Streptococcus Pneumoniae (pneumococcus) Flashcards
Gram-positive cocci
Diseases
- pneumonia, bacteremia,
meningitis, & upper respiratory tract infections (otitis media, mastoiditis, & sinusitis). - community-acquired
pneumonia, meningitis, sepsis in splenectomized individuals, otitis media, & sinusitis. - conjunctivitis in children.
Important Properties
- gram-positive lancet-shaped cocci arranged in pairs (diplococci) or short chains
- produce α-hemolysis on blood agar.
- lysed by bile or
deoxycholate & growth inhibited by optochin. - polysaccharide capsules 85 antigenically distinct types.
- With type-specific
antiserum, capsules swell (quellung reaction)-> identify type. - Specific antibody to capsule opsonizes organism, facilitates phagocytosis, & promotes resistance.
- develops by clinical or asymptomatic infection or administration of polysaccharide vaccine.
- Capsular polysaccharide elicits β-cell (Tindependent) response.
Important Properties:
C-reactive protein (CRP)
- teichoic acid in the cell wall called C-substance (C-polysaccharide).
- reacts with normal serum protein made by liver-> C-reactive protein (CRP).
- acute-phase protein elevated 1000-fold in acute inflammation.
- not antibody (γ-globulins) but β-globulin.
- nonspecific
indicator of inflammation-> elevated in presence of organisms, not just S. pneumoniae. - measured in lab by reaction with carbohydrate of S. pneumoniae.
- elevated CRP better predictor of heart attack risk than elevated
cholesterol level.
Transmission
- Humans-> natural hosts; no animal reservoir.
- not communicable.
- high Resistance in healthy young people, & disease results when predisposing factors present.
Pathogenesis
virulence factor -> capsular polysaccharide & anticapsular antibody-> protective.
Lipoteichoic acid-> activates complement induces inflammatory cytokine production->
inflammatory response & septic shock syndrome
(immunocompromised patients).
Pneumolysin->hemolysin-> α-hemolysis
produce IgA protease -> ability to colonize upper
respiratory tract mucosa by cleaving IgA.
reach alveoli-> outpouring of fluid & rbcs, wbcs -> lung consolidation.
Recovery->phagocytosis, mononuclear cells ingest
debris & consolidation resolves.
Pathogenesis:
Factors that lower resistance & predispose persons to infection
(1) alcohol or drug intoxication or cerebral impairment -> depress cough reflex & increase aspiration of secretions
(2) Respiratory tract abnormality (viral infections), mucus pooling, bronchial obstruction, & respiratory tract injury by irritants (disturb integrity
& movement of mucociliary blanket)
(3) abnormal circulatory dynamics (pulmonary congestion & heart failure)
(4) splenectomy
(5) chronic diseases
(sickle cell anemia & nephrosis).
- Patients with sickle
cell anemia auto-infarct their spleen, become functionally
asplenic-> predisposed to pneumococcal sepsis.
- Head Trauma-> leakage of spinal fluid through nose-> predisposes to pneumococcal meningitis
Clinical Findings
- sudden chill, fever, cough,
and pleuritic pain. - red or brown “rusty” Sputum.
- Spontaneous recovery-> 5 to 10 days with development of anticapsular antibodies.
- otitis media, sinusitis, mastoiditis, conjunctivitis,
purulent bronchitis, pericarditis, bacterial meningitis, & sepsis.
Lab Diagnosis
sputum-> lancet-shaped grampositive diplococci in Gram-stained smears
- quellung reaction with multitype antiserum.
- blood agar form small α-hemolytic bile-soluble colonies & growth
inhibited by optochin - positive Blood cultures
- Cerebrospinal fluid Culture + in meningitis.
- Rapid diagnosis -> detecting capsular polysaccharide in spinal fluid using latex agglutination test.
- detects urinary antigen (pneumonia & bacteremia).
- urinary antigen is C polysaccharide not capsular polysaccharide.
- Increasing penicillin resistant strains->antibiotic sensitivity tests done on
organisms isolated from serious infections.
Treatment
- severe ->penicillin G
- mild-> oral penicillin V
- fluoroquinolone with good antipneumococcal
activity (levofloxacin) - penicillin allergic-> erythromycin or azithromycin
- penicillin-resistant -> Vancomycin (severe)
- Ceftriaxone or levofloxacin (mild)
Prevention
- children under 5 immunized with 13-valent pneumococcal conjugate
vaccine (Prevnar 13). - Vaccine immunogen->
pneumococcal polysaccharide of 13 prevalent serotypes conjugated (coupled) to carrier (diphtheria toxoid).
Unconjugated 23-valent
pneumococcal vaccine (Pneumovax 23) given to
50 years or older.
Vaccines-> safe & effective & provide longlasting
(5 years) protection.
Immunization of children
reduces disease in
adults-> children main source of organism
for adults & immunization reduces carrier rate in
children.
Prevention: Booster shot recommended for
(1) older than 65 years, received vaccine more than 5 years ago & younger than 65 years when received vaccine
(2) between ages 2
& 64 years asplenic, HIV infected, receiving cancer chemotherapy, or immunosuppressants -> prevent transplant rejection.
Prevention vaccine problem: serotype replacement
- Will vaccine reduce disease caused by serotypes in vaccine but not overall disease -> serotypes not in vaccine will now cause disease?
- increase in disease by serotype 19A, not in past 7-valent vaccine.-> production of current conjugate vaccine containing 13 serotypes, including 19A.
