Gram-negative bacterial pneumonia

Many aerobic Gram-negative bacteria can cause pneumonia (Table 1).

Gram-negative bacterial pneumonia, Table 1. Most common Gram-negative bacteria causing pneumonia.

These organisms together with Staphylococcus aureus are the most frequent causes of nosocomial pneumonia and are a major cause of morbidity and mortality. Affected patients usually have known predisposing factors, such as chronic obstructive pulmonary disease (COPD) or a major medical condition, or have recently had surgery. The radiographic appearances vary from small ill-defined nodules to patchy consolidation, nodules which sometimes coalesce and resemble lobar pneumoniaor pulmonary oedema. Consolidations are multifocal, often bilateral, the lower lobes being frequently affected. Cavitation is common. Lung abscesses are often small and multiple, better depicted on CT scans than on radiographs. Parapneumonic effusions are common. Empyema is a frequent complication.

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