Community-Acquired Pneumonia Due to Gram-Negative Bacilli

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Enteric and nonfermentative Gram-negative bacilli (GNB) are recognized causes of community-acquired pneumonia (CAP). Clinical presentation is usually severe, often justifying the admission of patients to an intensive care unit. The great majority of cases occur in persons who harbor GNB in the oropharynx, as a consequence of suffering from an underlying disease or taking antibiotics. Less frequently, the disease is the result of the hematogenous seeding of the lung from a distant septic focus. Clinical manifestations and radiologic features are nonspecific. However, the concurrence of a severe clinical picture and evidence of lung necrosis in a patient with comorbidity suggest the involvement of GNB. Etiologic diagnosis is difficult without resorting to invasive procedures aimed to obtain respiratory samples free of salivary contamination. Sputum Gram’s stain and culture are devoid of specificity, even if performed on a high-quality sample. CAP due to Enterobacteriaceae can usually be treated with a single β-lactam antibiotic. If signs of radiologic cavitation or shock are present, the addition of an aminoglycoside is advisable. To prevent the emergence of resistance, infections due to Pseudomonas aeruginosa or other nonfermentative GNB require the combination of a β-lactam with an aminoglycoside or fluoroquinolone. Optimal duration of antibiotic therapy has not been well established, but 2 to 3 weeks are generally recommended.

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