Streptococcus pneumoniaeStreptococcus pneumoniae

Pavithra G. PalanPavithra G. Palan

INTRODUCTION:INTRODUCTION:

Common name Common name PneumococcusPneumococcus..

Formerly known as Formerly known as DiplococcusDiplococcus pneumoniaepneumoniae..

Has been reclassified as S. pneumoniae Has been reclassified as S. pneumoniae because of its genetic relatedness to because of its genetic relatedness to streptococcus.streptococcus.

Normal inhabitants of the upper respiratory Normal inhabitants of the upper respiratory tract of human beings.tract of human beings.

MORPHOLOGY:MORPHOLOGY: Pneumococci are Gram Pneumococci are Gram

positive small(1positive small(1μm), μm), slightly elongated cocci, slightly elongated cocci, with one end broad & other with one end broad & other end pointed, presenting a end pointed, presenting a flame shapedflame shaped or or lanceolate appearance.lanceolate appearance.

They occur in pairs, with They occur in pairs, with the broad ends opposing the broad ends opposing each other.each other.

They are capsulated & the They are capsulated & the capsule encloses each capsule encloses each pair.pair.

They are nonmotile & They are nonmotile & nonsporing.nonsporing.

CULTURE & CULTURAL CHARACTERISTICS:CULTURE & CULTURAL CHARACTERISTICS:

They grow only in enriched media.They grow only in enriched media.

They are aerobes & facultative anaerobes.They are aerobes & facultative anaerobes.

The optimum temperature being 37The optimum temperature being 37ºC & pH ºC & pH 7.8.7.8.

Growth is improved by 5-10% CO2.Growth is improved by 5-10% CO2.

Media used:Media used: Blood agar Blood agar

Colony morphology:Colony morphology: On blood agar, after On blood agar, after

incubation for 18 hours, the colonies are small, incubation for 18 hours, the colonies are small,

dome shaped & glistening, with an area of dome shaped & glistening, with an area of

α-haemolysisα-haemolysis..

On further incubation the coloniesOn further incubation the colonies

become flat with raised edges & central become flat with raised edges & central

umbonation called as umbonation called as DraughtsmanDraughtsman or or carromcarrom

coin coin appearance.appearance.

BIOCHEMICAL REACTIONS:BIOCHEMICAL REACTIONS:

1)1) Catalase test: Negative.Catalase test: Negative.

2)2) Bile solubility test: Positive.Bile solubility test: Positive.

3)3) It ferments inulin.It ferments inulin.

Catalase test

Bile solubility test

PATHOGENICITY:PATHOGENICITY:

Source of infectionSource of infection::

i)i) Endogenous- from the colonized area.Endogenous- from the colonized area.

ii)ii) Exogenous- patients or carriers.Exogenous- patients or carriers.

Mode of infectionMode of infection: By inhalation.: By inhalation.

Antigenic structure:Antigenic structure:

1.1. Capsular polysaccharideCapsular polysaccharide::

It is the most important antigen & type specific.It is the most important antigen & type specific.

Since it diffuses into infective tissue & culture Since it diffuses into infective tissue & culture medium it is called as medium it is called as specific soluble specific soluble substance(SSS)substance(SSS)..

Pneumococci are classified into types based on Pneumococci are classified into types based on the nature of capsular polysaccharide & more than the nature of capsular polysaccharide & more than 90 serotypes are recognised & named 1,2,3…...90 serotypes are recognised & named 1,2,3…...

2. 2. M proteinM protein:: It is not associated with virulence.It is not associated with virulence.

3. 3. ‘C’ Carbohydrate antigen‘C’ Carbohydrate antigen::

- It is present in all pneumococci so species specific. - It is present in all pneumococci so species specific.

- An abnormal protein(- An abnormal protein(β-globulin) that precipitates with β-globulin) that precipitates with ‘C’ carbohydrate antigen of pneumococci, appears ‘C’ carbohydrate antigen of pneumococci, appears in the acute phase sera of cases of pneumonia but in the acute phase sera of cases of pneumonia but disappears during convalescence. It also detected in disappears during convalescence. It also detected in sera of patients with some other illness. This is sera of patients with some other illness. This is known as the known as the CC--RReactive eactive PProtein(rotein(CRPCRP). It is an ). It is an ‘acute phase’ substance, produced in hepatocytes. ‘acute phase’ substance, produced in hepatocytes. Its production is stimulated by bacterial infections, Its production is stimulated by bacterial infections, inflammation, malignancies & tissue destruction.inflammation, malignancies & tissue destruction.

Virulence factorsVirulence factors::

1.1. Capsule: It is antiphagocytic.Capsule: It is antiphagocytic.

2.2. Pneumolysin: It is a membrane damaging Pneumolysin: It is a membrane damaging toxin has cytotoxic and complement toxin has cytotoxic and complement activating properties.activating properties.

Antigenic structure & virulence factors of S.pneumoniae

Mechanism of PathogenesisMechanism of Pathogenesis::

Entry of pneumococci into nasopharynxEntry of pneumococci into nasopharynx

Colonization of nasopharynx Colonization of nasopharynx

May cause infection of the middle ear, paranasalMay cause infection of the middle ear, paranasal sinuses & respiratory tract by direct spreadsinuses & respiratory tract by direct spread

Infection of meninges can also occur, by contiguity orInfection of meninges can also occur, by contiguity or through bloodthrough blood

Enters blood causing bacteremia, which may alsoEnters blood causing bacteremia, which may also lead to disseminated infections as in the heart,lead to disseminated infections as in the heart, peritoneum or jointperitoneum or joint

Disease:Disease:

1. Otitis media & sinusitis1. Otitis media & sinusitis

2. Pneumonia2. Pneumonia a. Lobar pneumoniaa. Lobar pneumonia b. Bronchopneumonia b. Bronchopneumonia

3. Tracheobronchitis3. Tracheobronchitis

4. Meningitis4. Meningitis

5. Other infections- empyema, pericarditis, 5. Other infections- empyema, pericarditis, conjunctivitis, suppurative arthritis & peritonitis. conjunctivitis, suppurative arthritis & peritonitis.

LABORATORY DIAGNOSISLABORATORY DIAGNOSIS::

Specimens to be collectedSpecimens to be collected: :

Sputum,Sputum, CSF,CSF, Blood, Blood, Synovial fluid,Synovial fluid, In children laryngeal swab can be taken if In children laryngeal swab can be taken if

sputum can not be collected.sputum can not be collected.

Methods of examinationMethods of examination::

1.1.Direct microscopyDirect microscopy::

Gram stainedGram stained

smears revealssmears reveals

Gram positiveGram positive

lanceolate shapedlanceolate shaped

diplococci withdiplococci with

numerous pus cells.numerous pus cells.

2. 2. Quellung( capsular swelling ) reaction:Quellung( capsular swelling ) reaction: It is described by Neufeld.It is described by Neufeld. On a slide the sputum is mixed with type On a slide the sputum is mixed with type

specific antiserum against capsular antigen & specific antiserum against capsular antigen & a loopful of methylene blue solution. The a loopful of methylene blue solution. The capsule becomes swollen & refractile.capsule becomes swollen & refractile.

3. 3. Antigen detectionAntigen detection: Capsular polysaccharide: Capsular polysaccharide

antigen in blood, CSF & urine can detected byantigen in blood, CSF & urine can detected by

Passive latex agglutination,Passive latex agglutination,

Counter immunoelectrophoresis,Counter immunoelectrophoresis,

Coaggutination.Coaggutination.

Counter immunoelectrophoresis

4. 4. CultureCulture::

a) Media used:a) Media used:

b) Colony morphology: b) Colony morphology:

c) Gram’s smear:c) Gram’s smear:Smears are examined Smears are examined from the culture plate from the culture plate and reveals Gram and reveals Gram positive lanceolate positive lanceolate

shaped diplococci.shaped diplococci.

d) Capsular swelling reaction: Positive. d) Capsular swelling reaction: Positive.

It is done by mixing the suspension of It is done by mixing the suspension of colonies from the culture plate and a loopful colonies from the culture plate and a loopful of type specific antiserum & a drop of of type specific antiserum & a drop of methylene blue solution on a slide.methylene blue solution on a slide.

e) Biochemical reactions:e) Biochemical reactions:

f) Optochin sensitivity: Sensitive.f) Optochin sensitivity: Sensitive.

5. 5. Animal inoculationAnimal inoculation: From specimens where : From specimens where organisms are expected to be scanty, organisms are expected to be scanty, isolation may be obtained by intraperitoneal isolation may be obtained by intraperitoneal inoculation in mice.inoculation in mice.

6. 6. Serology:Serology: Antibodies can be demonstrated Antibodies can be demonstrated by agglutination & precipitation test.by agglutination & precipitation test.

TREATMENT: TREATMENT:

For penicillin sensitive strains Penicillin is For penicillin sensitive strains Penicillin is drug of choice for serious cases & Amoxycillin drug of choice for serious cases & Amoxycillin for milder ones. for milder ones.

For penicillin resistant strains a third For penicillin resistant strains a third generation cephalosporin is indicated.generation cephalosporin is indicated.

Vancomycin is to be reserved for life Vancomycin is to be reserved for life threatening illness with highly resistant threatening illness with highly resistant strains.strains.

EPIDEMIOLOGY:EPIDEMIOLOGY:

Pneumococci occur in the throat of Pneumococci occur in the throat of approximately half the population sampled at approximately half the population sampled at the time. the time.

Spreading is facilitated by over crowding.Spreading is facilitated by over crowding.

Disease results only when the host resistance Disease results only when the host resistance is lowered by factors such as respiratory viral is lowered by factors such as respiratory viral infections, pulmonary congestion, infections, pulmonary congestion, malnutrition, immunodeficiency, stress & malnutrition, immunodeficiency, stress & alcoholism.alcoholism.

PROPHYLAXIS: PROPHYLAXIS: A polyvalent vaccineA polyvalent vaccine

containing the capsular antigens of 23 mostcontaining the capsular antigens of 23 most

prevalent serotypes is being used.prevalent serotypes is being used.

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