Streptococcus pneumoniae

(Pneumococci)

Sharq Elneil College

School of Medical Laboratory Sciences

Department of Microbiology

Medical Bacteriology course

Dr.Mahadi Hassan Mahmoud mahadi2010sd@yahoo.com

Bsc, Msc, MIBMS Microbiology

The natural habitat

pneumococci is provided by the

mucosa of the upper respiratory

tract.

About 40–70 % of healthy adults are

carriers. Pneumococcal infections .

Usually arise from this normal flora

(endogenous infections).

Morphology

Gram-positive, oval to lancet-

shaped cocci (0.5 and 1.25

micrometers in diameter)

usually occur in pairs or short

chains

surrounded by a thick capsule.

Culture &chaacteristics:

on blood agar,

Alpha -hemolytic colonies

Mucoid (smooth, shiny) appearance

Mutants without capsules produce

colonies with a rough surface (“R” form-

maintain integrity of nucleic acid target

streptococcus pneumoniae is a very

fragile bacterium

contains within itself the enzymatic

ability to disrupt and to disintegrate the

cells. autolysin.

The physiological role of this autolysin is

to cause the culture to undergo a

characteristic autolysis that kills the entire

culture when grown to stationary phase.

Virtually all clinical isolates of

pneumococci harbor this autolysin and

undergo lysis usually beginning between

18-24 hours after initiation of growth under

optimal conditions.

Autolysis is consistent with changes in

colony morphology.

Colonies initially appear with a plateau-

type morphology, then start to collapse in

the centers when autolysis begins.

Streptococcus pneumoniae is a

fermentative aerotolerant anaerobe

Unlike other streptococci, they do

not display an M protein.

they hydrolyze inulin, and their

cell wall composition is characteristic

both in terms of their peptidoglycan

and their teichoic acid.

Antigenic Structure

Classified in 90 different serovars

based on the fine chemical structure of

the capsule polysaccharides acting as

anti- gens.

This capsule antigen can be

identified using specific antisera in a

reaction known as capsular swelling

test ( Quelling reaction

Antiphagocytic.

Prevents the desposition of

complement and subsequent

phagocytosis (opsonisation) in the

absence of type-specific

antibodies.

These serotypes are number and

subdivided on the basis of

morphological similarity.

It was believed that most disease

is caused by the 23 serotype, this is

not the case locally. It causes:

otitis media, sinusitis, mastoiditis

and pneumonia ,joint infections,

endocarditis and meningitis.

Capsule protects the pathogens from

phagocytosis and is the most important

determinant of pneumococcal viru-lence.

Unencapsulated variants are not

capable of causing disease. Other

potential virulence factors include :

pneumolysin

IgA protease.

.

Pathology:

Predisposing factors include : primary cardiopulmonary diseases,

previous infections

(e.g., influenza)

extirpation of the spleen or

complement system defects.

Lobar pneumonia consolidated mass, in

contrast to the spongy texture of normal lung

tissue.

Bronchopneumonia.

Acute exacerbation of chronic

bronchitis

Otitis media

Sinusitis

important pneumococcal infections:

Meningitis

corneal ulcer.

Severe pneumococcal infections

frequently involve sepsis

Laboratory diagnosis

specimens:

Collection of Spacimen

Direct Exam

Culture

Identificaion

Serology

Molecular characterization

-

Pneumococci are sensitive to optochin

(ethylhydrocupreine hydrochloride).

Method: Placing a disc (5 g) on a primary

sputum culture and culturing the plate aerobically

(not in CO2) can help to provide a rapid

Result : The zone of inhibition should be at

least10 mm. Most viridans streptococci and other

alphahaemolytic streptococci are resistant to

optochin. If the zone of inhibition is less than 10

mm (6 mm disc) the colonies should be tested for

bile solubility

Optochin sensitivity

Method : a tube technique,

the results of which are easy to read.

Some workers, however, prefer to test

suspect alpha-haemolytic colonies directly

on a culture plate by touching a colony with

a loopful of 2% sodium deoxycholate

Incubation at 35–37 ºC for 30 minutes.

Result: examining for lysis (disappearance

of the colony, indicating S. pneumoniae).

*Bile solubility test

Agglutination Test

Latex agglutination tests are widely used

methods for identification and typing

The speed of the observed

agglutination reaction (positive

reactionwithin 10 s) is a great advantage.

The same is true for the ease of

interpreting a reaction as positive

compared to that in the normal capsular

reaction test.

pencillins

high-frequency occurrence of strains

resistant to penicillin

Cephalosporins

Cephalexin ceftriaxone

Macrolides

Treatments

Vancomycin

Erythromycin

Cotrimoxazole ( trimethoprim

+sulphamexazole)

extreme genetic flexibility

enabling S. pneumoniae to

acquire antibiotic resistance

switch the capsular serotype is a

result of the unique pneumococcal

feature: natural competence for

genetic transformation.

Antibiotic Resistant

Natural competence is a transient

physiological state enabling the

bacteria to acquire exogenous DNA.

Competence is regulated by

quorum sensing system and thus

depends on cell density and many

other factors

Pneumococcal infections are endemic

and occur in all seasons, more frequently

in the elderly. Humans are the natural

pathogen reservoir

Epidemiology and prophylaxis.

pathogen reservoir.

The vaccine product Pneumovax is

available for immunization purposes.

purified capsule polysaccharides

(PPV )

a seven-valent con-

seven-valent conjugate vaccine

effective in children of less than 2

year (PCV)

jugate vaccine that is effective in children under two years

form part of the normal microbial

flora of the upper respiratory tract

(particularly oropharynx) and

gastrointestinal tract.

They may therefore be found with

S. pneumoniae in sputum (as

commensals)

Streptococcus Viridans

Morphology

Gram-positive cocci

usually occur in pairs or long chains

Culture:

on blood agar,

Alpha -hemolytic colonies

the viridans group of streptococci can also

be nonhaemolytic and occasionally beta-

haemolytic.

A few species are pathogenic

.S. mutans,

S. sanguis,

S. mitior)

causing endocarditis, bacteraemia, and

dental caries.

S. anginosus group

(formerly S. milleri group)

associated with deep

abscesses in various sites in the

body (abdomen, chest, brain)

often in association with other

bacteria.

Compare between Pnuemoccci

and Viridans strepococci

Optrichoin Bile

solubility

Inulin

Ferment

pneumoco

cci

Sensetive Posotive Ferment

Viridans Resistant Negative Non

ferment

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