Question

2. A middle-aged man presents to the emergency room with chest pain and is found to have suffered a heart attack. He has a past history of hypertension, non-insulin-dependent diabetes mellitus (NIDDM), and high cholesterol. Medical evaluation suggested the need for a triple bypass procedure. This is performed on the fifth day of his hospital stay. During recovery, he develops septic shock with fever and pneumonia. Gram-positive cocci in clusters, isolated from both his lungs (via sputum) and the surgical incision, produce beta-hemolytic colonies on sheep blood agar. Kirby-Bauer testing demonstrates that the organism is resistant to oxacillin, penicillin, erythromycin, and gentamicin, but sensitive to vancomycin. Treatment with vancomycin is, therefore, immediately initiated. 1. What is the most likely organism infecting this man? Explain your reasoning. 2. How would you confirm your diagnosis? 3. How do you interpret the susceptibility data? 4. Name two other diseases this organism causes.

Answer 1

1. The organism is Staphylococcus aureus. Because it is a gram positive cocci which grows in clusters. The organism mainly seen in the skin, nasal cavity, and throat. The staphylococcus infections most commonly occur after the surgeries like cardiac or orthopedic etc.. Hospitalized clients are more easily prone to get this infection due invasive procedure and surgical wound. Once the organism enters the body, it can spread anywhere like blood, bone, fluids and also to any organs like lungs, heart and brain.

2. The confirmatory test to identify staphylococcus aureus is a BAP (Blood Agar). It is a common medium used to culture bacteria because 1) it is a great enrichment medium for fastidious bacteria and 2) Hemolysis of blood cell can be very useful as an identification test. Blood agar is made with 5% sheep blood.

3. The Kirby- Bauer test indicates the susceptibility testing method. The size of the growth free zone determined whether the bacterium was considered to be susceptible, resistant or intermediate to a particular antibiotic.

4. Cellulitis (it is an infection of the underlying layers of the skin) and Bacteremia (presence of bacteria in the blood stream)