A 65-year-old male presents with a rapid onset fever, chest pain and cough with rusty-yellow sputum. Chest x-ray was done. A Gram stain of a sputum sample contained many polymorphonuclear leukocytes and extracellular gram-positive diplococci. Biochemical reactions revealed the organism was bile soluble, optochin sensitive and fermented inulin. Characteristics of the colonies produced on the culture are given below. Which of the following is the most likely pathogen?
Correct Answer: Streptococcus pneumoniae
Description: Chest X-ray shows focal lobar infiltrates Capsule-specific antibodies bound to the diplococci resulted in a positive Quellung reaction. Classical draughtsman or carrom coin appearance colonies of Streptococcus pneumoniae are seen The most common cause of community acquired pneumonia in this age group is Streptococcus pneumoniae. The X-ray and microbiological findings are most consistent with a diagnosis of pneumococcal pneumonia. Following treatment, this patient should be advised to be vaccinated with the 23-valent pneumococcal vaccine. Streptococcus pyogenes does not typically present as pneumonia. Streptococcus agalactiae generally afflicts neonates. The enterococci (Enterococcus faecium and Enterococcus faecalis) do not exhibit the Quellung reaction and do not present as community acquired pneumonia.
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