Streptococcus pneumoniae Flashcards
Classify S. pneumoniae:
Gram + Strep = chains; Coccus = round Non-typable (i.e. they lack Lancefield antigens) Alpha-hemolytic Catalase negative Inhibited by optochin and bile salts
Appear as “Lancet shaped diplococci”*
What diseases does S. pneumoniae primarily cause?
1) Community-acquired pneumonia
2) Bacterial meningitis (except during epidemics, which Neisseria causes)
3) Otitis media in children and adults (H. influenza is second)
4) Acute purulent sinusitis (H. influenza is second)
What other diseases can S. pneumonia cause, but isn’t the primary agent that causes it?
1) Sepsis (secondary from primary pneumonia/meningitis)
* *Can be primary cause in asplenic and/or immunocompromised pts
2) Endocarditis (very infrequent cause)
There are 10 virulence factors (VF) of S. pneumoniae. Attempt to name them:
1) Polysaccharide capsule
2) Pneumolysin
3) Hyaluronidase
4) Neuraminidase
5) Pili
6) Lipoproteins
7) Peptidoglycan + Teichoic acid
8) Choline-binding proteins (CBPs)
9) Competence protein
10) Autolysic, LytA
Which VF is the most important for S. pneumonia? It’s purpose?
Polysaccharide capsule.
Prevents phagocytosis
What is a diagnostic test that uses the polysaccharide capsule to ID S. pneumonia?
Quellung reaction.
–anti-capsule antibodies bind to the bacteria, stabilizing the capsule (makes it appear to swell)
This VF is a pore-forming toxin the binds to cholesterol in cell membranes, causing cell lysis:
Pneumolysin
**cell lysis attracts PMNs, T&B lymphocytes, and mediates TLR4 inflammation
This VF is responsible for S. pneumonia being classified as alpha-hemolytic:
Pneumolysin
This VF allows increased adhesion to epithelia cells:
Pili
This VF allows increased spread into hyaluronic acid rich tissues:
Hyaluronidase
This VF allows S. pneumonia to obtain DNA from its environment:
Competence protein
This VF is a subtype of choline-binding proteins, important in cell wall remodeling during division and also for increased release of inflammatory contents from it’s own cell wall:
Autolysin, LytA
–if inactivated, S. pneumonia is much less virulent
This VF can:
1) be hydrolytic, releasing inflammatory cell wall fragments
2) bind nasopharyngeal or lung epithelia
3) bing complement factor H
Which VF is this?
Choline-binding proteins (CBPs)
- -LytA is the hydrolytic enzyme
- -PsaA binds to nasopharyngeal/lung tissue
- -PspA and PspC bind complement factor H, preventing phagocytosis
How is peptidoglycan + teichoic acid virulent?
They bind together, forming C-polysaccharide (CP)
–CP can bind to CRP, activating complement and increase inflammation
–CP can bind pathogen recognition receptors (PRR), causing cytokine release from macrophage
This VF is a cell-surface molecule that assists in iron uptake:
Lipoproteins
How is S. pneumonia transmitted?
Close contact in crowded areas
Where on the body can you find S. pneumonia?
Who is more likely to carry it?
1) It has a niche in the human nasal cavity
2) 60% healthy kids, 30% healthy adults asymptomatically carry it.
–primary vector is children, then 65+ y/o adults
When are you more likely to get a disease from S. pneumonia?
Midwinter
What are the tell-tale signs of pneumonia from S. pneumoniae?
Signs/Symptoms: Cough, fatigue, fever, shaking chills, sweats, SOB, pleuritic chest pain, rust-colored sputum
Physical exam: Diminished respiratory excursion (i.e. light breathing, due to chest pain), increased RR, increased tactile fremitis, inspiratory crackles, infiltrates on CXR
How do you diagnose pneumonia?
1) Sputum sample
- -sample should have little saliva, few epithelial cells
2) CXR
How do you treat pneumonia? (Outpatient and Inpatient)
1) Outpatient: give them a macrolide and doxycycline, amoxicillin (+/- clavulonic acid), or quinolone
2) Inpatient: Macrolide + penicillin, ampicillin, or ceftriaxone
As a general rule, you treat a person with pneumonia for 10-14 days. What is a possible complication from this?
1) Abx resistance
2) Clostridium difficile super-infection
How does a person with S. pneumonia most commonly acquire meningitis as a disease?
Bacteremia from a pneumonia infection.
Symptoms of meningitis?
HA, stiff neck, photophobia, seizures, coma, frontal bulge in infants above fontanel
How do you diagnose meningitis?
Blood and CSF cultures
Treatment for meningitis?
1) Vancomycin (#1 choice by doctors)
2) Ceftriaxone (if susceptible)
How does a person get an otitis media infection?
Nasal colony travels through the eustachian tube into the middle ear.
Neuroaminidase is an important VF here
How do you dx otitis media?
Look at the tympanic membrane for redness, swelling/bulging, and rupture.
How do you tx otitis media?
1) Amoxicillin + clavulanic acid (Augmentin)
2) Ceftriaxone (if amoxicillin doesn’t work)
How do you know sinusitis is a from a bacterial infection, like S. pneumonia?
Purulent discharge occurs.
Tx it like you would otitis media (amoxicillin + clavulonic acid, i.e. Augmentin)
What are 4 predisposing risk factors to increase one’s chance of getting disease from S. pneumonia?
1) Asplenia (less clearance of encapsulated bugs)
2) Complement/antibody defects
3) Diabetes, chronic lung disease, CHF, alcohol abuse, (bad PMN’s)
4) Prior URI
What can you give to ppl that have predisposing rick factors for infection from S. pneumonia?
1) Pneumovax: vaccine with 23 capsular polysaccharides from the 23 most common serotypes
2) Prevnar 13: 13 most common serotypes attached to attenuated diptheria toxin
