (MRSA)
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8. MRSA = Methicillin Resistant Staphylococcus aureus
MRSA: Also Resistant to Cloxacillin & Flucloxacillin
Treatment For MRSA = Vancomycin
Treatment of Staphylococcus aureus
 95% Resistant to Penicillin so treated by Cloxacillin if
Resistant to Cloxacillin or Methicillin = MRSA = so treat
with Vancomycin.
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9. Lecture 6: Streptococci
 Characters of Streptococci
 Gram positive cocci (GPC)
 1µm in diameter
 Chains or pairs
 Usually capsulated
 Non motile
 Non spore forming
 Facultative anaerobes
 Fastidious
 Catalase negative (Staphylococci are catalase positive)
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10. Classification of Streptococci
 Streptococci can be classified according to:
 Oxygen requirements
• Anaerobic (Peptostreptococcus)
• Aerobic or facultative anaerobic (Streptococcus)
 Serology (Lanciefield Classification): Carbohydrate
antigens
 Hemolysis on Blood Agar (BA)
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11. Serology: Lanciefield Classification
 Streptococci classified into many groups from A-K & H-V
 Classification based on C- carbohydrate antigen of cell wall
1. Groupable streptococci
• A, B and D (more frequent)
• C, G and F (Less frequent)
2. Non-groupable streptococci
• S. pneumoniae (pneumonia)
• viridans streptococci: e.g. S. mutans
 Causing dental carries
Streptococci
Group A
S. pyogenes
Group B
S. agalactiae
Group C
S. equisimitis
Group D
Enterococcus
Lanciefield classification
Other groups
(E-U)
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12. Classification of Streptococci Based on Hemolysis on
Blood Agar
Hemolysis on BA
– -hemolysis
Partial hemolysis
Green discoloration around the colonies
e.g. non-groupable streptococci (S. pneumoniae & S. viridans)
– -hemolysis
Complete hemolysis
Clear zone of hemolysis around the colonies
e.g. Group A & B (S. pyogenes & S. agalactiae)
– -hemolysis
No lysis
e.g. Group D (Enterococcus spp)
Streptococci
-hemolysis -hemolysis -hemolysis
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13. Hemolysis on Blood agar
-hemolysis
-hemolysis
-hemolysis
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14. Group A streptococci
 Include only S. pyogenes
 Group A streptococcal infections affect all ages peak
incidence at 5-15 years of age
 90% of cases of pharyngitis
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15. Disease caused by S. pyogenes
1. Suppurative (pyogenic infection)
 Non-Invasive
• Pharyngitis (“strep throat”)-inflammation of the pharynx
 Invasive
• Scarlet fever-rash that begins on the chest and spreads
across the body
• Pyoderma-confined, pus-producing lesion that usually occurs
on the face, arms, or legs
• Necrotizing fasciitis-toxin production destroys tissues and
eventually muscle and fat tissue
2. Non Suppurative
 Rheumatic fever: Life threatening inflammatory disease that
leads to damage of heart valves muscle
 Glomerulonephritits: Immune complex disease of kidney
• inflammation of the glomeruli and nephrons which obstruct
blood flow through the kidneys
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16. Identification of -hemolytic streptococci
 The following tests can be used to differentiate
between -hemolytic streptococci
1. Lanciefield Classification
2. Bacitracin susceptibility Test
• Specific for S. pyogenes (Group A)
3. CAMP test
• Specific for S. agalactiae (Group B)
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17. CAMP test
 Principle:
 Group B streptococci produce extracellular protein (CAMP factor)
 CAMP act synergistically with staph. -lysin to cause lysis of RBCs
 Procedure:
 Single streak of Streptococcus to be tested and a Staph. aureus are
made perpendicular to each other
 3-5 mm distance was left between two streaks
 After incubation, a positive result appear as an arrowhead shaped
zone of complete hemolysis
 S. agalactiae is CAMP test positive while non gp B streptococci are
negative
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18. CAMP test
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19. Bacitracin sensitivity
 Principle:
 Bacitracin test is used for presumptive
identification of group A.
 To distinguish between S. pyogenes
(susceptible to B) & non group A such as S.
agalactiae (Resistant to B).
 Bacitracin will inhibit the growth of group A
Strep. pyogenes giving zone of inhibition
around the disk.
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20. Differentiation between -hemolytic
streptococci: Viridans streptococci
 The following definitive tests used to differentiate
between S. pneumoniae & viridans streptococci
 Optochin Test
 Bile Solubility Test
 Inulin Fermentation
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21. Optochin Susceptibility Test
 Principle:
 Optochin (OP) test is presumptive test that is used to identify S.
pneumoniae
 S. pneumoniae is inhibited by Optochin reagent (<5 µg/ml) giving a
inhibition zone ≥14 mm in diameter.
 S. pneumoniae is positive (S) while S. viridans is negative (R)
Optochin susceptible
S. pneumoniae
Optochin resistant
S. viridans
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22. Bile Solubility test
 Principle:
 S. pneumoniae produce a self-lysing enzyme to inhibit the
growth
 The presence of bile salt accelerate this process.
Results: Positive test appears as clearing in the presence
of bile while negative test appears as turbid
 S. pneumoniae soluble in bile whereas S. viridans
insoluble
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23. Differentiation between -hemolytic streptococci
CAMP test
Bacitracin
sensitivity
Hemolysis
Negative
Susceptible

S. pyogenes
Positive
Resistant

S. agalactiae
Inulin
Fermentation
Bile
solubility
Optochin
sensitivity
Hemolysis
Not ferment
Soluble
Sensitive (≥
14 mm)

S. pneumoniae
Ferment
Insoluble
Resistant
(≤13 mm)

Viridans strep
Differentiation between -hemolytic streptococci
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24. Outline of differentiation between Gram-Positive cocci
e.g. S. epidermidis
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25. Prevention & Control
 Proper hygiene, Fairly readily killed by heat or by common
disinfectants
 Chemoprophylaxis
 Vaccination
Treatment
 By antibiotics : Penicillin G is the drug of the choice.
 In patients allergic to penicillin, erythromycin or cephalexin is
used.
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26.  Mention culture media for staph.
 Temp and pH for staph
 Activity of Hyaluronidase
 Activity of Leucoccidin
 Mention treatment of pus caused by Staphylococcus Infection
 Mention characteristics of Streptococci
 Lanciefield Classification
 -hemolysis
 Non Suppurative infection of S. pyogenes
 Principle of Bacitracin Sensitivity,
 Principle of bile solubility test
 Differentiation between -hemolytic streptococci
 Test to Identify -hemolytic streptococci
 Principle of CAMP test
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