Dr. Taghreed Khudhur Mohammad
Lec.9 /2015
‫ المكورات الرئوية‬Streptoccocus pneumoniae
General characters: ‫الصفات العامة‬
1.
They are Gram-positive.
2.
Diplococci ‫مكورات ثنائية‬
3.
Capsulated. ‫تحتوي على كبسولة‬
4.
occur primarily in the human throat ‫بلعوم‬
and are the most common cause of pneumonia.
5.
They require enriched medium with blood,
serum for their growth. ‫تحتاج الى وسط غني‬
6.
On blood agar they produce alpha hemolysis,
Greenish . ‫تحلل جزئي اخضر‬
It is typically small (1 µ) slightly
It occurs in pairs ‫بشكل ثنائي تحيطها كبسولة‬
capsule enclosing each pair.
8. It is non-motile and non-sporing. ‫غير متحركة‬
9.
In India ink preparation
capsule appears as a clear halo ‫عند صبغها بصبغة‬
‫الحبر الهندي السالبة تنصبغ االرضية للساليد‬
10.
It grows best at 37°C and at
pH 7.6. It is aerobic and facultative anaerobic.
Growth is improved by providing them 5 to 10
percent CO2. ‫ ثاني اوكسيد الكاربون‬% 01 ‫تنمو بوجود‬
7.
On blood agar
On chocolate agar
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11. Biochemical reaction: It ferments many sugars forming acid only.
Inulin is fermented by all pneumococci. They are bile soluble (+) (few
drops of 10 percent sodium desoxycholate solution are added to 1 ml of
overnight broth culture.
12.catalase negative .
13. oxidase negative.
14.It is sensitive to optochin (ethyl hydrocuprein) in 1/80,000 and it is
useful in differentiating them from streptococci.
Antigenic structures:
a. Nucleoprotein: It is neither species specific nor type specific. Antibody to this
antigen is not protective.
b. Species specific polysaccharides hapten: It is situated at the cell surface and
is not related with capsular antigen.
c. Capsular polysaccharide is found in capsulated form. It determines type
specificity of organism and virulence. Pneumococci isolated from lobar
pneumonia are classfied into 4 types: I, II, III and heterogenous group IV.
Members of group IV are further classified into various types. Now about 90
types are known named 1, 2, 3, etc.
Typing may be carried out by:
1. Agglutination of cocci with type specific antiserum.
2. Precipitation of capsular polysaccharides with specific serum.
3. Capsular swelling reaction (Quellung reaction): Here suspension of pneumococci is
mixed with type specific antiserum. In presence of homologous antiserum the capsule
becomes apparently swollen, elineated and refractile.
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Toxin and Other Virulence Factors
1. Hemolysin: Pneumococcus produces soluble hemolysin in young culture.
It gives characteristic green coloration around colonies. ‫تنتج سم محلل للدم‬
2. It is oxygen labile and its role in the pathogenesis of pneumococcal
infection is not known.
3. Capsular polysaccharide: It is specific soluble substance which protects
the organism from phagocytosis. It is acidic and has hydrophilic
properties. Hence this substance has association with virulence.
4. Pneumococci produce large amount of enzyme resembling receptor
destroying enzyme of influenza virus ‫تنتج كميات كبيرة من االنزيمات تمثل كمستقبل محطم‬.
‫النزيمات فايروس االنفلونزا‬
5. Leucocidin: It kills leukocytes. ‫سم قاتل لكريات الدم البيض‬
Pathogenesis: ‫األمراضية‬
Pneumococci get attached to nasopharyngeal cell through bacterial
surface adhesion (pneumococcal surface antigen-A or choline binding
proteins) with epithelial cell receptors. Epithelial binding sites include
glycol-conjugates containing the disaccharide GlcHAc1-4 Gal or assialoGM1 glycolipid.
Pneumococci produce disease through their ability to multiply in the tissue.
They produce no toxins of significance. The virulence of organism is a
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function of its capsule, which prevents or delays ingestion of encapsulated
cells by phagocytes.
1. Pneumococcal infection causes an out pouring of fibrinous edema fluid
into alveoli, followed by red cells and leukocytes, which results in
consolidation of portion of lung. Many pneumococci are found
throughout this exudate. Later mononuclear cells actively phagocytose
the debris, and this liquid phase is gradually reabsorbed. The
pneumococci are taken up by phagocytes and are digested
intracellularly ‫ تسبب تليف في سوائل داخل القصيبات بعدها تجمع كريات الدم الحمر والبيض‬.
2.
suppurative infection ‫اصابات قيحية‬in various parts of body as Lobar
pneumonia ‫ في الفص الرئوي‬: Airborne infection ‫ بكتريا تنتشر في الهواء‬of
respiratory tract is a frequent occurrence. The organism is generally
eliminated by natural defense mechanism. If resistance is lowered,organism
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penetrates bronchial mucosa and spreads through lung along peri-bronchial
tissue and lymphatics. ‫تخترق الغشاء المخاطي للجهاز التنفسي وتنتشر في الرئة والقصيبات والعقد اللمفاوية‬
3.
Bacteremia is frequent during early stages. ‫وجود البكتريا في الدم‬
4. Toxemia ‫ وجود السم في الدم‬is due to diffusion of capsular polysaccharide
into blood and tissue. The fall of temperature by crisis and relief coincide
with complete neutralization of capsular polysaccharide by anti-capsular
antibodies. Serotypes 1 to 8, 12 ,41,are mostly the cause of pneumonia. Type
3strain produces particularly severe infection ‫تسبب اصابات قوية‬.
5. Bronchopneumonia: It is always secondary infection following viral
infection of respiratory tract. Bronchopneumonia may be caused by
any serotype of pneumococci. ‫رئوي قصبي يحدث بعد االصابة باالنفلونزا كاصابة ثانوية‬
6. Pneumococcal meningitis ‫السحايا‬is most serious pneumococcal infection.
It occurs when pneumococcal pneumonia is persistant. Disease is
common in children .
7. Suppurative lesions like empyema ‫وجود قيح وسوائل‬, pericarditis ‫التهاب‬
‫غشاف القلب‬, otitis media ‫ألتهاب االذن‬, sinusitis ‫ ألتهاب الجيوب االنفية‬,
conjunctivitis ‫ألتهاب القزحية‬and peritonitis ‫ألتهاب البريتون‬.
Laboratory Diagnosis ‫التشخيص المختبري‬
Bacteriological tests:
Specimens: Sputum, cerebrospinal fluid,pleural fluid, pericardial fluid,
peritoneal fluid , ear swab , and pus discharge are collected in a sterile
container.
1. Smear examination: Gram staining shows flame-shaped cocci
arranged in pairs and they are Gram-positive capsulated.
2. Culture: sample is inoculated on blood agar plates and incubated at
37°C under 5 - 10 % (CO2). Growth occurs after overnight
incubation. Blood culture: It shows flat, umbonated colonies showing
alpha hemolysis.
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3. The colonies are treated for inulin fermentation.
4. Bile solubility .
They are bile soluble (+) (few drops of 10 percent sodium deoxycholate solution are added to 1 ml of overnight broth culture.
5. Optochin sensitivity test to differentiate it from Streptococcus
viridans.
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6. Catalase negative.
Catalase is an enzyme, which is produced by microorganisms that live in
oxygenated environments to neutralize toxic forms of oxygen metabolites; H2O2. The
catalase enzyme neutralizes the bactericidal effects of hydrogen peroxide and protects
them. Anaerobes generally lack the catalase enzyme.
7. Oxidase negative:
This oxidase enzyme catalyzes the oxidation of cytochrome c.
Organisms which contain cytochrome c as part of their respiratory chain are
oxidase-positive and turn the reagent blue/purple. The test reagent, N, N, N’,
N’-tetramethyl-p-phenylenediamine dihydrochloride acts as an artificial
electron acceptor for the enzyme oxidase. The oxidised reagent forms the
coloured compound indophenol blue.
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Immunologic methods:
The detection of pneumococcal capsular polysaccharides in sputum and
other body fluids by immunologic methods such as counter
immunoelectrophoresis or latex agglutination provides an alternative to
bacteriologic techniques for presumptive diagnosis of pneumococcal
infection. Because of cross-reactions between the polysaccharides of
pneumococci and other bacterial species, immunologic diagnosis is less
specific than bacteriologic diagnosis. The Quelling reaction is a
biochemical reaction in which antibodies bind to the bacterial capsule of
Streptococcus pneumoniae .
Animal pathogenecity:
Mice are most susceptible to pneumococcal infection (except type 14). It is
used for rapid diagnosis. Sputum is emulsified with saline. One ml is
inoculated intraperitoneally into 2 mice. Animal usually dies within 24
hours. The encapsulated diplococci can be demonstrated in heart blood and
peritoneal fluid.
Treatment: Sulfonamides and penicillins are quite effective drugs.
Resistance may develop with antibiotics like sulfonamides and tetracycline.
Rarely penicillin resistant strains of pneumococci do occur.
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Q- Compare between Streptococcus pneumoniae and Streptocccus viridanse ?
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