Pneumonia Workshop
Bacterial Etiology
Streptococcus pneumonia is Gm+ lancet shaped diplocci that can grow in chains. Alpha
hemolytic on BAP. Optochin-sensitive. Strict human respiratory pathogen carried in the
nasopharynx. Lots of colonization, most common in children or adults around children.
Serotype-specific immunity exists, but lots of serotypes. Higher carriage in winter. Disease
comes from new serotype exposure. Bacteria grow in edema fluid in alveolar spaces.
Erythrocytes accumulate in alveoli, creating a bloody cough. Neutrophils and macrophage then
accumulate. Rapid onset, shaking chill, sustained fever, productive bloody cough, chest pain.
Typically localized to a single lower lobe. Can also cause otitis media, bacteremia, and
meningitis. Pneumolysin is a toxin that autolysis, promoting virulence and induces monocytes
to produce TNF, enhancing IS response. Encapsulated bacteria are virulent. Require choline
nutritionally. Use choline-binding protein to sequester choline. IgA protease cleases IgA so
they can’t bind Ag. Neuraminidase removes sialic acids from host cell surfaces, exposing cells
for pneumococcal adherence. Dx. By Gm stain of sputum culture. Culture on BAP for optichin
sensitivity and hemolysis. Ag detection is also possible.Tx. with beta-lactam (1st), macrolide
(2nd), and vancomycin (3rd). Vaccine contains capsular antigen from common strains.
Haemophilus influenzae can cause pneumonia. Often accompanies S. pneumonia. Colonizes
respiratory tract. Dx. Culture. Tx. Cephalosporins, macrolides, and fluoroquinolones. Vaccine
linked to capsule polysaccharide linked to tetanus toxoid.
Mycoplasma pneumonia is prokaryote with no cell wall. Contains sterols, aerobic, fastidious.
“Walking pneumonia” is where pathogen attaches to the ciliated respiratory epithelial cells.
Mycoplasma matches TLR2 on respiratory epithelial cells and erythrocytes. This stops ciliary
action-> desquamate. Leads to immune response. Less than 3 y.o. URTI, 5-20 y.o. LRTI (primary
age group infected). Spread is via respiratory droplets. 2-3 wk. incubation period. Most infx.
result in disease. Fever, malaise, headache, cough. Sever cough but non-productive. Gm stain
negative. PE unremarkable but CXR with interstitial infiltrates. Can present with rash or
Raynaud’s when mycoplasma reaches erythrocytes. Dx. Cold agglutinin test. Also IgM and IgG
Ab to mycoplasma Ag. Culture of sputum takes 1-2 wks. to grow. Tx. Macrolides preferably.
Azithromycin is usually best choice.
Psudomonas aeruginosa particulary causes respiratory system infections with cystic fibrosis.
Causes ilateral diffuse infiltrates. Uses proteases to survive on thick mucus by killing IgA.
Alginate is an adhesion on the capsule that provides a mucoid aspect to colonies. Causes ADP
ribosylation of eukaryotic elongation factor 2 by exotoxin A, the same as diphtheria. Very
colorful under UV light. Also characteristic fruity odor. Sugar use and hemolysis. Tx.
Fluoroquinolones, aminoglycosides, and third generation beta lactams.
Rothia mucilaginosa is a major colonizer of oropharynx. Gm+ coccoid, grows in clusters. Very
mucoid and sticky. In immunocompromised can cause pneumonia.
Klebsiella pneumonia particularly in alcoholics. Capsule is major virulence determinant,
polysaccharide, thick and inhibits C3b activity. Dx. Positive chest x-ray, cavities due to necrosis
from abscess. Positive blood and sputum cultures, look like “currant jelly.” Short, Gm- rods,
nonmotile, lactose fermenting, urease positive. Tx. Extended-spectrum beta-lactams, newer
cephalosporins combined with aminoglycosides.
Legionella pneumophila Gm- rod. Thin watery secretions in upper airway. (most other
pneumonias are thick, purulent). Bronchoalveolar washings show the Gm- sample. Legionella
does do thick secretions in lower airway. No known person-to-person. Legionella found in tap
water and cooling reservoirs. Inhalation of aerosolized contaminated water. Most at risk are
smokers and immunosuppressed. The integrity of the mucociliary escalator is very important.
Pneumonia causes serious permanent damage. Pontiac fever comes with a higher attack rate
but is milder and self-limiting. Dx. Culture in Buffered Charcoal Yeast Extract. No growth on
BAP. Grows inside alveolar macrophages. Extracellular protease causes most of the lung
damage. “moth-eaten” lungs with fluid filled patches. Grow in amoeba Hartmanella
vermiformis. Must be inhalation of infected amoeba. Modified Gm stain using fuchsin instead
of safranin. Urinary Ag test plus sputum culture is best combination. Tx. Macrolide 1st
(azithromycin, clarithromycin), fluoroquinolone 2nd (ciprofloxacin, levofloxacin). If not caught
early there could be permanent loss of some lung function.
Staphylococcus aureus can cause pneumonia b/c of bacteremia. Can cause necrotizing
pneumonia via community acquired strains. Can adhere to mucosal cells/nasal epithelial cells
via teichoic acid.
Viral Etiology
SARS Coronavirus ssRNA+. Similar to rhinoviruses except there is usually no fever and coughs
and sore throat are rare. Replicates in the lungs and cuases extensive pneumonia. Dx. PCR,
ELISA, and viral culture. Only found in URT. No vaccines just Tx. with supportive care.
Adenoviruses can lead to LRT pneumonias. Usually benign though. Dx. Immunofluorescence or
virus isolation. Linear dsDNA.
Influenza (orthomyxoviridae) can cause pneumonia, more on that in the “Influenza workshop”.
Influenza usually starts in URT and can spread to the LRT. Causes destruction of cilia and leads
to heavy immune response.
Respiratory syncytial virus (paramyxoviridae) is a childhood disease targeting children under 2
y.o. Giant multinucleated cells called syncytia form. It is highly contagious and is closely
related to Parainfluenza virus. It is spread by aerosol and contact with hands/fomites.
Symptoms are similar to rhinovirus with expiratory wheeze normally. Shedding of virus
continues for 3 weeks after acute phase. Dx. With syncytia in culture. RSV affects LRT, causing
necrotizing bronchiolitis (mediated by the immune response). Peribronchial infiltration results
in interstitial pneumonia. Palivizumab is a monoclonal Ab that binds the F proteins and blocks
fusion. Male = female (PIV < 5 y.o. men>women).
Measles (paramyxoviridae) can be transmitted by aerosol. Characterized by a maculopapular
rash that starts on face and spreads to trunk and limbs. High fever and Koplik spots are key
indicators. In those with defective immunity, giant cell pneumonia may form. Passive
protection can come from immunoglobulin and vaccination comes from the MMR vaccine.
Varicella zoster virus (an alpha-herpesvirus): Can cause immune-mediated interstitial
pneumonia in adults and can be fatal. Maculopapular rash develops and is more severe in the
trunk than in the limbs. Vesicles form from the lesions and then crust over. It enters through
the respiratory system. There are vaccines now which are effective.
Cytomegalovirus (a beta-herpesvirus) in immunocompromised pts can cause pneumonia. In
adults it is sexually transmitted. Histologically shows “owl eye” inclusions. The virus is often
latent but can also remain persistent. Tx. With ganciclovir, valganciclovir, cidofovir, and
foscarnet to inhibit viral DNA synthesis.