Q. The patient was a 44-year-old male with a past medical history significant for hypertension, non-insulin-dependent-diabetes, hypercholesterolemia, and a history of heavy smoking (two packs per day for 15 years). He presented to the ER with chest pain and was found to have suffered a myocardial infarction. A cardiac catheterization showed three-vessel coronary artery disease, and he underwent triple coronary artery bypass graft surgery. Two days later he develops septic shock with acute renal and respiratory failure. Two blood cultures were obtained. Chest radiography showed a left lower lobe infiltrate with pleural effusion. A chest tube was placed to drain the effusion. On hospital day 11, pus was noted to be seeping from his sternal wound. A gram stain of the culture and a blood agar culture is shown below.

1. What is the likely organism causing this infection?

2. What is the reaction of the organism on the blood agar plate?

3. Is this organism recovered more frequently as a nosocomial pathogen, as a community-acquired pathogen, or at similar rates in both settings? Elucidate your choice.

4. This species of bacterium was found to have infected five other patients in this same hospital unit. All had undergone open heart surgery over 3-week period. What could be done to determine if these patients were infected with the same or different strains of this bacterium? (Remember that biochemical testing would not be able to differentiate between strains of the same organism).

5. If it was determined that the same strain infected all five patients, what steps would you take to prevent further infections from occurring? In your conversation, give details how this organism can be spread.