A 45-year-old man goes to his family doctor complaining of a constant, non-productive cough. The man also has severe chest pains which he says have bothered him for the past week. The man also says that this is unusual for him because it is summer and he usually gets his "colds" in the winter and not in July. When the physician examines the man's chest, he hears an abnormal or pathological sound upon auscultation. The man had pneumonia with consolidation in both lobes. No organism was isolated from his sputum on blood agar, but the physician gave him a shot of penicillin "just in case". As it turned out, the penicillin shot did nothing to relieve the man's distress. After 96 hours, a Gram-negative bacterium from the man's sputum did grow on buffered charcoal yeast extract. What disease did this man have?
Legionnaires' disease is a disease caused by infection with Legionella pneumophila. It is a disease caused by the organism growing in the air conditioning systems in buildings. Therefore, it is a disease that is most often seen in the summer. Legionnaires' disease is a disease primarily affecting the lungs. The organism will not grow on blood agar but will grow on buffered charcoal yeast extract as a Gram-negative rod. Because it produces a penicillinase, the antibiotic penicillin is ineffective against it. The mild form of Legionnaires' disease is called Pontiac fever because it was first observed in Pontiac, Michigan. Psittacosis, which is caused by Chlamydophila psittaci, is a lung infection, but the organism will not grow on buffered charcoal yeast extract agar. Klebsiella pneumoniae will cause a lobar lung infection and is a Gram-negative rod, but it will grow on blood agar media. Streptococcus pneumoniae will also cause a lobar pneumonia, but it is a Gram-positive coccus, and it will grow on blood agar media. Finally, tuberculosis, which is caused by Mycobacterium tuberculosis, is not a Gram-negative bacterium, and will not even stain with the Gram-stain due to the high concentration of lipid in its cell wall.
Legionnaires' disease
Lobar pneumonia caused by Klebsiella pneumoniae
Lobar pneumonia caused by Streptococcus pneumoniae
Psittacosis
Bacteria