Gram-positive — MCQs

A 50-year-old farmer presents to a physician with painless, black, severely swollen pustules on the left hand. Examination reveals extensive swelling around the wound. Microscopy reveals gram-positive bacilli with a bamboo stick appearance. Culture shows large, gray, non-hemolytic colonies with irregular borders. Which of the following is the most likely diagnosis?

A 63-year-old man with aortic valve disease is admitted to the hospital for a 3-week history of progressively worsening fatigue, fever, and night sweats. He does not smoke, drink alcohol, or use illicit drugs. Temperature is 38.2°C (100.8°F). Physical examination shows a systolic murmur and tender, erythematous nodules on the finger pads. Blood cultures show alpha-hemolytic, gram-positive cocci that are catalase-negative and optochin-resistant. Which of the following is the most likely causal organism?

A 2-day-old newborn male delivered at 38 weeks' gestation is evaluated for poor feeding and irritability. His temperature is 35°C (95°F), pulse is 168/min, respirations are 80/min, and blood pressure is 60/30 mm Hg. Blood culture on sheep agar grows motile, gram-positive bacteria surrounded by a narrow clear zone. Further testing confirms the presence of a pore-forming toxin. Which of the following is the most important factor in successful clearance of the causal pathogen?

A 63-year-old female recovering from a total shoulder arthroplasty completed 6 days ago presents complaining of joint pain in her repaired shoulder. Temperature is 39 degrees Celsius. Physical examination demonstrates erythema and significant tenderness around the incision site. Wound cultures reveal Gram-positive cocci that are resistant to nafcillin. Which of the following organisms is the most likely cause of this patient's condition?

A 7-year-old boy is brought by his parents to his pediatrician with a one-day history of fever, chills, and pain in the right upper extremity. The patient's mother says that he has injured his right index finger while playing in the garden 3 days earlier. His temperature is 38.8°C (101.8°F), pulse is 120/min, respiratory rate is 24/min, and blood pressure is 102/70 mm Hg. On physical examination, there is an infected wound present on the tip of the right index finger. Irregular linear subcutaneous red streaks are seen on the ventral surface of the right forearm, which is warm and tender to palpation. There is painful right infraclavicular lymphadenopathy present. Which of the following is the most common microorganism known to cause this patient's condition?

A 44-year-old woman with type 2 diabetes mellitus comes to the physician with a 3-day history of fever, right calf pain, and swelling. Her temperature is 38.7°C (101.7°F). Physical examination shows a 5 x 6-cm erythematous, warm, raised skin lesion with well-defined margins over the right upper posterior calf. The organism isolated from the lesion forms large mucoid colonies on blood agar. Further evaluation shows that the organism has a thick hyaluronic acid capsule. The causal organism of this patient's condition is most likely to have which of the following additional characteristics?

A 65-year-old man presents to the emergency department with a complaint of intense pain in his right foot for the past month, along with fever and chills. He denies any traumatic injury to his foot in recent memory. He has a medical history of poorly-controlled type II diabetes and is a former smoker with extensive peripheral vascular disease. On physical exam, the area of his right foot around the hallux is swollen, erythematous, tender to light palpation, and reveals exposed bone. Labs are notable for elevated C-reactive protein and erythrocyte sedimentation rate. The physician obtains a biopsy for culture. What is the most likely causative organism for this patient’s condition?

A 2-year-old boy presents with multiple skin abscesses caused by Staphylococcus aureus. Past medical history is significant for recurrent infections by the same organism. The nitroblue tetrazolium (NBT) test demonstrates an inability to kill microbes. Which of the following defect is most likely responsible for the findings in this patient?

A 3100-g (6.9-lb) male newborn is brought to the emergency department by his mother because of fever and irritability. The newborn was delivered at home 15 hours ago. He was born at 39 weeks' gestation. The mother's last prenatal visit was at the beginning of the first trimester. She received all standard immunizations upon immigrating from Mexico two years ago. Seven weeks ago, she experienced an episode of painful, itching genital vesicles, which resolved spontaneously. Four hours before going into labor she noticed a gush of blood-tinged fluid from her vagina. The newborn is ill-appearing and lethargic. His temperature is 39.9°C (103.8°F), pulse is 170/min, respirations are 60/min, and blood pressure is 70/45 mm Hg. His skin is mildly icteric. Expiratory grunting is heard on auscultation. Skin turgor and muscle tone are decreased. Laboratory studies show: Hemoglobin 15 g/dL Leukocyte count 33,800/mm3 Platelet count 100,000/mm3 Serum glucose 55 mg/dL Which of the following is the most likely causal organism?

A 71-year-old woman presents with high-grade fever and chills, difficulty breathing, and a productive cough with rust-colored sputum. She complains of a sharp left-sided chest pain. Physical examination reveals increased fremitus, dullness to percussion, and bronchial breath sounds on the lower left side. A chest X-ray shows left lower lobe consolidation. The offending organism that was cultured from the sputum was catalase-negative and had a positive Quellung reaction. The organism will show which gram stain results?