Problem
A 68-year-old homeless man is examined at the local clinic with complaints of fever, cough, and worsening shortness of breath. The patient had been diagnosed several years earlier with COPD and underwent breathing treatments.
Upon examination, the patient's vital signs showed a temperature of 100 F, a pulse of 92 beats/minute, respiration of 22/minute, and Blood Pressure of 124/78 mm Hg. A chest X-ray revealed small infiltrates in both upper lobes, and in many small cavities. Sputum was collected for both cultures, gram stain, and AFB stain. The sputum was cultured to SBAP, Mac agar, Choc agar, and Middlebrook agar.
The gram stain results revealed > 25 neutrophils/lpf, a rare squamous epith cell, moderate gram-positive cocci, a few gram-negative bacilli, and a few corynebacteria. At 24 hrs, the routine culture showed mixed flora of a moderate amount of viridians Streptococcus, a few Haemophilus, and a few corynebacteria.
The AFB stain revealed 10 - 12 AFB organisms on the entire slide. The AFB culture grew a tan-buff colored colony in 5 days when incubated in the dark. The plate was exposed to direct light for 5 hours (100 watts), then reincubated. Within 48 hrs, the colonies developed an orange to yellow pigment. The organism was negative for Niacin but positive for Heat Stable catalase, Nitrate reduction, and Tween 80 hydrolysis.
Task
A. What is the significance of the gram stain results?
B. What is the significance of the AFB stain results?
C. What is the significance of the change in color from tan-buff to orange-yellow after exposure to light?
D. Based on the category of mycobacterium, name all the possible causes of infection.
E. Based on the subculture results, what is the most likely identity of the mycobacterium?
F. What is the most likely mode of transmission for this infection?