Genus Streptococcus Gram positive, Catalase negative cocci - PowerPoint Presentation

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Genus Streptococcus

Gram positive, Catalase negative cocci

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objectives* Study systemic bacteriology* Describe Genus Streptococcus, its types, pathogenesis, and lab diagnosis.

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When grown on sheep blood agar, streptococci display one

of three types of hemolysis of the red blood cells in the agar.

Alpha hemolysis-

-The red blood cells in the media are partially digested producing a greening of the agar.

Beta hemolysis-

-The red blood cells in the media are completely digested producing a clearing of the agar.

Gamma hemolysis-

-No change is noted in the agar. The red blood cells are not lysed.

Expected Hemolysis:

Streptococcus

pyogenes

always beta

hemolylic

Streptococcus

agalactiae

usually beta hemolytic

Streptococcus

pneumoniae

and

Viridans

streptococci

are always alpha

hemolylic

Enterococcus

faecalis

gamma hemolytic

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Hemolysis patterns on blood agar

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S.pyogenes on blood agar (beta hemolysis)

(Beta hemolysis) clear zone around colonies

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Alpha hemolysis (green discoloration)

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GENERAL CHARACTERISTIC:

* G+ve cocci , arrange in chains or pairs.* Some strains are capsulated

* Majority are facultative anaerobic, few are obligatory anaerobic.

*

Catalase –ve

* Non motile.

* Non spore forming

* Fastidious microorganism

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S.pyogenes (Group A β- hemolytic,GABH):

M-protein80 serotypes

Reservoir

Human throat

and

skin(N.F.)

Transmission

Spread by respiratory droplets or direct contact

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DISEASES S.pyogenes

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Acute Tonsillitis

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Laboratory Diagnostic steps

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Lab dx.of strept. Pyogenes

Specimens: sputum, throat swab, nasopharyngeal swab, blood, CSF…etc.Gram stain: G+ve cocci,

arrange in chains.

Culture:

on

blood agar



pinpointed, Grayish white, translucent, matte or glossy colonies with large zone of β- hemolysis.

Bacitracin disc

(0.04 U)



sensitive



causes zone of growth inhibition.

Serology

: Lancefield grouping, M-protein

serotyping

and

ASO test

(

Antistreptolysin

-O test).

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ASO test:* Measure Ab against Streptolysin O*ASO test uses in post streptococcal infection complication. This test used to determine significance streptococcal infection

by measuring the ASOT:* ASOT (Ab Titer): Normal < 200 < significance result

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S.pyogenes on blood agar (beta hemolysis)

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S.agalactia

(Group B β- hemolytic):

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Biochemical IdentificationChristie-Atkins, Munch-Petersen (CAMP) testDetects the production of enhanced hemolysis that occurs when b

-lysin and the hemolysins of Group B streptococci come in contact

Group B streptococci showing the classical “arrow-shaped hemolysis near the staphylococcus streak

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Identification

of group D Streptococci:

Lancefield Group D streptococci are divided into two groups: (1) Enterococci, and (2)

nonenterococci

.

Enterococcus

faecalis

and

Enterococcus

faecium

are the species of

Enterococcus

.

Strep.

bovis

and

Strep.

equinus

are species of "Group-D streptococci, not Enterococci".

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Enterococcus

(E.faecalis,

E.faecium

)

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Bile-

Esculin

Hydrolysis Test:

The purpose of this test is to determine the ability of an organism to hydrolyze the glycoside

esculin

to

esculatin

and glucose in the presence of bile (10 - 40%). This test aids in the differentiation of group D streptococci from other "not group D streptococci".

Procedure:

1. Inoculate the organism to be tested into the bile

esculin

medium. Incubate at 37

o

C for 24 hours (stab into

medium,then

streak on slant).

Positive Test: Presence of a black to dark brown color on the slant -(

Enterococcus

faecalis

) Negative Test: No blackening of the medium - (

Streptococcus

agalactiae

or Streptococcus

pyogenes

)

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Viridans Streptococcus

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Alpha hemolysis (green discoloration)

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S.pneumoniae

(Pneumococci,

Diplococcus

pneumoniae

)

Capsular polysaccharide

Gram +VE diplococcus

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Diseases

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CHARACTER

PNEUMOCOCCI

VIRIDANS STREPTOCOCCI

Morphology

Ovoid or

lanceolate

diplococci

Rounded cocci in short or long chains.

Capsule

Present

Absent

Optochin sensitivity

+

ve

-

ve

Bile solubility

+

ve

-

ve

Capsular swelling test (

Quelling reaction

)

+

ve

-

ve

Virulence in mice

+

ve

-

ve

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Lab dx

.

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Optochin disc for

S.pneumococci

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Question? Name this test

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THANKS