gr b strep
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Group B Streptococci
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General features & Morphology
• Gram positive cocci in chains
• Ex. Streptococcus agalactiae
•
25% are colonizers in female vagina• Neonates are at risk during delivery
• May cause infection in mother
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Clinical features
• Important pathogen to cause neonatal
septiceamia and meningitis
• Genital tract infections in pregnancy
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Lab diagnosis
• Sample: vaginal swab
• Gram stain:
•
Culture: BA plate• CAMP TEST positive
• Hippurase positive
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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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CAMP Factor Test
S. aureus
(Spingomyelinase C) Group BStreptococcus
(CAMP Factor)
Group AStreptococcus
EnhancedZone of
Hemolysis
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Hippurase POS
Grp B Streptococci
and
Campylobacter
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Hippurase NEG
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Enterococcus faecalis
Enterococcus faecium
•
GI tract of humans and animals• Group D carbohydrate cell wall antigen
• Formerly Streptococcus
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Features and morphology
• Gram positive cocci in pairs
• Non heamolytic
•
Heat resistant-60 degree for 30 min• Grow in presence of 40% bile & 6.5% NaCl
• PYR test positive
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Clinical diseases
• Urinary tract infection
• Wound infections-mainly intraabdominal
•
Bacteremia• septicemia
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Lab diagnosis
• Grows in non selective media
• Forms non hemolytic colonies on BA
•
On MA-forms magenta colored colonies• Resistant to bile
• Esculin hydrolysis
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Bile Esculin Agar
POS
Enterococcus
Group D Streptococcus
Bile Esculin Agar
NEG
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Streptococci viridans
• Gram positive in long chains
• S.mutans is known to cause dental caries
•
Forms alpha hemolytic colonies on BA• Normal commensal in mouth
• Usually non-pathogenic
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Pathogenesis of dental caries
• Streptococcus mutans
• Breaks down dietary sucrose to acid and
dextran
• Dextran binds to food debris, mucus, and
epithelial cells to form dental plaque, while
Acid damages dentine
• Plaque leads to dental caries
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• Following tooth extraction these bacteria's
can deposited on damaged heart valves to
form vegetation's
• Causes subacute bacterial endocaritis in
persons with valvular heart disease, CHD and
cardiac surgery
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Lab diagnosis and treatment
• Optochin resistant
• Alpha hemolytic colonies on BA
•
Antibiotic prophylaxis before tooth extractionin patients with heart diseases.