Learning Radiology xray montage

Pneumonia - Gram positive and Gram negative

Gram Positive Pneumonias 

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


  • 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


  • 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


  • 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


  • 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


  • 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


  • 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)