Pneumococcal pneumonia

Most common gram positive pneumonia
90% community acquired
Organism: strep pneumoniae
Usually found in compromised hosts, elderly, debilitated
Most often types 8, 4, 5 and 12
Type 3 is especially fatal to elderly
Sicklers are particularly prone to pneumococcal pneumonia
Produces inflammatory edema in the alveoli which spreads via pores of Kohn to more lateral alveoli

Imaging

Extensive infiltrate usually abutting pleural surface
Prominent air bronchograms (DDX: Staph has no air bronchogram)
Organism is aspirated into the lungs from the upper airways so it shows a predilection for lower lobes
Does not respect segmental boundaries
Resolution begins promptly with antibiotics – frequently within 24 hours
DDX for alveolar infiltrates with clearing in 24 hours includes

Hemorrhage into lungs,
Pulmonary edema
Pneumococcal pneumonia
Aspiration

Staph aureus pneumonia

Most common bronchopneumonia
Overwhelming majority hospital-acquired
Most common cause of death during influenza epidemics
Rarely develops in healthy adults
Hemolyzes blood agar

Coagulase positive

Its ability to produce pathology in humans is due to its production of coagulase
Produces its pathologic reaction in the conducting airways

Imaging

Rapid spread through the lungs
Empyema, especially in children
No air bronchogram
Pneumothorax

Pyopneumothorax

Abscess formation
Bronchopleural fistula
In children

Rapidly developing lobar/multilobar consolidation
Pleural effusion (90%)
Pneumatocoele
In adults
Patchy bronchopneumonia of segmental distribution, frequency bilateral
May be associated with atelectasis since airways are filled (not so with pneumococcal)
Pleural effusion (50%)

Streptococcus pyrogenes pneumonia

Most common in winter

Only 5% of bacterial pneumonias

Group A Beta hemolytic strep
Predisposed: Newborns and following measles

Imaging

Looks like staph pneumonia but with less of a tendency to produce pneumatocoeles
Almost always in the lower lobes
Patchy bronchopneumonia
Empyemas do form
Complications:

Bronchiectasis
Lung abscess
Glomerulonephritis

Associated with delayed onset of diaphragmatic hernias in newborns

Gram Negative Pneumonias

Pseudomonas aeruginosa

Gram negative rod
Frequently hospital acquired
Affects patients with COPD, CHF alcoholism, kidney disease, those with trachs
Frequently related to use of inhalators or nebulizers
Many patients are on multiple antibiotics and/or steroids

Imaging

Resembles staph pneumonia
Predilection for the lower lobes
Usually affects both lungs
Has multiple small lucencies within it
Lung abscess greater than 2 cm may also occur
Widespread nodular shadows is another manifestation

Klebsiella, Enterobacter, Serratia

Encapsulated, gram negative rods
Most are hospital acquired
Most are chronic alcoholics
Aspirated into lungs so most are unilateral and right sided

Imaging

Produces excessive amounts of inflammatory exudate which cause the affected lung to gain volume and the fissures to bulge
Abscess and cavity formation are common
Pleural effusion and empyema are common
May result in gangrene of the lung where massive pieces of lung tissue fall into an abscess cavity
Serratia marcescens may cause bronchopneumonia

Anaerobic organisms

Frequently from aspiration of gastric contents
Organisms include Bacteroides melaninogenicus, B. fragilis

Imaging

Almost always lower lobes
Frequently right sided
Homogeneous consolidation
About 70% will have pleural involvement–effusion, empyema–which may progress very rapidly
Half develop abscesses

Pneumococcal pneumonia

Pneumococcal pneumonia produces consolidation in the right upper lobe with multiple air bronchograms (black branching structures) present since the spaces surrounding the air-filled bronchi normally contain air but now are filled with inflammatory exudate. There is no cavitation, the disease is in the lower lobe and it contains air bronchograms, all characteristics of pneumonia caused by Streptococcus Pneumoniae (formerly known as Diplococcus Pneumoniae)