Gram-positive — MCQs

A 28-year-old primigravid woman at 31 weeks' gestation comes to the physician because of fever, myalgia, abdominal pain, nausea, and diarrhea for 3 days. Her pregnancy has been uncomplicated. Her only medication is a prenatal vitamin. Her temperature is 39.4°C (102.9°F). Physical examination shows diffuse abdominal pain. Blood cultures incubated at 4°C (39.2°F) grow a gram-positive, catalase-positive organism. The pathogen responsible for this patient's presentation was most likely transmitted via which of the following modes?

A 7-year-old boy is brought to the physician because of a 5-day history of fever, malaise, and joint pain. He had a sore throat 4 weeks ago that resolved without treatment. His temperature is 38.6°C (101.5°F) and blood pressure is 84/62 mm Hg. Physical examination shows several firm, painless nodules under the skin near his elbows and the dorsal aspect of both wrists. Cardiopulmonary examination shows bilateral basilar crackles and a blowing, holosystolic murmur heard best at the cardiac apex. Both knee joints are warm. Laboratory studies show an erythrocyte sedimentation rate of 129 mm/h. The immune response seen in this patient is most likely due to the presence of which of the following?

A previously healthy 23-year-old African-American man comes to the physician because of a painless swelling on the left side of his jaw for 2 months. It has been progressively increasing in size and is draining thick, foul-smelling fluid. He does not have fever or weight loss. He had a molar extracted around 3 months ago. One year ago, he developed a generalized rash after receiving amoxicillin for streptococcal pharyngitis; the rash was managed with oral steroids. There is no family history of serious illness. Vital signs are within normal limits. Examination shows a 4-cm, tender, erythematous mass in the left submandibular region that has a sinus draining purulent material at its lower border. Submandibular lymphadenopathy is present. His hemoglobin is 14.5 g/dL, leukocyte count is 12,300/mm3, and erythrocyte sedimentation rate is 45 mm/h. A Gram stain of the purulent material shows gram-positive filamentous rods. Which of the following is the next best step in management?

A 62-year-old man comes to the physician because of an oozing skin ulceration on his foot for 1 week. He has a history of type 2 diabetes mellitus and does not adhere to his medication regimen. Physical exam shows purulent discharge from an ulcer on the dorsum of his left foot. Pinprick sensation is decreased bilaterally to the level of the mid-tibia. A culture of the wound grows beta-hemolytic, coagulase-positive cocci in clusters. The causal organism most likely produces which of the following virulence factors?

A 29-year-old G1P1 woman presents to her primary care physician with unilateral breast pain. She is currently breastfeeding her healthy 3-month-old baby boy. She has been breastfeeding since her child's birth without any problems. However, 3 days prior to presentation, she developed left breast pain, purulent nipple discharge, and malaise. Her past medical history is notable for obesity and generalized anxiety disorder. She takes sertraline. She does not smoke or drink alcohol. Her temperature is 100.8°F (38.2°C), blood pressure is 128/78 mmHg, pulse is 91/min, and respirations are 17/min. On exam, she appears lethargic but is able to answer questions appropriately. Her right breast appears normal. Her left breast is tender to palpation, warm to the touch, and swollen relative to the right breast. There is a visible fissure in the left nipple that expresses minimal purulent discharge. Which of the following pathogens is the most likely cause of this patient's condition?

A 65-year-old man presents with low-grade fever and malaise for the last 4 months. He also says he has lost 9 kg (20 lb) during this period and suffers from extreme fatigue. Past medical history is significant for a mitral valve replacement 5 years ago. His temperature is 38.1°C (100.6°F), respirations are 22/min, pulse is 102/min, and blood pressure is 138/78 mm Hg. On physical examination, there is a new onset 2/6 holosystolic murmur loudest in the apical area of the precordium. Which of the following organisms is the most likely cause of this patient’s condition?

A 24-year-old woman presents to her primary care physician with a 3 day history of pain with urination. She says that this pain has been accompanied by abdominal pain as well as a feeling like she always needs to use the restroom. She has no past medical history and no family history that she can recall. She is currently sexually active with a new partner but has tested negative for sexually transmitted infections. Physical exam reveals suprapubic tenderness and urine culture reveals gram-positive cocci. Which of the following best describes the organism that is most likely causing this patient's symptoms?

A microbiology student was given a swab containing an unknown bacteria taken from the wound of a soldier and asked to identify the causative agent. She determined that the bacteria was a gram-positive, spore-forming bacilli, but had difficulty narrowing it down to the specific bacteria. The next test she performed was the Nagler's test, in which she grew the bacteria on a plate made from egg yolk, which would demonstrate the ability of the bacteria to hydrolyze phospholipids and produce an area of opacity. Half the plate contained a specific antitoxin which prevented hydrolysis of phospholipids while the other half did not contain any antitoxin. The bacteria produced an area of opacity only on half of the plate containing no antitoxin. Which of the following toxins was the antitoxin targeting?

A 15-year-old boy presents to the emergency department for evaluation of an ‘infected leg’. The patient states that his right shin is red, swollen, hot, and very painful. The body temperature is 39.5°C (103.2°F). The patient states there is no history of trauma but states he has a history of poorly managed sickle cell anemia. A magnetic resonance imaging (MRI) scan is performed and confirms a diagnosis of osteomyelitis. Which of the following is the most likely causative agent?

A 13-year-old boy presents to his pediatrician with a 1-day history of frothy brown urine. He says that he believes he had strep throat some weeks ago, but he was not treated with antibiotics as his parents were worried about him experiencing harmful side effects. His blood pressure is 148/96 mm Hg, heart rate is 84/min, and respiratory rate is 15/min. Laboratory analysis is notable for elevated serum creatinine, hematuria with RBC casts, and elevated urine protein without frank proteinuria. His antistreptolysin O titer is elevated, and he is subsequently diagnosed with post-streptococcal glomerulonephritis (PSGN). His mother is distraught regarding the diagnosis and is wondering if this could have been prevented if he had received antibiotics. Which of the following is the most appropriate response?