Gram Negative Pneumonia

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