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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.