A 12-year-old girl presents to the casualty with symptoms of fever, shoness of breath, and cough. A chest X-ray reveals complete consolidation of the lower lobe of the left lung. Cultures of the lower lobe of the left lung would most likely reveal which organism?

The history and findings are consistent with a lobar pneumonia. The most common etiologic agent of lobar pneumonia is Streptococcus pneumoniae. ESSENTIALS OF DIAGNOSIS Productive cough, fever, rigors, dyspnea, early pleuritic chest pain Consolidating lobar pneumonia on chest radiograph Lancet-shaped gram-positive diplococci on Gram stain of sputum Ref: Papadakis MA, McPhee SJ, "Pneumonia, Pneumococcal." Quick Medical Diagnosis & Treatment