Enterococci — MCQs

A 37-year-old woman with a history of anorectal abscesses complains of pain in the perianal region. Physical examination reveals mild swelling, tenderness, and erythema of the perianal skin. She is prescribed oral ampicillin and asked to return for follow-up. Two days later, the patient presents with a high-grade fever, syncope, and increased swelling. Which of the following would be the most common mechanism of resistance leading to the failure of antibiotic therapy in this patient?

A 75-year-old man presents to his primary care provider with malaise and low-grade fever after he underwent a cystoscopy for recurrent cystitis and pyelonephritis two weeks ago. His past medical history is significant for coronary artery disease and asthma. His current medications include aspirin, metoprolol, atorvastatin, and albuterol inhaler. Temperature is 37.2°C (99.0°F), blood pressure is 110/70 mm Hg, pulse is 92/min and respirations are 14/min. On physical examination, there are painless areas of hemorrhage on his palms and soles. Cardiac auscultation reveals a new pansystolic murmur over the apex. An echocardiogram shows echogenic endocardial vegetation on a leaflet of the mitral valve. Which of the following pathogens is most likely responsible for his condition?

A scientist is studying the mechanisms by which bacteria become resistant to antibiotics. She begins by obtaining a culture of vancomycin-resistant Enterococcus faecalis and conducts replicate plating experiments. In these experiments, colonies are inoculated onto a membrane and smeared on 2 separate plates, 1 containing vancomycin and the other with no antibiotics. She finds that all of the bacterial colonies are vancomycin resistant because they grow on both plates. She then maintains the bacteria in liquid culture without vancomycin while she performs her other studies. Fifteen generations of bacteria later, she conducts replicate plating experiments again and finds that 20% of the colonies are now sensitive to vancomycin. Which of the following mechanisms is the most likely explanation for why these colonies have become vancomycin sensitive?

A 47-year-old woman comes to the physician because of a 6-week history of fatigue and low-grade fever. She has no history of serious illness except for a bicuspid aortic valve, diagnosed 10 years ago. She does not use illicit drugs. Her temperature is 37.7°C (99.9°F). Physical examination shows petechiae under the fingernails and multiple tender, red nodules on the fingers. A new grade 2/6 diastolic murmur is heard at the right second intercostal space. Which of the following is the most likely causal organism?

A 22-year-old man presents to clinic with a chief concern about a painless ulcer on his penis that he noticed 4 weeks ago and resolved one week ago. He denies any pain on urination or changes in urinary patterns. He admits to having multiple sexual partners in the past 3 months and inconsistent use of barrier protection. His vitals are within normal limits and his physical exam is unremarkable. He is given the appropriate antibiotic for this condition and sent home. What molecular structure is mimicked by the antibiotic most likely prescribed in this case?

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?

While testing various strains of Streptococcus pneumoniae, a researcher discovers that a certain strain of this bacteria is unable to cause disease in mice when deposited in their lungs. What physiological test would most likely deviate from normal in this strain of bacteria as opposed to a typical strain?

A 51-year-old man is admitted to the hospital because of a 2-day history of fever, nausea, and abdominal pain. His temperature is 39.4°C (102.9°F) and pulse is 106/min. Physical examination shows tenderness in the right upper quadrant. Blood cultures grow nonhemolytic, gram-positive cocci that grow in hypertonic saline. Antibiotic sensitivity testing of the isolated organism shows that gentamicin has a minimum inhibitory concentration (MIC) of 16 μg/mL. The addition of ampicillin, which has an MIC of 2 μg/mL alone, decreases the MIC of gentamicin to 0.85 μg/mL. The decrease in the MIC of gentamicin with the addition of ampicillin is most likely due to which of the following mechanisms?

A 45-year-old man comes to the physician because of a 1-month history of fever and poor appetite. Five weeks ago, he underwent molar extraction for dental caries. His temperature is 38°C (100.4°F). Cardiac examination shows a grade 2/6 holosystolic murmur heard best at the apex. A blood culture shows gram-positive, catalase-negative cocci. Transesophageal echocardiography shows a small vegetation on the mitral valve with mild regurgitation. The causal organism most likely has which of the following characteristics?

A previously healthy 24-year-old woman comes to the physician because of a 1-day history of nausea and weakness. She is sexually active with 2 male partners and uses an oral contraceptive; she uses condoms inconsistently. Her last menstrual period was 4 days ago. Her temperature is 38.4°C (101°F). Physical examination shows right costovertebral angle tenderness. Pelvic examination is normal. Which of the following is the most likely cause of this patient's condition?